Alternatives for Ground Water Cleanup (1994) / Chapter Skim
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4 Capabilities of Enhanced Pump-and-Treat and Alternative Technologies
4 Capabilities of Enhanced Pump-and-Treat and Alternative Technologies
Pages 125-192
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From page 125... ...
For example, while conventional pump-and-treat systems were selected for use at 73 percent of Superfund sites with ground water contamination through fiscal year 1992, at the remaining 27 percent of sites the most common "remedies" were not innovative technologies but nontreatment measures such as providing alternative water supplies, aquifer use restrictions, and wellhead treatment (Kelly, 1994; K Lovelace, Environmental Protection Agency, unpublished data, 1992~.
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From page 126... ...
The most striking example of this desired technical evolution is the increased use of soil vapor extraction systems, which have now become a leading cleanup technology for soil (Kovalick, 1993~. For cleaning up petroleum hydrocarbons, in situ bioremediation is also becoming increasingly common.
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From page 127... ...
is one of the few innovative technologies that has gained wide use. The technology extracts organic contaminants (primarily from the unsaturated zone)
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From page 128... ...
:::::::.::-~: -- ::~:-~-:.~:-2::::::::::::-.. :::::~:~:::~:~:::~.: :~::::::~:~:::-.::::::~: ,,,,.,,,, ,,,., , ,,.,, ,.,.,.,, / Residual NAPL Contamination FIGURE 4-1 Process diagram for soil vapor extraction.
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From page 129... ...
If the air stream bypasses zones of low permeability, the slow process of diffusion will dominate, making contaminant removal extremely slow. As a rough rule of thumb for feasibility assessment, SVE is likely to
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From page 130... ...
. Most of these systems addressed contaminant removal from the unsaturated zone rather than from dewatered portions of the saturated zone.
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From page 131... ...
In situ bioremediation near the land surface can be achieved by using infiltration galleries that allow water amended with nutrients arid electron acceptors to percolate through the soil. When contamination is deeper, in situ bioremediation systems Inject the amended water through Nutrients i Injection Water _ ~ Microorganisms FIGURE 4-2 Process diagram for ~ situ bioremediatiorr.
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From page 132... ...
Although in situ bioremediation of other types of organic contaminants, such as chlorinated solvents, is possible, the technology has not yet been demonstrated for these other applications. Before an in situ bioremediation project is initiated, a specific microbial enhancement feasibility study and a general hydrogeologic site investigation are essential.
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From page 133... ...
Fortunately, the soluble concentrations of hydrocarbons normally observed at field sites are well below the toxic range. Another limitation of in situ bioremediation is the requirement for a minimum contaminant concentration to maintain the microbial population and to induce the enzymes necessary for degradation.
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From page 134... ...
Fourth, certain microorganisms are able to move toward regions of higher contaminant concentration through a process known as chemotaxis, helping to expand the zone of biodegradation and eventually achieve complete treatment (Bosma et al., 1988) Bioventing Description Bioventing is in situ bioremediation of the unsaturated zone.
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From page 135... ...
The change in soil moisture can also affect the load-bearing capacity of the soil an important consideration when treating soil under or near a building. In addition, flushing nutrients through the soil may transport contaminants from the unsaturated into the saturated zone.
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From page 136... ...
~ , . , Application Pulsed and variable pumping have application for sites with large areas of residual contamination spread through the saturated zone
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From page 137... ...
Therefore, in situ bioremediation of chlorinated solvents often requires circulation not only of electron acceptors and elemental nutrients, but also of other growth-stimulating materials specific to the metabolic process by which the contaminants are degraded. Application Laboratory- and pilot-scale studies, along with a limited number of field tests, have documented two metabolic pathways for chlorinated solvent destruction.
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From page 138... ...
In the process of consuming the methane, the bacteria produce an enzyme, methane-monooxygenase, that incidentally transforms the chlorinated compound. Therefore, stimulating methanotrophic bacteria to transform chlorinated solvents requires adding methane to the site, in addition to oxygen and nutrients.
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From page 139... ...
Limitations All of the limitations that apply to in situ bioremediation of hydrocarbons also apply to in situ bioremediation of chlorinated solvents. In situ bioremediation of chlorinated solvents also has limitations that are not factors in hydrocarbon bioremediation.
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From page 140... ...
~ '' ~ i'' W~ ~ r_hiF ~ ~ f; _ ~-~t A, '; ir -~ ~i! Construction of an infiltration trench for delivering fluids In an In situ bioremediation system.
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From page 141... ...
Finally, while in situ bioremediation using reductive dechlorination may be slow, in situ bioremediation using methanotrophs is relatively rapid. In Situ Bioremediation Metals Description The physical systems used to promote in situ bioremediation of metals are like those for bioremediation of hydrocarbons and chlorinated solvents (see Figure 4-21.
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From page 142... ...
Application Of all the applications of in situ bioremediation, cleanup of metals is the least tested, with few published studies available. A nitrogen-fixing bacterial species isolated from coal-cleaning waste was capable of dissolving several metal oxides under anaerobic conditions (Francis and Dodge, 1988~.
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From page 143... ...
The principles upon which air sparging is based are similar to those for soil vapor extraction, except air sparging applies to the saturated zone while soil vapor extraction is primarily for the unsaturated zone. Air sparging systems inject air either directly into the aquifer formation or into specially designed extraction wells.
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From page 144... ...
As for soil vapor extraction, the effectiveness of air sparging depends
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From page 145... ...
Injected air flows upward through the saturated zone, volatilizing contaminants and carrying them into the vadose zone, where they are captured by a vapor extraction system (Angel!
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From page 146... ...
The design parameters for horizontal wells are similar to those for standard vertical well air sparging systems. A field trial conducted at the Savannah River site indicated that two horizontal wells were effective at removing a mixture of volatile chlorinated solvents (Looney et al., 1991~.
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From page 147... ...
Limitations Although air sparging shows promise, particularly when the contaminants are volatile and biodegradable, significant questions remain about the ability of this technology to achieve health-based cleanup levels throughout the saturated zone. While laboratory studies of these technologies have been published, no peer-reviewed articles exist that demonstrate their efficacy in the field.
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From page 148... ...
For example, a gasoline mixture will at first respond favorably to air injection, but the extraction efficiency will decline over time as the mixture's boiling point increases with the loss of the more volatile fractions. Use of air sparging at depths greater than approximately 10 meters below ground surface may also be problematic because the air flow path may be difficult to predict.
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From page 149... ...
The amount of organic contaminant mobilized during soil flushing depends on the chemical structure of the cosolvent or surfactant, the cosolvent or surfactant concentration, geochemical conditions, the chemical structure of the contaminant, and temperature. Cosolvent concentrations must typically be greater than 20 percent to cause effective mobilization.
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From page 150... ...
The inhibition may have resulted from surfactant molecules interfering with the microorganism's biochemistry or from limited bioavailability due to low contaminant exit rates from the micelles. Limitations As with conventional pump-and-treat systems, geologic conditions can limit the performance of soil flushing systems.
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From page 151... ...
Chemical treatment also could enhance in situ bioremediation. Preoxidation of refractory organics with ozone or hydrogen peroxide can increase their biodegradability.
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From page 152... ...
\ Residual NAPL Contamination FIGURE 4-7 Process diagram for in situ chemical treatment. Surface Soil/Cap Unsaturated Ze.ne Saturated Zone First, like in situ bioremediation, this method is limited by geologic complexities that complicate delivery of chemicals to the contaminants.
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From page 153... ...
Only steam injection and radio frequency heating are applicable to the saturated zone, however, and radio frequency heating would require dewatering of the contaminated zone. The capabilities, advantages, and disadvantages of these two technologies are described below.
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From page 154... ...
Steam-Enhanced Extraction Surface Soil/Cap Unsaturated Zone Saturated Zone Description Steam injection has been proposed as a technique to enhance the extraction of a variety of contaminants that are difficult or impossible to remove by water flushing. Steam injection is widely used in the petroleum industry to enhance petroleum extraction from deep formations.
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From page 155... ...
While laboratory tests have shown nearly complete removal of volatile and semivolatile organic contaminants with steam injection, field tests have shown promise but have not resulted in complete contaminant removal, probably due to the presence of low-permeability zones through which the steam will not flow. Udell carried out a detailed assessment of steam technology to remove LNAPLs at a gasoline spill site (K.
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From page 156... ...
present a simplified model of the steam injection process that can be used to determine the optimum number and placement of injection wells. Information on the efficiency and design of this process is also available through the EPA's Superfund Innovative Technology Evaluation (SITE)
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From page 157... ...
Organic contaminants then vaporize, desorb, or decompose, with released contaminant gases captured through soil vapor extraction systems or with the use of a surface vapor barrier and appropriate appurtenances for gas management and treatment. A typical system consists of the radio frequency energy deposition array (electrodes)
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From page 158... ...
Intrinsic Bioremediation Description Intrinsic bioremediation is essentially in situ bioremediation without human intervention. In this approach, the native microbes transform contaminants without stimulation from added electron acceptors, nutrients, or other materials (although these materials must be present naturally for biodegradation to occur)
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From page 159... ...
Application Many recent studies have demonstrated that diverse microbial populations indigenous to subsurface environments can degrade important classes of organic contaminants. However, whether intrinsic bioremediation is sufficient to eliminate the contamination is highly site specific.
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From page 160... ...
While at many low-priority sites regulators may have assumed that intrinsic biodegradation would adequately control contaminant migration, very few of these sites have been monitored sufficiently to determine if this approach is actually effective or to identify factors that influence the efficiency of intrinsic bioremediation. Use of intrinsic bioremediation involves somewhat greater risk of failure than engineered bioremediation because active measures are not used to control plume migration.
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From page 161... ...
During in situ vitrification, an electrical input heats the subsurface to between 1600 and 2000°C. The high temperatures pyrolyze organic contaminants, and vapors can be captured at the land surface for treatment.
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From page 162... ...
A second approach is to use slurry wall construction technology to create a deeper and larger permeable curtain. In this approach, a polymer mixed with reactive materials replaces subsurface materials as FUNNEL Perrneabe FUNNEL In~perrneable Reacton Wall In~pernneable Barner Wall (Abiotic or Biotic Barrier Wall / 1 \ FIGURE 4-9 Process diagram for in situ reactive barriers.
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From page 163... ...
One possible physical method uses granular activated carbon to adsorb organic contaminants. Other possible physical/ chemical methods use redox controls to precipitate metals and metal catalysts to degrade halogenated organic compounds (Gilham and O'Hannesin, 1991~.
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From page 164... ...
Mixtures of contaminants with varying physical and chemical properties, such as chlorinated solvents and polycyclic aromatic hydrocarbons, chlorinated solvents and phenols, gasolines and acetone, and any organic contaminant with one or more heavy metals, are much more likely to be present. Because a single remedial process may be effective at removing only a subset of the compounds in a waste mixture, a combination or sequence of processes is likely to be necessary.
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From page 165... ...
ENHANCED PUMP-AND-TREAT AND ALTERNATIVE TECHNOLOGIES 1 65 lions and contaminant chemistry. Table 4-1 gives the relative effectiveness of the enhancements and alternatives described in this chapter as a function of contaminant chemistry.
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From page 168... ...
. Technologies not applicable for certain contaminants are marked "NA." For example, bioremediation would not be employed for contaminants that do not degrade, and processes relying on volatilization, such as vacuum extraction, air sparging, and steam stripping, would not be employed for nonvolatile contaminants.
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From page 169... ...
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From page 171... ...
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From page 172... ...
Each of these prospective buyers influences the potential size of and the timing of the demand for innovative technologies. During this first phase in the life cycle of an innovative technology, numerous barriers may inhibit the translation of creative ideas into a potentially viable technology.
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From page 173... ...
In most areas of process technology development, bench- or pilot-scale testing is a necessary precursor to implementation of the technology on a larger scale. However, innovative technologies for subsurface cleanup tested on the bench or small pilot scale often cannot be scaled up for field application due to the heterogeneous nature of the problem.
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From page 174... ...
The process of selecting technologies for hazardous waste site remediation is well defined under both RCRA and the Superfund act and has been presented in detail in various EPA guidance documents. Either a feasibility study or corrective measure study, under the Superfund act or RCRA, respectively, provides the background for screening and selecting innovative technologies.
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From page 175... ...
Technological uncertainties due to site complexity pose difficult dilemmas for consultants and regulators, who may be either unfamiliar with the potential effectiveness of an innovative technology or unable to obtain information on the potential applicability of that technology. On the one hand, innovative technologies may promise cost and efficiency advantages for site cleanup compared to conventional technologies.
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From page 176... ...
Also contributing to the liability problem is the unwillingness of many federal agencies or potentially responsible parties to indemnify consultants and engineering contractors when innovative technologies are recommended or selected. A key difference in the selection of technologies for Superfund sites compared to selection of technologies at non-Superfund sites is the need for public approval of the remedy.
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From page 177... ...
If more than one innovative technology is included, the project becomes even more complex and more difficult to implement. Institutional Barriers Many of the institutional barriers complicating the selection process for innovative technologies are also relevant to the procurement stage.
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From page 178... ...
Adequacy of Action to Address Barriers Despite these barriers, use of innovative technologies to clean up waste sites has increased substantially. For example, in 1984, only one innovative technology was selected for use at Superfund sites.
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From page 179... ...
Significant efforts to expand the use of innovative technologies are under way through government programs and laboratories, cooperative research agreements between government agencies and private organizations, and various educational initiatives. Overcoming Technical Barriers The federal government is making significant investments in development of new waste site characterization and cleanup technologies through the EPA, DOE, and DOD.
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From page 180... ...
The state of California, for example, has an Office of Appropriate Technologies, which has used cost-sharing approaches to encourage innovative technology development. Overcoming Institutional Barriers Several initiatives are under way to reduce institutional barriers to innovative technologies.
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From page 181... ...
In the public sector, the "investments" are being made by a number of federal and state agencies, and the "benefits" are difficult-if not impossible to quantify. The committee recommends that the EPA, DOE, DOD, and other federal agencies supporting the development of innovative technologies either collectively or individually assess, on a regular basis, the effectiveness of the programs to promote new environmental technologies for hazardous waste site remediation.
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From page 182... ...
The committee believes that focused research could lead to especially promising advances for engineered in situ bioremediation, intrinsic bioremediation, soil vapor extraction, air sparking, containment methods, and inorganic contaminant treatment methods. Engineered and Intrinsic In Situ Bioremediation Engineered and intrinsic in situ bioremediation are promising cleanup methods because they treat contaminants in place instead of requiring extraction, can convert contaminants to innocuous products, and minimize or eliminate pumping requirements.
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From page 183... ...
· How can protocols for monitoring and evaluating the progress of bioremediation be improved? Soil Vapor Extraction and Air Sparging Soil vapor extraction and air sparging have the potential to rapidly remove large quantities of volatile organic contaminants from shallow zones, as documented in this chapter.
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From page 184... ...
EDUCATIONAL NEEDS As discussed in this chapter, an important barrier to the use of innovative technologies is lack of technical expertise on the many possible innovative cleanup methods. Advancing use of these technologies will require improved education, especially of the people in direct decisionmaking positions.
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From page 185... ...
Soil vapor extraction, air sparging, and horizontal wells can improve cleanup efficiency by removing volatile contaminants via air, a more effective transport medium than water. Soil flushing and in situ thermal technologies can improve cleanup efficiency by enhancing contaminant removal from soil above the water table, preventing contaminant migration into the ground water.
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From page 186... ...
For innovative cleanup technologies as for conventional pump-and-treat systems, the geologic conditions at the site and the chemical nature of the contaminants can prevent restoration of ground water to health-based standards. Nevertheless, the use of innovative technologies should be encouraged even if the technologies cannot currently reach health-based cleanup goals, because new technologies may outperform conventional systems and because wider use of the technologies may lead to discoveries that improve their performance.
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From page 187... ...
1989. Removing volatile contaminants from the unsaturated zone by inducing advective air-phase transport.
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From page 188... ...
1992. Proposal for Joint Industry-Government Evaluation of Innovative Technologies and Treatment Trains at Federal Facility Sites.
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From page 189... ...
1990. In-situ remediation of volatile contaminants in groundwater by a new system of "under-pressure-vaporizer wells." In Proceedings of the Conference on Subsurface Contamination by Immiscible Fluids, K
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From page 190... ...
1994. Applying innovative technologies to site contamination: historical trends and future demand.
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From page 191... ...
Pp. 66-67 in Proceedings of In Situ Bioremediation Symposium '92, Niagara-on-the-Lake, Ontario, Canada, September 20-24, 1992.
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From page 192... ...
1987. Opportunities for bioreclamation of aquifers contaminated with petroleum hydrocarbons.
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