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-2 Report ofthe Panel on Land Disposal Stanley I. Auerbach, Chairman, Oak Ridge National Laboratory Charles Andrews, Woodward Clyde Consultants Dean Eyman, Oak Ridge National Laboratory Dale D. Huff, Oak Ridge National Laboratory Philip A. Palmer, E.I. du Pont de Nemours & Company Warren R. Uhte, Brown & Caldwell 3.1 INTRODUCTION Society has used land for the disposal of wastes since time immemorial. The history of earlier civilizations is reflected in ancient cities whose trash dumps became themselves the foundations for cities built as replace- ments. Not until the advent of public health concepts in the nineteenth century was any systematic attention given to the disposal of waste in ways aimed at minimizing harm to the public. Even after the most pressing aspects of waste treatment and disposal (e.g., sewage) were well recognized and modes of treatment established, almost another century passed before there was widespread recog- nition that land resources are finite and subject to multiple demands and that we could no longer indiscrimi- natelv dispose of unwanted residuals on the basis of institutional convenience. This recognition is reflected in the laws and regulations governing the disposal of wastes in or on the land. The land option for disposal is difficult to understand because of the physical and chemical complexity of the medium, the wide range of regional land differences, and the long history of multiple land use in many regions that has altered many of its properties. Land is often in short supply; fills a wide variety of needs related to food, fiber, living space, recreational needs, and indus- trial development; and serves as a source of diminishing . . . . 73
74 mineral and usable groundwater resources. We therefore need continuously to re-examine and refine our institu- tional mechanisms for waste disposal to avoid irrevocably committing land resources to a single-purpose use whose total costs will be greater than the benefits derived. This chapter describes the criteria and information needed in considering land as a disposal medium. One set of criteria deals with the properties of the wastes to be disposed of and how these properties may affect the choice of a land option. A second set of criteria involves hydrologic, geologic, and other basic properties of a land system that might affect or be affected by use of the land for disposal. The chapter also describes what information is needed to apply these criteria, where these data are obtainable, and what research is necessary to supply the data that do not exist. The basic concerns with respect to land disposal are the long-term security of the disposal facility and the effects of both unexpected and routine discharges from the facility. Security is dependent to a large degree on the hydrology and geology of the disposal site, on whether the disposal process has been engineered to complement site conditions, on long-term maintenance and monitoring, and to a lesser degree on the toxic properties of the waste itself. The primary concerns in land disposal include, but are not necessarily limited to, two major categories: (1) long-term environmental effects, includ- ing contamination of surface or groundwater resources, potential threats to human health, and secondary effects on valuable natural or agricultural ecosystems, and (2) long-term commitment of land resources. Consideration of land disposal options must include recognition of the significant time lag between waste inputs and outputs resulting from migration processes. Years or decades may elapse before a subsurface contami nation plume moves far enough to create a problem. As a result, knowledge of the effects of recent land disposal practices, especially those focused on minimizing or eliminating contaminant migration, is limited. Many groundwater contamination problems today are the result of past disposal practices, and it is important to distinguish between those situations and the consequences of present-day practices. In other words, it is unfair and misleading to associate all groundwater contamination with land disposal inputs alone Ideally, information of all the types presented below would be used to model a disposal technique from the - . -
76 TABLE 3.1 Waste Properties Property Availability Relative Cost of of Dataa Obtaining Datab Comments Pathogen content Low Medium Toxicity Acute Chronic Toxicant mobility Water/soil Air Biodegradability/ persistence High Low Medium High Low High Medium Medium Low Medium Bioaccumulation High Medium Waste interaction High Low Phytotoxicity High Medium Incompatability with containment system Volume Low Medium High Low Especially critical for land application and agricultural use Major need is for organic mixtures Organic data are far less avail- able than are inorganic data; organic data are more expensive to generate May not be required if facility ac- ceptable with no biodegradability Large data base on metals Especially critical for agricultural use and land reclamation aHigh, readily available data base. bHigh, >$1 million; ; medium, fair data base; low, practically no medium, $100,000 to $1 million; low, <$100,000
77 with the containment system, and volume (Congress of the United States). 3.2.1 Pathogen Content The presence of pathogenic agents in waste material will be a key factor in deciding on the acceptability of that waste for application to farmland or for other types of reuse. In those instances where the presence of pathogens does not preclude land application, it may restrict future use of the sites. Pathogens include bacteria, fungi, protozoa, viruses, and parasites. Some species of bacteria decline in number when exposed to soil. Viruses' however, can persist for a relatively long time in the natural environment. The most hardy of the pathogens appear to be parasites and those bacteria that form spores. These can survive in soil for years. Adding to the problems caused by pathogen survival are (1) the limited technology available for isolating and detecting viruses and other pathogens and (2) the introduction of increased concentrations of parasites into the environment in the United States and elsewhere. Bacteria and parasites are detectable in most waste materials. Determination of virus die-off has been hampered by the difficulty in preparing samples and in detecting and enumerating viruses to assure sufficient data for statistical analyses. More work needs to be done on identifying natural indicators of viruses and formulating improved methods of virus recovery that can be used to determine survival and persistence. Toxicity must be defined in order to determine the potential problems if containment of the waste cannot be assured. Toxicity must be considered in conjunction with mobility; measurements should be based on the toxic mobile constituents rather than on the waste itself. 3.2.2 Acute Toxicity The definition of what constitutes acute toxicity to mammals via oral ingestion or to aquatic organisms is of only moderate importance in evaluating a land disposal plan. Generally, significant toxic effects will occur at lower than lethal dosages (or environmental concentra- tions). Consequently, acute toxicity information should be used primarily as an indicator of unusually toxic materials that may require special scrutiny.
78 Acute mammalian and aquatic toxicity data are available for a significant number of chemical compounds, and many data are available for inorganic materials (metals). Virtually no information is available, however, for mixtures of wastes that may be encountered in practice. Relatively inexpensive and standardized test methods are available for determining the acute toxicities of waste mixtures, however . 3.2.3 Chronic Toxicity In evaluating most land disposal plans, potential exposure over a long time to low concentrations or dosages in groundwater or surface waters must be considered. Chronic mammalian toxicity is a concern where there is potential for discharge to potable groundwaters or surface waters. Chronic aquatic toxicity may also be important where there is potential for discharge to surface waters. Estimates of the concen- tration that will produce harmful doses to target species are needed for the evaluation process. Chronic toxicity information is more readily available for inorganic materials than for organic materials. There is little documentation of the chronic effects of mix- tures. While test methods are available to determine the possibility of chronic effects, they become prohibitively expensive when applied to higher life forms (Brusick, 1978; EPA, 1979). 3.2.4 Toxicant Mobility The ability of land-disposed waste or its constituents to move in the environment depends on the liquid nature of the waste as well as on its leachability (solubility of constituents), but movement may also depend on climate and soil properties. Soil systems may retard the mobility of or sequester certain constituents. Relative mobility in soils may be measured directly through partition coefficient determinations or indirectly through the use of such parameters as cation exchange capacity. An additional aspect of mobility is volatility, or the ability of waste constitutents to enter the atmosphere. Volatility can result in toxicity or odor problems. Volatility may also affect the transport of pathogens that are attached to particles.
79 There are few standardized test protocols or tabula- tions that delineate mobility directly. The Environmental Protection Agency (EPA) has developed an extraction procedure (Appendix II, EPA Toxicity Test Procedure, 40 C.F.R. §261.24) designed to simulate solubilizing effects and leachate production, but it is not site-specific (Lowenbach et al., 1977). While some partition coeffici- ents are available for materials in certain soils, few are available for complex mixtures (EPA, 1979; Far rah and Pickering, 1977; Ramamoor thy and Rust, 1979). Method- ologies have been developed to predict volatilization from liquid waste in impoundments, but there has been little work in predicting air emissions from covered landfills or land farms (Hwang, 1980; Thibedeaux, 1981) Consequently, additional research is needed to develop standardized test methods that simulate or allow calculation of mobility. 3.2.5 Biodegradability/Persistence . Toxic constituents may be mobilized from wastes that are applied as soil amendments or placed in shallow land burial, and the biodegrada- tion products of such mobile constituents may be more toxic than the parent compounds are. On the other hand, rapid disappearance of the parent compound may be beneficial. The long-term persistence of toxic components of wastes will be a key factor in deter- mining disposal methodology. The probability of direct exposure of biota (including humans) is much greater with disposal as soil amendment than with disposal in land- fills. Where there may be indirect discharge to surface waters from a land disposal facility, degradation of nonpersistent compounds may be significant. Where only groundwater is affected, assessments of persistence may not be fruitful because biodegradation may be slow. Data and standardized methodologies are available to define rates of biodegradation and degradation of com- pounds in aqueous systems in treatment plants or surface waters. Far less information is available for these phenomena in soil systems or groundwaters. Even though experimental work is being done, considerably more research effort is needed to develop standardized test methods.
84 saturated (groundwater) zone. Climatic, vegetative, and topographic (slope and drainage density) properties of the site, together with soil hydraulic properties, control the degree of saturation of the near-surface soils and the partitioning of both precipitation and effluent waters between runoff and percolation. Climate and Vegetation The most important long-term control on water movement is evapotranspiration, which includes evaporation from the soil surface and uptake and release of water by vegetation. Evapotranspiration controls the moisture in soils between precipitation and water application events. The rate of movement of water and associated contaminants through the soil depends in large measure on the soil's moisture content. The infiltration rate will generally decrease as moisture content increases, and the amount of additional water that can be stored in the soil and released slowly will also decrease with increased antecedent moisture. Thus, in considering the application of large amounts of water to a disposal site, either by irrigation or injection- type methods or storm events, a knowledge of water uptake by vegetation or direct evaporation is essential to quantitative estimation of subsequent transport pathways. In some situations, evaporation is the key factor in determining acceptable loading rates. Many methods are available for computing actual evapotranspiration and soil moisture status (e.g., Federer, 1982; Spittlehouse and Black, 1981; and Swift et al., 1975), which are the essential components of a water balance at the disposal site. The minimum data requirements on climate for modern computational models are daily solar radiation, maximum and minimum daily air temperature, and pre- cipitation. More-complex models also require daily dew point temperature and wind movement. With the foregoing variables, a combined mass transport and energy budget approach will also allow simulation of snowpack accumula- tion, sublimation, and melt in addition to complete quantification of the site's water budget (Huff et al., 1977). Because rainfall intensity affects the par- titioning of surface and subsurface flows, precipitation totals may be needed at hourly or shorter intervals for some water budget and transport simulations where the hazard is great. Often, data collected at a nearby site can be used. Vegetation plays a dual role. It determines inter- ception and transpiration losses of precipitation inputs,
91 use is difficult to project, and faulty predictions introduce uncertainties into long-term evaluations. The rate of groundwater discharge to surface waters i generally difficult to determine accurately, but this information is essential for estimating waste fluxes to the surface-water environment. Groundwater discharge to springs can be measured directly, but most groundwater outflow occurs as nonpoint discharges. Water-balance type models, using either analytical or numerical solution techniques, are conventionally used to calculate groundwater discharges to surface-water bodies. To determine the waste concentrations that will result from groundwater discharges in surface-water bodies, it is necessary to know the flow and mixing characteristics of the surface-water bodies. 3.3.1.5 Transport in Surface-Water Systems s Two factors are associated with transport in surface-water (freshwater) systems: (1) migration rates and chemical and biological interactions within the stream or estuarial channels and (2) water resource utilization, such as proximity of discharge points to municipal or industrial water intakes or sensitive aquatic habitats. The former determine the temporal and spatial distribution of possible contaminants or nutrients throughout the aquatic system, while the latter deal with potential pathways into the human food chain. Migration Rates and Chemical and Biological Interactions Experience has shown that discharge of wastes, nutrients, or contaminants into surface waters will probably result in a buildup of contaminants in sediments and biota, but spatial distribution will vary with the situation. Contaminant scavenging can be characterized in terms of the relative flow rates of the input and the receiving waters, the chemical composition and form (such as oxidation state or biological availability) of the waste or leachate and receiving waters, and the physical and chemical properties of streambed and suspended sediments. Because of the usually strong interaction between the water column and bed sediments, sediment transport characterizations (particle size distribution, exchange properties, and physical characteristics of the stream channel) must be specified. Continuous simulation models are available for examining the physical transport
92 processes and can be used as a framework for detailed specification of data needs. Water-Resource Utilization Withdrawal of water resources in the vicinity of disposal sites inevitably raises the question of the contribution of disposal operations to the water's contaminant loading. As noted earlier, the fate of wastes or leachates that may be discharged from land disposal sites is a function of the physical, chemical, and biological conditions in the receiving waters as well as the relative magnitude of the input. An order-of-magnitude estimate of concentration may be made by simple conservation of mass calculations involv- ing the flux of waste or leachate from the disposal site and the total water flow at the point of intake. Estimates can be refined by considering degradation, uptake reactions, and ambient flow properties, such as velocity and sediment transport capacity. The most practical approach to water-use considerations is to focus on specific indicator contaminants and their potential impact on downstream users. 3.3.1.6 Summary of Hydrologic Considerations The hydrologic transport information needs are generally as listed above; it may be expensive and time consuming to collect the data. It is assumed that the nature of the waste constituents and their chemical form (especially the associated hazard) will dictate the degree of detail or observation frequency required. There are clear trade-offs between site performance characterization, predisposal waste treatment, use of engineered barriers, and the relative hazards associated with waste. The most common approach starts with a "worst case" involving minimum waste pretreatment and engineered barriers. If computed contamination levels for this case are unacceptable, more refined analyses are undertaken until a satisfactory engineering option has been found or until all options have been rejected. The main difficulty with such an approach lies in determining the worst case. From a hydrologic viewpoint, assumptions of homogenous isotropic aquifers and average annual (or even seasonal) flow rates for a given source are not valid. Much more emphasis should be placed on extreme events and on the anisotropic properties of the site,
93 such as preferred flow pathways associated with aquifer structure and fractures, macropores, or faults. 3.3.1.7 Land-Use Considerations Irrespective of other factors utilized in site selection for land disposal, current and prior use of the land and contiguous areas may need to be factored into the decision process. The presence of unique or fragile ecosystems that could be impacted on by either the construction or operation of a land disposal site needs careful considera- tion. Special situations involving habitats that contain rare or endangered species must also be evaluated. Cul- tural factors that require analysis include the presence or proximity of cultural resources, such as archaeological sites, recreational areas, population distribution, and past and current land-use practices. 3.3.2 Terrestrial Ecological Considerations Because terrestrial ecosystems include communities with very different levels of resilience (deserts, rain forests, chaparral, grasslands, alpine habitats), it is difficult to generalize about the ecological effects of land disposal options. Even if soil conditions are undamaged, successional processes and rates are very different. In most cases the greatest damage results from activities associated with disposal. Once the disposal program is completed, restoration of surface conditions and natural succession may lead to recovery. In other cases (e.g., desert, riparian, marsh, or cypress habitats), however, in which propagules are not readily available or that need nurse trees or special habitats for colonization, artificial reclamation may be necessary. This is especially true for large areas in which dispersal limitations mitigate against adequate succession. For land disposal involving surface amendments (sludges, liquid wastes), a primary concern is the buildup of potentially toxic substances in the soil zones where they may be taken up by plants or animals and thereby enter food chains. Particularly worrisome are organic compounds (e.g., PCBs, PBBs) that are readily transferable. Here the potential damage to the eco- system per se has not been examined, but the ecosystem
94 processes serving as vectors of transport to human consumption must be assessed. The significant role of microorganisms in bioaccumulation and food chain transfer needs to be understood. Information on surface and subsurface drainage patterns is needed to evaluate the potential impacts of disposal on adjacent but different ecosystems. Examples of such potential problem situations are adjacent marshes or other water bodies that are habitats for waterfowl, fish populations, or other wildlife. Marshes are natural discharge points for regional groundwater flow systems. They are, therefore, more likely than other types of ecosystems to receive any contaminants or residuals that have become entrained in groundwater. 3.4 FACILITY DESIGN PROPERTIES To determine the relative merits of a disposal system, the properties of a waste and the disposal setting must be considered together. This is because the relative hazard a waste may present and the relative cost of the disposal method will depend to a major degree on site- specific conditions. Site conditions, in turn, are dependent on the engineered design as well as the natural geographic, hydrologic, and geologic setting. Engineered design and operation may complement natural site con- ditions, improving the disposal method. Characteristics that can have a major effect on the desirability and acceptability of a land-based waste disposal site include location; site selection con- siderations; engineered containment; segregation of wastes; maintainability of the site; site development, monitoring, and closure. 3.4.1 Location The basic considerations in assessing the location of a site are accessibility (Can the waste be delivered to the site at the rate at which it is generated?) and proximity (Can the waste be transported to the site from its point of origin?). A site with ideal properties may be unac- ceptable if economic, social, or institutional constraints limit its accessibility. Transportation of wastes, especially those clearly recognized as hazardous, over long distances can create economic, social, or insti
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