National Academies Press: OpenBook

Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization (1997)

Chapter: 3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION

« Previous: 2 MARKET-BASED APPROACHES FOR STIMULATING REMEDIATION TECHNOLOGY DEVELOPMENT
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

3
State of the Practice of Ground Water and Soil Remediation

Innovation in the environmental industry is driven by the need to solve difficult problems and the desire to improve upon existing solutions. When a ground water or soil cleanup technology is developed and applied, frequently in response to an unsolved problem, its acceptance and application are often limited initially to specific contaminants and specific hydrogeologic conditions. As the technology matures, it typically addresses the same range of contaminant types, but its range of application in subsurface environments becomes better defined. This evolutionary process is similar for most remediation technologies, but the rate at which new technologies are adopted varies considerably. For example, soil vapor extraction (SVE) technologies, used for removing volatile contaminants from soil, were virtually unused at Superfund sites in 1985 but by 1995 had been selected for source control at 20 percent of Superfund sites (EPA, 1996a). However, for other technologies, especially those for cleaning up contaminants in situ, this evolution is occurring much more slowly than one would predict based on the large number of contaminated sites and the hundreds of billions of dollars in projected cleanup costs for these sites. There is no shortage of new ideas for improving the ability to restore contaminated ground water and soil. However, for reasons explained in Chapter 2, successful commercialization of all but a few new ideas has been limited.

This chapter reviews the state of development of technologies for cleaning up ground water and soil, highlighting knowledge and information gaps, and describes challenges and strategies for cleaning up different types of contaminants. The chapter defines all technologies for cleaning up contaminants below the water table as "ground water cleanup technologies" and all technologies for cleaning up contaminants above the water table as "soil cleanup technologies." This dis-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

tinction is somewhat artificial, because many technologies for restoring areas below the water table address contaminated geologic materials rather than the water itself. Nevertheless, although these technologies do not specifically treat the water, but rather contaminants in the geologic materials, users of the technologies generally refer to them as ground water cleanup technologies because their primary intent is to prevent the contaminants from dissolving in and contaminating the ground water.

Included in this chapter are technologies that treat ground water contaminants in place in the subsurface and soil technologies that treat the soil either in place or on site in a treatment unit. The chapter does not cover technologies for removing contaminants from ground water once it has been pumped to the surface. The challenge of removing contaminants from water at the surface has already been largely addressed through the development of systems for treating municipal and industrial wastewater. In comparison, relatively few technologies are available for removing contaminants from soil or geologic materials to which the contaminants have tightly bound. Even fewer technologies exist for treating contaminated ground water in place in the subsurface. Furthermore, the processes that can be exploited in these technologies are still not fully understood.

WHAT IS INNOVATIVE REMEDIATION TECHNOLOGY?

"Innovative technology" as applied to the cleanup of ground water and soil is an elusive term, for two primary reasons. First, government agency representatives and others involved in waste-site cleanup may have different perspectives on which technologies are innovative. For example, the Environmental Protection Agency's (EPA's) 1996 Innovative Treatment Technologies: Annual Status Report classifies in situ bioremediation of contaminated soils as an innovative technology, while the Air Force specifies bioventing (a type of in situ bioremediation) as the standard remedy for soils contaminated with petroleum hydrocarbons and other volatile organic compounds (DOD Environmental Technology Transfer Committee, 1994). The Department of Energy (DOE) considers any technology innovative if it has not been used at DOE sites (J. Walker, DOE, personal communication, 1995). Thus, the definition of innovative varies depending on the perspective of the user.

A second reason why "innovative" is hard to define is that technologies are continually evolving. In the ground water and soil remediation business, only a few technologies represent true breakthroughs, in the sense that they apply concepts never before used in the field. More commonly, innovation occurs incrementally, evolving from existing technologies. This evolution is a product of several factors. The first factor is increased experience. As a technology is implemented at various sites, the experience gained provides a basis for defining and overcoming limitations, establishing best practices, and expanding the technology's application to new contamination problems. The second factor is com-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

petition, both among the technologies and among practitioners who design the technologies. The third factor is the technology's performance limitations. All technologies have practical limitations that affect their market viability; a given technology may not perform well initially for certain contaminant types and hydrogeologic settings, but as these limitations are addressed, the applicability and marketability of the technology may increase. The fourth factor is cross-fertilization with other technologies. A technique or even a whole new technology may be incorporated into an existing technology to improve its performance or overcome a limitation.

The net result of this evolution is that remediation technologies go through a cyclical or generational life cycle. The first stage is the initial, and often crude, application of the technology. During this period, acceptance of the technology increases as it is successfully applied and its success is communicated. During the second stage of evolution, design practices for the technology become established. Acceptance and application grow rapidly as the benefit of the technology becomes known. The third stage is the mature, common practice of the technology. In this stage, the focus shifts from the benefits of the technology to its limitations, and acceptance and application may decline. During this mature application stage, the technology is vulnerable to replacement. However, use of the technology may increase again, either as its limitations are overcome or as the technology becomes applicable to new contaminant types and/or hydrogeologic settings. When a significant limitation is overcome, the technology enjoys a rebirth. The two best examples of remediation technologies that have developed through this evolutionary process are in situ bioremediation and SVE (see Boxes 3-1 and 3-2).

This chapter reviews a broad range of remediation technologies other than those based on conventional pumping and treating of ground water or digging and either hauling or burning of soil. Many of the technologies discussed in the chapter, including SVE and in situ bioremediation, have a significant experience base and are not new. In addition, many are enhancements to conventional approaches rather than new developments. Nevertheless, all of these technologies have in common the ability (whether potential or proven) to increase the effectiveness and/or decrease the costs of subsurface cleanup when compared to the historical approaches of pumping and treating ground water and hauling or burning soil.

AVAILABILITY OF INFORMATION ON INNOVATIVE REMEDIATION TECHNOLOGIES

Application of innovative remediation technologies has been slowed by lack of uniform, synthesized information about remediation technology performance. While considerable effort is being invested in researching and developing remediation technologies, these efforts are often isolated and do not benefit the general industry because circulation of information is limited. Broad acceptance of a tech-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-1 Innovations in Engineered in Situ Bioremediation

Engineered in situ bioremediation, the purposeful stimulation of microorganisms in ground water and soil to degrade contaminants, was first applied in 1972 to clean up a spill of gasoline from a pipeline in Ambler, Pennsylvania (Raymond et al., 1977). At that time, in situ bioremediation addressed the unsolved problem of residual petroleum contamination in soil and ground water. The related generations of technology that followed this first in situ bioremediation system focused primarily on petroleum hydrocarbons and were essentially water-based systems: both the oxygen and nutrients necessary to stimulate growth of contaminant-consuming organisms were supplied by circulating ground water. From 1972 to 1983, only about a dozen in situ bioremediation projects were conducted nationwide (Brown et al., 1993). Performance was limited by the low solubility of oxygen in water.

The second generation of in situ bioremediation systems used hydrogen peroxide (H2 O2) to provide a more efficient method of supplying oxygen in soluble form. H2 O2 supplied 10 to 50 times more oxygen equivalents than did the existing aeration systems. The third-generation in situ bioremediation system employed SVE (see Box 3-2) to supply oxygen above the water table and used H2 O2 to provide oxygen below the water table. Both the second- and third-generation technologies were limited by the expense and difficulty of using H2 O2 , and there was a significant effort to find an alternative. Several alternatives to H2 O2 were explored, but the most successful was air sparging, which involves injecting air directly into the subsurface. Air sparging was initially developed as a separate technology to remove volatile contaminants by evaporative processes, but it was soon incorporated into bioremediation technology, sometimes called biosparging. Due in part to the success in improving oxygen delivery systems, in situ bioremediation systems are now in use at thousands of underground storage tank sites and dozens of Superfund sites (see Chapter 1).

Parallel to the development of the different generations of in situ bioremediation systems for treatment of petroleum hydrocarbons has been the development of a number of spin-off technologies. The first of these was improved ex situ soil bioremediation technology. Ex situ bioremediation employs the principles and techniques of in situ bioremediation to treat excavated soils. A second improvement has been the increased understanding of bioremediation of chlorinated hydrocarbons, which was largely unknown until the mid-1980s (McCarty and Semprini, 1994). A third spin-off has been the development of intrinsic bioremediation (bioremediation without using engineered systems to stimulate native soil microbes) to control and mitigate contaminant plumes.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Petroleum-contaminated soils being treated in above-ground bioremediation cells engineered with vapor extraction systems. Courtesy of Fluor Daniel GTI.

nology requires documentation of the technology's performance and accessibility of performance information. Often in the development of remediation technology, data collection is minimal. As a result, much of the available information is anecdotal and empirical. This relative lack of documented performance data makes it difficult to judge the benefits and limitations of a technology without trying it. As a result, remediation technology development is somewhat repetitive, as individual practitioners tend to repeat the same work until the experience base is sufficiently distributed that knowledge of the technology is also well distributed.

The lack of consistent information is pervasive in the remediation market and encompasses all of the following problems:

  • technology reports are often incomplete;

  • critical scientific evaluation of technology application most often is not conducted or is not conducted with the goal of collecting comparable data sets;

  • reliable cost data are lacking and inconsistent;

  • methods for determining costs and evaluating successes can vary enormously; and

  • much information is proprietary.

These factors combine to make it very difficult to conduct rigorous comparisons

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

between technologies and across problem contexts with existing data. In addition, there are no complete, centralized data bases that cross markets and government programs. The 1995 publication Accessing Federal Data Bases for Contaminated Site CleanUp Technologies lists 25 different data bases that could be potentially useful in evaluating remediation technologies (Federal Remediation Technologies Roundtable, 1995a), but these data bases are not coordinated, and many of them are difficult to access (see Appendix A for a listing of data bases). In fact, the existence of such a large number of data bases in itself creates confusion, because the data bases contain information in different formats that may not be comparable, and the quality of the data from different data bases is variable and difficult to assess.

A few programs exist or are developing to facilitate evaluation of technologies. The EPA's Technology Innovation Office is collecting information on Superfund technology selections. The Federal Remediation Technologies Roundtable (a consortium of federal agency personnel involved in remediation) has developed protocols for standardized cost evaluations (Federal Remediation Technologies Roundtable, 1995b). Joint programs between states allowing sharing of information collected for technology evaluation are being created, and the results from these programs should help alleviate some of the information deficit. The EPA has established the Ground Water Remediation Technologies Analysis Center to help disseminate information on new remediation technologies (GWRTAC, 1995). These efforts are useful for developing a global view of what categories of remediation technologies are being tested and implemented. However, the fact remains that there are few reports that contain well considered evaluations of technologies, rather than mere compilations of information lacking careful analysis. A few examples of thoughtful technology evaluation may serve as models for future work.

The American Academy of Environmental Engineers' WASTECH® project has produced eight monographs of innovative waste-site remediation technologies. Generally, the scope of the analysis for this project was limited to technologies that are not commonly applied; have been sufficiently developed so that they can be used in full-scale applications; have sufficient data available to describe and explain the technology; and have sufficient data to assess effectiveness, limitations, and potential applications. An important contribution of this effort was applying such criteria to a wealth of information and synthesizing the findings by a task group of experts, whose work was peer reviewed, to produce a discussion of potential applications, process evaluations, limitations, and technology prognoses. Although restricted in scope and not uniform in coverage, the WASTECH® monographs provide a measure of consensus on performance of the technologies reviewed in the series; the philosophy and approach are laudable. A follow-up WASTECH® series of seven monographs emphasizing remediation technology design and implementation is in preparation.

An example of a focused report on a particular problem context is Dávila et

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-2 Innovations in Soil Vapor Extraction (SVE)

SVE has been used to treat volatile hydrocarbons since the mid-1970s. Originally, the technology was used to remove vapors from soils to prevent the vapors from entering buildings. This first-generation technology was derived from methane collection systems employed at landfills and typically consisted of lateral collection pipes placed along building foundations. A vacuum was applied to these lateral pipes to collect the organic vapors. Engineers soon observed, however, that the removal of vapors led to significant contaminant mass removal and a reduction of the level of contamination in the soil.

The second-generation (circa 1983) SVE technology focused specifically on the removal of volatile organic compounds (VOCs) from soil instead of the simpler collection of vapors. Two theories developed concerning SVE. The first postulated that the function of the vacuum was to ''vacuum distill" the VOCs from the soil matrix and was based on the principle that the boiling point of most VOCs decreases with decreasing pressure. With this approach, typically a high vacuum (greater than 500 mm, or 20 in., Hg) was applied to decrease the boiling point of the VOCs and allow them to volatilize. The second theory of SVE postulated that the process was an evaporative one. The purpose of the vacuum was to induce air flow through the subsurface to evaporate the VOCs. This theory has become the dominant SVE theory and is the basis for most SVE designs. The evaporative model uses low to moderate vacuums of less than 380 mm (15 in.) Hg.

The main evolution of SVE has been in the design tools. The second-generation systems were typically designed on the basis of vacuum radius. Designers assumed that as long as there was a detectable vacuum,

al. (1993), which discusses technology applications for cleanup of soil and sediment contaminated with polychlorinated biphenyls (PCBs). This report discusses succinctly a number of technologies from an engineering perspective, pointing to specific examples of successes and problems from field evaluations. A report by Grubb and Sitar (1994) that discusses in situ remediation of dense nonaqueousphase liquid (DNAPL) contaminants provides another example of a report that critically evaluates technologies for solving a particular type of contamination problem. A report by Troxler et al. (1992) on thermal desorption for petroleum-contaminated soils provides a useful perspective on a particular technology application and its status of development. Reports by Vidic and Pohland (1996) on in situ treatment walls and by Jafvert (1996) on cosolvent and surfactant flushing systems provide peer-reviewed evaluations of these technologies.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

there was sufficient air flow. With this simple design basis, however, many SVE systems proved less effective than planned. Designs based on simple vacuum readings do not reflect true air flow unless they are adjusted for air permeability using Darcy's law. Once models were used to adjust vacuum readings to actual air flow rates, the performance of SVE systems improved. In retrospect, use of air flow-based designs seems like an obvious improvement. However, implementation has not been easy because of the need to use flow models.

While SVE has not evolved as extensively as bioremediation, it has engendered a much more varied set of spin-off technologies. This may be in part due to the clarity of the limitations of SVE, which removes volatile compounds from unsaturated soils by induced air flow. By this definition, there are three basic limitations: (1) the volatility of the contaminant, (2) the lack of air in saturated environments, and (3) the permeability of the soil matrix to air flow.

The limitation of volatility has fostered two other innovations. The first is the use of thermal energy to increase the contaminant volatility. Thermal systems under development use hot air, steam, radio waves, microwaves, or electrical resistance to heat the soil. The second is the use of biodegradation to enhance contaminant removal. While SVE was recognized as an efficient source of oxygen for bioremediation as early as 1984, the full development of bioventing did not occur until about 1990.

The lack of air in the saturated zone has fostered the development of dual-phase technology. This is the direct use of a high vacuum to dewater and vent saturated soils. Dual-phase technology has allowed SVE to treat contamination below the water table. Finally, the lack of air permeability has led to the development of fracturing systems. Fracturing systems inject pressurized air or water to open channels in the soil, which then allow air to circulate more freely.

STATE OF INNOVATIVE REMEDIATION TECHNOLOGY DEVELOPMENT

The current state of remediation technology development is relatively rudimentary. That is, technologies are available for treating easily solved contamination problems—mobile and reactive contaminants in permeable and relatively homogeneous geologic settings—but few technologies are available for treating recalcitrant contaminants in complex geologic settings. Figure 3-1 shows a conceptual diagram of where innovation is most needed to improve the performance and reduce the costs of ground water and soil remediation projects.

The greatest successes in remediation to date have been in the treatment of petroleum hydrocarbon fuels—gasoline, diesel, and jet fuel—which are generally mobile and biologically reactive and to a lesser extent in the treatment of chlori-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Figure 3-1 Technology needs for remediation of contaminated ground water and soil. At the left side of the figure, improvements are needed primarily to reduce costs. At the right side, new technologies are needed to solve contamination problems that are currently intractable.

nated solvents, which are generally mobile but are less readily biodegraded than petroleum hydrocarbons. The greatest challenge in remediation is in the location and cleanup of contaminant source material. This source material may comprise organic solids, liquids; or vapors; inorganic sludges and other solid-matrix wastes; compounds adsorbed on mineral surfaces; and compounds adsorbed in natural organic matter such as humus. Often, contaminant sources are difficult to locate and delineate because of lack of information about the contaminant spill or disposal history at the site and because contaminant source material may migrate away from where it was originally lost to the environment. Once found, source material may be inaccessible, lying under structures, or at great depth, or in fractured rock. Because of the possibility of continual contaminant release, partial source removal may not result in a proportional increase in ground water quality. The time for source diminution may be excessively long. Further, directing pumped fluids to the region where such fluids are most beneficial may be very difficult because of the problem of preferential flow, which causes fluids to bypass altogether the less permeable regions containing contaminants. A special challenge in the cleanup of source material is in the development of methods to enhance the mobility or reactivity of material that, by its nature, is not particularly mobile or reactive.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Three Categories of Remediation Technologies

Remediation technologies can be divided into three general categories: (1) technologies for solidification, stabilization, and containment; (2) technologies exploiting biological and chemical reactions to destroy or transform the contaminants; and (3) technologies involving separation of the contaminants from the contaminated media, mobilization of the contaminants, and extraction of the contaminants from the subsurface. Box 3-3 provides definitions of the different types of technologies in each of these three categories.

Solidification and stabilization processes are directed at decreasing the mobility and/or toxicity of contaminants by reducing contaminant solubility or volatility and medium permeability. Most such techniques have been developed for ex situ treatment of soil contaminated with heavy metals, although a few methods for in situ treatment of relatively shallow contaminated soils are in use. These processes are generally not suited for contaminants located at significant depth or for very volatile or soluble organic contaminants, although some of the methods are now being applied to a limited number of organic contaminants.

Containment methods are designed to prevent movement of contaminants away from the zone of contamination by providing a physical or hydraulic barrier. Low-permeability clay and/or geotextile caps and low-permeability slurry walls are fairly standard technology. Combinations of reactive processes with physical containment systems are a new innovation being implemented in the field. Pump-and-treat systems are also often used to hydraulically contain contaminated ground water.

Biological and chemical reaction processes use biological or chemical reactions to transform contaminants to innocuous, or at least less harmful, products. Biological processes, known generally as bioremediation, rely on microorganisms to mediate contaminant transformation reactions and degrade the compounds. Many organisms native to soils can use contaminants as sources of carbon and energy for growth. Some organisms (known as aerobes) require oxygen to thrive, while others (known as anaerobes) thrive in oxygen-free environments and use other electron acceptors, such as nitrate, iron, sulfate, and carbon dioxide. Addition of nutrients, moisture, or the appropriate electron acceptors can increase microbial activity and thus enhance the reaction rates. Pretreatment with enzymes or chemical oxidants can make complex chemicals more readily degradable. For in situ bioremediation applications, the primary challenges are largely related to creating the necessary environmental conditions in situ that will cause biodegradation of the contaminants; this includes delivery of the necessary amendments to contaminated locations. Chemical reaction processes are not used as frequently as biological processes. Few chemical reaction processes are available, and even fewer have been tested extensively. However, several technologies are now being tested, as shown in Box 3-3. Reaction processes, whether biological or chemical, are the only processes that can completely destroy organic contaminants. The

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-3 A Glossary of Remediation Technologies

Stabilization/Solidification and Containment Technologies

Asphalt batching. Encapsulates contaminated soil in an asphalt matrix. Volatile organic compounds (VOCs) generally volatilize during the process and are captured and treated in an off-gas system.

Biostabilization. An ex situ microbial process to rapidly degrade the bioavailable components (the more volatile and soluble fractions of contaminant mixtures). The process leaves behind a much less mobile and less bioavailable residue.

Enhanced sorption. A passive-reactive barrier (see definition below) that creates zones that cause contaminant sorption, either microbiologically (biosorption) or chemically (using surfactant coatings).

In situ precipitation/coprecipitation. A passive-reactive barrier (see definition below) that causes the precipitation of a solid (usually carbonate, hydroxide, or sulfide mineral) to maintain a toxic metal in an immobile form. Formation of solid phases is controlled primarily by pH, redox potential, and concentration of other ions.

In situ soil mixing. A method of achieving stabilization of contaminated soil in situ. Soil is mixed with stabilizing agents using large augers in successive drillings across a site.

Lime addition. A method that decreases permeability of soils by filling interstitial pore spaces and forming weak bonds between soil particles. Heat generated due to hydration can aid in thermal desorption of VOCs.

Passive-reactive barriers. Permeable containment barriers that intercept contaminant plumes and remove contaminants from ground water solution using chemical and/or biological reactions within the barrier.

Pozzolonic agents. Cement-like materials that form chemical bonds between soil particles and can form chemical bonds with inorganic contaminants, decrease permeability, and prevent access to contaminants. The most common pozzolonic materials are portland cement, fly ash, ground blast furnace slag, and cement kiln dust.

Slurry walls, sheet pile walls, and grout walls. Low-permeability barriers designed to prevent contaminant transport in situ. The success of these technologies depends on achievement of a long-lived, low-permeability barrier. Because these walls create hydraulic confinement, fluid must either be allowed to flow around them or be removed from the system and treated if necessary. Alternatively, the barrier wall must contain permeable zones in which reactions can occur.

Vitrification. Melting of contaminated soil combined with amendments as needed to form a glass matrix from the soil, either in place (in situ vitrification) or in a treatment unit. Nonvolatile metals and radioactive contaminants become part of the resulting glass block after cooling. Organic contaminants are either destroyed or volatilized by the ex-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

tremely high temperatures. The method is generally expensive due to large energy requirements.

Biological Reaction Technologies

Biopile. Soil placed around or over ventilation pipes and often amended with nutrients (during emplacement, or by irrigation or batch additions). Biopiles are supplied with oxygen by vacuum-induced air flow.

Bioslurry reactor. Biological (ex situ) reactors that slurry, suspend, and typically aerate solids. Reactors can be enclosed or in the form of treatment lagoons. When volatile constituents are present, vapor capture and treatment may be necessary. This technology is usually used for sludges with high water content.

Biostabilization. See above definition (under "Stabilization, Solidification, and Containment Technologies").

Bioventing and biosparging. A form of engineered in situ bioremediation involving addition of oxygen to stimulate aerobic microbial activity. Oxygen is added by soil vapor exchange (bioventing) in the vadose zone and by air sparging (biosparging) in the saturated zone. Air flow is generally lower in bioventing and biosparging than in SVE and air sparging systems, which are designed to maximize extraction of volatile components from the subsurface.

Composting. Related to biopiles. Additional carbon, in the form of manure, sludge, plant byproducts, or wood chips, is added to increase biological activity and pore size.

Engineered in situ bioremediation. Addition of electron acceptors (usually oxygen) or donors and nutrients in situ to ground water or soil to facilitate biodegradation. Biodegradation occurs in the ground water system downgradient from the point of nutrient addition. The systems generally do not require large energy inputs.

Enhanced sorption. See above definition (under "Stabilization, Solidification, and Containment Technologies").

Fungal treatment. Addition of wood-degrading fungi, either white rot or brown rot, to a biopile or land farming application. The fungi degrade complex organic compounds by producing extracelluar enzymes.

Intrinsic bioremediation. The use of native soil microorganisms to degrade contaminants without human intervention other than careful monitoring. The method can be used both to destroy contaminants and to control the spread of contaminant plumes. It requires monitoring and modelling to document the existence and rate of biodegradation. Treatment time can be very long (decades).

Land farming. Spreading of contaminated soil over a prepared bed on the land surface in shallow lifts followed by tilling to provide aeration. Treatment time depends on contaminant and soil properties, including the rate of compound release from the solids. Tilling and nutrient addition frequencies can affect remediation rates.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Organic biofilters. A form of engineered in situ bioremediation that uses a large mass of microorganisms for sorption or transformation of contaminants. Electron acceptors and nutrients are added to sustain the microorganisms.

Passive-reactive barriers. See above definition (under "Stabilization, Solidification, and Containment Technologies").

Phytoremediation. Remediation of contaminated soil in situ using vegetation.

Sparge barriers. A form of engineered in situ bioremediation in which oxygen is provided to the subsurface via air injection wells placed directly into the formation or in a permeable trench.

Chemical Reaction Technologies

Chemical oxidation. Use of strong oxidants to destroy organic contaminants. The process works best on compounds, such as olefins and substituted aromatics, that contain unsaturated carbon-carbon bonds. Several chemical combinations can be used: peroxide, peroxide and iron (Fenton's reagent), ozone, hydrogen peroxide and ozone (peroxone), and potassium permanganate.

Incineration. Oxidation of organic compounds at extremely high temperatures (ex situ). Organic compounds that are difficult to treat by other methods can be destroyed by incineration.

Substitution. Use of ex situ organic chemical reactions to convert soil contaminants into components that are less toxic or unregulated, typically by replacing a halogen with a hydrogen or functional group, such as an ether.

Thermal reduction. Use of hydrogen (ex situ) at elevated temperatures to reduce and decompose organic contaminants in soils to nontoxic compounds.

Zero-valent iron barrier. A passive-reactive barrier (see above definition) that creates very reducing conditions, resulting in hydrogen generation. Dissolved chlorinated solvents (ethenes, ethanes, and methanes) are chemically degraded at relatively rapid rates. Some metals form relatively insoluble solids at low redox potential and can be treated with this method.

Separation, Mobilization, and Extraction Technologies

Air sparging. Injection of air under pressure below the water table in unconfined aquifers. The method removes VOCs by volatilization while incidentally stimulating aerobic biodegradation processes. It is applicable in permeable and homogeneous soils.

Cosolvent flushing. Addition of a solvent to significantly increase the solubility of nonaqueous-phase liquids (NAPLs) and, in the case of heavy organic mixtures, to reduce overall NAPL viscosity and improve re-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

covery. Cosolvents greatly increase the solubility of sorbed organic contaminants.

Dual-phase extraction. A process of simultaneously removing water and air from a common borehole by the application of a high vacuum. The process dewaters the area to be treated and subsequently removes the contaminant by volatilization.

Electrokinetics. The migration of chemicals through a soil matrix under the application of electrical and hydraulic gradients to effect contaminant removal. The process can function in both saturated and unsaturated environments.

Electroosmosis. Use of an electrical potential to cause movement of pore water through a clay aquifer formation to treatment zones. This technique has been long understood as a means to control water movement in fine-grained media and is currently being investigated at waste sites to treat contaminants in ground water.

Fracturing technology. Injection of fluid under pressure into the soil matrix to break up the soil and facilitate movement of treatment fluids. The process employs the principle that if the overburden pressure is exceeded, the soil will fracture, creating fissures. Both pneumatic and hydraulic fracturing are employed. In many cases, a prop material is injected into the fracture at the time of fracturing or before the pressure is released to keep the fracture open while filling it with a transmissive material. Fractures generally occur along weak points in the soil matrix, such as in preexisting fractures, lenses, bedding planes, discontinuities, or desiccation cracks. In some cases, the soil may be notched to promote fractures at a particular horizon or in a particular direction. Once created, fractures provide a transmissive pathway for the injection or extraction of fluids.

In situ soil mixing. Use of augers or impellers to break apart the soil structure and increase its transmissivity. The increase in transmissivity is accomplished by the disruption of the soil matrix, creating channels throughout the soil. A diluent or bulking agent can be added to further increase transmissivity.

NAPL recovery. The physical removal of separate-phase organic liquids. The simplest form is a gravity drainage system, in which NAPLs flow into downgradient collection points. For light NAPLs (LNAPLs), recovery can be enhanced by depressing the water table and increasing the hydraulic gradient. The rate and extent of product recovery are inversely related to NAPL viscosity and proportional to hydraulic gradient; recovery is greatest for lighter products such as gasoline, diesel, and jet fuel. Dense NAPLs (DNAPLs) may be pumped from a depression in a confining layer located at the interface between relatively coarse- and fine-grained media.

Pump-and-treat system. A process for removing dissolved contaminants

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

from ground water by pumping the water to the surface and treating it. The process is effective for controlling and diminishing the size of plumes of dissolved contaminants. However, for source areas, it is effective only as a containment or control method due to the low solubility and large masses of contaminants present.

Soil flushing. An in situ process that uses chemical amendments and fluid pumping to mobilize and recover contaminants (see also cosolvent flushing and surfactant flushing).

Soil vapor extraction (SVE). The removal of volatile organic contaminants from unsaturated soils by inducing air flow and thus speeding contaminant volatilization. The treatment rate is a function of the volatility of the contaminant and the ratio between the air flow rate and contaminant mass. A secondary benefit of technology is that it stimulates aerobic biodegradation.

Soil washing. An ex situ process that first segregates the most contaminated soils and then washes them with a water-based solution. Generally, soil fines have a high concentration of contaminants, while coarse materials may be sufficiently clean that contaminant concentration are below action levels, allowing coarse materials to be disposed of separately. Once fines are separated from coarse soils, the fines are washed with a solution that may include surfactants, acids, chelating agents, or other amendments to enhance desorption and solubilization.

Steam sparging. Addition of steam to enhance contaminant volatilization in air sparging systems. Treatment rates are significantly faster than in standard air sparging systems.

Surfactant flushing. Application of anionic and nonionic surfactants in situ to enhance the removal of organic contaminants. Using surfactant doses greater than the critical micelle concentration for the surfactant (usually greater than 0.5 to 1.0 percent in soils), organic contaminants partition into mobile micelles, allowing them to be transported with ground water at concentrations many orders of magnitude greater than would otherwise be possible. The contaminant-laden solution is collected and treated ex situ. Surfactants also decrease surface tension between the NAPL and water and can cause remobilization of NAPL. Remobilization can be used to increase recovery of LNAPLs, but it is generally not considered favorable in most DNAPL treatment schemes. Variations on surfactant flushing systems include the use of foams and stable gases.

Thermal desorption. A process (different from incineration) that removes volatile and semivolatile organic compounds from excavated soils by transfer to a gas phase. Volatilization is a function of compound volatility, surface area, and temperature. The simplest desorbers use soil shredding to expose surface area. Either hot gases are applied to the

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

soil, usually in a rotary kiln or fluidized bed, or heat is transferred by solid-solid contact with the contaminated soil as it travels along a heated screw or conveyor. The vaporized contaminants are captured and collected or destroyed. The process may be augmented with the addition of quick lime, which generates heat as it hydrates. With compounds having medium to low volatility, thermal energy is added to enhance volatilization.

Thermally enhanced NAPL recovery. Use of steam or radio-frequency energy to supply heat and reduce NAPL viscosity. For heavy fuels or oils, the process can increase recovery by as much as an order of magnitude.

Thermally enhanced SVE. Addition of thermal energy to accelerate SVE cleanups or extend SVE application to less volatile organic mixtures such as diesel or fuel oil. Thermal energy can be supplied by steam, hot air, radio waves, microwaves, or electrical resistance.

Vacuum-assisted NAPL recovery. Application of a vacuum to reduce interstitial pressure, allowing NAPLs to move through soil more easily. Vacuum assistance can increase the rate and ultimate amount of product recovery by several fold.

In above-ground bioremediation cells (under construction), oxygen is supplied to soil via a network of embedded piping. Courtesy of Fluor Daniel GTI.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Monitoring an air sparging and soil vapor extraction system. Courtesy of Fluor Daniel GTI.

vast majority of the practices in this category are biological treatment methods for hydrocarbon-contaminated sites. For all other classes of chemicals, far fewer tested reactive treatment options are available.

Separation, mobilization, and extraction processes are designed to separate contaminants from geologic materials in the subsurface, mobilize them into the ground water or air in soil pores, and extract them from the subsurface. Some of these technologies use heat, chemicals, vacuums, or electrical currents to separate the contaminants from geologic materials and move the contaminants to a location where they can be extracted. For example, heat has a pronounced effect on decreasing the viscosity of nonaqueous-phase liquids (NAPLs) and increasing the vapor pressure of organic chemicals, making it easier to mobilize and extract them. Other technologies in this category alter the physical structure of the soil matrix by fracturing or mixing it, which facilitates the addition or extraction of fluids for subsurface treatment. Separation, mobilization, and extraction processes can enhance the efficiency of conventional pump-and-treat or SVE systems.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Availability of Remediation Technologies for Various Problem Contexts

Table 3-1 shows the availability of technologies in the three categories for treating four different types of contaminated media: (1) surface soils, sediments, and sludges; (2) the unsaturated zone (soil contamination below the surface but above the water table); (3) the saturated zone (contamination below the water table); and (4) subsurface source zones. As shown in Table 3-1, the availability of technologies is greatest for treatment of soils, sediments, and sludges. The deeper and more entrenched the contamination problem, the more limited is the menu of technology options.

Table 3-2 shows the availability of the three general categories of technologies for treating different classes of contaminants. As shown in the table and in Figure 3-1, a range of treatment alternatives has been developed for the relatively mobile and biodegradable contaminants (petroleum hydrocarbons and chlorinated solvents). The number of potential treatment technologies is much smaller for the other classes of chemicals. The remainder of this chapter discusses in detail the technology options for treating the six categories of contaminants shown in Table 3-2. These classes of contaminants are representative of contaminants typically found at hazardous waste sites.

CLEANUP OF PETROLEUM HYDROCARBONS

Sources

The presence of petroleum hydrocarbons in the subsurface is generally related to the transport, distribution, and use of fuels and oils. There are five main sources of petroleum hydrocarbon contamination: underground or above-ground storage tanks, tanker trucks, transfer terminals, pipelines, and refineries. Contamination in the subsurface typically is a result of leakage or spillage (slow, periodic, or catastrophic) or of disposal of wastes (separator sludges, waste oils, and refinery sludges and residuals). The vast majority of hydrocarbon-contaminated sites are associated with underground storage tanks. As shown in Table 1-2 in Chapter 1, there are an estimated 300,000 to 400,000 leaking underground storage tanks in the United States. In comparison, refinery and pipeline sites are fewer but typically much greater in both affected area and volume of contaminant released. According to the American Petroleum Institute, there are approximately 150 refineries in the United States (API, 1996).

Fate

Hydrocarbons are biodegradable and volatile with moderate to low solubility. Hydrocarbon contaminants in the subsurface can be found distributed among four phases: (1) sorbed to solids, (2) as an NAPL, (3) dissolved in the ground

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

TABLE 3-1 Technology Types Applicable to Different Contaminated Media

Context

Solidification, Stabilization, and Containment

Biological and Chemical Reaction

Separation, Mobilization, and Extraction

Surface soils, sediments, and sludges

Excavation, e

Pozzolanic agents, e, i

Lime / fly ash, e, i

Vitrification, e, i

Asphalt batching, e

Biopiles, e

Composting, e

Land farming, e

(Fungal treatment, e)

Bioslurry systems, e, (i)

Incineration, e

Phytoremediation, i

(Biostabilization, e, i)

Substitution, e

Thermal reduction, e

Solvent extraction, e

Thermal desorption, e

Soil washing, e

(Electrokinetic systems, e, i)

Unsaturated zone

Deep soil mixing

Excavation

(Polymer walls)

Grout walls

Slurry walls

Sheet pile walls

Bioventing

SVE

Thermally enhanced SVE

(Soil flushing with surfactants or cosolvents)

(Electrokinetic systems)

Saturated zones

Excavation

(Polymer walls)

Grout walls

Engineered in situ bioremediation

Intrinsic bioremediation

Biosparging

Pump-and-treat systems

Sparging: air and steam

(Electrokinetic systems)

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

 

Slurry walls

Sheet pile walls

(Passive-reactive barriers using enhanced sorption)

(Chemical oxidation / reduction)

Passive-reactive barriers

- using iron reactions

- using organic or microbiological reactions (- using enhanced sorption)

- using nutrient additions

Dual-phase recovery (Soil flushing with surfactants or cosolvents)

High-concentration source areas in the saturated zone

Pump-and-treat systems

Grout walls

slurry walls

(Polymer walls)

Sheet pile walls

Biosparging

Bioventing

(Chemical oxidation / reduction)

Engineered in situ bioremediation

Intrinsic bioremediation

NAPL recovery

Dual-phase extraction

(Soil flushing with surfactants or cosolvents)

Sparging: air and stream

NOTE: Applications that are not commercially available are shown in parentheses. For surface soils, sediments, and sludges, ''e" signifies an ex situ treatment method, and "i" signifies an in situ method. Technologies for surface soils, sediments, and sludges are predominantly ex situ processes, although there are some in situ alternatives. Because these technologies can potentially be applied either in situ (i) or ex situ (e), the modes of application are noted in the table.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Table 3-2 Treatment Technology Options for Different Classes of Contaminants

 

Petroleum Hydrocarbons

Chlorinated Solvents

Polycyclic Aromatic Hydrocarbons and Semivolatile Organic Compounds

PCBs

Inorganic Chemicals

Pesticides and explosives

Solidification, Stabilization, and Containment

Asphalt batching

X

na

X

 

X

 

Biostablization

X

na

?

?

na

 

Excavation (stabilization)

X

X

X

X

X

X

Grout walls

 

 

X

X

X

 

Lime addition

X(h)

na

 

 

X

 

Passive barriers using sorption or precipitation

?

?

?

 

?

 

Polymer walls

 

?

 

 

?

 

Pozzolanic agents

X(h)

na

?

?

X

 

Pump-and-treat systems

X

X

X

na

X

X

Sheet pile walls

 

X

X

X

 

X

Slurry walls

 

X

X

X

 

X

Vitrification

na

na

na

?

X

 

Chemical and Biological Reaction

Biopiles

X

na

X

?

na

X

Bioslurry systems

X

na

X

?

na

X

Biosparging

X(1)

?

?

 

na

na

Bioventing

X(1)

na

?

 

na

na

Chemical oxidation

?

?

?

 

na

?

Chemical reduction

 

?

 

 

X

X

Engineered bioremediation (in situ)

X

?

?

 

?

?

Incineration

X

X

X

X

na

X

Intrinsic bioremediation

X

X

?

?

na

?

NOTES:

X(h): applicable primarily for heavy fuels or high-molecular-weight solvents

X(l): applicable to light hydrocarbons only

na: technology not applicable to this class of contaminants

?: application not commercially available or exists in an experimental stage

blank: lack of information for qualitative comparison

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

 

Petroleum Hydrocarbons

Chlorinated solvents

Polycyclic aromatic Hydrocarbons and Semivolatile Organic Compounds

PCBs

Inorganic Chemicals

Pesticides and Explosives

Land farming

X

na

X

?

na

X

Passive-reactive barriers

 

 

 

 

 

 

- using iron

na

X

na

na

X

 

-using organic / microbiological reactions

X

X

?

 

?

 

-using enhanced sorption

na

?

?

 

?

 

-using passive / active nutrient additions

X

X

?

?

na

?

Phytoremediation

?

?

 

 

X

?

Substitution

na

X

na

X

na

 

Thermal destruction/reduction

X

?

X

?

na

 

Separation, Mobilization, and Extraction

 

 

 

 

 

 

Dual-phase extraction

X(l)

X

na

na

na

 

Electrokinetic systems

na

?

na

na

?

 

Soil washing

X

X

X

?

X

?

Soil flushing

 

 

 

 

 

 

-acid, base, or chelating agent

 

 

 

 

?

 

-steam

?

?

?

 

 

 

-foam

?

?

?

 

na

 

-surfactant / cosolvent

?

?

?

?

na

?

Sparging: air / steam

X(l)

X

?

na

na

 

Recycling / re-refining

X

na

na

na

X

 

Thermal desorption

X

X

X

X

 

X

Thermally enhanced SVE

X(h)

X

?

na

na

 

Solvent extraction

X

 

X

?

na

 

SVE

X(l)

X

na

na

na

 

NOTES:

X(h): applicable primarily for heavy fuels or high-molecular-weight solvents

X(l): applicable to light hydrocarbons only

na: technology not applicable to this class of contaminants

?: application not commercially available or exists in an experimental stage

blank: lack of information for qualitative comparison

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

water, and (4) as a vapor in unsaturated soil. Because hydrocarbon mixtures have low solubility, most of the hydrocarbon mass is typically in the sorbed or NAPL phase. For example, a typical phase distribution of gasoline in sand is 30 to 50 percent as NAPL, 40 to 50 percent sorbed, 2 to 5 percent dissolved, and less than 0.5 percent in the vapor phase (Brown et al., 1987b).

When hydrocarbon liquids are released to soil, they migrate downward until they are retained as a residual in soil pores. The amount of hydrocarbon liquid retained is a function of the fluid viscosity and the soil texture, which vary widely. More viscous (heavier) hydrocarbon mixtures and fine soil textures generally result in greater hydrocarbon retention within the soil. The residual hydrocarbon concentration in soil ranges from approximately 10,000 to 15,000 mg/kg for gasoline in fine sand to 60,000 to 80,000 mg/kg for no. 6 fuel oil in fine sand (Lyman et al., 1992). Because hydrocarbon mixtures are less dense than water, they typically accumulate in a layer on the water table when sufficient hydrocarbon has spilled or leaked to saturate the soil, allowing free-phase liquid to migrate to the water table.

Three mechanisms serve to attenuate petroleum hydrocarbon liquids in the subsurface: (1) biodegradation, (2) volatile transport and exhaust to the soil surface and (3) dissolution. Because the effective solubilities and vapor pressures of the various components of hydrocarbon mixtures are low, removal of these source materials by solubilization or volatilization is slow. Biodegradation is usually the more significant mechanism for attenuation of hydrocarbons except near the soil surface, where volatilization may play a more significant role. Biodegradation is relatively slow for sorbed hydrocarbons, but biodegradation of dissolved hydrocarbons is relatively rapid.

Biodegradation is carried out by ubiquitous native soil microorganisms (Claus and Walker, 1964; Alexander, 1994; Chapelle, 1993). The number of hydrocarbon-degrating microorganisms is much greater in hydrocarbon-contaminated sediments than in uncontaminated zones (Aelion and Bradley, 1991). The rate of biodegradation and the metabolic products produced are controlled primarily by the types of hydrocarbons present and the availability of electron acceptors and nutrients needed by the microorganisms to conduct the reactions (National Research Council, 1993). Aerobic biodegradation is more rapid than anaerobic biodegradation, but oxygen is generally limited in the immediate vicinity of subsurface hydrocarbons because of the low solubility of oxygen and the high oxygen demand created by the hydrocarbon-degrading organisms. In the absence of sufficient oxygen, microorganisms can use alternative electron acceptors such as nitrate, iron, sulfate, and carbon dioxide to biodegrade hydrocarbons (Chapelle, 1993; Hutchins and Wilson, 1994; Barbaro et al., 1992; Wilson et al., 1994).

Dissolution, volatilization, and biodegradation do not rapidly or completely remove hydrocarbon mass from the subsurface. However, these processes together cause weathering of the petroleum product. As a product weathers, the

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

TABLE 3-3 Treatability of Petroleum Hydrocarbons Volatile Fraction

Hydrocarbon

Volatile Fraction (Percent)

Degradability

Treatability

BTEX solvents

100

High

Very high

Gasoline

>95

High

High

Jet fuel

75

High

High

Diesel/kerosene

35

High

Moderate-high

No. 2 fuel oil

20

Moderate

Moderate

No. 4 fuel oil

10 –20

Low-moderate

Low-moderate

Lube oil

10 –20

Low-moderate

Low-moderate

Waste oils

<10

Low

Low

Crude oils

<10

Low

Low

 

SOURCE: Brown and Norris, 1986.

more mobile (volatile and soluble) and degradable fractions are removed. The remaining residue is more viscous and less soluble than the original contaminant mixture, reducing the risk of continued contamination of soil and ground water.

Remediation Technology Options

Because some components of petroleum hydrocarbons are relatively mobile and biodegradable compared to other types of contaminants, a large number of technologies are applicable to hydrocarbon remediation. Applicable technologies include NAPL recovery, dual-phase extraction, in situ bioremediation, biopiles, land farming, SVE, bioventing, biosparging, soil washing, and soil flushing. The processes that can be applied to various sources of hydrocarbon contaminants vary considerably and are a function of the type of hydrocarbon product. In general, which remediation technologies will be applicable to hydrocarbon contamination is a function of the mobility and reactivity of the hydrocarbon. Mobility and reactivity, in turn, are functions of the properties and quantities of the particular hydrocarbon and the hydrogeologic setting in which it is found. In general, lighter hydrocarbons are more volatile and degradable and thus more readily treatable than other types of hydrocarbons. Table 3-3 shows the treatability of various petroleum hydrocarbon products (Brown et al., 1987a).

Separation Techniques

Soil Vapor Extraction. SVE removes petroleum hydrocarbons by two mechanisms: violatilization and biodegradation (P. Johnson et al., 1990; R.L.Johnson et al., 1992). Volatilization occurs when the air stream contacts residual hydrocarbons or films of water containing dissolved hydrocarbons in soil. Biodegradation

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

occurs because the induced air flow supplies oxygen for aerobic biodegradation. All petroleum hydrocarbon fuels are essentially biodegradable (Chapelle, 1993). However, the volatile fraction, and therefore the rate of treatment of hydrocarbons, varies. Hydrocarbon fuels with a high volatile fraction will be removed most rapidly using SVE; those with a low volatile fraction will be less responsive. Volatility ranges from more than 90 percent for gasoline to less than 10 percent for crude oil (see Table 3-3). Based on approximate volatilities. SVE is a primary technology for the remediation of gasoline, jet fuel, and mineral spirits. SVE can be used to treat the other, less volatile hydrocarbon mixtures as part of a biodegradation strategy, a process often termed bioventing.

SVE is commonly limited by the permeability of the soil and by the degree of saturation. SVE will not work well in low-permeability soils such as silts and clays or in highly saturated areas, such as the capillary fringe or below the water table.

SVE is a widely used commercial technology for the treatment of petroleum hydrocarbon releases; as of 1995, it was in use or had been used at 139 Superfund sites and nearly 9,000 underground storage tank sites (see Figures 1-7 and 1-8 in Chapter 1). It has moderate to high success in achieving specific regulatory goals. Generally, SVE is most successful for treating more volatile hydrocarbon products and more permeable soils.

Soil Washing and Soil Flushing. Significant quantities of petroleum hydrocarbons can be retained in soils as a residual, discontinuous NAPL phase. One approach to removing residual petroleum products is to use surfactants or cosolvents. Surfactants and cosolvents can desorb hydrocarbons from soils and can decrease the interfacial tension of the NAPL, forcing it from the soil matrix and allowing it to coalesce into a recoverable, continuous NAPL phase (Gotlieb et al., 1993).

There are two basic types of surfactant and cosolvent applications. One is soil washing, which is a process for removing hydrocarbons from excavated soils. The other is soil flushing, which is the in situ application of surfactants or cosolvents to contaminated soils. Both of these processes have significant variations. With both types of applications, site-specific blends of additives are generally used. A significant portion of the cost is associated with unrecovered additives and disposal of generated fluids.

In soil washing, the petroleum-contaminated soil is excavated, slurried, and processed. In some soil washing systems, the soil slurry is processed by soil sizing to concentrate the hydrocarbons in the finer soil fractions. The surfactant or cosolvent is then added to the fine soil slurry fraction, minimizing the amount of additives required. Other systems add the remedial agent directly to the soil and then agitate the slurry. The soil, water, and NAPL phases are then separated. Some soil sizing may be used to enhance the separation (coarser fractions are easier to dewater). Soil washing is used commercially to treat petroleum-contaminated soils (Delta Omega Technologies, 1994). It is not as commonly used to

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

treat lighter, more volatile products such as gasoline, jet fuel, or mineral spirits, because removing these products by volatilization is more cost effective. While soil washing is used to treat a wide range of soil types, it has limited applicability to soils with high clay content due to problems in separating the fine clay particles.

There are three principal variations to in situ soil flushing: (1) enhanced solubilization, (2) emulsification, and (3) displacement. In the first approach, chemical additives (such as surfactants and cosolvents) are used to enhance the aqueous solubility of contaminants in order to more efficiently dissolve or desorb the petroleum hydrocarbons (or other organic contaminants). In the second approach, higher concentrations of these additives are used to emulsify the NAPLs, either as microemulsions or middle-phase emulsions, and flush them out more effectively. The contaminant molecules dissolve into mobile micelles of the additive, which are entrained in the water. In the third approach, additives that decrease NAPL-water interfacial tensions to very low values (less than 1 dyne/cm) are used to mobilize the trapped ganglia and displace the resulting bank of free-phase liquid. The first approach involves miscible displacement (i.e., resident and introduced fluids mix completely), while the other two methods involve immiscible displacement (two immiscible fluids—oil and water—are displaced). Combinations of various surfactants and cosolvents can be used to achieve solubilization, emulsification, or displacement. In situ flushing with steam has also been attempted. All of these technologies have been tested and used for enhanced recovery in oil fields, but use for site remediation purposes has been limited to several pilot-scale and a few commercial-scale tests (Grubb and Sitar, 1994; EPA, 1995a).

Thermal Desorption. Thermal desorption is a commonly used technology for treating excavated petroleum-contaminated soils. It is based on the principle that volatility increases with increasing temperature. What distinguishes thermal desorption from incineration is that the soil does not contact a flame. The petroleum product is volatilized off the soil, and the resulting vapor stream is captured and treated. There are two variations: low temperature and high temperature. Low temperature thermal desorption uses temperatures of less than 200 °C (400 °F). It is used to treat more volatile products such as gasoline, jet fuel, mineral spirits, and sometimes diesel. High temperature thermal desorption uses temperatures of 320 to 430 °C (600 to 800 °F). It is used to treat soil contaminated with diesel and fuel oil. Neither process is effective with very heavy products such as no. 6 crude oils. With thermal desorption, the heat is applied either through hot air or through radiant or convectional heating. With hot air systems, a fuel is combusted, and the combustion gases are fed into the desorption unit.

Thermal desorption is used for a wide range of products, but use is most common for motor fuels (gasoline, diesel, and jet fuel). Units range in size from those that can process 5 to 10 tons per hour to those that can handle more than 40

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

tons per hour. The process is generally able to achieve regulatory standards that allow the soil to be reused or disposed of on site.

NAPL Recovery. NAPL recovery is the removal of separate-phase liquid hydrocarbons (at amounts greater than residual saturation) from the soil matrix. NAPL recovery is best accomplished with low viscosity hydrocarbon products. Viscous products such as no. 6 fuel oil or crude oils do not flow readily through soils and are not typically recovered. Most NAPL recovery systems also produce water. Because gravity drives the collection of NAPLs, the water table is often depressed to increase the flow of NAPL into the collection point.

The variations in NAPL recovery are a function of how and where the NAPL and water phases are separated. In permeable formations and with low viscosity products, the separation process is accomplished in situ using dual pumps (product and water), automatic bailers, or oil skimmers. In low-permeability formations, a total fluid extraction system is used to recover both product and water. These are then separated on the surface with conventional technologies for separating oil and water. A recent innovation in NAPL recovery is vacuum-assisted NAPL recovery (Kittel et al., 1995). In this process, a vacuum is applied to the recovery well to promote the flow of NAPL into the collection point. The vacuum application minimizes the amount of water that is collected by creating a driving force that is an alternative to depressing the water table. The vacuum may be applied to the well bore directly or through an inner tube (drop tube). The use of a drop tube is sometimes referred to as "bioslurping" (Kittel et al., 1995).

NAPL recovery is a standard remediation technology employed at almost any site having recoverable NAPL. Most applications use water table depression as the driving force for NAPL recovery. Vacuum assisted recovery is being increasingly used because it minimizes the amount of water that needs to be treated and disposed. NAPL recovery is generally able to remove NAPLs to the point where all that remains is a thin film of oil noticeable only by its iridescent sheen on the water. It is ineffective for NAPLs present as residual saturation in soil.

Thermally Enhanced Product Recovery. Highly viscous petroleum products such as no. 4 and no. 6 fuel oils or crude oils do not flow readily through geologic formations and are therefore not easily recovered with conventional NAPL recovery techniques. A means of promoting their recovery directly from soils is to use thermally enhanced product recovery. Viscosity is a function of temperature: the higher the temperature, the lower the viscosity. Typically, subsurface temperatures need to be in the range of 66 to 93°C (150 to 200°F) for the technology to be effective. The subsurface temperature may be raised using hot air, steam, electrical heating, or radio frequency heating. Hot air has limited application because of its low thermal capacity. The application of heat has been demonstrated to increase recovery of heavy oil products by an order of magnitude.

Thermally enhanced product recovery is a commercial technology but has

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

limited utility (EPA, 1995b). Generally, it is used for heavy products and where steam is readily available, such as at sites with existing boilers. The cost of a transportable boiler makes this technology too expensive for routine operations.

Thermally enhanced product recovery is generally able to remove NAPL's from wells down to about a tenth of a meter (several inches). It can remove some, but not all, NAPLs present as residual saturation in soil.

Dual-Phase Extraction. Dual-phase extraction is the simultaneous removal of vapors and water from a common borehole by the application of a high vacuum. The purpose of the technology is to treat soil contamination below the water table so that the volatile components may be removed. The technology combines dewatering and venting. It is generally applied to lower permeability formations to minimize the amount of water that needs to be recovered or treated.

There are two variations of this technology. The first uses an internal drop tube to apply the vacuum to the bottom of the borehole. The drop tube removes the water in the well; once the well is dewatered, it will also remove vapors. The second variation uses conventional down-hole water pumps and applies a vacuum to the borehole. The applied vacuum aids in water removal and promotes volatilization in the dewatered soil.

Dual-phase extraction is best applied to hydrocarbon mixtures (such as gasoline, jet fuel, and mineral spirits) that have highly volatile components. It also

Sparging point being checked during regular site inspection. Courtesy of Fluor Daniel GTI.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

may be used in conjunction with bioremediation to treat less volatile but degradable hydrocarbons. Use of this technology is increasing due to reports that it can be applied at low-permeability or heterogeneous sites for which few other remediation options exist (Brown and Falotico. 1994).

Air Sparging. Air sparging is the injection of air directly into the saturated zone (Brown. 1992). The injected air treats adsorbed and dissolved hydrocarbons through volatilization and/or biodegradation. The success of air sparging depends on the distribution of air through the saturated zone and the degree of mixing of the ground water. Air sparging works best in homogeneous, moderately permeable media such as fine to medium sands.

Air sparging is used to treat both volatile and nonvolatile hydrocarbon mixtures. With volatile mixtures such as gasoline and jet fuel, air sparging operates as both an extraction (volatilization) and a transformation (biodegradation) process. With less volatile mixtures, it is primarily a means of supplying oxygen to enhance biodegradation. For volatile hydrocarbons, air sparging systems are generally applied with an SVE system to capture and released hydrocarbons.

Air sparging is more effective for treating dissolved hydrocarbon plumes than for treating source areas (Bass and Brown, 1996). Air sparging has achieved regulatory goals with little rebound in contaminant levels for plumes of dissolved hydrocarbons at numerous field sites. Because of its effectiveness in treating dissolved hydrocarbons, air sparging can be used as a barrier system, in which a line of sparge wells is placed across a plume to intercept and remove dissolved constituents. The ability of air sparging to treat dissolved contaminants has made it an alternative to conventional pump-and-treat systems.

When air sparging systems are used to treat contaminant source areas, there is a higher probability of rebound of contaminant concentrations after treatment, especially when the NAPLs are present. The use of air sparging to treat source areas requires close well spacing and moderate to high air flows.

A related technology is "biosparging" which uses low air flows to minimize the amount of volatilization, so that any volatilized hydrocarbons are biodegraded in the vadose zone before being discharged to the atmosphere. This technique eliminates the need for an SVE system to accompany the sparging system.

Air sparging is a commonly used technology, especially for gasoline contaminated sites. It is also, used, although less commonly, at sites contaminated with diesel and jet fuel.

Biological Reaction Techniques

As Table 3-3 shows, bioremediation techniques (including biopiles, land farming, bioventing, biosparging, sparge barriers, and intrinsic bioremediation, as well as other bioremediation systems) are widely applicable for the control and

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

remediation of petroleum hydrocarbons. Many of the current bioremediation technologies on the market were initially developed to treat petroleum hydrocarbons.

The rate at which petroleum products biodegrade varies. Generally, the heavier the product, the slower the rate of biodegradation. Natural hydrocarbon biodegradation rates can be enhanced when the substance that most limits microbial growth is supplied to the contaminated zone. This premise provides the basis for most bioremediation processes. Because the hydrocarbon contaminants supply carbon for growth, in most cases the growth-limiting factor is the electron acceptor. In unsaturated soil, oxygen can be supplied by increasing air circulation. SVE, bioventing (see Box 3-4), and biopiles are three technologies designed to increase air circulation. The U.S. Air Force has applied bioventing systems at sites across the country, with consistent hydrocarbon degradation rates of 2.4 to 27 mg hydrocarbon per kg soil per day at soil temperatures between 4 and 25°C (39 and 77°F) (Ong et al., 1994). In the presence of sufficient oxygen, elements such as nitrogen, phosphorus, and potassium in nutrient-poor soils can limit microbial growth and biodegradation (Aelion and Bradley, 1991; Armstrong et al., 1991; Allen-King et al., 1994a,b), and addition of these limiting nutrients can also enhance biodegradation rates (Allen-King et al., 1994b).

Oxygen (O2) can also be added to the saturated zone using one of several methods (Brown et al., 1990). The first bioremediation systems used aerated water, but these systems were limited by the relatively low solubility of O2 in water (8–12 mg/liter) relative to air. Typically, about 2 to 3 g of O2 are required per g of hydrocarbon for complete mineralization; only about 3 mg/liter of total dissolved hydrocarbon can be mineralized in water saturated with respect to atmospheric O2. The next generation of bioremediation technology used hydrogen peroxide (H2O2) to stimulate saturated-zone biodegradation (Brown et al., 1993). Air sparging is currently the most common method for supplying O2 for enhanced biodegradation (Brown and Jasiulewicz, 1992). Solid O2-releasing sources can also be used to promote biodegradation by adding O2 to the ground water in situ as it flows through a permeable barrier (Bianchi-Mosquera et al., 1994).

With petroleum hydrocarbons, intrinsic remediation is a significant process. Intrinsic remediation is the reliance on natural processes, including volatilization, sorption, dilution, reactions with naturally occurring chemicals, and, most commonly, biodegradation, to decrease contaminant concentrations without human intervention other than careful monitoring. Intrinsic bioremediation (the type of intrinsic remediation in which biological processes predominate) has been well documented to occur in plumes of dissolved petroleum hydrocarbon contaminants. As documented in a survey of sites in California, petroleum hydrocarbon plumes reach an equilibrium point, often within 60 to 90 m downgradient of the source, beyond which ground water contamination generally does not pass (Rice et al., 1995). The location of the equilibrium point depends on the size of the source area, the ground water flow rate, and other environmental conditions. Equilibrium is reached though a combination of anaerobic and aerobic degradation

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-4 History of Development of Bioventing

The development of bioventing illustrates the evolution of a technology driven by market need. The market for hydrocarbon treatment technology has been significant because of the widespread use and environmental release of hydrocarbon fuels by government, industry, and the public and the enactment of legislation requiring contaminated site cleanup. While technology existed for the treatment of hydrocarbon contamination, the cost and complexity of treatment often precluded widespread use of these technologies other than in areas of heightened exposure, such as at retail gasoline stations in urban and suburban areas. The Department of Defense (DOD), in particular the Air Force, has a large number of fuel handling and storage areas, many of which have associated environmental problems. Many of these sites are in remote locations where the installation and operation of treatment systems is difficult and costly. Thus, there was a need for a simple but effective technology that could address hydrocarbon contamination in remote areas. This need for inexpensive but effective treatment technology was the market driver for the development of bioventing.

The basis for bioventing lies in two technologies: SVE (see Box 3-2) and bioremediation. Early in its application, SVE was considered a very cost-effective technology as long as the recovered vapors could be discharged directly to the atmosphere without treatment. However, concerns about air quality necessitated the use of vapor treatment, which significantly raised costs. Parallel to the development of SVE, developers of in situ bioremediation recognized that oxygen supply was a key to stimulating the biodegradation of hydrocarbons (see Box 3-1). However, the oxygenation systems used for in situ bioremediation were either ineffective or costly. Early in its development, the potential of SVE to supply oxygen and stimulate biodegradation was recognized (Thorton and Wooten, 1982; Texas Research Institute, 1982; Ely and Heffner, 1991). Despite these parallel developments, SVE and bioremediation remained separately applied technologies. Keeping SVE and bioremediation apart were concerns that bacteria would be unable to effectively scavenge oxygen from an SVE flow stream and that typical SVE systems generated considerable vapors, which often required costly vapor collection and treatment. Thus, practitioners believed that SVE would be an ineffective and costly from of bioremediation.

Several factors changed the separate application and development of SVE and bioremediation and led to the emergence of bioventing. First was the recognition that bacteria were able to effectively use oxygen from an SVE system. Early work at Hill Air Force Base demonstrated that, even at high SVE flow rates, oxygen levels were significantly depleted due to hydrocarbon biodegradation activity (Hinchee et al., 1989), demonstrating the ability of bacteria to scavenge oxygen from an air

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

stream. Second was the recognition that vapor levels produced during SVE operation were a function of the rate of air flow and could be controlled. (Hoag and Bruel, 1988; Johnson and Ettinger, 1994). Third was the finding that many fuels at DOD sites had diminished concentrations of volatile hydrocarbon components compared to gasoline, making the control of vapor emissions even less problematic.

Based on these findings, researchers postulated that an air-based bioremediation system could be developed; the rate of volatilization could be balanced with the rate of biodegradation so that there would be no appreciable volatile discharge. Early test work on Air Force sites demonstrated that such a balanced system could be designed and operated (Miller et al., 1990; Hinchee and Ong, 1992). This early work was expanded into the Air Force's bioventing initiative, as a result of which more than 150 bioventing projects have been installed to date.

Bioventing has now evolved from an adapted form of SVE to a separate, low-cost technology. Early forms of bioventing used a vacuum-based withdrawal system augmented with nutrient addition. With the demonstration that vapor levels could be readily controlled by adjusting the air flow rate, bioventing systems switched to lower cost air injection systems. Test work demonstrated that nutrient addition was not usually necessary because oxygen is the factor limiting microbial growth, making bioventing a simple air injection system. Finally, the understanding of how hydrocarbon-utilizing bacteria scavenge oxygen has led to the development of an effective but low-cost monitoring method: in situ respirometry. With in situ respirometry, the rate of oxygen uptake and/or carbon dioxide production is used as an indicator of biodegradation activity. When the respiration rate approaches background levels (i.e., the rate determined in a nearby uncontaminated location), remediation is considered complete. This method eliminates the need for expensive soil sampling.

processes. As noted above, O2 is limited in the immediate vicinity of subsurface hydrocarbons. In the absence of sufficient O2 organisms will use alternate electron acceptors. Alternate electron acceptors become important when the dissolved O2 level drops below approximately 2 mg/liter (Salanitro, 1993).

As pictured in Figure 3-2, plumes of dissolved hydrocarbons typically have an anaerobic core area surrounded by an aerobic zone (Norris and Matthews 1994). In the anaerobic core, hydrocarbons may be degraded by denitrification iron reduction, sulfate reduction, and methanogenesis (see National Research Council, 1993). In the aerobic zone, they are oxidized by O2

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

FIGURE 3-2 Plumes of petroleum hydrocarbons in ground water typically have an anaerobic (oxygen-free) core area surrounded by an aerobic (oxygen-containing) margin. Anaerobic microorganisms degrade contaminants in the core, while aerobes degrade them in the margin. SOURCE: Reprinted, with permission, from Norris and Matthews, 1994 © 1994 by Lewis Publishers.

Research Needs

While an abundance of technologies is available for cleaning up sites contaminated with petroleum hydrocarbons, some problem areas still need resolution. The main needs are technologies for treating heavy hydrocarbon mixtures and hydrocarbons in low-permeability or highly heterogeneous formations. Heavy hydrocarbons have very low solubilities, sorb strongly, and resist degradation, rendering existing technologies relatively ineffective. At the same time, the impact of heavier, less soluble hydrocarbons on ground water quality needs careful study, because lack of mobility and bioavailability may limit adverse effects. Existing technologies are most limited in cleaning up low-permeability or heterogeneous geologic media because of the reduced circulation of fluids (air, water, NAPLs) in these media; technologies are needed to improve the ability to move fluids through such media. In addition, there is a continual need for investigation of ways to optimize existing processes for the treatment of all types of petroleum hydrocarbons and for the development of more cost-effective processes for hydrocarbon treatment.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

CLEANUP OF CHLORINATED SOLVENTS

Sources

Chlorinated solvent use has been ubiquitous in society since these compounds were widely introduced after World War II, although in recent years use has declined somewhat due to more stringent environmental regulations. Global use of the chlorinated solvents trichloroethylene (TCE), perchloroethylene (PCE), and 1,1,1-trichloroethan e (1,1,1-TCA) in 1994 totaled 900,000 metric tons, with U.S. use accounting for 40 percent of the total (Leder and Yoshida, 1995). Users vary from large manufacturing facilities, to local businesses such as garages, photographic shops, and neighborhood dry cleaners, to homeowners. Chlorinated solvents can dissolve oily materials, have low flammability, and are fairly stable, both chemically and biologically. They are commonly used in industry as chemical carriers and solvents, paint removers, and cleaning solvents. Some of the common cleaning applications of these materials are metal degreasing, circuit board cleaning, metal parts cleaning, and dry cleaning. Chlorinated solvents are also used as intermediates in chemical manufacturing and as carrier solvents in the application of pesticides and herbicides. They have also been employed as fumigants. For a period of time, because of their solvent properties and density, TCA, TCE, and PCE were also used as household drain cleaners (Pankow and Cherry, 1996).

Because of their widespread use in industry, commercial establishments, agriculture, and homes, chlorinated solvents are among the most common ground water contaminants. Nine of the 20 most common chemicals found in ground water at Superfund sites are chlorinated solvents. TCE is the contaminant most commonly detected in ground water at Superfund sites, and PCE is third most common (National Research Council, 1994).

Fate

Chlorinated solvents may be released to the environment through the use, loss, or disposal of the neat liquids or through the use or disposal of wash and rinse waters containing residual solvents. In the latter case, the site will be affected primarily by dissolved-phase contaminants with concentrations as high as tens to hundreds of parts per million.

The movement and dispersion of chlorinated solvents in the subsurface vary depending on whether the solvents were released as a neat liquid or in dissolved form. If released in dissolved form, chlorinated solvent migration is governed largely by hydrogeological processes. The presence of solubilizing agents such as soaps (from wash waters) that counteract natural soil sorption-retardation mechanisms may facilitate the migration of the dissolved solvents. If the chlorinated solvent was released as a neat liquid, the liquid solvent will migrate downward

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

through the soil column under the force of gravity. A portion of the solvent will be retained in the soil pores, but if sufficient solvent is present, the solvent will saturate the available soil pore space and continue moving downward until it encounters a physical barrier or the water table. When the solvent encounters the water table, it will spread out along the water table until enough mass accumulates to overcome capillary forces (Schwille, 1988). At this point, the chlorinated solvent will penetrate the surface of the water table due to the much greater density of the chlorinated solvent relative to water and travel downward by gravity until the mass of moving liquid is diminished by sorption or until it encounters an aquitard. If there is sufficient liquid mass, the solvent can accumulate along the aquitard as a DNAPL (Cohen and Mercer, 1993). (For an illustration of chlorinated solvent transport, see Figure 1-5 in Chapter 1.)

Contamination due to the release of large quantities of chlorinated solvent can comprise several distinct problems (see Figure 1-5), including gas-phase solvent in the vadoze zone, sorbed solvent and residual DNAPL both above and below the water table, and dissolved-phase contamination that can occur in both shallow and deep sections of the aquifer. The amount of solvent retained by the soils can range from 3 to 30 liter/m 3 in saturated soils and from 5 to 50 liter/m 3 in saturated soils (Mercer and Cohen, 1990). Generally, more solvent will be retained in finer soils. Retained DNAPL can occupy as much as 5 to 25 percent of the available pore space in sandy soils (Mercer and Cohen, 1990).

In general, the difficulty of treating chlorinated solvent contamination problems is, in increasing order and without regard to the geologic matrix, as follows:

  1. residual-phase solvents in the unsaturated zone,

  2. dissolved-phase solvents,

  3. residual-phase solvents in the saturated zone, and

  4. solvents present as pools of DNAPLs.

Residual-phase chlorinated solvents in the vadose zone are the easiest to treat because of the high vapor pressure of most of these solvents and because moving air through soils is easier than moving water through the saturated zone. Dissolved-phase chlorinated solvents can be treated if there are no appreciable residual-phase solvents present—that is, if the dissolved plume is the result of the discharge of wash waters or low-level use of solvents. Residual-phase solvents in the saturated zone are treatable, but they must be located. Delineating the affected area can be the most difficult part of remediation. If the saturated zone residual-phase solvents are present in clays or fractured rock, treatment is difficult because of limited access. Solvents present as DNAPLs are the most difficult to treat because they are difficult to locate (National Research Council, 1994). There are no reliable techniques for detecting the presence of DNAPLs, and their detection is often fortuitous, or their presence may simply be inferred from contaminant concentration data in the ground water. In addition, when DNAPL sources are

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

TABLE 3-4 Solubilities and Vapor Pressures of Chlorinated Solvents

Compound

Solubility (mg/liter)

Vapor Pressure (mm Hg)

Methylene chloride

20,000

349

Chloroform

8,200

160

Carbon tetrachloride

800

900

1,1-Dichloroethylene

400

495

trans-1,2-Dichloroethylene

600

265

1,1-Dichloroethane

5,500

182

1,2-Dichloroethane

8,700

64.0

Trichloroethylene

1,100

57.8

Tetrachloroethylene

150

14.0

1,1,1-Trichloroethane

1,360

100

 

SOURCE: Cohen and Mercer, 1993.

located, they are often difficult to access because they are usually at the bottom of the aquifer. A complication that frequently results with the loss of significant quantities of neat solvents is their penetration of fractures in clays or rock (Pankow and Cherry, 1996). Flow through fractures can be rapid and can occur in both saturated and unsaturated environments. Retention of the chlorinated solvents in the fractures makes remediation a difficult process.

Once chlorinated solvents have penetrated into the subsurface, their fate is quite complex. While chlorinated solvents are stable, undergoing neither rapid chemical nor biological transformations, they are nevertheless subjects to several processes (including volatilization, biodegradation, and chemical transformation) that can cause their concentrations to slowly decrease. These processes can be exploited in remediation.

Chlorinated solvents are relatively soluble and highly volatile. Thus, dissolution, dispersion, and volatilization are significant transport mechanisms. Table 3-4 provides the solubilities and vapor pressures for a number of chlorinated solvents. The aqueous solubilities are several orders of magnitude higher than drinking water standards, and thus dilution by hydrodynamic dispersion of chlorinated solvents is not a viable mechanism for managing sites contaminated with these compounds.

Recent research has demonstrated that chlorinated solvents biodegrade under certain conditions. However, there is little information on in situ rates or how to manipulate the rate of degradation. For less-chlorinated solvents (e.g., those having fewer than about two chlorine atoms per molecule), aerobic degradation can occur if sufficient O2 is present (National Research Council, 1993). Aerobic degradation of more highly chlorinated solvents (e.g., TCE) can occur by cometabolic pathways, wherein bacteria live off a second substrate (carbon and

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

energy source) but fortuitously degrade the chlorinated solvent (National Research Council, 1993). This may occur when chlorinated solvents exist as co-contaminants with the petroleum fuel components benzene, toluene, ethylbenzene, and xylene, provided that O2 is not depleted, because toluene is an effective cometabolite (Chapelle, 1993). Under aerobic conditions, chlorinated solvents such as vinyl chloride, dichloroethylene (DCE), and TCE may be transformed to harmless byproducts, as was observed in pilot field tests at Moffett Field, California. In these tests, methanotrophic bacteria cometabolized chlorinated aliphatic solvents in the presence of methane and O2 (Semprini et al., 1990).

Chlorinated solvents also may be transformed under anaerobic conditions. In this case, the chlorinated compounds undergo a process of reductive dechlorination, in which the solvents are transformed to less chlorinated compounds. For example, anaerobic microorganisms can convert TCE to DCE and DCE to vinyl chloride (Chapelle, 1993). Recent work has shown that anaerobes can in turn reduce vinyl chloride to ethene, which is in turn converted to methane, carbon dioxide, and hydrogen chloride (Chapelle, 1993). Current research is characterizing degradation of chlorinated solvents by bacterial communities that use a variety of electron acceptors, including nitrate, iron, and sulfur, as well as by methane-producing bacteria (methanogens). Most of these organisms thrive more readily on low levels of dissolved contaminants than on NAPL or sorbed-phase contaminants. High concentrations of chlorinated solvents are toxic to microorganisms.

Chlorinated solvents also may undergo chemical transformation through hydrolysis, losing chlorine atoms and creating a less chlorinated daughter product. This hydrolysis reaction has been observed at sites contaminated with 1,1,1-TCA (D. Bass, Fluor Daniel GTI, unpublished data, 1996).

Remediation Technology Options

Cleaning up chlorinated solvents is significantly more difficult than cleaning up petroleum hydrocarbons. Because the neat solvent, unlike petroleum hydrocarbons, is more dense than water, it can migrate below the water table. Once below the water table, it can penetrate deep into the saturated zone without appreciable spreading and contaminate areas below the water table that are difficult to locate and reach. In addition, chlorinated solvents have a high relative solubility, and their aqueous-phase transport is not significantly slowed by adsorption to aquifer solids. Therefore, a substantial amount of contamination will dissolve from chlorinated solvent source areas and form large plumes of contamination in ground water (Pankow and Cherry, 1996). Despite these difficulties, considerable progress has been made in the past decade in developing and refining methods for cleanup of sites contaminated with chlorinated solvents.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Separation Techniques

Because chlorinated solvents are relatively volatile and soluble, the primary treatment technologies currently used for sites contaminated with chlorinated solvents are separation and extraction processes. The four most widely used technologies for chlorinated solvent cleanup are pump-and-treat systems, SVE, air sparging, and dual-phase extraction (Fluor Daniel GTI, unpublished market survey data, 1996). Because of the high volatility of many solvents, the most efficient of these technologies for dealing with source areas are aeration processes: SVE, air sparging, and dual-phase vacuum extraction. Pump-and-treat systems are effective primarily as containment systems or as a means of treating low concentrations of dissolved contaminants (National Research Council, 1994).

The persistent problems in the treatment of sites contaminated with chlorinated solvents are related to removing the solvents from low-permeability zones and fractured rock and treating residual material and pools of separate-phase DNAPLs. In low-permeability zones, not only is delivering air or water to volatilize or dissolve the contaminant very difficult, but, as discussed above, chlorinated solvents can also penetrate into clays and fractures, making them difficult to find and limiting their extractability. Two approaches are being developed to address these limitations. The first is chemically enhanced removal using surfactants, foams, or cosolvents (Pope and Wade, 1995; Annable et al., 1996; Jafvert, 1996). These processes are designed to desorb, solubilize, or displace residual-phase solvents or DNAPLs. The contaminants are removed through liquid recovery in either an aqueous or nonaqueous phase. The second is thermally enhanced mobilization through the injection of steam (Udell and Stewart, 1989, 1990). These processes have a potential drawback in that they may cause further, unwanted migration of DNAPL. This unintended migration may occur when the remediation processes cause coalescence and/or lowering of the surface tension of the residual-phase material, leading to the formation of a pool of free-product DNAPL that may penetrate deeper into the subsurface (Pennell et al., 1996).

Reaction Techniques

Dissolved chlorinated solvents are somewhat biologically and chemically reactive, and efforts are under way to develop reactive technologies for cleaning up these contaminants. Chemical oxidation is a developing technology that has promise for the direct oxidation of chlorinated ethylenes, which have a carbon-carbon double bond that is vulnerable to oxidative attack. Either ozone or Fenton's reagent (iron-catalyzed H2O2 ) can be used. In addition, chlorinated solvents may be chemically transformed by zero-valent iron (Gillham and O'Hannesin, 1994; Wilson, 1995; Gillham, 1995). The process employs an iron-filled trench (a passive-reactive barrier) through which the contaminated ground water flows; the chlorinated solvents are chemically reduced upon contact with the iron (see Box

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-5 Metallic Iron Barrier for In Situ Treatment of Chlorinated Solvents: Concept and Commercial Application

Over the past several years, numerous laboratory batch and flow-through column experiments have demonstrated that zero-valent iron causes transformation of dissolved chlorinated solvents, such as TCE and PCE, and the reduction and precipitation of chromium (e.g., Gillham and O'Hannesin, 1994; Matheson and Tratnyek, 1994; Powell et al., 1995; Roberts et al., 1996; Burris et al., 1995). The reaction rates for chlorinated solvents depend primarily on the degree of chlorination (highly chlorinated compounds are transformed more rapidly due to favorable energetics) and the reactive surface area of the iron. Relatively rapid rates have been measured, with half lives on the order of a few minutes to hours, for many compounds (Johnson et al., 1996).

The laboratory evidence that iron causes the reduction of chlorinated solvents has been combined with funnel-and-gate systems, a method for directing ground water flow to a reactive treatment zone (Wilson, 1995). The ground water is funnelled through a permeable treatment zone containing iron filings. As the water passes through, the chlorinated solvents are chemically reduced.

The first full-scale in situ permeable iron barrier was installed in Sunnyvale, California, in the fall of 1994 (see Figure 3-3) (ETI, 1995). The contaminated ground water at the site is relatively shallow, and the aquifer is comprised of interfingered sands and sandy silts. The ground water velocity is approximately 0.3 m (1 ft) per day. Treatability studies consisted of laboratory and field column experiments with site ground water containing the primary volatile organic contaminants of concern at the site: cis-1,2-dichloroethene (1,415 µg/liter), TCE (210 µg/liter), and vinyl chloride (540 µg/liter). Vinyl chloride had the longest half life, 4 hours. The reaction rates determined in the treatability studies, combined with information about the ground water flow rate and contaminant concentrations, were used to design the permeable barrier (Yamane et al., 1995).

The reactive zone, comprised of 100 percent reactive iron, is approximately 1.2 m (4 ft) wide and 12 m (40 ft) long and extends between 2 and 6 m (7 and 20 ft) below ground surface. The reactive zone specifications were designed to ensure transformation of the contaminants to less than the cleanup standard. Because vinyl chloride is transformed most slowly and was present at relatively high concentrations at the site, it was the analyte of greatest concern in the design process.

The reactive zone was flanked by slurry walls to direct ground water flow into the zone. A high-permeability zone, comprised of pea gravel, was installed both upgradient and downgradient of the reactive zone to reduce the effects of local heterogeneities on flow through the reactive zone. To date, no chlorinated organic products have been detected in the four downgradient monitoring wells (J. L. Vogan, EnviroMetal Technology, personal communication, 1996).

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

FIGURE 3-3 Plan view of permeable iron barrier for treatment of chlorinated solvents.

SOURCE: Reprinted, with permission, from Yamane et al. (1995) © 1995 by American Chemical Society.

3-5). The long-term effectiveness of this approach depends on maintaining a reactive surface free of iron precipitates and biofilms.

Engineered in situ bioremediation of chlorinated solvents has been developing in two areas. The first is the continued study of aerobic cometabolic pathways, in which the bioremediation systems add toluene, natural gas, or propane to the subsurface to stimulate cometabolism of the solvent. This technology was successfully demonstrated at Moffett Naval Air Station in California (Semprini et al., 1990). A second area of development has been the use of sulfate-reducing conditions. This type of bioremediation technology, developed by DuPont (Beeman, 1994), adds sulfate and benzoate to degrade TCE and PCE.

In addition to these engineered forms of bioremediation, considerable research is under way to define anaerobic and aerobic biological processes that lead to intrinsic bioremediation of chlorinated solvents without human intervention (EPA, 1996b). Intrinsic bioremediation of chlorinated solvents in ground water occurs most frequently by reductive dechlorination under anaerobic conditions generated by anthropogenic carbon sources (Chapelle, 1993). Case examples of this are generally scenarios in which chlorinated solvents occur as co-contaminants with anthropegenic sources of dissolved organic carbon, typically hydrocarbon fuels or landfill leachates. Intrinsic bioremediation of chlorinated solvents requires greater than stoichiometric amounts of carbon to serve as a source of energy for the microbes (McCarty, 1996). To date, reports of intrinsic bioremediation of chlorinated solvents are from sites where anthropogenic car-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

bon sources (such as petroleum hydrocarbons) serve as the electron donor (Wiedemeier et al., 1996).

Research Needs

Considerable progress has been made in the last 10 years in treating sites contaminated with chlorinated solvents. However, innovation and development are still needed to improve the efficiency and decrease the costs of existing technologies and to develop new technologies, especially for cleaning up low-permeability zones and chlorinated solvents present as DNAPLs.

Locating source zones of pooled chlorinated solvents poses a major problem, not only for characterizing contaminant distribution at sites but also for designing remediation systems. Costly, extensive sampling often is inadequate to locate chlorinated solvent source zones because of the complexity of DNAPL flow paths and the uncertainties associated with predicting these flow paths.

Research is also needed to improve the scientific basis for designing in situ bioremediation systems for the treatment of chlorinated solvents. A number of laboratory investigations and a few field studies have shown that microbes can degrade chlorinated solvents using various cometabolic pathways and electron acceptors. However, data on process rates and how to control them in situ are insufficient for optimizing remediation system design. Similarly, existing data and models are inadequate for developing accurate predictions of the dynamics of intrinsic remediation.

Chemical or thermal processes that solubilize or mobilize chlorinated solvents require thorough understanding of subsurface fluid movement to ensure that unwanted contaminant migration does not occur. While research has progressed on understanding the physicochemical phenomena that may enhance the mobility of chlorinated solvents, much work is needed to understand how to optimize control of such process fluids in the subsurface.

A final promising area for research related to the treatment of chlorinated solvents is in the assessment of the long-term effectiveness of zero-valent iron barriers for controlling dissolved solvents in ground water. While zero-valent iron barriers are being installed at field sites, the long-term performance of these systems is unknown.

CLEANUP OF POLYCYCLIC AROMATIC HYDROCARBONS

Sources

Polycyclic aromatic hydrocarbon (PAH) compounds are a generally hazardous class of organic compounds found in petroleum and emissions from fossil fuel utilization and conversion processes. PAHs are neutral, nonpolar organic molecules that comprise two or more benzene rings arranged in various configu-
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Nonaqueous-phase liquid coal tar aged one year. The coal tar develops an interfacial film that may affect solute dissolution and NAPL wettability characteristics. Courtesy of Richard Luthy, Carnegie Mellon University.

rations. PAHs may also contain alkyl substituents or may be heterocyclic, with the substitution of an aromatic ring carbon with nitrogen, oxygen, or sulfur. Members of this class of compounds have been identified as exhibiting toxic and hazardous properties, and for this reason the EPA has included 16 PAHs on its list of priority pollutants to be monitored in water and wastes.

PAHs are found in process wastes from coal coking, petroleum refining, and coal tar refining and thus may be present in lagoons, sediments, and ground waters that received such products or wastes. Many instances of soil and ground water contamination are reported at facilities where creosote was used for wood treating. Another source of PAH contamination is former manufactured gas plants. Manufactured gas, or town gas, was produced at several thousand such plants. Soil and ground water contamination problems currently exist at many former manufactured gas plants because of prior process operations and residuals management practices (Luthy et al., 1994). Coal tar and associated PAHs are the principal contaminants of concern at these sites.

Fate

The aqueous concentrations of PAHs in natural systems are governed by the hydrophobic character of these compounds and are highly dependent on adsorptive/desorptive equilibria with sorbents present in the system (Dzombak and Luthy, 1984; Means et al., 1980). Also important is whether the PAHs exist as a DNAPL. Because PAHs dissolve only very slowly from DNAPLs, the source of contamination may persist for many years. Indeed, for tar-contaminated soils and

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

FIGURE 3-4 Relative rates of biodegradation of PAHs in soil. SOURCE: Reprinted, with permission, from Bossert and Bartha (1986).

sediments at manufactured gas plants, the source of PAHs has persisted literally for as long as 100 years (Luthy et al., 1994).

Bacteria, fungi, and algae play important roles in the metabolism of PAHs in terrestrial and aquatic environments (Cerniglia, 1984). Current research indicates that effective microbial degradation of PAHs requires aerobic environments, although microbial degradation of lower-ring PAHs under denitrification conditions has been reported in laboratory studies (Mihelcic and Luthy, 1988). Figure 3-4 shows the relative biodegradability of several PAHs in soil when oxygen is present.

In soils and sediments, the rate of microbial degradation of PAHs may depend on various physicochemical factors affecting the bioavailability of the target compounds to the microorganisms (see Figure 3-5). This is a problem especially with aged and/or weathered samples, which appear to bind PAHs strongly and which often contain a resistant fraction of PAH material that is not amenable to microbial degradation (GRI, 1995; Office of Naval Research et al., 1995; Swiss Federal Institute for Environmental Science and Technology, 1994).

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Figure 3-5 Illustration of the physicochemical processes in a representative elemental volume that affect the bioavailability of hydrophobic organic compounds for microbial degradation in soil. Contaminants generally degrade when they are dissolved in the bulk ground water. Sorbed contaminants, NAPL-phase contaminants, and contaminants in micropores of solid material are not easily accessible to the microorganisms that cause biodegradation. SOURCE: Reprinted, with permission, from Luthy and Ortiz (1996).

Remediation Technology Options

PAH compounds are relatively persistent in the environment, being resistant to both chemical and microbial transformations. These compounds are not very soluble or volatile, and they tend to sorb to soil surfaces or remain entrapped within an organic phase. Hence, cleanup of PAHs generally focuses on soils and sediments, often ex situ, rather than on contaminants dissolved in ground water. The resistance of PAHs to chemical and microbial transformation, their affinity for soils, and their lack of solubility and volatility make it difficult to treat PAH contamination.

Solidification and Stabilization Techniques

Stabilization/solidification is not commonly the technology of choice for treating soils or sediments contaminated with PAHs or high concentrations of other organic material, although asphalt batching may be appropriate in some instances for tarry matter.

Separation Techniques

Thermal Treatment. Because of the low volatility of PAHs. SVE and other air stripping treatments are not effective remediation techniques for these contaminants. Consequently, separating PAHs from soils requires the use of temperature

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

or chemical solubilizing agents. Thermal destruction using rotary kiln combustion chambers and ex situ thermal treatment to separate volatile and semivolatile contaminants from solids are established technologies and have been used to treat PAHs at full-scale (Magee et al., 1994; EPA, 1994c). In a demonstration at a former manufactured gas plant site under the Superfund Innovative Technology Evaluation Program, ex situ thermal desorption was successful in reducing overall PAH levels, but an important conclusion was that materials handling was a significant factor in controlling process performance; the ability to maintain stable desorber operations was linked to soil feed consistency (Maxymillian et al., 1994). In general, most reliability problems occur with material handling, not with the desorption system. Some systems may foul or plug due to the deposition of tarlike material on internal system components. Also, dioxins and furans may be formed during the cleanup process (EPA, 1994c), and this possibility needs to be assessed on a case-by-case basis. An example of an emerging thermal treatment technology is one that employs gas-phase reduction of organic compounds by hydrogen at elevated temperatures; this technology has been tested on harbor sediments containing coal tar (ECO LOGIC, 1995).

Soil Washing and Soil Flushing. Soil washing without chemical amendments is appropriate for treatment of PAHs in only a few situations, such as in sandy soils having few fines and significant PAH residues associated with separable matter such as wood material (Stinson et al., 1992). Experience with chemical enhancements for soil washing for removal of PAH compounds is limited to a few pilot-scale tests. The few examples include using surfactant with heat (Amiran and Wilde, 1994; EPA, 1994b) and drying and hydrocarbon solvent extraction (Trobridge and Halcombe, 1994). Experience with chemical enhancements for soil flushing is very limited; most information is available from bench-scale tests and a few small field pilot tests. Soil flushing using alkaline reagents, polymer, and surfactant has been pilot tested in a test cell at a wood-treating site (Mann et al, 1993), and an evaluation of in situ steam heating and hot water displacement has been conducted at a former manufactured gas plant site (EPA, 1994c).

Although field experience with chemically enhanced soil flushing and soil washing is limited, considerable research on this topic is under way. One area of research is the use of high concentrations of water-miscible cosolvents, which greatly enhance the solubility of hydrophobic organic contaminants, thereby increasing the mass removal per unit volume of fluid used to flush the contaminated soils (Luthy et al., 1992; Augustijin et al., 1994; Roy et al., 1995). A pilot demonstration of in situ solvent extraction has been conducted at Hill Air Force Base in Utah using ethanol-propanol mixtures injected into gravely sand in a 3 by 5 m test cell having jet fuel as the primary contaminant. In the test, solvent flushing removed on the order of 80 to 90 percent of the hydrocarbon material (Annable et al., 1996). The use of water-miscible solvents has been studied in laboratory tests to evaluate solvent extraction for possible use in cleaning coal tar-contaminated

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

soils. The kinetics of tar dissolution affect treatment duration, although predictions based on laboratory data for a very simple site with no hydrogeologic complexities suggest greater than 90 percent removal in a one-year time frame (Ali et al., 1995).

Another area of research is the surfactants that may benefit in situ soil flushing by enhancing the solubility of hydrophobic organic compounds and by lowering the interfacial tension between water and NAPL, resulting in direct mobilization of the NAPL. Surfactant enhancements have been evaluated in various laboratory tests to assess physicochemical phenomena affecting the partitioning of PAH compounds in soil-water systems (Edwards et al., 1991, 1994a,b). Only limited laboratory data are available on how surfactants might affect the PAH trasport rate in subsurface environments.

Biological Reaction Techniques

Current understanding of achievable treatment rates and end points for biological treatment of PAHs is very incomplete. Various laboratory tests have described PAH biodegradation in well-controlled systems, but it is unclear how these results translate into understanding of what may occur in field tests. The limited understanding of PAH biodegradation is a particular concern for aged samples from field sites; release of PAHs from aged samples may be much slower than release from freshly applied material. Often, PAHs are completely degradable when freshly applied to soil, but the soil may retain a residual concentration of the same compound after prolonged biological treatment (see Box 3-6). This residual PAH may result from a combination of complex physical and chemical factors controlling solubilization, desorption, and diffusion. Moreover, biodegradation of complex chemical mixtures such as coal tar may be further complicated by substrate interactions causing unpredictable biodegradation patterns (Alvarez and Vogel, 1991), which may include inhibition, competition, and cometabolism.

Various studies have indicated qualitatively that mass transfer limitations may prevent significant biodegradation of PAHs in contaminated soils (Nakles et al., 1991; Morgan et al., 1992; Erickson et al., 1993). Mass transfer limitations could be due to the slow solubilization of PAHs from residual weathered NAPLs or from slow dissolution of PAHs trapped in micropores and sorbed to solid surfaces. As a consequence of these factors, the design of soil treatment systems for PAH compounds requires site-specific laboratory and field tests. Laboratory tests with site samples in aerobic slurry systems may provide an indication of maximum potential biodegradation rates and feasible biotreatment end points.

Bioslurry treatment of PAHs has been evaluated at bench, pilot, and full-scale (EPA, 1993b). The bioslurry process uses solids mixing to assist oxygen and nutrient transfer and to enhance mass transfer of solutes and contact with microorganism. Bench-scale bioslurry treatment of PAHs from creosote-contaminated soil with a 30 percent solids for a 12-week period resulted in

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-6 Biotreatment of PAHs in Extended Field Trials

The biotreatment of PAHs in field trials often shows a ''hockey stick" effect on a plot of PAH concentrations versus time (see Figure 3-6). Total PAH, as represented mainly by 2-, 3-, and 4-ring PAH, may decrease in overall concentration relatively rapidly over several months, but then it often levels off at a residual plateau concentration, which may exceed regulatory limits. Current understanding of PAH biodegradation is insufficient to allow prediction of how this plateau concentration may change with time.

In one study, PAH-contaminated soil was treated in a land treatment field test plot in four lifts from May 1986 to December 1987 at a former creosote wood preserving site (J. Smith et al., 1994). During the period of active biotreatment, involving tillage and nutrient addition, in 1986-1987, total PAH decreased from an initial range of 1,200-3,500 mg/kg to about 800-1,200 mg/kg, with an average of about 50 percent reduction from 2,000 mg/kg. There was noticeable reduction of 2-, 3-, and 4- ring PAH concentrations but hardly any reduction of 5-ring and no reduction of 6-ring PAH concentrations. During the six-year period from 1987-1993, the treated soil was left in place unattended. Sampling in 1993 showed that total PAH had decreased from about 1,000 mg/kg to about 200 mg/kg during the six-year unattended period. Soluble PAH from standard leaching tests was less than 20ug/liter, with no 4- ,5-, or 6-ring PAH detected and only some 2- and 3- ring PAH (in the parts per billion range) detected. At the end of 1987, the 5- and 6-ring PAH concentrations were about 60-70 mg/kf and 20-30 mg/kg, respectively; in 1993, these values were about half the 1987 concentrations.

These data illustrate that gradual reductions in PAH concentrations may continue at a very slow rate over a number of years in land treatment systems. In addition, as a result of biodegradation and weathering, the remaining contaminants may be much less mobile, as evidenced by field and laboratoryleaching assessments.

reduction of total PAHs by 86 percent from initial values of 2,460 mg/kg, with the greatest reduction (more than 98 percent) for 2and 3-ring PAHs and lower removal rates (72 percent) for the 4-, 5- and 6-ring PAHs (EPA, 1993b).

A pilot-scale demonstration of slurry-phase biotreatment of weathered petroleum sludges was evaluated using a 3.8 x 10(3) m(3) (1 x 10(6) gal) reactor retrofitted from a concrete clarifier (EPA, 1993b). The process entailed 56 days of batch operation at about 10 percent solids loading using float-mounted mixers and aerators. Overall, the system reduced PAH concentrations by more than 90 percent.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

FIGURE 3-6 Typical "hockey stick" pattern observed in degradation of PAHs in soil biotreatment systems. The biodegradation pattern often exhibits a labile fraction and a resistant fraction; the latter may decrease very slowly over time (see Box 3-6).

Large-scale complete mix pilot reactors are used to evaluate bioslurry treatment technologies. Courtesy of Remediation Technologies, Inc.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Soil contaminated with coal tar. The residual coal tar may release PAHs at a very slow rate, prolonging biological treatment through lack of adequate bioavailability. Courtesy of Richard Luthy, Carnegie Mellon University.

Greater reductions would probably have been achieved with improved mixing to maintain more solids in suspension. The sludge was a good candidate for bioslurry treatment because it contained mostly 2and 3-ring PAHs, as opposed to 4-, 5-, and 6-ring PAHs.

An in situ bioslurry system was implemented at full-scale to treat wastes at the French Limited site, an abandoned industrial waste lagoon in Harris County, Texas (EPA, 1993e). Process equipment used to optimize oxygenation and contact between microorganisms and the contaminants included mechanical aerators, centrifugal pump sludge mixers, and hydraulic dredge subsoil mixers. Liquid oxygen was injected in pipeline contactors, where it was mixed with the slurry at elevated pressure. This provided more rapid oxygen dissolution with less pumping. The treatment achieved remediation objectives for the compounds, including benzene and benzo(a)pyrene, that were used as indicators of overall contamination.

Research Needs

Additional data are needed to assess thermal treatment processes for PAHs.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Relationships among treatment temperatures, retention times, and overall efficiencies and costs need to be quantified. Materials handling methods need to be optimized.

Various factors remain to be resolved for practical implementation of soil washing and flushing systems that use cosolvents or surfactants for remediation of PAHs. Although laboratory work has been performed to advance the basic science of soil washing and flushing, experience with pilot- or field-scale demonstrations is very limited. Research is needed to improve management of pumped fluids in large-scale applications (including improving delivery of fluids to contaminated zones), evaluate possible reuse of recovered chemicals, and determine the fate of residual contaminants and chemicals remaining in soil.

Although biological treatment of PAHs in soils and sediments has been widely studied, the design of biological PAH treatment systems remains largely empirical. Rate controlling parameters are often unknown. The bioavailability of hydrophobic compounds needs to be enhanced. Degradation rates are highly variable and cannot be predicted reliably. Treatment end points are uncertain. The factors that determine the concentration of PAHs (see Box 3-6 and Figure 3-6) attained after prolonged biotreatment are unknown. The biotreatable fraction of total PAH in a sample is not predictable, nor are the chemical or physical phenomena that may sequester PAHs in soil or sediment known. The effects of aging and weathering on the bioavailability of PAHs cannot be estimated. Data comparing decrease of PAHs by biotreatment with decrease in leachability and toxicity are lacking. The mobility of residual PAHs after biotreatment cannot be predicted. Finally, the ecological effects of residual, relatively insoluble PAHs that may remain after biotreatment are unknown.

CLEANUP OF POLYCHLORINATED BIPHENYLS

Sources

PCB compounds comprise the biphenyl structure with 1 to 10 chlorine atoms, resulting in 209 different structural configurations, or congeners. Each congener has a different number and different positioning of chlorine atoms. PCBs were sold as mixtures of congeners called Aroclors, with each Aroclor having a different weight percent of chlorine. Aroclors were used in a variety of industrial products, including capacitor dielectrics, transformer coolants, heat transfer fluids, plasticizers, and fire retardants in hydraulic oils. Although the use of Aroclors has been banned in many countries, PCBs can be found at low levels dispersed through certain sediment and aquatic systems.

Typically, site contamination problems with PCBs are related to the direct on-site use or disposal of Aroclors at industrial facilities, including the discharge of Aroclors to floor drains, sewers, and lagoons. Many of these disposal practices enhanced migration of the PCBs by providing conduits (drains, sewers, drain

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

fields, boreholes, and wells) to the deeper subsurface. The release of Aroclors to soils also occurred at metal recycling facilities that processed used electrical transformers. There are also instances in which PCB-containing oils were spread on soil and dirt roads for dust and erosion control.

Fate

While each Aroclor mixture is composed of a range of compounds, assessment of the environmental fate and transport of PCBs has been performed typically using average properties of Aroclors (Luthy et al., 1997; Adeel et al., in press). Congener properties, especially solubility and sorption potential, vary widely and strongly affect the fate and transport of PCB compounds (Dzombak et al., 1994). Sorption can significantly retard the movement of PCB compounds and often controls how far the compounds will migrate (Oliver, 1985; Coates and Elzerman, 1986). As with PAHs, the central concern in cleaning up PCB-contaminated sites is the soil, because chemical properties of PCBs limit their migration in ground water.

Remediation Technology Options

The stable chemical properties that made PCBs attractive for use in industrial applications strongly affect remediation technology options. PCBs have very limited solubility in water and are practically nonvolatile. Therefore, containment or stabilization processes are effective for managing PCB-contaminated soils, but separation processes (thermal treatments or chemical extractions) require significant energy inputs. The chemical transformation of PCBs requires elevated temperatures (i.e., incineration or substitution-type processes). Microbial transformations occur very slowly but show promise for toxicity reduction and biostabilization.

Containment and Stabilization Techniques

Various proprietary formulations, consisting of cementing agents or pozzolanic materials, are available in the marketplace for solidification and stabilization of PCB-contaminated soil and sediment. Solidification/stabilization has been used at full-scale in an ex situ process to treat PCB-contaminated soil using approximately 30 percent proprietary pozzolanic material and in an in situ process to treat PCB residues using approximately 15 percent calcium oxide and 5 percent kiln dust (Weitzman and Howel, 1989). Technologies for containment of source-area PCBs in the subsurface include slurry trench cut-off walls (made of soil-bentonite, cement-bentonite, or plastic concrete), grout curtains (comprised of cement or chemical grouts), and steel sheet curtains. These barriers are used in conjunction with ground water extraction wells to provide hydraulic containment.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

In situ soil mixing is a relatively new technology that avoids excavation by employing a special auger and mixing shaft that permits injection of a slurry consisting of bentonite and water or bentonite and cement. Columbo et al. (1994) and Stinson (1990) summarize an EPA test of a proprietary additive and deep-soil mixing process for an in situ demonstration for stabilizing PCB-contaminated soil. The process decreased PCB mobility by causing ground water to flow around, not through, the monolith. The presence of organic wastes may inhibit the setting and hardening of cement-based or pozzolan-based stabilization technologies.

The EPA has listed one demonstrated in situ vitrification process capable of treating PCBs in soil or sediment (Davila et al., 1993).

Separation Techniques

Thermal Desorption. PCB-contaminated soils and sediments have been treated in thermal desorbers in field trials (EPA, 1993c). Thermal desorption with reduction of gas-phase PCBs at high temperature with hydrogen has been demonstrated (as part of the EPA Superfund Innovative Technology Evaluation Program) for coal-tar and PCB-spiked harbor sediments (ECI ECO LOGIC, 1992). Material handling, sizing, screening, and conveying often present considerable challenges, depending on the material and type of equipment employed (Lightly et al., 1993). Operation of thermal desorption systems may create up to eight process residual streams requiring attention (Lightly et al., 1993).

Soil Washing and Soil Flushing As a result of weathering and aging, PCBs may become tightly bound to soils. The physical washing or scrubbing of soil helps to disaggregate the soil matrix and expose the contaminants to the washing media. Soil washing has been demonstrated as effective for separating fine-grained and coarse-grained media (Davila et al., 1993; EPA, 1993a). In such processes, the fines and humic fractions may be enriched in PCBs, resulting in a smaller volume of material needing subsequent treatment.

There are almost no examples in the literature of field- or pilot-scale tests of soil flushing for PCB removal, except for two tests at an automotive plant site containing PCBs and oils in fill material (Abdul and Ang, 1994; Abdul et al., 1992). Laboratory studies showed that a nonionic alcohol-ethoxylate surfactant could recover more than 80 percent of oil and PCBs from sandy soils. Encouraged by these results, a pilot study was conducted in a 3-m-diameter, 2-m-deep test plot at the automotive plant. The field test employed 0.75 percent aqueous surfactant solution applied with a sprinkler system; the system removed 10 percent (1.6 kg) of the PCB contaminants in 5.5 pore volume displacements. A second test, conducted a year later, employed 2.3 pore volume displacements with 0.75 percent surfactant; in this test, an additional 15 percent (2.5 kg) of the PCB contaminants was removed. The more efficient removal of PCBs in the second

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

test may have been due to an intermittent washing effect, in which the time interval between the first two tests may have allowed for continued diffusion of the contaminant from dead-end pores to the bulk solution. However, subsequent laboratory column tests result showed that complete removal of PCBs by surfactant washing would not be practical.

Solvent Extraction. Solvent extraction has been proven effective for treating soils or sediments containing PCBs (EPA, 1994a). Solvent extraction processes may be divided into three classes, depending on the solvent used: (1) standard, which employs liquid solvents (alkanes, alcohols, and ketones) at near a ambient conditions; (2) liquefied gas, which uses gases pressurized at near ambient temperatures; and (3) critical solution temperature, which uses solvents such as triethylamine, which is miscible in water at temperatures less than 18°C (64°F) and only slightly miscible above this temperature. Each of these process types has been evaluated in the field with PCB-contaminated soil or sediment (EPA, 1993d, 1994a, 1995a; Dávila, 1993). Low absolute concentrations of PCBs may not be attained or may require a n number of extraction steps.

Reaction Techniques

Chemical. Substitution processes have been used to treat soils contaminated with PCBs and chlorodibenzodioxins. Although some substitution processes have been available for more than a decade, they have not been used extensively because incineration is cheaper and more widely available and because design problems identified in field tests were not addressed in follow-up work due to lack of funding (Weitzman et al., 1994). Ferguson and Rogers (1990a,b) and GRC Environmental, Inc. (1992) provide technology descriptions and results of some field trials of lower-temperature processes for potassium hydroxide and polyethylene glycol treatments; Friedman and Halpern (1992) provide a description of a process using methoxyethanol and potassium hydroxide. Results of high-temperature substitution processes in field trials with PCB-contaminated soils or sediments are described by Vorum (1991) and EPA (1992) for a reactor employing fuel oil and alkaline polyethylene glycol and Dávila et al. (1993) for treatment using carbonate, hydrocarbon oil, and a catalyst.

Biological. Laboratory and field monitoring studies indicate that PCBs biodegrade in the environment but at a rate (see Box 3-7). However, work is needed to demonstrate that PCB biodegradation is viable for use in site cleanups (Dÿvila et al., 1993).

PCB biodegradation occurs through a combination of anaerobic and aerobic microbial processes. Biodegradation under anaerobic conditions can result in reductive dechlorination of highly chlorinated PCBs. As the anaerobic processes progress, the accumulated degradation products may be destroyed aerobically.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Thus, for example, monochlorobenzene that is generated anaerobically from hexachlorobenzene, or likewise the compounds that accumulate in the metabolism of PCBs under anoxic conditions, can be transformed aerobically (Bé dard et al., 1987; Mohn and Tiedje, 1992). Such two-stage processes involving an initial anaerobic phase followed by a final aerobic phase represent a promising means for treating PCBs (Alexander, 1994). Harkness et al. (1993) showed in field trials in the Hudson River that lightly chlorinated PCBs were degraded aerobically by native microorganisms when stimulated with oxygen, a mixture of nutrients, and biphenyl to promote cometabolism.

Research Needs

The effectiveness of in situ soil mixing in reducing permeability and stabilizing PCB contaminants is not documented sufficiently. Due to the drophobic nature of PCBs, leachability test results are often inconclusive, typically now showing significant differences between treated and untreated material. Furthermore, the effectiveness of soil mixing in thoroughly blending the soil, with no unreacted soil pockets, is not well documented.

To various degrees, substitution reactions convert some of the target molecules to unregulated forms. Although the resultant compounds may be unregulated, the environmental impact of these compounds still needs to be considered. Further proof of the degree of substitution is needed.

Problems with soil washing or flushing include the generation and treatment of large volumes of water; uneven treatment in soil flushing due to nonhomogeneous conditions, including the presence of NAPLs; and the need for improved control of pumped fluids. Problems with surfactant-aided technologies include assessing surfactant losses by degradation or sorption and evaluating surfactant recovery and reuse. Factors affecting the kinetics of surfactant solubilization of PCBs in heterogeneous systems need to be understood to improve process efficiency and chemical use.

Considerable research is needed to understand phenomena affecting the bioremediation of PCB-contaminated soil and sediment in order to properly evaluate the performance of the technology before it can be used for site remediation. In general, the current state of this technology does not permit treatment with confidence at commercial scale. Factors that control the rates of microbial reactions with PCBs, including the coupling of anaerobic andaerobic processes, need to be better understood. The fate and rate of further biodegradation of residual PCBs following active aerobic biological treatment is unknown.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-7 Biostabilization of PCBs

Biostabilization refers to the ex situ biodegradation of organic contaminants in soil such that any residual material is not readily released from the soil matrix, or such that residuals are released so slowly that they pose little or no risk to ecological or human health. Following a period of active biological treatment, biostabilized material may be placed in an engineered containment facility and monitored for release of contaminants and to assess whether intrinsic biodegradation processes are adequate to control contaminants released slowly over time.

The Aluminum Company of America is evaluating biostabilization as a method for treatment of sludges and sediments contaminated with PCBs, PAHs, and hydraulic oils (Alcoa Remediation Projects Organization, 1995). Biostabilization is being tested in complete-mix batch slurry bioreactors and in land treatment test plots. The leaching of PCBs before and after treatment is evaluated in laboratory batch leaching tests and in flow-through column tests. The goal of this work is to assess whether aerobic biological treatment with indigenous organisms can substantially reduce the concentrations of potentially mobile, less-chlorinated PCB homologs, thereby permitting placement of treated material in a controlled disposal facility.

Results from an eight-week field test showed 31 to 43 percent overall reduction in PCBs from initial values of 15 to 17 mg/kg of total PCBs based on congener-specific analyses. There was nearly complete re-

CLEANUP OF INORGANIC CONTAMINANTS

Sources

Inorganic contaminants at hazardous wastes site are typically classed as metals1 (transition or heavy) or radioactive compounds. Some of the most common sources of metal contamination are mine tailing impoundments, plating and smelting operations, and battery recycling plants (National Research Council, 1994). Radioactive contaminants in soil and ground water are a concern primarily at DOE sites as a result of nuclear weapons production. Radioactive elements are also found in nature, but naturally occurring concentrations pose ecological or human health risks in few cases. Although metallic and radioactive contaminants can occur at modest scales, many of the sources of these contaminants, such as

1  

The term "metals" is used in this text to refer to transition metals, heavy metals, and radioactive metals metalloids.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

moval of dichloro-PCBs, approximately 60 to 70 percent reduction in the concentration of trichloro-PCBs, and 10 to 15 percent reduction in the concentration of tetrachloro-PCBs, with no significant removal of PCB homologs with 5, 6, or 7 chlorine atoms. The data from laboratory column leach tests showed that aqueous leachate from untreated samples consisted mostly of di-, tri- and tetrachlorobiphenyls. The data from leaching of treated material showed that the concentrations of dichloro-PCBs were substantially reduced, indeed almost eliminated in the land-treated samples, while trichloro-PCBs were removed by about 60 percent, with little change in tetrachloro-PCBs (Adeel et al., in press).

Continued monitoring of the field test plots will occur through subsequent years. Sampling one year later has shown continued decreases in trichloroand tetrachloro-PCB concentrations. The concentrations of these two homolog groups decreased by about 90 and 55 percent, respectively, from initial levels in the first 460 days of biotreatment (active and passive). Decreased concentrations of more highly chlorinated PCBs were observed during passive biotreatment (J. Smith et al., in press).

Biostabilization is an emerging technology that needs further investigation and development at the laboratory, pilot, and field scales to assess what it may achieve in practice. The concept is being assessed as part of understanding environmentally acceptable end points for soil treatment. More information is needed about the factors controlling the biotransformation, bioavailability, weathering, and release of hydrophobic organic contaminants from soil and sediment in order to provide a stronger underpinning for this technology.

mine tailing impoundments, result in very large sources of potential contamination.

The most commonly detected inorganic and radioactive contaminants in ground water, nitrate and tritium, respectively, are generally not treated (Woodruff et al., 1993). Nitrate occurs in ground water as a result of widespread point and nonpoint sources of pollution, such as farms using nitrogen fertilizers, manure from animal feed lots and pastures, and septic systems. Tritium, a radioactive form of hydrogen, occurs as part of a water molecule and is a concern only at DOE sites. Both nitrate and tritium migrate essentially unretarded in ground water. Nitrate can be treated by osmosis or can serve as an electron acceptor in microbial processes. However, because its occurrence is so widespread and health effects are thought to be limited, ground water restoration is usually not considered, although well-head treatment of drinking water sources is necessary to protect infants from blue baby syndrome. Because tritium is a radioactive element, the only effective way to treat it is to isolate the tritiated water until radioactive decay reduces the concentration to an acceptable level. Because these compounds

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

are not typically of greatest concern at hazardous waste sites (other than DOE sites), they are not discussed in the following text.

Fate

Unlike many organic contaminants, most inorganic contaminants, particularly radioactive ones, cannot be eliminated from the environment by a chemical or biological transformation. Also unlike most organic contaminants, the form of inorganic contaminants significantly affects mobility and toxicity. The form, or speciation, of inorganic contaminants is often determined by the basic geochemistry (e.g., acidity, reduction potential) of the ground water system. Chromium (Cr), for example, is usually present as either Cr(III) (the reduced form), or hexavalent chromium, Cr(VI) (the oxidized form). Cr(VI), which occurs in the mobile anionic forms CrO42- and CrO72-, is often present in ground water at contaminated sites and is toxic and mobile. In contrast, Cr(III) typically forms relatively insoluble precipitates, which are not readily oxidized and which cause chromium to be relatively permanently immobilized in the environment (Palmer and Wittbrodt, 1991). The inability to eliminate inorganic contaminants by biological or chemical reactions and the strong effect of geochemistry on inorganic contaminant mobility present major challenges in the cleanup of sites containing these contaminants.

For two primary reasons, relatively few metals are soluble and mobile enough to form significant plumes of contamination in typical ground water environments. First, many toxic metals, like chromium, form relatively insoluble carbonate, hydroxide, or sulfide minerals. Precipitation effectively immobilizes the contaminant because the concentration of dissolved contaminant in equilibrium with the precipitate is so low. Formation and dissolution of solid precipitates are controlled primarily by pH, redox conditions, and concentrations of other ions in the ground water. Second, at the near-neutral pH conditions typical of ground water, common hydroxide and silicate mineral surfaces present in aquifers carry a negative charge and thus will strongly sorb many cationic heavy metals by cation exchange, resulting in very low mobility. (If the system is acidic, such as in acidic mine drainage or battery recycling wastes, mineral surfaces typically become positively charged, and cationic metal ions tend not to sorb and to be very mobile.) Thus, most of the metals of greatest concern due to mobility in ground water are present either as anionic (negatively charged) oxides or are present in acidic ground water. An additional concern is the possibility that metals may be transported either by forming complexes with organic matter in the ground water or by sorbing to mobile colloidal particles. Such facilitated transport of metals in ground water is an emerging area of research.

When more than one inorganic contaminant is present at a site, it is important to consider the effect of varying geochemical conditions on the mobility of all the contaminants. Conditions that lower the mobility of one compound may enhance

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

TABLE 3-5 Speciation and Mobility of Several Inorganic Contaminants (Metals and Radionuclides) of Concern at Hazardous Waste Sites

Dissolved Species

Representative Inorganic Contaminants

Geochemical Conditions Affecting Mobility

Anion or oxyanion

Arsenic (AsO33-, AsO43-) Chromium (CrO42-, Cr2O72-) Cyanide (CN) Selenium (SeO32-, SeO42-) Technetium,99 Tc Uranium (234, 235, 238U, UO2(CO3)22-, UO2(CO3)34)

Mobile in moderate to very oxic environments. All oxyanions form relatively insoluble mineral precipitates or coprecipitates, usually with iron and/or sulfide, under very reducing conditions, rendering them relatively immobile in these circumstances. Arsenic can occur in several valences; the most mobile form is AsO33-, which occurs under slightly reducing conditions. Uranium can also occur as sulfate complexes and oxide ions.

Cation

Barium (Ba2+) Cadmium (Cd2+ Copper (Cu+, Cu2+ Lead (Pb2+) Mercury (Hg+, Hg2+ Nickel (Ni2+) Strontium (90SR2+ Zinc (Zn2+

Cations are mobile in acidic environments. Most of those listed are relatively immobile at moderate to high pH because of the formation of insoluble hydroxide, carbonate, or sulfide minerals. Mercury can form very mobile, highly toxic organic (methyl mercury) complexes in some environments. Strontium mobility is also strongly affected by the presence of calcium, magnesium, and other divalent (2+) cations.

NOTE: Radionuclide isotopes are designated by the isotope number (e.g., 90Sr). Strontium-90 is regulated because it is radioactive, while nonradioactive isotopes of Sr are not regulated.

SOURCES: Hem, 1985; Fetter, 1993; Brookins et al., 1993; L. Smith et al., 1995.

the mobility of another. Table 3-5 indicates the effect of geochemical conditions on the mobility of some of the inorganic contaminants of greatest concern. As shown in the table, species present as cations, such as lead and strontium, are generally mobile only under acidic conditions. Species that are present as oxyanions (oxygen-containing negatively charged species), such as chromium and technetium, are typically relatively mobile in oxic water but form stable precipitates under reducing conditions. Some inorganic contaminants, such as arsenic and mercury, form complexes with organic compounds. Organic complexes tend to be more toxic than the inorganic forms.

Remediation Technology Options: Ground Water

The current standard practices for controlling metal contamination in ground water are to either use a pump-and-treat system to contain the plume or to use

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

institutional controls to restrict human exposure to the contamination. Pump-and-treat systems are not usually effective for plume remediation unless the sources of contamination have been entirely removed. Once extracted, ground water is usually treated by standard water treatment protocols, such as use of pH neutralization, precipitation, flocculation, and sedimentation or reverse osmosis to concentrate and separate the metals into sludge (L. Smith et al., 1995). The sludge must then be disposed of in an appropriate manner. Sludge containing radioactive contaminants can be difficult to dispose of because of cost and lack of adequate disposal facilities.

Because inorganic contaminants cannot be destroyed, innovative technologies focus on either stabilizing the contaminants by decreasing contaminant mobility and toxicity or separating the contaminants from the soil or ground water.

Solidification, Stabilization, and Containment Techniques

In Situ Precipitation and Coprecipitation. Strategies that exploit precipitation or coprecipitation under reducing conditions are being used or tested for acidic mine drainage water and for mobile oxyanions (L. Smith et al., 1994, 1995). Generally, the goal of these treatments is to immobilize the contaminant in a relatively thermodynamically stable form. In the case of heavy metals in acidic mine drainage, the goal is to precipitate the metals as the reduced sulfide species that were originally present in the mined ore (Wildeman et al., 1994).

At one site, a passive-reactive barrier (permeable treatment wall) for treatment of metal-containing acidic ground water eluting from mine tailings has been operating since 1995. The permeable barrier consists of organic carbon sources (leaf compost, wood chips, and sawdust) mixed with sand to maintain permeability. Within the treatment zone, naturally occurring microorganisms oxidize the carbon source and use the sulfate as the primary electron acceptor. In the process, acid is consumed, neutralizing the pH; reducing conditions are created; and sulfide concentrations are elevated. Metals are sequestered by precipitation as sulfide minerals and by sorption on organic matter. At this site, acidity has decreased (pH has increased from less than 5 to about 7.5), and sulfate concentrations have decreased from about 3,000 mg/liter to less than 10 mg/liter (the detection limit for the experiments) upgradient and downgradient of the wall. Concentrations of iron and nickel, present in the drainage water at 1,000 and 2 mg/liter, respectively, have decreased to less than detectable limits (5 mg/liter and 0.05 mg/liter) in the treatment wall. Theoretically (based on stoichiometric calculations), the mass of carbon in the wall should allow for continued treatment for 20 to 50 years. Although nickel was the only metal at this site present at a concentration greater than the drinking water standard, laboratory column studies have shown that zinc, cadmium, copper, chromium, and cobalt, which also form relatively insoluble sulfide minerals, also may be treatable by this method (D. Blowes, University of Waterloo, personal communication, 1996). Methods for optimizing the

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

carbon sources, reaction rates, and long-term performance of such treatment walls are still under study.

Methods for generating a reducing treatment zone to immobilize oxyanions are also being studied. The approach is to develop reducing conditions in situ such that mobile metals precipitate or coprecipitate as relatively insoluble solid phases; unlike the acidic mine drainage schemes, shifting pH is not a priority for these technologies. Treatment by generating reducing conditions abiotically in a permeable wall containing zero-valent iron is currently being tested at the pilot scale at a site with a plume of chromate-contaminated water from an electroplating facility (Blowes and Ptacek, 1992; Puls et al., 1995; Blowes et al., 1995; Powell et al., 1995). Laboratory studies and initial field results appear promising. The amount of reduced iron installed contains such a large reserve of reducing potential that, theoretically, it should last nearly indefinitely, although research is needed to assess the long-term performance of such systems. The concept is also being considered for treatment of technetium oxide. Long-term field performance is yet to be tested, and optimal techniques for replacing a zone of aquifer material with iron are still evolving.

Other methods for generating a reduced zone in the aquifer by biological or chemical treatment have been laboratory tested but not field tested. Possible strategies include creating an in situ reduced zone in the aquifer by chemically or biologically reducing iron in the sediments, which would result in reduction of contaminants within the treatment zone (DOE, 1994a, b). Such strategies may have an advantage over permeable treatment walls in that they would not require digging up or replacing aquifer solids. However, the methods would have to overcome the potentially large effects of both physical and chemical aquifer heterogeneity and generally would not produce the extreme reducing conditions created by metallic iron.

Geochemically reduced conditions are not favorable for solving all metal contamination problems. Arsenic, for example, can form a more mobile anion in moderately reduced geochemical conditions compared to the species normally present in aerobic ground water. Metals that do not form insoluble solids under reducing conditions would require different treatment methods.

Enhanced Sorption In Situ. Several methods for enhancing sorption of metals are being tested in the laboratory (DOE, 1994a). The goal of these methods, like in situ precipitation methods, is to immobilize the contaminants. Emplacement of zeolites, immobilized organic chelates, metal-sorbing microorganisms, or iron oxyhydroxide surface coatings on aquifer solids can increase sorption of metals.

Ex Situ Precipitation, Coprecipitation, and Enhanced Sorption. Over the past decade, constructed wetlands have been increasingly used for treating acidic mine drainage ex situ (Thomson and Turney, 1995) using both aerobic and anaerobic processes (Gusak, 1995). One example is the wetland created at the Big Five

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

BOX 3-8 Created Wetland for Cleanup of Metals

An artificial wetland is successfully treating metals in acidic mine drainage at the Clear Creek/Central City Superfund site near Idaho Springs, Colorado (Morea et al., 1989; Wildeman et al., 1990; Machemer and Wildeman, 1992; Wildeman, 1992; Whiting et al., 1994). The mine drainage at this site has pH less than 3 and high concentrations of zinc (50–70 mg/liter), cadmium (greater than 0.1 mg/liter), and manganese (2–3 mg/liter), as well as some copper and iron. Within the wetland, metals are removed from solution largely by microbiologically mediated precipitation of metal sulfides and by ion exchange on organic matter. Naturally occurring microorganisms use sulfate in the acidic drainage as an electron acceptor, creating an excess of sulfide and neutralizing acidity.

The redox reactions are driven by the carbon source (composted manure) provided to the wetland. In a pilot test at the site, pH increased from 3.0 to greater than 6.5; dissolved concentrations of zinc and copper decreased by more than 98 percent; and dissolved lead and iron concentrations decreased by more than 94 and 86 percent, respectively. The wetland was not effective in removing manganese. Iron removal was variable and depended on seasonal activity of the microorganisms.

Several important operating parameters for designing the full-scale wetland were determined through bench- and pilot-scale testing. The parameters studied included physical, chemical, and microbiological performance of several carbon sources; metals removal mechanisms; requirements for microbiological amendment; and hydraulic requirements (Machemer and Wildeman, 1992; Wildeman, 1992). Pilot-scale testing included design modifications, such as adding baffles to increase contact between the contaminated water and organic matter. Long-term stability of the wetland environment and successful removal of metals is continuing to be studied as full-scale remediation cells are put into place (Whiting et al., 1994).

Constructed wetlands are expected to provide treatment at a fraction of the cost of conventional systems over time and to function much more effectively than conventional systems in remote locations where maintenance is difficult (Wildeman et al., 1990).

Tunnel (see Box 3-8) near Idaho Springs, Colorado. The Big Five Tunnel wetland removes heavy metals from the sulfur-containing water primarily as sulfide precipitates in the anaerobic portion of the wetland (Wildeman et al., 1994). Passive treatment by constructed wetlands is projected to be cost effective relative to lime precipitation for some sites (Gusak, 1995), but the acid neutralization capacity of a wetland can be limited. Wetland treatment basins may need to be cleaned

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Field demonstration of the use of created wetlands for the removal of metals from acid mine drainage at a site near Idaho Springs, Colorado (see Box 3-8). Courtesy of Roger Olsen, Camp Dresser & McKee.

periodically (Gusak, 1995). Mining the sludge for the metals may be desirable in some cases.

Electrokinetic Separation Techniques

Use of electrical currents to separate metals from contaminated ground water systems is receiving increasing attention. When a low electrical current is applied to an aqueous system, ions migrate to and are concentrated at the electrodes (Aear and Alshawabkeh, 1993). The reactions can be used to stabilize the metals in situ or the contaminants can be removed in a concentrated form from the water or process solution surrounding the electrode. Proposed applications focus on ex situ water treatment and in situ or ex situ treatment of fine-grained soils that are difficult to flush because of low permeability. When conducted in situ, the process is similar to dewatering of clays by electroosmosis. Site-specific soil properties control the efficacy of this method. In order to enhance mobility of the target ions, electrode solutions must be added in some cases.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Remediation Technology Options: Soil

The conventional methods for treating soil contaminated with metals include excavation and disposal at an appropriate waste facility, capping the site to prevent infiltration, and institutional controls to reduce exposure to the metals.

At many sites contaminated with metals, such as mine and smelting sites, the volume of contaminated waste solids and soils is so high that removal of the contaminated soil is economically prohibitive. At these sites, the standard treatment is to cap the site to restrict ground water recharge and then to monitor the ground water. Recent efforts at sites where acidic drainage occurs emphasize minimization of contact with the atmosphere (by capping or submerging the tailings) to inhibit acid generation by sulfide mineral oxidation.

For soil contaminated with radioactive substances, the cost of excavation and disposal can be very high. DOE recently estimated that the cost of excavating and disposing of buried transuranic waste from Idaho National Engineering Laboratory was $24,000/m3 of soil (DOE, 1994a). For some highly radioactive contaminated soils, viable disposal locations may not exist.

Solidification and Stabilization

For representative nonradioactive excavation and disposal applications, solidification and stabilization is a relatively low-cost alternative. Consideration of the metal ion chemistry is essential in producing a material resistant to leaching (Soundararajan, 1992). A disadvantage of this method is the increased waste volume. Additionally, mixtures of metals, which may not be immobilized by the same chemical treatments, can be problematic (L. Smith et al., 1995). The lifetime and/or end use of the stabilized materials must be considered because weathering can potentially remobilize the contaminants (Wiles and Barth, 1992).

Ex situ solidification and stabilization technologies are well established. In situ technologies have not been used extensively but are being developed (L. Smith et al., 1995). A demonstration to treat arsenic-contaminated soil in the San Francisco Bay area with in situ solidification and stabilization was carried out in October 1992 under the Superfund Innovative Technologies Evaluation Program. Post-treatment samples were below the toxicity characteristic leaching procedure arsenic limit of 5 mg/liter for soil with an arsenic concentration ranging from 500 to 5,000 mg/kg.

Because of the potential for remobilization by weathering, the importance of limiting exposure during remediation, and the long half-lives of many radioactive contaminants, many of the standard methods used for solidification and stabilization of heavy metals (see Box 3-3) are inappropriate for radioactive contaminants. As an alternative, the DOE has been developing vitrification techniques, both in situ and ex situ, which were initially used in the nuclear industry as a method for long-term retention of radioactive contaminants. Vitrification is ap-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

plicable to soils, sludge, or other earthen materials that contain radioactive, inorganic, or organic wastes or waste mixtures. Leach tests have indicated that retention of inorganic and radioactive elements in vitrified material is very good. Factors affecting process performance include the presence of water, large void volumes, or combustible organic material; soil composition; and the electrical conductivity of the waste material. Considerable electrical energy, in the range of 800 to 1,000 kW-hours per ton of soil processed, is required (EPA, 1993e). The technology has been widely tested, primarily at DOE facilities, and has reached the commercialization stage. Cost is generally high (EPA, 1993e). However, for sites at which multiple technologies would otherwise be required or for which there are no other feasible alternatives (i.e., sites containing radioactive waste), this technology may be advantageous.

Biological Reaction

At least three companies are now commercializing phytoremediation systems for the treatment of waste sites contaminated with metals (Watanabe, 1997). Phytoremediation is carried out by growing plants that hyperaccumulate metals in the contaminated soil. The soil is prepared in advance of planting with appropriate amendments, such as chelating agents, to make the contaminants available to the plants. The plants are allowed to grow and accumulate the contaminants and are then harvested. Plant species have been identified that can accumulate zinc, cadmium, lead, cobalt, copper, chromium, manganese, and selenium from contaminated soils. Phytoremediation researchers generally define hyperaccumulators as plants that can store more than 1,000 mg/g of cobalt, copper, chromium, lead, or nickel or 10,000 mg/g of manganese or zinc in their dry matter (Watanabe, 1997). In one field application at a New Jersey industrial site, phytoremediation reportedly restored a site contaminated with 1,000 parts per million of lead during one summer (Watanabe, 1997). Disposal of the harvested plants, especially if they contain high levels of heavy metals, can be a problem. Some believe that the harvested plants may eventually have market value if the metals can be extracted from them and reused, but currently no market for such plants exist.

Separation

Soil washing solutions to remove metals typically contain acids and/or chelating agents, which chemically remove the contaminants from the soil. The process water must be treated before disposal. A number of specific technologies have been tested in recent years (L. Smith et al., 1995). In one demonstration, soil washing with acidification and selective chelation resulted in a two-thirds reduction of lead contamination in the fine fraction of sediment from Toronto Harbor (EPA, 1993e). For inorganic contaminants, soil flushing is not as well developed

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

as soil washing. However, soil flushing has been applied at a few Superfund sites for treatment of chromium, lead, nickel, mercury, and ferrous sulfate (L. Smith et al., 1995).

Research Needs

Radioactive isotopes and mixtures of heavy metals having different chemistries present major challenges in treatment of inorganic contaminants. The only commercially available technology for mixed radionuclides (vitrification) is relatively expensive. Because many technologies focus on immobilizing the contaminants, long-term effectiveness (maintaining the immobile form) is of concern. Most commercially available inorganic contaminant remediation schemes rely on linking several ex situ technologies. Extracting contaminants located at depth in the subsurface is problematic for these technologies. Few technologies are available and tested for treating inorganic contaminants in situ.

CLEANUP OF PESTICIDES

Sources

There are four general classes of pesticides (Grayson and Eckroth, 1985): (1) complex synthetic organics, (2) volatile organics (fumigants), (3) naturally occurring organics, and (4) inorganics. Some of these classes represent a very large number of chemicals. Table 3-6 provides examples of specific pesticides in each class. The following discussion applies primarily to the cleanup of organic pesticides; cleanup of inorganic contaminants is discussed earlier in this chapter.

Pesticide contamination of soil and ground water results from the manufacture, transportation, formulation, and application of herbicides and insecticides. Pesticides are applied as solutions (in water or oil), dusts, or fumigants (vapors). The pure compound or a concentrate is diluted near the point of application to application strength. Often, contamination results from dumping wash waters and residuals from pesticide storage tank cleaning.

The degree of contamination varies as a function of the concentration at which the pesticide was released into the environment. There are generally three types of pesticide contamination scenarios: (1) point-source contamination from pure compounds, (2) point-source contamination from concentrated mixtures, and (3) nonpoint-source contamination from application of the pesticide. In the first case, soil and ground water contamination results from shipping, distributing, and handling the pure compound. In the second case, formulation of the pure compound into dusts or sprays or use of the formulated product (for example at seed treating operations) can result in the release of formulated mixtures. Hydrophobic pesticides are typically formulated with at least one oil and at least two surfactants to allow the chemical to form an emulsion in a water solution and then either

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

TABLE 3-6 Classes and Uses of Chemical Pesticides

Class

Example

Use

Synthetic organic compounds

Carbamates (propham, aldicarb)

Herbicide, insecticide

 

Thiocarbamates (EPTC)

Herbicide

 

s-Triazines (atrazine, simazine)

Herbicide

 

Dinitroanalines (trifluralin)

Herbicide

 

Organosulfur compounds (bentazon, endosulfan)

Herbicide, insecticide

 

Phenols (dinoseb)

Herbicide, insecticide

 

Organochlorine compounds

 

 

DDT

Insecticide

 

Alachlor

Herbicide

 

Cyclodienes (chlordane, heptachlor)

Insecticide

 

DCPA

Herbicide

 

Chlorinated phenoxy-alkanoic acids (2,4-D)

Herbicide

 

Organophosphates (diazanon, malathion)

Insecticide

 

Petroleum oils

Insecticide

Fumigants

Ethylene dibromide (EDB)

Insecticide

 

Methyl bromide

Insecticide

 

Dichlorodibromo propane (DCBP)

Insecticide

 

Dichlorodiethyl ether

Insecticide

Naturally occurring organic compounds

Pyrethroids

Insecticide

 

Nicotine

Insecticide

 

Rotenone

Insecticide

Inorganic compounds

Arsenicals (As2O3, PbHAsO4)

Insecticide, herbicide

 

Boron compounds

Insecticide, herbicide

 

Sulfamates

Herbicide

 

SOURCE: Grayson and Eckroth, 1985.

stick to the plant leaf or drop to the soil. These formulation chemicals can affect the mobility of the active pesticide ingredients in the environment. The third contamination scenario results from application of the pesticide, whether for agricultural use, golf course maintenance, home lawn care, or other purposes.

Higher contaminant concentrations in ground water and soil result from point sources of pesticides, rather than from nonpoint sources. Proximity to a pesticide formulator, dealer, or applicator has been correlated with high frequency of pesticide detections (Holden et al., 1992). Barbash and Resek (1996) determined that high pesticide concentrations (greater than 100 µg/liter) are not uncommon in ground water beneath agrichemical facilities. Maximum soil concentrations at agrichemical facilities are typically greater than 1,000 µg/kg (Barbash and Resek,

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

1996). High concentrations of pesticides in ground water have been correlated with proximity to a pesticide distribution plant (Holden et al., 1992).

The frequency of detection of individual pesticides across the United States is most closely related to the frequency of use of the particular pesticide, chemical properties (solubility, volatility, and degradability) of the pesticide, and detection limits of the methods used to analyze for the presence of pesticides. Pesticides consistently detected in several multi-state surveys include the frequently used chemicals atrazine, simazine, alachlor, bentazon, chlordane, dibromochloropro-pane, and ethylene dibromide (Barbash and Resek, 1996). The EPA's National Pesticide Survey, which sampled rural and community ground water supply wells in all 50 states, found as the most frequently detected pesticides dimethyl tetrachloroterephthalate (DCPA) acid metabolites (EPA, 1990). DCPA is widely used for control of broad-leaved weeds and grasses on home and golf course lawns and on farms (EPA, 1990).

Fate

The fate of pesticides is a function of how the pesticide was released to the environment and of the pesticide's chemical properties (solubility, volatility, and degradability). When pure pesticide products are released to the environment, they can behave similarly to organic solvents. Depending on the physical properties of the pesticide, NAPL transport can occur if the pesticide is a liquid or is incorporated in an organic solvent. As with other NAPLs, a portion of the bulk liquid will become entrapped in the soil pores. Subsequent transport processes for the entrapped pesticides include solubilization into ground water and volatilization.

Formulated pesticides that have not been diluted to application strength can behave differently from pure products. The surfactants and solvents used in formulated products can entrain the pesticide and transport it much farther and at higher concentrations than would be predicted based on the solubility of the active ingredient. For example, some pesticides were historically formulated with toluene, a mobile solvent with the potential to transport the pesticide great distances.

Some organic pesticides (such as glyphosate and glufosinate) are relatively soluble and are supplied in a concentrated aqueous solution. When accidentally spilled, these pesticides are transported in aqueous form rather than as an NAPL (although migration of some such pesticides, including glyphosate, may be slowed due to strong sorption by soils). Similarly, pesticides that have been released to the environment as rinse or wash waters enter the environment in dissolved form. As the water solution passes through the soil, some of the dissolved pesticide may sorb to and contaminate the soil. This contaminated soil can then become a long-term source of ground water contamination as the pesticide slowly redissolves.

When formulated pesticides are purposefully applied to a site to control

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

weeds or insects, widespread, low-level contamination of ground water can occur from direct transport to ground water and from leaching of the adsorbed pesticides from the soil into the ground water. Typically, soil fumigants and inorganic pesticides are more soluble and readily leached than more complex and higher-molecular-weight organic pesticides. However, even pesticides that are not readily leached, such as organochlorine and organophosphorus pesticides, can contaminate ground water and surface water (van der Leeden et al., 1990). Because highly insoluble pesticides sorb to soils, they can be transported on soil particles in surface runoff or through the migration of colloidal clay particles in ground water systems.

Volatilization processes can account for significant losses of pesticides applied to the field. Volatilization processes include direct volatilization, wick evaporation, and azeotropic distillation. Under field conditions, the rates of these processes vary widely, both spatially and temporally, depending on soil and pesticide properties and soil environmental conditions (such as soil water content and temperature). In some circumstances, for very volatile pesticides such as methyl bromide and other fumigants, volatilization can account for loss of as much as 80 to 90 percent of the total amount of pesticide applied (Treigel and Guo, 1994). Three competing factors control volatilization processes: (1) the pesticide's vapor pressure and aqueous solubility, (2) the multi-phase distribution of the pesticide in the subsurface, and (3) the water content of the soil (Treigel and Guo, 1994). Biodegradation or other transformation processes can also affect the rate of volatilization. The distribution of pesticides among various phases depends on the sorption coefficient and Henry's law constants as well as the soil water content. Volatile losses are significant primarily for pesticides with very high vapor pressures, low aqueous solubilities, and a very low tendency for sorption. Migration of the pesticide into the subsurface significantly decreases losses due to volatilization.

Once applied to the field, some pesticides will attenuate biologically due to either microbial degradation or plant uptake. The biodegradability of pesticides varies considerably. Naturally occurring organic pesticides are generally biodegraded when the proper nutrients are present. Organophosphate and organonitrogen compounds are often biologically active. Chlorinated compounds such as the cyclodienes and chlorinated aromatics such as dichlorodiphenyltrichloroethane (DDT) are extremely resistant to aerobic degradation. However, many organochlorine pesticides can be partially transformed via reductive dechlorination (an anaerobic process), as in the conversion of DDT to dichlorodiphenyldichloroethane (DDD) and dichlorodiphenylchloroethane (DDE). The byproducts of reductive dechlorination of organochlorine compounds can also be hazardous and quite resistant to further degradation. Byproducts also may be more mobile than the parent compound.

Microbial transformation of pesticides is often much slower in the subsurface than in surface soils, even for pesticides made of natural organic products. A

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

case example is glufosinate ammonium (used to control broad-leaved weeds), which in one examination transformed rapidly in surface soil, with 50 percent disappearance in three to seven days (Gallina and Stephenson, 1992). However, in sandy aquifer sediments in both the laboratory and field settings, glufosinate persisted at high concentrations through three months of experiments (Allen-King et al., 1995). Glufosinate persists because microorganisms use it only as a source of nitrogen, not as a source of carbon and energy, and microbes prefer other sources of nitrogen (such as ammonium) over the glufosinate. Thus, when a competing nitrogen source is present or when carbon is in short supply, glufosinate will not degrade. Other pesticides exhibit similar behavior in that they may be transformed rapidly in warm, high-nutrient surface soil, while transformation rates in ground water are much slower.

Chemical degradation is a more limited pathway but can have an impact on the persistence of pesticides. The primary chemical reactions for many pesticides are hydrolysis, protonation (for amine groups), and oxidation. These reactions may be catalyzed by soils, especially clay minerals. Chemical reactivity is a function of soil pH, moisture, temperature, redox potential, and soil mineralogy.

In summary, pesticide transport properties are extremely complex, perhaps among the most complex of all contaminant groups, and highly variable depending on the type of pesticide, how it entered the environment, and the environmental conditions at the contaminated site.

Remediation Technology Options

The options appropriate for treating pesticide-contaminated soil depend on the nature of the pesticide and the way in which the pesticide was released to the environment. The treatability of pesticides depends on the chemical structure and functional groups of the pesticide because these affect solubility, volatility, degradability, and sorption characteristics. In addition, the surfactants and emulsifiers commonly included in formulated pesticides affect the feasibility of using various remediation technologies.

Conventional approaches to pesticide remediation have been primarily excavation followed by incineration or disposal for contaminated soil and treatment of extracted ground water at the well head. A review of pesticide-contaminated sites in Singhvi et al. (1994) indicates that many alternatives exist for treating pesticide-contaminated soil, but few if any alternatives to conventional pumping and treating have been documented in technical literature for treating pesticide-contaminated ground water. One of the only available case studies reporting on treatment of pesticide-contaminated ground water (Carter et al., 1995) involved ground water and soil remediation at a pesticide processing facility. In this case, dinoseb, metalochlor, volatile organic compounds, and nitrosamine compounds were treated by first excavating and removing the soil and then by pumping the ground water and treating it ex situ with a carbon adsorption and advanced oxidation

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

system. Thus, the following discussion addresses remediation of pesticide-contaminated soil.

Solidification and Stabilization Techniques

Pesticide-contaminated soils and residues can be treated using solidification techniques to reduce contact with water, hence reducing potential dissolution into ground water, or can be altered chemically to reduce mobility. Applications can be performed in situ or (more commonly) ex situ by mixing the soil with a cement-based matrix. Toxicity reduction does not usually occur. This approach is often applied in combination with other pretreatment methods.

Generally, solidification and stabilization techniques have limited applicability to naturally occurring organic compounds with high vapor pressures, complex synthetic organics that form low-concentration plumes in ground water, or organic pesticides that are readily soluble in water. These methods are not preferred for organic or alkylated metal pesticides because the organic fractions may degrade, and the organic ligand can increase the volatility of the metal compound (Singhvi et al., 1994). In other cases, the cementitious materials used to bind the pesticide may not be compatible with the chemical form of the pesticide. Redox-sensitive metals that form soluble oxyanions (such as arsenate and chromate) or become soluble at high pH (such as cadmium hydroxide) would not be appropriate for these methods.

Biological Reaction Techniques

Bioremediation can be applied to treat soil, sludge, and sediments contaminated by halogenated or nonhalogenated organic pesticides that are sufficiently degradable. Bioremediation is not effective for inorganic pesticides containing toxic heavy metals. Ex situ applications may use either a slurry-phase or solid-phase approach. Slurry-phase bioremediation includes mixing of excavated soil or sludge with water and appropriate nutrients in reactor vessels. Generally, biological treatment will not be effective for highly chlorinated pesticides or pesticides present at high concentrations. Degradation of dinoseb and other pesticides in soil from 22 mg/kg to nondetectable levels after 22 days of treatment has been reported in a pilot-scale reactor system (EPA, 1993e).

Two companies 2 are developing coupled anaerobic/aerobic bioremediation as a two-step process for ex situ treatment of pesticide-contaminated soils. In the first step, organochlorine pesticides such as DDT are reductively dechlorinated under strictly anaerobic conditions. In the second stage, the metabolites are degraded aerobically. In most cases, a labile carbon source is added to create an

2  

The two companies developing this technology are Zeneca and J. R. Simplot.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

anaerobic system. In some cases, water is also used as an oxygen barrier, achieved by saturating the soil, to attain and maintain anaerobic conditions. The aerobic cycle is created by physically turning the soil or mechanically mixing it to aerate it. This process has been shown to degrade DDT, lindane, and methoxychlor (F. Peters, Zeneca Corporation, personal communication, 1996).

Bioremediation of pesticides also may be achieved through land farming and, more recently, composting. During land farming, soil is placed in lined or unlined beds, irrigated, aerated, and supplemented with nutrients as appropriate to maintain biological activity in the soil. Rates of decomposition are pesticide specific and may be influenced by climatic or environmental factors. Below-grade bioremediation cells where the soil is aerated and amended have been specifically designed to treat cyclodiene insecticides (chlordane, heptachlor) and other biodegradable compounds (EPA, 1993e). Preliminary results indicated accelerated degradation and treatment times of between three months and two years. Bicki and Felsot (1994) reported a case study at an Illinois site where soil containing alachlor, atrazine, trifluralin, and metalochlor was treated in experimental plots by land farming. Prolonged persistence of herbicide residues and crop phytotoxicity were potential problems with land application of herbicide-contaminated soil even after 528 days. At a second site, rapid initial degradation of trifluralin after 30 days was followed by slower rates of degradation. Bicki and Felsot (1994) suggest that degradation rates may be related to the length of time herbicide residues are present in the soil and their concentration. Land farming in combination with application of white-rot fungi has also indicated promising results for degradation of pentachlorophenol and other wood treatment wastes (EPA, 1993e).

Composting is conducted by mixing highly contaminated soil with organic matter in piles and providing aeration. Aerobic biological activity causes decomposition of the waste at elevated temperatures within the compost pile.

Intrinsic bioremediation can be an important attenuation route for some types of pesticides, especially for the more mobile fumigants, but many pesticides are quite persistent. Recent research has shown that chlorinated organic compounds composed of carbon chains having two or three carbon atoms can serve as an electron acceptor (Wiedemeier et al., 1995). For such reactions to occur, other degradable organics in addition to the chlorinated organic must be present. The degree of intrinsic degradation of the more complex pesticides is unknown.

Chemical Reaction Techniques

Some pesticides are amenable to oxidation with strong oxidants such as ozone, H2O2, Fenton's reagent (H2O2 and iron), or potassium permanganate. Some of these oxidants can be enhanced with catalysts and/or ultraviolet radiation. Pesticides can be oxidized in situ through the injection of oxidants, but typically application is ex situ in slurry reactors. Performance is best for aromatic and phenolic compounds and for pesticides (such as cyclodienes) containing unsatur-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

ated bonds. Ethers, highly chlorinated compounds, and those with saturated bonds are less amenable to oxidation. The addition of chemical oxidizing agents has been demonstrated at three pesticide-contaminated sites (Singhvi et al., 1994).

Chlorinated pesticides also may be detoxified through removal of the halogenated atoms from the molecule using innovative ex situ treatment processes such as KPEG/APEG (which stands for potassium polyethylene glycol/alkaline polyethylene glycol). This process is applicable to soil containing compounds such as DDT, DDE, lindane, toxaphene, heptachlor, dieldrin, ethylene dibromide, and 2,4-D. It uses alkaline reaction conditions and the reaction of the pesticide with potassium hydroxide polyethylene glycol in the presence of a cosolvent at elevated temperature. This technology is not applicable to inorganic metal pesticides. Newer dechlorination processes use solvated electrons formed by the dissolution of calcium metal in liquid anhydrous ammonia (Abel, 1995).

Separation Techniques

Several separation techniques are applicable to pesticide-contaminated soils. Applicable in situ technologies include soil flushing, SVE, air sparging, steam extraction, and radio frequency heating. These in situ technologies are less frequently applied than ex situ techniques such as those discussed above and thermal desorption (discussed below) because they require more data on the location and distribution of the pesticide to implement and therefore can be more costly than ex situ techniques. Soil flushing, steam extraction, and radio frequency heating are considered emerging technologies.

SVE, possibly combined with air sparging, is applicable to pesticides with vapor pressure greater than 0.5 mm Hg in hydrogeologic settings sufficiently permeable to permit the extraction of vapors. Fumigant compounds (ethylene dibromide, dibromodichloropropane, and methyl bromide), thiocarbamates, and oxide n-acylcarbamates are amenable to this treatment. SVE and air sparging are not applicable to most inorganic and halogenated pesticides because these are typically nonvolatile. SVE has been used to recover pesticides and other volatile compounds at the Sand Creek Superfund site in Colorado (Singhvi et al., 1994).

Ex situ thermal desorption has been selected for at least three Superfund sites and is applicable to volatile and semivolatile compounds, which must be condensed or sorbed in a treatment phase following desorption. Ex situ thermal desorption has demonstrated high removal efficiencies for soils containing toxaphene, DDT, DDE, DDD, endosulfan, dieldrin, endrin, atrazine, diazinon, prometryn, and simazine (Singhvi et al., 1994). Selection of appropriate bed temperatures and residence times is critical in achieving performance standards, particularly with mixtures of pesticide compounds. Volatile metal compounds such as alkyl-mercury or arsenic compounds may also be treated with this technology.

Three in situ techniques are being developed that can treat pesticide-contaminated soils using a combination of heating and vacuum extraction to volatil-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

ize and remove the pesticides. Because of the low volatility of many pesticides, the soil often needs to be heated to temperatures at or above the boiling point of water. The first technique used to heat soil and cause contaminant volatilization is electrical resistance heating. Electrodes are placed in the ground, and a current is passed through the soil. Resistance to current flow causes the soil to heat. Simultaneous application of vacuum extraction removes contaminants that volatilize. Electrical resistance heating is effective for attaining temperatures in the range of 80 to 110°C (180 to 230°F) (Heath et al., 1992). The second technique uses radio frequency heating. Antennas (electrodes) are placed in the ground to broadcast microwave energy through the soil. Radio frequency heating can attain temperatures in the range of 250 to 400°C (480 to 750°F) (Roy, 1989). The third heating technique uses radiant heating. A heater element is placed in a steel well. The inwell temperature is raised to approximately 820°C (1500°F), and temperatures of approximately 430°C (810°F) are attained in the sand pack around the well. The wells are placed close enough to attain temperatures of approximately 260°C (500°F) in the surrounding soil. Volatilized contaminants are drawn in through the heated well pack and are partially destroyed (Sheldon, 1996).

Research Needs

The most important research need related to technologies for cleaning up pesticide-contaminated sites is the development of in situ techniques for treatment of contaminated ground water. There is currently essentially a complete absence of experience with technologies other than pump-and-treat systems for treating pesticide-contaminated ground water.

Existing options for treatment of pesticide-contaminated soil need to be optimized and new processes developed. Improved design bases are needed for ex situ biological systems (including coupled anaerobic/aerobic reactors and land farming systems) for treatment of pesticides. Considerable research is also needed to understand the potential for in situ bioremediation of various classes of pesticides. While recent research has demonstrated the potential for intrinsic remediation of pesticides, this research needs to be expanded before the potential for intrinsic remediation to achieve regulatory goals can be accurately predicted. In addition, research is needed to provide a basis for designing in situ bioremediation and phytoremediation systems for treatment of pesticides. Similar work is needed to optimize performance of ex situ chemical reaction systems for treating pesticides and to develop in situ chemical reaction systems. The scientific basis for designing in situ systems that use heat and applied vacuums to remove pesticides also needs to be developed.

An additional area of research applicable to all potential technologies for pesticide remediation is the development of improved pesticide fate and transport models for use in the environmental industry. Many such models have been developed for agricultural purposes, but this knowledge needs to be transferred for

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

application to pesticide remediation. As explained above, pesticides have a wide range of properties; some have high volatility, reactivity, or solubility, while others have very limited volatility, reactivity, or solubility. Effort is needed to organize pesticides into groups of like compounds that can be treated with similar types of remediation technologies.

CONCLUSIONS

From a national perspective, there is little field experience with innovative technologies for treating contaminants other than petroleum hydrocarbons and, to a lesser extent, chlorinated solvents in relatively homogeneous geologic settings. While successes are now quite common in extracting or biologically treating volatile organic compounds in permeable soils, extrapolating such experiences to complex geologic settings, contaminant mixtures, nonaqueous-phase contaminants located at great depth, and contaminants having low volatility or solubility remains a highly uncertain process. For these classes of problems, owners of contaminated sites, the consultants hired to advise them on site remediation, and regulators tend to be risk averse. The vast majority of available technologies are designed for remediation of soils at the surface or in the vadose zone; few options are available for treating contaminated ground water in situ. Research and field work are needed to expand the range of technologies available in the remediation marketplace for treating complex contamination scenarios (see the research recommendations below).

For all types of contamination problems—from sites that are relatively amenable to treatment with existing technologies to the most complex sites—a great deal of uncertainty remains in designing remediation technologies and predicting the results they will achieve. Current designs are often empirical, involving many qualitative assumptions about performance. Research and field work are needed to improve the scientific basis for remediation technology design.

Adding to the uncertainty associated with remediation technology design is lack of information. Obtaining reliable information about innovative remediation technologies is difficult because of the lack of comprehensive data bases, thorough project reports, data collected according to consistent protocols, and peer review of reported data. Much information about remediation technology effectiveness is from literature that has not been peer reviewed. Information and use of technologies at the field scale, especially for sites not covered under the Superfund or underground storage tank programs, is lacking. Data on the success of field trials vary in quality and completeness, and most often such data are not peer reviewed. Methods for determining technology effectiveness and costs vary widely. As a result of the difficulty of obtaining data and the variability of existing data, evaluating and comparing alternative remediation technologies is difficult.

In summary, improving the availability of technologies for cleaning up con-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

taminated sites and the ability to compare these technologies based on rational scientific evaluation will require research, field work, and improved data collection and technology transfer. The development of new remediation approaches will require close links between laboratory and field studies and access to field demonstration sites with the freedom to change process operations during testing. Parallel activities involving field investigations in concert with laboratory and theoretical work will help identify key issues and thus focus scientific and engineering activities on the most critical topics related to remediation.

RECOMMENDATIONS: TECHNOLOGY INFORMATION AND DISSEMINATION

To improve the quality and availability of data on remediation technology performance, the committee recommends the following actions:

  • The EPA, in collaboration with other stakeholders, should increase the scope and compatibility of data bases containing remediation technology performance information and should make these data bases available on the Internet, with a single World Wide Web page including links to all of the data bases. Improvements in information collection, assessment, and dissemination are needed to speed development and commercialization of remediation technologies. While a single, centralized data base will likely be unwieldy and may not satisfy the diverse interests of various users, a goal for the EPA should be to help develop comprehensive and electronically accessible data bases that can be readily distributed and manipulated by different contributors and users. These data bases could be established from currently available but incomplete and incompatible systems. To increase portability, a consistent framework for data entry and retrieval should be developed and used in all the data bases. The format for data entry should be simple. The data bases could provide a tiered approach for data entry, with data at the lowest level (consisting of an abstract and short description) not being peer reviewed and data at the highest level having been extensively peer reviewed. The data bases should be widely advertised in peer reviewed and trade journals and at technical conferences so that those who provide data will benefit from increased access to potential technology users.

  • Government agencies, remediation consultants, and hazardous waste site owners should work to increase the sharing of information on remediation technology performance and costs. Keeping technology performance information proprietary, whether by design or because of lack of dissemination of the information, slows progress in applying the technology elsewhere. Incentives should be developed to encourage submission of technology performance and cost data to the coordinated national data bases recommended above.

  • Government agencies, regulatory authorities, and professional organizations should undertake periodic, comprehensive peer review of innova-

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

tive remediation technologies. This type of activity will help define the state of the art, build consensus, and provide a standard for design and implementation of new remediation technologies.

RECOMMENDATIONS: TECHNOLOGY RESEARCH

To expand the range and efficiency of technologies available for cleaning up hazardous waste sites and improve the ability to select and design remediation technologies based on rational scientific analysis, the committee recommends research in the following areas:

  • Hydrogeologic and geochemical phenomena governing contaminant behavior in low-permeability, heterogeneous media. The fate of contaminants in low-permeability, heterogeneous geologic settings is difficult to predict, and design of remediation systems to access contaminants in these settings is difficult. Improved understanding of contaminant behavior in these complex subsurface systems needs to be coupled with engineering evaluations and rational risk assessment tools to help guide site management decisions.

  • Methods for predicting the fate, effects, and risks of DNAPLs in a wide range of hydrogeologic settings and for removing DNAPLs from the subsurface. Although long discussed, the problems of locating and treating DNAPL contamination have not been resolved.

  • Treatment of contaminants having limited reactivity and/or mobility, including PAHs, PCBs, pesticides, metals, and radionuclides. These contaminants are difficult to treat because they can either partially or completely resist destruction by biological or chemical reactions and/or mobilization and extraction from the subsurface. Treatment processes for radionuclides must address the added concern of disposal of extracted radionuclides or risks of radionuclides that are left in place in stabilized or solidified soils.

  • Treatment of contaminant mixtures. Treatment of contaminant mixtures poses a major challenge because of the variable effects of treatment processes on different types of contaminants. For example, a treatment process that immobilizes, transforms, or degrades one type of contaminant may have little effect on another. Research is needed to identify the types of contaminant mixtures commonly found at hazardous waste sites and the appropriate treatment trains for managing these mixtures. Treatment of mixtures including radioactive contaminants poses a special challenge that needs to be addressed.

  • Factors controlling the bioavailability of hydrophobic organic compounds (especially residual contamination from petroleum hydrocarbons, chlorinated solvents, PAHs, PCBs, and pesticides). Little information is available on the chemical processes that control slow release and diffusion of compounds through organic contaminant liquids and natural soil organic matter. New investigative methods, conceptual hypotheses, and model frameworks are needed

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

to predict when contaminants are bioavailable, either to microorganisms that can degrade the contaminants or to sensitive human and ecological receptors that may be harmed by the contamination. Information is also needed to determine how biodegradation of hydrophobic organic compounds affects the mobility and toxicity of residuals that remain after active biotreatment. Such information is needed to determine whether contaminants that remain in place but are not bioavailable warrant further remediation.

  • Effectiveness and rates of bioremediation processes, especially those capable of treating organic contaminant mixtures, compounds having low solubilities, strongly sorbed compounds, and compounds resistant to degradation. Although widely studied, the design of bioremediation processes is, in general, empirical. Rate-controlling parameters are largely unknown, and treatment end points are unpredictable, especially for contaminants other than easily degradable petroleum hydrocarbons.

  • Physical, chemical, and biological processes affecting the rate of intrinsic bioremediation. As for engineered bioremediation processes, current scientific knowledge is inadequate to provide accurate predictions of the rate and extent of intrinsic bioremediation, especially for contaminants other than easily degradable petroleum hydrocarbons. Such work should address techniques for predicting the rate of intrinsic bioremediation in advance and identifying suitable monitoring strategies for sites where this approach is appropriate.

  • Factors affecting the performance of solvent-and surfactant-based processes for contaminant remediation. The scientific basis for predicting the performance and kinetics of these processes needs to be improved. Factors related to process performance include hydrologic control of pumped fluids, management and reuse of pumped fluids, doses of solvents and surfactants, effects of residual chemical additives, and heterogeneities in the geologic media.

  • Materials handling for remediation technologies involving mixing and/or moving and processing of large quantities of solids. Handling of large volumes of soil and sludge can pose equipment and materials problems for both in situ stabilization and solidification techniques and ex situ soil treatment systems. For in situ stabilization and solidification techniques, the ability to achieve desired results requires attention to sampling and geostatistical techniques to ensure the thoroughness of treatment.

  • Long-term effectiveness of in situ solidification, stabilization, and containment techniques. Having a scientific basis for determining the life of these systems is essential for long-term protection of public health and the environment. Current understanding of the longevity of solidification, stabilization, and containment techniques is inadequate.

  • Long-term effectiveness of in situ biotic and abiotic processes that decrease the mobility of metals. The effectiveness of novel sorbents for capture of metals needs greater evaluation at the field scale. Soil flushing systems need similar study for metals remediation. Capture of metals by wetlands and other

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

phytoremediation systems appears promising, but many details need to be studied to explain the process and guarantee reliability. Handling mixtures of metals presents substantial problems because of the varying effects of geochemistry on different metals.

REFERENCES

Abel, A. 1995. PCB destruction in soils using solvated electrons. Presented at American Institute Chemical Engineers National Meeting, Boston, August 1, 1995.

Abdul, A., and C. C. Ang. 1994. In situ surfactant washing of polychlorinated biphenyls and oil from a contaminated field site: Phase II pilot study. Ground Water 32 (September–October): 727–734.

Abdul, A. S., T. L. Gibson, C. C. Ang, J. C. Smith, and R. E. Sobczynski. 1992. In situ surfactant washing of polychlorinated biphenyls and oils from a contaminated site. Ground Water 30(March–April):219–231.

Acar, Y. B., and A. N. Alshawabkeh. 1993. Principles of electrokinetic remediation. Environmental Science & Technology 27:2638–47.

Adeel, Z., R. G. Luthy, D. A. Dzombak, S. B. Roy, and J. R. Smith. In press. Leaching of PCB compounds from untreated and biotreated sludge-soil mixtures. Journal of Contaminant Hydrology.

Aelion, C. M., and P. M. Bradley. 1991. Aerobic biodegradation potential of subsurface microorganisms from a jet fuel-contaminated aquifer. Applied and Environmental Microbiology 57:57–63.

Alcoa Remediation Projects Organization. 1995. Bioremediation Tests for Massena Lagoon Sludges/Sediments, Vol. 1. Report prepared for the U.S. EPA and New York State Department of Environmental Conservation. Pittsburgh, Pa.: Aluminum Company of America.

Alexander, M. 1994. Biodegradation and Bioremediation. San Diego: Academic Press.

Ali, M. A., D. A. Dzombak, and S. B. Roy. 1995. Assessment of in situ solvent extraction for remediation of coal tar sites: Process modeling. Water Environment Research 67:16–24.

Allen-King, R. M., J. F. Barker, R. W. Gillham, and B. K. Jensen. 1994a. Substrate and nutrient limited toluene biotransformation in sandy soil. Environmental Toxilogical Chemistry 13:693–705.

Allen-King, R. M., K. E. O'Leary, R. W. Gillham, and J. F. Barker. 1994b. Limitations on the biodegradation rate of dissolved BTEX in a natural unsaturated, sandy soil: Evidence from field and laboratory experiments. Pp. 175–191 in Hydrocarbon Bioremediation, R. E. Hinchee, B. C. Alleman, R. E. M. Hoeppel, and R. N. Miller, eds. Ann Arbor: Lewis Publishers.

Allen-King, R. M., B. J. Butler, and B. Reichert. 1995. Fate of the herbicide glufosinate ammonium in the sandy, low organic-carbon aquifer at CFB Borden, Ontario, Canada. Journal of Contaminant Hydrology 18:161–179.

Alvarez, P., and T. Vogel. 1991. Substrate interactions of benzene, toluene, and para-xylene during microbial degradation by pure cultures and mixed culture aquifer slurries. Applied and Environmental Microbiology 57(10):2891-1985.

Amiran, M. C., and C. L. Wilde. 1994. PAH removal using soil and sediment washing at a contaminated harbor site. Remediation (Summer):319–330.

Annable, M. D., P. S. C. Rao, R. K. Sillan, K. Hatfield, W. D. Graham, A. L. Wood, and C. G. Enfield. 1996. Field-scale application of in situ cosolvent flushing: Evaluation approach. In Proceedings of ASCE Conference on NAPLs, Washington, D.C., November 10–14, 1996. New York: American Society of Civil Engineers.

API (American Petroleum Institute). 1996. Petroleum Industry Environmental Performance. Washington, D.C.: American Petroleum Institute.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Armstrong, A. Q., R. E. Hodson, H. M. Hwang, and D. L. Lewis. 1991. Environmental factors affecting toluene degradation in ground water at a hazardous waste site. Environmental Toxicological Chemistry 10:147–158.

Augustijin, D. C. M., R. E. Jessup, P. S. C. Rao, and A. L. Wood. 1994. Remediation of contaminated soils by solvent flushing. ASCE Journal of Environmental Engineering 120(1):42–57.

Barbaro, J. R., J. F. Barker, L. A. Lemon, and C. I. Mayfield. 1992. Biotransformation of BTEX under anaerobic, denitrifying conditions: Field and laboratory conditions. Journal of Contaminant Hydrology 11:245–272.

Barbash, J. E., and E. R. Resek. 1996. Pesticides in Ground Water: Distribution, Trends and Governing Factors. Chelsea, Mich.: Ann Arbor Press.

Bass, D., and R. Brown. 1996. Air sparging case study data base update. Presented at First International Symposium on In Situ Air Sparging for Site Remediation, Las Vegas, Nevada, October 26–27, 1996.

Bedard, D. L., R. E. Wagner, M. J. Brennan, M. L. Haberl, and J. F. Brown, Jr. 1987. Applied and Environmental Microbiology 535:1094–1102.

Beeman, R. E. 1994. In Situ Biodegradation of Ground Water Contaminants. U.S. Patent Number 5, 277, 815. Washington, D.C.: U.S. Patent and Trademark office

Bianchi-Mosquera, G. C., R. M. Allen-King, and D. M. Mackay. 1994. Enhanced degradation of dissolved benzene and toluene using a solid oxygen-releasing compound. Ground Water Monitoring and Remediation 9(1):120–128.

Bicki, T. J., and A. S. Felsot. 1994. Remediation of pesticide contaminated soil at agrichemical facilities. In Mechanisms of Pesticide Movement into Ground Water, R. C. Honeycutt and D. J. Schabacher, eds. Boca Raton, Fla.: CRC Press.

Blowes, D. W., and C. J. Ptacek. 1992. Geochemical remediation of groundwater by permeable reactive walls: Removal of chromate by reaction with iron-bearing solids. Presented at Subsurface Restoration Conference, Third International Conference on Groundwater Quality Research, Dallas, Texas, June 21–24, 1992.

Blowes, D. W., C. J. Ptacek, C. J. Hanton-Fong, and J. L. Jambor. 1995. In situ remediation of chromium contaminated groundwater using zero-valent iron. Pp. 780–784 in Preprints of Papers Presented at the 209th American Chemical Society National Meeting, Anaheim, Calif., April 2–7, 1995. Washington, D.C.: American Chemical Society, Division of Environmental Chemistry.

Bossert, I. A., and R. Bartha. 1986. Structure-biodegradability relationships of polycyclic aromatic hydrocarbons in soil. Bulletin of Environmental Contamination and Toxicology 37:490–495.

Brookins, D. G., B. M. Thomson, P. A. Longmire, and P. G. Eller. 1993. Geochemical behavior of uranium mill tailing leachate in the subsurface . Radioactive Waste Management and the Nuclear Fuel Cycle 17(3–4):269–287.

Brown, R. A. 1992. Air Sparging: A Primer for Application and Design. Trenton, N.J.: Fluor Daniel GTI.

Brown, R. A., and F. Jasiulewicz. 1992. Air sparging: A new model for remediation. Pollution Engineering (July):52–55.

Brown, R. A., and R. D. Norris. 1986. An in-depth look at bioreclamation. Presented at HazMat, Atlantic City, N.J., June 2–4, 1986.

Brown, R. A., and R. Falotico. 1994. Dual phase vacuum extraction systems: Design and utilization. Presented at Twenty-sixth Mid-Atlantic Industrial and Hazardous Waste Conference, Newark, Del., August 7–9, 1994.

Brown, R. A., E. L. Crockett, and R. D. Norris. 1987a. The principles of in situ biological treatment. Presented at HazMat West, Long Beach, Calif., December 3–5, 1987.

Brown, R. A., G. E. Hoag, and R. D. Norris. 1987b. The remediation game: Pump, dig or treat. Presented at Water Pollution Control Federation Conference, Philadelphia, October 5–8, 1987.

Brown, R. A., J. Crosby, and R. D. Norris. 1990. Oxygen sources for in situ bioreclamation. Presented at Water Pollution Control Federation Conference, Washington, D.C., December 1990.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Brown, R. A., W. Mahaffey, and R. D. Norris. 1993. In situ bioremediation: The state of the practice. Pp. 121–135 in In Situ Bioremediation: When Does It Work? Washington, D.C.: National Academy Press.

Burris, D. R., T. J. Campbell, and V. S. Manoranjan. 1995. Sorption of trichloroethylene and tetrachloroethylene in a batch reactive metallic iron-water system. Environmental Science & Technology 29:2850–2855.

Carter, R. W., H. Stiebel, P. J. Nalasco, and D. L. Pardieck. 1995. Investigation and remediation of groundwater contamination at a pesticide facility: A case study. Water Quality Research Journal Canada 30(3):469–491.

Cerniglia, C. E. 1984. Microbial metabolism of polycyclic aromatic hydrocarbons. Advances in Applied Microbiology 30:31–71.

Chapelle, F. H. 1993. Ground-Water Microbiology and Geochemistry. New York: John Wiley & Sons.

Claus, D., and N. Walker. 1964. The decomposition of toluene by soil bacteria. Journal of General Microbiology 36:107–122.

Coates, J. T., and A. W. Elzerman. 1986. Desorption kinetics for selected PCB congeners from river sediments. Journal of Contaminant Hydrology 1:191–210.

Cohen, R. M., and J. W. Mercer. 1993. DNAPL Site Evaluation. Boca Raton, Fla.: C. K. Smoley.

Columbo, P., E. Barth, P. Bishop, J. Buelt, and J. R. Connor. 1994. Stabilization/Solidification. Vol. 4 of Innovative Site Remediation Technology, W. C. Anderson, ed. Annapolis, Md.: American Academy of Environmental Engineers.


Dávila, B., K. W. Whitford, and E. S. Saylor. 1993. Technology Alternatives for the Remediation of PCB-Contaminated Soil and Sediment. EPA/540/S-93/506. Washington, D.C.: EPA, Office of Solid Waste and Emergency Response.

Delta Omega Technologies. 1994. Creo-Solv Technical Report: Soil Washing Applications for Creosote Removal. DOT-CS-1601. Houston, Tex.: Delta Omega Technologies.

DOD (Department of Defense) Environmental Technology Transfer Committee. 1994. Remediation Technologies Screening Matrix and Reference Guide, Second Edition. NTIS PB95-104782. Springfield, Va.: National Technical Information Service.

DOE (Department of Energy). 1994a. In Situ Remediation Integrated Program: Technology Summary. DOE/EO134P. Springfield, Va.: National Technical Information Service.

DOE. 1994b. Technology Catalogue. Springfield, Va.: National Technical Information Service.

Dzombak, D. A., and R. G. Luthy. 1984. Estimating Sorption of Polycyclic Aromatic Hydrocarbons on Soils. Soil Science 137:292–308.

Dzombak, D. A., R. G. Luthy, Z. Adeel, and S. B. Roy. 1994. Modeling Transport of PCB Congeners in the Subsurface. Report to the Aluminum Company of America, Environmental Technology Center, Alcoa Center, Pa. Pittsburgh, Pa.: Carnegie Mellon University, Department of Civil and Environmental Engineering.


ECI ECO LOGIC International, Inc. 1992. Pilot-Scale Demonstration of Contaminated Harbor Sediment Treatment Process: Final Report. Rockwood, Ontario: ECI ECO LOGIC.

ECO LOGIC. 1995. The ECO LOGIC Process: A Gas-Phase Chemical Reduction Process for PCB Destruction. Rockwood, Ontario: ECO LOGIC Corporation.

Edwards, D. A., R. G. Luthy, and Z. Liu. 1991. Solubilization of polycyclic aromatic hydrocarbons in micellar nonionic surfactant solutions. Environmental Science & Technology 25:127–133.

Edwards, D. A., Z. Adeel, and R. G. Luthy. 1994a. Distribution of nonionic surfactant and phenanthene in sediment/aqueous systems . Environmental Science & Technology 28:1550–1560.

Edwards, D. A., Z. Liu, and R. G. Luthy. 1994b. Surfactant solubilization of organic compounds in soil/aqueous systems. ASCE Journal of Environmental Engineering 120:5–22.

Ely, D. L., and D. A. Heffner. 1991. Process for In Situ Biodegradation of Hydrocarbon Contaminated Soil. U.S. Patent 5,017,289. Washington, D.C.: U.S. Patent and Trademark Office.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

EPA. 1990. National Pesticide Survey: Summary Results of EPA's National Survey of Pesticides in Drinking Water Wells. Washington, D.C.: EPA. EPA. 1992. Demonstration Bulletin: AOSTRA—SoilTech Anaerobic Thermal Processor: Wide Beach Development Site, Superfund Innovative Technology Evaluation. EPA/540/MR-92/008. Cincinnati, Ohio: EPA, Risk Reduction Engineering Laboratory.

EPA. 1993a. Applications Analysis Report: Bergmann USA Soil/Sediment Washing Technology, Preliminary Draft. Cincinnati, Ohio: EPA, Risk Reduction Engineering Laboratory.

EPA. 1993b. Pilot-Scale Demonstration of a Slurry-Phase Biological Reactor for Cresote Contaminated Soil: Applications Analysis Report. EPA/540/A5-91/009 Washington, D.C.: EPA, Office of Research and Development.

EPA. 1993c. Demonstration Bulletin: X*TRAX Model 200 Thermal Desorption System, Superfund Innovative Technology Evaluation. EPA/540/MR-93/502. Cincinnati, Ohio: EPA, Risk Reduction Engineering Laboratory.

EPA. 1993d. Resources Conservation Company B.E.S.T. Solvent Extraction Technology, Application Analysis Report. EPA/540/AR-92/079. Washington, D.C.: EPA, Office of Research and Development.

EPA. 1993e. Superfund Innovative Technology Evaluation Program Technology Profiles, Sixth Edition. EPA/540/R-93/526. Washington, D.C.: EPA.

EPA. 1994a. Engineering Bulletin—Solvent Extraction. EPA/540/S-94/503. Washington, D.C.: EPA, Office of Emergency and Remedial Response.

EPA. 1994b. Status Reports on In Situ Remediation Technologies for Ground Water and Soils at Hazardous Waste Sites: Surfactant Enhancements (Draft). EPA 542-K-94-003. Washington, D.C.: EPA, office of Solid Waste and Emergency Response.

EPA. 1994c. Status Reports on In Situ Remediation Technologies for Ground Water and Soils at Hazardous Waste Sites: Thermal Enhancements (Draft). EPA 542-K-94-009. Washington, D.C.: EPA, Office of Solid Waste and Emergency Response.

EPA. 1995a. In Situ Remediation Technology Status Report: Surfactant Enhancements. EPA 542-K-94-003. Washington, D.C.: EPA.

EPA. 1995b. In Situ Remediation Technology Status Report: Thermal Enhancements. EPA-542-K-94-009. Washington, D.C.: EPA.

EPA. 1996a. Innovative Treatment Technologies: Annual Status Report (Eighth Edition). EPA-542-R-96-010. Washington, D.C.: EPA, Office of Solid Waste and Emergency Response.

EPA. 1996b. Symposium on Natural Attenuation of Chlorinated Organics in Ground Water, Dallas, September 11-13, 1996. EPA540/R-961509. Washington, D.C.: EPA, Office of Research and Development.

Erickson, D. C., R. C. Loehr, and E. F. Neuhauser. 1993. PAH loss during bioremediation of manufactured gas plant soils. Water Research 27:911-919.

ETI (EnviroMetal Technology Inc.). 1995. Performance history of the environmetal process, Internal document. October 1995.

Federal Remediation Technologies Roundtable. 1995a. Accessing Federal Data Bases for Contaminated Site CleanUp Technologies. Washington, D.C.: EPA.

Federal Remediation Technologies Roundtable. 1995b. Guide to Documenting Cost and Performance for Remediation Projects. EPA-542-B-95-002. Washington, D.C.: EPA.

Ferguson, T. L., and C. J. Rogers. 1990a. Field Applications of the KPEG Process for Treating Chlorinated Wastes: Project Officers Report. PB89-212-724/AS. Springfield, Va.: National Technical Information Service.

Ferguson, T. L., and C. J. Rogers. 1990b. Comprehensive Report on the KPEG Process for Treating Chlorinated Wastes. EPA/600/S2-90/026. Cincinnati, Ohio: Risk Reduction Engineering Laboratory.

Fetter, C. W. 1993. Contaminant Hydrogeology. New York: Macmillan.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Friedman, A.J., and Y. Halpern. 1992. Untreated and biotreated sludge-soil mixtures. Journal of Contaminant Ecology.

Gallina, M. A., and G. R. Stephenson. 1992. Dissipation of [14 C]glufosinate ammonium in two Ontario soils. Journal of Agricultural and Food Chemistry 40:165-168.

Gillham, R. W. 1995. Resurgence in research concerning organic transformations enhanced by zero-valent metals and potential application in remediation of contaminated groundwater. Pp. 691-694 in Preprints of Papers presented at the 209th American Chemical Society National Meeting, Anaheim, Calif., April 2-7, 1995. Washington, D.C.: American Chemical Society, Division of Environmental Chemistry.

Gillham, R. W., and S. F. O'Hannesin. 1994. Enhanced degradation of halogenated aliphatics by zero-valent iron. Ground Water 32:958-967.

Gotlieb. I., J. W. Bozzelli, and E. Gotlieb. 1993. Soil and water decontamination by extraction with surfactants. Separation Science and Technology 28(1-3):793-804.

Grayson, M., and D. Eckroth, eds. 1985. Kirk-Othmer Concise Encyclopedia of Chemical Technology. New York: John Wiley & Sons.

GRC Environmental, Inc. 1992. Alkaline Dechlorination Using Dimethyl Sulfoxide. East Syracuse, N.Y.: GRC Environmental, Inc.

GRI (Gas Research Institute). 1995. Proceedings of Workshop on Environmentally Acceptable Endpoints in Soil, Washington, D.C., May 4-5, 1995. Chicago, III.: GRI.

Grubb, D. G., and N. Sitar. 1994. Evaluation of Technologies for In Situ Cleanup of DNAPL Contaminated Sites. EPA/600/R-94/120. Ada, Okla.: EPA, R. S. Kerr Environmental Research Laboratory.

Gusak, J. J. 1995. Passive-treatment of acid rock drainage: What is the potential bottom line? Mining Engineering 47(3):250-253.

GWRTAC (Ground-Water Remediation Technologies Analysis Center). 1995. NETAC selected to operate national ground-water remediation technology center (news release). Pittsburgh, Pa.: GWRTAC (http://www.chmr.com/gwrtac).


Harkness, M.R., J.B. McDermott, D.A. Abramowicz, J.J. Salvo, W.P. Flanagan, M.L. Stephens, F.J. Mondello, R.J. May, J.H. Lobos, K.M. Carroll , M.J. Brennan, A.A. Branco, K.M. Fish, G.L. Warner, P.R. Wilson, D. K. Dietrich, D. T. Lin, C. B. Morgan and W. L. Gately. 1993. In situ stimulation of aerobic PCB biodegradation in Hudson River sediment. Science 259:503-507.

Health, W. A., J. S. Roberts, D. L. Lenor, and T. M. Bergman. 1992. Engineering scale-up of electrical soil heating for soil decontamination. Presented at Spectrum '92, Boise, Idaho, August 23-27, 1992. Richland, Wash.: Pacific Northwest Laboratory.

Hem, J. D. 1985. Study and Interpretation of the Chemical Characteristics of Natural Water. U.S. Geological Survey Water-Supply Paper 2254, Third Edition. Washington, D.C.: Government Printing Office.

Hinchee, R.E., D.C. Downey, and T. Beard. 1989. Enhancing biodegradation of petroleum hydrocarbons through soil venting. In Proceedings, Petroleum Hydrocarbons and Organic Chemicals in Ground-Water: Prevention, Detection, and Restoration, Houston, November 5-7, Houston. Worthington, Ohio: National Water Well Association.

Hinchee, R.E., and S. K. Ong. 1992. A rapid in situ respiration test for measuring aerobic biodegradation rates of hydrocarbon in soil. Journal of Air and Waste Management 42(10):1305.

Hoag, G. E., and C. Bruel. 1988. Use of soil venting for treatment/reuse of petroleum contaminated soil. Pp. 301-306 in Soil Effects, E.J. Calabrese and P.T. Kostecki, eds. New York: John Wiley & Sons.

Holden, L. R., J. A. Graham, R. W. Whitmore, W. J. Alexander, R. W. Pratt, S. K. Liddle, and L. L. Piper. 1992. Results of the national alachlor well water survey. Environmental Science & Technology 26:935-943. ­­

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Hutchins, S. R., and J. T. Wilson. 1994. Nitrate-based bioremediation of petroleum-contaminated aquifer at Park City, Kansas: Site characterization and treatability study. Pp. 80-92 in Hydrocarbon Bioremediation, R. E. Hinchee, B. C. Alleman, R. E. M. Hoeppel, and R. N. Miller, eds. Ann Arbor, Mich.: Lewis Publishers.

Jafvert, C. T. 1996. Surfactants/Cosolvents. Technology Evaluation Report TE-96-62. Pittsburgh, Pa.: Ground Water Remediation Technologies Analysis Center.

Johnson, P. C., and R. A. Ettinger. 1994. Considerations for the design of in situ vapor extraction systems: Radius of influence vs. radius of remediation. Groundwater Monitoring and Remediation 14(3):123-138.

Johnson, P. C., C. Stanley, M. Keblowski, D. Byers, and J. Corhart. 1990. A practical approach to design, operations, and monitoring of in situ soil-venting systems. Ground Water Monitoring Review 10(2):159.

Johnson, R. L., W. Bagby, M. Perrott, and C. Chen. 1992. Experimental examination of integrated soil vapor extraction techniques. In Proceedings of Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Restoration. Dublin, Ohio: National Ground Water Association.

Johnson, T. J., M. M. Scherer, and P. G. Tratnyek. 1996. Kenetics of halogenated organic compound degradation by iron metal. Environmental Science & Technology 30:2634-2640.


Kittel, J. A., A. Leeson, R. E. Hinchee, R. N. Miller, and P. Haas. 1995. Results of a multisite treatability test for bioslurping: A comparison of LNAPL rates using vacuum-enhanced recovery (bio-slurping), passive skimming, and pump drawdown recovery techniques. In Proceedings, Organic Chemicals in Groundwater: Detection, Prevention, and Remediation. Dublin, Ohio: National Ground Water Association.


Leder, A., and Y. Yoshida. 1995. C[2] Chlorinated Solvents (www-cmrc.sru.com/CIN/mar-apr95/article10.html). Menlo Park, Calif.: SRI International.

Lightly, J., M. Choroszy-Marshall, M. Cosmos, V. Cundy, and P. DePercin. 1993. Thermal Desorption. Vol. 6 of Innovative Site Remediation Technology, W. C. Anderson, ed. Annapolis, Md.: American Academy of Environmental Engineers.

Luthy, R. G., D. A. Dzombak, C. A. Peters, M. A. Ali and S. B. Roy. 1992. Solvent Extraction for Remediation of Manufactured Gas Plant Sites. Final Report TR-10185, Research Project 3072-02. Palo Alto, Calif.: Electric Power Research Institute.

Luthy, R. G., D. A. Dzombak, C. A. Peters, S. B. Roy, A. Ramaswami, D. V. Nakles, and B. R. Nott. 1994. Remediating tar-contaminated soils at manufactured gas plant sites. Environmental Science & Technology 28:266A-276A.

Luthy, R. G., and E. Ortiz. 1996. Bioavailability and biostabilization of hydrophobic organic compounds. Paper presented at UIB-GBR-CSIC-TUB Symposium on Biodegradation of Organic Pollutants, Mallorca, Spain, June 29-July 3, 1996.

Luthy, R. G., D. A. Dzombak, M. Shannon, R. Utterman, and J. R. Smith. 1997. Aqueous solubility of PCB congeners from an Aroclor and an Aroclor/hydraulic oil mixture . Water Research 31(3):561-573.

Lyman, W. J., P. J. Reidy, and B. Levy. 1992. Mobility and Degradation of Organic Contaminants in Subsurface Environments. Chelsea, Mich.: C. K. Smoley.


Machemer, S. D., and T. R. Wildeman. 1992. Adsorption compared with sulfide precipitation as metal removal processes from acid mine drainage in a constructed wetland. Journal of Contaminant Hydrology 9(112):115-131.

Magee, R. S., J. Cudahy, C. R. Dempsey, J. R. Ehrenfeld, F. W. Holm, D. Miller, and M. Modell. 1994. Thermal Destruction. Vol. 7 of Innovative Site Remediation Technology, W. C. Anderson, ed. Annapolis, Md.: American Academy of Environmental Engineers.

Mann, M. J., D. Dahlstrom, P. Esposito, L. Everett, G. Peterson, and R. P. Traver. 1993. Soil Washing/Soil Flushing. Vol. 3 of Innovative Site Remediation Technology, W. C. Anderson, ed. Annapolis, Md.: American Academy of Environmental Engineers.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Matheson, L. J., and P. G. Tratnyek. 1994. Reductive dechlorination of chlorinated methanes by iron metal. Environmental Science & Technology 28:2045–2053.

Maxymillian, N. A., S. A. Warren, and E. F. Neuhauser. 1994. Thermal Desorption of Coal Tar Contaminated Soils from Manufactured Gas Plants. Pittsfield, Mass.: Maxymillian Technologies.

McCarty, P. L. 1996. An overview of anaerobic transformation of chlorinated solvents. Paper presented at Conference on Intrinsic Remediation of Chlorinated Solvents, Airport Hilton, Salt Lake City, Utah, April 2, 1996.

McCarty, P. L., and L. Semprini. 1994. Ground water treatment for chlorinated solvents. Section 5 in Handbook of Bioremediation, R. D. Norris, ed. Boca Raton, Fla.: CRC Press.

Means, J. C., S. G. Wood, J. J. Hassett, and W. L. Banwart. 1980. Sorption of polynuclear aromatic hydrocarbons by sediments and soils. Environmental Science & Technology 14:1524–1528.

Mercer, J. W., and R. M. Cohen. 1990. A review of immiscible fluids in the subsurface: Properties, models, characterization and remediation. Journal of Contaminant Hydrology 6:(2)107–163.

Miller, R. N., R. E. Hinchee, C. M Vogel, R. R. DuPont, and D. C. Downey. 1990. Field investigation of enhanced petroleum hydrocarbon degradation in the vadose zone of Tyndall AFB. In Proceedings, Petroleum Hydrocarbons and Organic Chemicals in Groundwater: Prevention, Detection, and Remediation, Houston, October 31-November 2, 1990. Worthington, Ohio: National Water Well Association.

Mihelcic, J. R. and R. G. Luthy. 1988. Degradation of polycyclic aromatic hydrocarbon compounds under various redox conditions in soil-water systems. Applied and Environmental Microbiology 54:1182–1187.

Mohn, W. W., and J. M. Tiedje. 1992. Microbial reductive dehalogenation. Microbial Review 56:482–507.

Morea, S. C., R. L. Olsen, and R. W. Chappelle, in conjunction with scientists and engineers from the Colorado School of Mines and Denver Knight Piesold. 1989. Assessment of a passive treatment system for acid mine drainage. Paper presented at 62nd Annual Conference of the Water Pollution Control Federation, San Francisco, California, October 16–19, 1989.

Morgan, D., A. Battaglia, B. Hall, L. Vernieri, and M. Cushney. 1992. The GRI Accelerated Biotreatability Protocol for Assessing Conventional Biological Treatment of Soils: Development and Evaluation Using Soils from Manufactured Gas Plant Sites. Technical Report GRI-92/0499. Chicago, Ill.: Gas Research Institute.

Nakles, D., D. Linz, and I. Murarka. 1991. Bioremediation of MGP soils: Limitations and potentials. Presented at EPRI Technology Transfer Seminar on Management of Manufactured Gas Plant Sites . Atlanta, Ga., April 2-3, 1991.

National Research Council. 1993. In Situ Bioremediation: When Does It Work? Washington, D.C.: National Academy Press.

National Research Council. 1994. Alternatives for Groundwater Cleanup. Washington, D.C.: National Academy Press.

Norris, R. D., and J. E. Matthews. 1994. Handbook of Bioremediation. Ann Arbor, Mich.: Lewis Publishers.


Office of Naval Research, Air Force Office of Scientific Research, Army Research Office, and 7 Army Corps of Engineers, Waterways Experiment Station. 1995. A Tri-Service Workshop on Bioavailability of Organic Contaminants in Soils and Sediments, Monterey, Calif., April 9–12, 1995. Arlington, Va.: Office of Naval Research.

Oliver, B. G. 1985. Desorption of chlorinated hydrocarbons from spiked and anthropogenically contaminated sediments. Chemosphere 14(8): 1087–1106.

Ong, S. K., A. Leeson, R. E. Hinchee, J. Kittel, C. M. Vogel, G. D. Sayles, and R. N. Miller. 1994. Cold climate applications of bioventing. Pp. 444–453 in Hydrocarbon Bioremediation, R. E. Hinchee, B. C. Alleman, R. E. M. Hoeppel, and R. N. Miller, eds. Ann Arbor, Mich.: Lewis Publishers.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Palmer, C. D., and P. R. Wittbrodt. 1991. Processes affecting the remediation of chromium-contaminated sites. Environmental Health Perspectives 92:25–40.

Pankow, J. F., and J. A. Cherry, eds. 1996. Dense Chlorinated Solvents and Other DNAPLs in Ground Water: History, Behavior, and Remediation. Portland, Oreg.: Waterloo Press.

Pennell, K. D., G. A. Pope, and L. M. Abriola. 1996. Influence of viscous and buoyancy forces on the mobilization of residual tetrachloroethylene during surfactant flushing. Environmental Science & Technology 30(4):1328–1335.

Pope, G. A., and W. H. Wade. 1995. Lessons learned from enhanced oil recovery research for surfactant enhanced aquifer remediation. In Surfactant Enhanced Subsurface Remediation: Emerging Technologies. Washington, D.C.: American Chemical Society.

Powell, R. M., R. W. Puls, S. K. Hightower, and D. A. Sabatini. 1995. Coupled iron corrosion and chromate reduction: Mechanisms for subsurface remediation. Environmental Science & Technology 29:1913–1922.

Puls, R. W., R. M. Powell, and C. J. Paul. 1995. In situ remediation of ground water contaminated with chromate and chlorinated solvents using zero-valent iron: A field study . Paper presented at the 209th American Chemical Society National Meeting, Anaheim, Calif., April 2–7, 1995. Washington, D.C.: American Chemical Society, Division of Environmental Chemistry.


Raymond, R. L., V. W. Jamison, and J. O. Hudson. 1977. Beneficial stimulation of bacterial activity in groundwater containing petroleum hydrocarbons. American Institute of Chemical Engineers Symposium Series 73(166):390–404.

Rice, D., B. P. Dooher, S. J. Cullen, L. G. Everett, W. E. Kastenberg, R. D. Gose, and M. A. Marino. 1995. California Leaking Underground Fuel Tank (LUFT) Historical Case Analyses. UCRLAR-122207. Livermore, Calif.: Lawrence Livermore National Laboratory.

Roberts, A. L., L. A. Totten, W. A. Arnold, D. R. Burris, and T. J. Campbell. 1996. Reductive elimination of chlorinated ethylenes by zero-valent metals. Environmental Science & Technology 30:2654–2659.

Roy, K. 1989. Electrifying soil cleanup. HazMat World (July):14–15.

Roy, S. B., D. A. Dzombak, and M. A. Ali. 1995. Assessment of in situ solvent extraction for remediation of coal tar sites: Column studies . Water Environment Research 67(1):4–15.


Salanitro, J. 1993. An industry's perspective on intrinsic bioremediation. Pp. 104–109 in In Situ Bioremediation: When Does It Work? Washington, D.C.: National Academy Press.

Schwille, F. 1988. Dense Chlorinated Solvents in Porous and Fractured Media (translated by J. F. Pankow). Chelsea, Mich.: Lewis Publishers.

Semprini, L., P. V. Roberts, G. D. Hopkins, and P. L. McCarty. 1990. A field evaluation of in situ biodegradation of chlorinated ethenes: Part 2—the results of biostimulation and biotransformation experiments. Groundwater 28:715–727.

Sheldon, R. B. 1996. Field demonstration of a full-scale in situ thermal desorption system for the remediation of soil containing PCBs and other hydrocarbons. Presented at Superfund XVII, Washington, D.C., October 1996.

Singhvi, R., R. N. Koustas, and M. Mohn. 1994. Contaminants and Remedial Options at Pesticide Sites. EPA/600/R-94/202. Washington, D.C.: EPA.

Smith, J., P. Tomiceck, R. Weightman, D. Nakles, D. Linz, and M. Helbling. 1994. Definition of biodegradation endpoints for PAH contaminated soils using a risk-based approach. Paper presented at the Ninth Annual Conference on Contaminated Soils Using a Risk-Based Approach , University of Massachusetts, Amherst, Mass., October 18–20, 1994.

Smith, J. R., M. E. Egbe, and W. J. Lyman. In press. Bioremediation of polycholorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs). In Bioremediation of Contaminated Soils. Madison, Wis.: American Society of Agronomy/Soil Science Society of America.

Smith, L. A., B. C. Alleman, and L. Copley-Graves. 1994. Biological treatment options. Pp. 1-12 in Emerging Technology for Bioremediation of Metals, J. L. Means and R. E. Hinchee, eds. Ann Arbor, Mich.: Lewis Publishers.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Smith, L. A., J. L. Means, A. Chen, B. Alleman, C. C. Chapman, J. S. Tixier, Jr., S. E. Brauning, A. R. Gavaskar, and M. D. Royer. 1995. Remedial Options for Metals-Contaminated Sites. Boca Raton, Fla.: Lewis Publishers/CRC Press.

Soundararajan, R. 1992. Guidelines for evaluation of the permanence of a stabilization/solidification technology. Pp. 33–39 in Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, Vol. 2, T. M. Gilliam and C. C. Wiles, eds. ASTM STP 1123. Philadelphia: American Society for Testing and Materials.

Stinson, M. K. 1990. EPA SITE demonstration of the international waste technologies/geo-con in situ stabilization/solidification process. Journal of Air and Waste Management Association 40:1569–1576.

Stinson, M. K., H. Skovronek, and W. D. Ellis. 1992. EPA SITE demonstration of the BioTrol soil washing process. Journal of Air and Waste Management Association 42:96–103.

Swiss Federal Institute for Environmental Science and Technology. 1994. Workshop on biological degradation of polycyclic aromatic hydrocarbons (PAHs) in soil: state of the art and identification of research needs, Zurich, Switzerland, April 7–8, 1994.

Texas Research Institute. 1982. Enhancing the Microbial Degradation of Underground Gasoline by Increasing Available Oxygen, Final Report. Washington, D.C.: American Petroleum Institute.

Thomson, B. M., and W. R. Turney. 1995. Minerals and mine drainage. Water Environment Research 67:527–529.

Thornton, J. C., and W. L. Wooten. 1982. Venting for the removal of hydrocarbon vapors from gasoline contaminated soil. Journal of Environmental Science and Health A17(1):31– 44.

Treigel, E. K., and L. Guo. 1994. Overview of the fate of pesticides in the environment, water balance; runoff vs leaching. Pp. 1–13 in Mechanisms of Pesticide Movement Into Ground Water. R. C. Honeycutt and D. J. Schabacker, eds. Boca Raton, Fla.: Lewis Publishers.

Trobridge, T. D., and T. C. Halcombe. 1994. Waste treatment via solvent extraction/dehydration with the Carver-Greenfield process. Presented at the I&EC Special Symposium, Atlanta, September 19–21, 1994. Washington, D.C.: American Chemical Society.

Troxler, W. L., J. J. Cudahy, R. P. Zink, S. I. Rosenthal, and J. J. Yezzi. 1992. Treatment of petroleum contaminated soils by thermal desorption technologies. Presented at 85th Annual Meeting of the Air and Waste Management Association, Kansas City, Mo., June 21–26, 1992.


Udell, K. S., and L. D. Stewart. 1989. Field Study of In Situ Steam Injection and Vacuum Extraction for Recovery of Volatile Organic Solvents. UCB-SEEHRL Report No. 89–2. Berkeley, Calif.: University of California, Environmental Health Research Laboratory.

Udell, K. S., and L. D. Stewart. 1990. Combined steam injection and vacuum extraction for aquifer cleanup. Presented at the International Association of Hydrologists Conference, Calgary, Alberta, Canada, April 1990.


van der Leeden, F., F. L. Troise, and D. K. Todd, eds. 1990. The Water Encyclopedia. Chelsea, Mich.: Lewis Publishers.

Vidic, R. D., and F. G. Pohland. 1996. Treatment Walls. Technology Evaluation Report TE-96– 01. Pittsburgh, Pa.: Ground Water Remediation Technologies Analysis Center.

Vorum, M. 1991. Dechlorination of polychlorinated biphenyls using the SoilTech anaerobic thermal processing unit, Wide Beach Superfund site, New York. Presented at HazTech International 91, Pittsburgh, Pa., May 14–16, 1991.


Watanabe, M. 1997. Phytoremediation on the brink of commercialization. Environmental Science & Technology 31(4): 182A–186A.

Weitzman, L., and L. E. Howel. 1989. Evaluation of Solidification/Stabilization as a Best Demonstrated Available Technology for Contaminated Soils. EPA/600/2–89/049. Washington, D.C.: EPA.

Weitzman, L., K. Gray, F. K. Kawahara, R. W. Peters, J. Verbicky. 1994. Chemical Treatment. Vol. 2 of Innovative Site Remediation Technology, W. C. Anderson, ed. Annapolis, Md.: American Academy of Environmental Engineers.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×

Whiting, K., R. L. Olsen, J. N. Cevaal, and R. Brown. 1994. Treatment of mine drainage using a passive biological system: Comparison of full-scale results to bench- and pilot-scale results. In Proceedings of the Society for Mining, Metallurgy and Exploration Annual Conference, Albuquerque, New Mexico, February 14, 1994. Littleton, Colo.: Society for Mining, Metallurgy and Exploration.

Wiedemeier, T. H., J. T. Wilson, D. H. Campbell, R. Miller, and J. Hansen. 1995. Technical Protocol for Implementing Intrinsic Remediation with Long-Term Monitoring for Natural Attenuation of Fuel Contamination in Ground Water. Brooks Air Force Base, Tex.: Air Force Center for Environmental Excellence.

Wiedemeier, T. H., L. A. Benson, J. T. Wilson, D. H. Kampbell, and R. Miknis. 1996. Patterns of natural attenuation of chlorinated aliphatic hydrocarbons at Plattsburgh Air Force Base, New York. Presented at Conference on Intrinsic Remediation of Chlorinated Solvents, Airport Hilton, Salt Lake City, Utah, April 2, 1996.

Wildeman, T. R. 1992. Constructed wetlands that emphasize sulfate reduction. Paper 32 in Proceedings of the 24th Annual Operators Conference of the Canadian Mineral Processors. Ottawa, Ontario: Canadian Institute of Mining, Metallurgy, and Petroleum.

Wildeman, T. R., S. P. Machemer, R. W. Klusman, R. H. Cohen, and P. Lemke. 1990. Metal removal efficiencies from acid mine drainage in the Big Five constructed wetland. Pp. 417– 424 in Proceedings of the Mining and Reclamation Conference and Exhibition, Charleston, West Virginia, April 23–26, 1990, J. Skousden, J. Sencindiver, and D. Samuel, eds. Washington, D.C.: U.S. Bureau of Mines.

Wildeman, T. R., D. M. Updegraff, J. S. Reynolds, and J. L. Bolis. 1994. Passive bioremediation of metals from water using reactors or constructed wetlands. Pp. 13–25 in Emerging Technology for Bioremediation of Metals, J. L. Means, and R. E. Hinchee, eds.. Ann Arbor: Lewis Publishers.

Wiles, C. C., and E. Barth. 1992. Solidification/stabilization: Is it always appropriate? Pp. 18–32. in Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, Vol. 2, T. M. Gilliam, and C. C. Wiles, eds. ASTM STP 1123. Philadelphia: American Society for Testing and Materials.

Wilson, E. K. 1995. Zero-valent metals provide possible solution to groundwater problems. Chemical & Engineering News (July 3):19–22.

Wilson, J. T., D. H. Kampbell, and J. Armstrong. 1994. Natural bioreclamation of alkybenzenes (BTEX) from a gasoline spill in methanogenic groundwater. Pp. 201– 218 in Hydrocarbon Bioremediation, R. E. Hinchee, B. C. Alleman, R. E. M. Hoeppel, and R. N. Miller, eds. Ann Arbor, Mich.: Lewis Publishers.

Woodruff, R. K., R. W. Hanf, and R. E. Lundgren, eds. 1993. Hanford Site Report for Calendar Year 1992. PNL-86821UC-602. Richland, Wash.: Pacific Northwest Laboratory.

Yamane, C. L., S. D. Warner, J. D. Gallinatti, F. S. Szerdy, T. A. Delfino, D. A. Hankins, and J. L. Vogan. 1995. Installation of a subsurface groundwater treatment wall composed of granular zero-valent iron. Pp. 792–795 in Preprints of Papers Presented at the 209th American Chemical Society National Meeting, Anaheim, Calif., April 2–7, 1995. Washington, D.C.: American Chemical Society, Division of Environmental Chemistry.

Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 80
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 81
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 82
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 83
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 84
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 85
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 86
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 87
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 88
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 89
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 90
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 91
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 92
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 93
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 94
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 95
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 96
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 97
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 98
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 99
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 100
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 101
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 102
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 103
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 104
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 105
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 106
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 107
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 108
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 109
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 110
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 111
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 112
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 113
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 114
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 115
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 116
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 117
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 118
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 119
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 120
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 121
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 122
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 123
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 124
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 125
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 126
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 127
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 128
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 129
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 130
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 131
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 132
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 133
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 134
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 135
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 136
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 137
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 138
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 139
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 140
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 141
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 142
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 143
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 144
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 145
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 146
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 147
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 148
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 149
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 150
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 151
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 152
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 153
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 154
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 155
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 156
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 157
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 158
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 159
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 160
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 161
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 162
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 163
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 164
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 165
Suggested Citation:"3 STATE OF THE PRACTICE OF GROUND WATER AND SOIL REMEDIATION." National Research Council. 1997. Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization. Washington, DC: The National Academies Press. doi: 10.17226/5781.
×
Page 166
Next: 4 MEASURES OF SUCCESS FOR REMEDIATION TECHNOLOGIES »
Innovations in Ground Water and Soil Cleanup: From Concept to Commercialization Get This Book
×
Buy Hardback | $68.00 Buy Ebook | $54.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Most books on ground water and soil cleanup address only the technologies themselves—not why new technologies are or are not developed. Innovations in Ground Water and Soil Cleanup takes a holistic approach to the entire field, addressing both the sluggish commercial development of ground water and soil cleanup technologies and the attributes of specific technologies. It warns that, despite cleanup expenditures of nearly $10 billion a year, the technologies remain rudimentary.

This engaging book focuses on the failure of regulatory policy to link cleanup with the financial interests of the company responsible for the contamination. The committee explores why the market for remediation technology is uniquely lacking in economic drivers and why demand for innovation has been so much weaker than predicted.

The volume explores how to evaluate the performance of cleanup technologies from the points of view of the public, regulators, cleanup entrepreneurs, and other stakeholders. The committee discusses approaches to standardizing performance testing, so that choosing a technology for a given site can be more timely and less contentious. Following up on Alternatives for Ground Water Cleanup (NRC, 1994), this sequel presents the state of the art in the cleanup of various types of ground water and soil contaminants. Strategies for making valid cost comparisons also are reviewed.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!