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The Land Disposal Restrictions Surface Impoundment Study Executive Summary


EPA's study, Industrial Surface Impoundments in the United States, originates from the Land Disposal Program Flexibility Act (LDPFA), an amendment to the Resource Conservation and Recovery Act (RCRA) enacted in 1996. The LDPFA exempts certain decharacterized wastes from provisions of the RCRA land disposal restrictions. "Decharacterized" wastes are hazardous wastes that have had their hazardous characteristics-that is, ignitability, corrosivity, reactivity, or toxicity-removed through dilution or other treatment. The LDPFA exemption allows decharacterized wastes to be either: (1) placed in surface impoundments that are part of wastewater treatment systems whose ultimate discharge is regulated under the Clean Water Act (CWA), or (2) disposed of in Class 1 nonhazardous injection wells regulated under the Safe Drinking Water Act. Because of concerns regarding constituents that might remain in the wastes after removal of the characteristic, Congress required, in the LDPFA, that the Environmental Protection Agency (EPA) conduct a study "to characterize the risks to human health or the environment associated with managing decharacterized wastes in CWA treatment systems" and to "evaluate the extent to which risks are adequately addressed under existing State or Federal programs and whether unaddressed risks could be better addressed under such laws or programs." (1)

Additionally, in 1997 EPA agreed to an amendment to an existing consent decree, Environmental Defense Fund vs. Whitman, D.C. Circuit, 89-0598 (EDF consent decree), to include a requirement for a study of air risks from surface impoundments. The amended consent decree required a study of air risks from several different kinds of waste management units and an evaluation of gaps in regulatory controls for air risks posed by waste management practices. The specific part of the air risk consent decree requirement pertaining to surface impoundments in essence became a complementary study for the LDPFA study, since its time frame for completion matched the LDPFA study and it imposed similar requirements on EPA-a risk assessment and evaluation of regulatory coverage. Two of the major differences between the consent decree requirements and the LDPFA study were the consent decree requirement's focus on a single route of human exposure to pollutants-the air inhalation route-and the regulatory status of the wastes required to be studied. While the LDPFA requires a study of nonhazardous wastes that, at some point in time, exhibited a characteristic of hazardous waste, the consent decree requires EPA to study nonhazardous wastes that have never been classified as hazardous wastes. The consent decree also requires EPA to identify potential regulatory gaps in the current RCRA hazardous waste characteristics and the Clean Air Act (CAA) programs.

This report summarizes EPA's study. It begins by describing the nature and variety of industrial surface impoundments and the wastewaters they manage. In 1996, when EPA began this study, there was limited information on industrial impoundment sizes, designs, and operating characteristics, and there was limited information on the wastewaters managed in industrial impoundments. This report, comprising an analysis of survey data, risk analysis, and regulatory coverage findings, is the result of EPA efforts over the past 5 years to fill information gaps and meet legislative and consent decree obligations. The report quantifies and describes the potential risks to human health and the environment posed by chemical constituents present in the wastewaters managed by industrial surface impoundments. It also identifies existing regulatory controls and nonregulatory programs that can be used to address potential risks.

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Overview of Survey and Risk Assessment Findings


EPA estimates that, in the 1990s, there were approximately 18,000 industrial surface impoundments in use throughout the United States. These surface impoundments were present at about 7,500 facilities located primarily east of the Mississippi River and in Pacific Coast states. Because of the scope of the universe, EPA conducted the study focusing on a sample of U.S. facilities that use impoundments to manage industrial nonhazardous waste. Most of the facilities selected for the study were chosen randomly to ensure that the sample facilities would be representative of the facilities in the study population. EPA sent surveys to 221 facilities to collect information on their impoundments and the wastes managed in them. EPA requested information on the presence and quantities of 256 chemical constituents in the impoundments, as well as on the impoundments' design and operation. EPA used these data to characterize the potential risks that may be posed by managing the wastes in impoundments. The survey responses on the presence and concentrations of specific chemical constituents were particularly central to EPA's analysis. EPA also collected and analyzed wastewater and sludge from impoundments at 12 facilities in the study and used that information to illuminate the completeness and accuracy of the survey data. EPA also used data from a variety of other sources such as facility permit files, U.S. Census data, and technical references.

In the first part of this report, EPA presents the survey findings, then the risk assessment findings. The survey data provide information on the sizes and nature of the industrial impoundment population, the impoundments' environmental settings, historical summaries of liner failure and overtopping events, and the impoundments' designs and operating practices. EPA conducted a risk assessment using the survey data and other sources of data. The risk assessment consisted of a risk analysis in which EPA developed estimates of the chronic risks that are potentially posed by three pathways (air, groundwater, and groundwater to surface water) and a risk screening in which EPA considered the potential for other indirect pathway and ecological hazards.

EPA conducted the risk analysis and risk screening in stages in order to screen the thousands of possible data points, focus the analysis where most warranted, and, ultimately, characterize the potential risks associated with industrial surface impoundments. In the first stage, EPA applied precautionary exposure assumptions to screen out impoundments of no concern and identify those that merited additional analysis. In subsequent stages, EPA used data on actual exposure and used various fate and transport modeling tools to estimate potential risks. EPA's risk screening of the other indirect pathways and ecological hazards was similar to the initial stages of the risk analysis. Thus, the characterization of the other indirect pathway hazards and ecological hazards developed in this study is less certain than the characterization of risks via air, groundwater, and groundwater to surface water.

In the risk analysis, EPA used several chronic risk and hazard measures to evaluate potential threats to human and ecological receptors from chemical constituents managed in surface impoundments. EPA developed estimates of the excess individual lifetime cancer risk posed to humans by exposure to carcinogenic chemicals. Chemicals with noncancer health effects were evaluated using threshold measures of hazard. EPA developed hazard quotients (HQs), which are the ratio of the dose of contaminant expected at an exposure point to an appropriate safe reference dose. Other risk measures were also developed for the risk screening to examine the threats associated with consumption of contaminated fish and with ecological hazards. In determining what risks were of concern at each stage of the analysis, EPA generally used a cancer risk of 1 or more in 100,000 and an HQ of 1 or more as the criteria for deciding whether to retain an impoundment for the next stage of evaluation.

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Characterization of Surface Impoundments

In the United States, industrial surface impoundments are an important and widely used industrial materials management unit. Surface impoundments serve a variety of beneficial uses in a number of industrial processes. Industrial facilities that produce wastewaters often use surface impoundments to perform necessary wastewater treatment prior to discharge into surface waters. In other cases, industrial facilities may need to control wastewater flows and use surface impoundments for storing excess wastewater. In still other cases, industrial facilities may use surface impoundments to manage their excess wastewaters through evaporation or seepage into the ground.

EPA's best estimate is that two-thirds of the 18,000 industrial impoundments in the United States, or about 11,900 impoundments located at 4,500 facilities, contain at least one of the 256 chemical constituents that were of interest for this study or contain high (11 to 12.5) or low (2 to 3) pH wastewater. Surface impoundments are used by many industrial sectors, such as manufacturing, bulk petroleum storage, air and truck transportation, waste management, and national security. The wastewaters managed in these surface impoundments are primarily from manufacturing and washing processes and certain contaminated stormwaters. More than half of the impoundments with chemical constituents or pH of interest are in the chemical, concrete, paper, and petroleum industries.

Industrial impoundments vary greatly in size, from less than a quarter of a hectare (1/3 of an acre) to several hundred hectares. The larger impoundments provide the bulk of the total national industrial impoundment capacity. On a volume basis, the paper and allied products sector manages roughly two-thirds of the total quantity of wastewater, more waste in impoundments than all of the other industry categories combined.

Industrial impoundments frequently use management techniques that increase the potential for chemical releases and frequently are found in environmental settings that increase the potential for impacts to humans or ecosystems in the event of a chemical release. In this study, EPA found that most industrial impoundments are located only a few meters above groundwater and that, in most cases, shallow groundwater discharges to a nearby surface waterbody. More than half of the impoundments do not have liner systems to prevent the release of wastes to soil or groundwater. In addition, about 20 percent of impoundments are located within 150 meters of a fishable waterbody, so migration through the subsurface to the nearby surface water is possible. Finally, while aeration can have certain benefits, it also increases volatilization and the potential for airborne contaminant migration. EPA found that about 45 percent of the total wastewater quantity managed in impoundments is aerated.

There is potential for people to be exposed to chemical constituents released from industrial impoundments. EPA estimates that more than 20 million people live within 2 kilometers (or about 1.2 miles) of an industrial impoundment that was in operation during the 1990s, and about 10 percent of the impoundments have a domestic drinking water well located within 150 meters of the impoundment's edge.

After evaluating impoundment settings and operations and confirming there was potential for releases, EPA went a step further and conducted a risk assessment to examine the degree to which the chemicals found in impoundments were likely to be released from impoundments and ultimately expose people to harmful chemicals.

The results of the survey are presented in Chapter 2. Appendix A outlines the survey methodology and quality assurance procedures. Appendix B presents more comprehensive and detailed reporting of results. Appendix E discusses the field sampling effort.

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Risk Analysis Findings

EPA is basing its conclusions on two sets of risk results. The first set of risk results are those calculated using reported survey values for specified constituent concentrations present in the impoundments. These risk results, therefore, reflect model results from reported concentrations. The second set of risk results are those calculated either using imputed values, where survey respondents reported constituents as being present but did not provide quantities, or using detection limit levels when constituents were reported at less than a limit of detection. Consequently, the second set of risk results are considerably more uncertain.

On a national scale across all pathways in the risk analysis, EPA found that only 5 percent of the estimated 4,500 in-scope facilities and 2 percent of the estimated 11,900 impoundments may pose risks to human health. However, EPA also found that 21 percent of facilities nationally, corresponding to 24 percent of impoundments, have the potential for environmental releases to occur from impoundments. While these releases do not appear to pose risk to human health, they do indicate that selected contaminants in excess of health-based levels have the potential to move beyond the surface impoundment confines and into the environment.

In the risk analysis, in addition to the national aggregated results, EPA developed risk estimates for three pathways of potential exposure by which chemical constituents could move from an impoundment, through the environment, and be available to be inhaled or ingested by people nearby:

Direct inhalation risks can occur if a constituent of concern evaporates from the impoundment's water surface, is carried by air dispersion to nearby residences, and then is inhaled by residents. EPA developed risk estimates for the closest residences, based on locations reported in the surveys or identified through census information, and generated national estimates.

About 92 percent of impoundments were found to pose no air inhalation risk of concern. About 1 percent of impoundments are estimated to have a risk of concern from the inhalation of airborne contaminants. In addition, an estimated additional 3 percent of impoundments do not pose air inhalation risks to people nearby, but do generate releases to the air that exceed health-based levels at a distance of 25 meters from the impoundments. The remaining 4 percent of impoundments could not be evaluated conclusively because of the use of detection limits or inferred data due to incomplete reporting.

Groundwater risks also appear low; 67 percent of impoundments have no evidence of risk. Less than 1 percent of impoundments are estimated to have the potential for risk exceedances. In addition, 11 percent of impoundments have the potential to generate contaminated groundwater plumes that may extend 150 meters or more beyond the unit boundary. The remaining 22 percent of impoundments, while not estimated to cause a risk, could not be evaluated conclusively for their potential to result in a release to the environment because of incomplete reporting of concentration information.

Groundwater to surface water risks can occur if constituents in an impoundment migrate through groundwater, discharge into nearby surface water, and contaminate fish and make drinking the surface water a concern. From the survey data, EPA generated national risk estimates that identified situations where human health ambient water quality criteria (HH-AWQC) might be exceeded in surface waterbodies.

EPA estimates that less than 1 percent of impoundments contribute to exceedances of HH-AWQC in nearby surface waters. EPA estimates 19 percent of impoundments, while not causing exceedances of HH-AWQC once dilution has occurred in the surface water, are estimated to generate releases that could cause groundwater to exceed the HH-AWQC at the point of groundwater discharge into the surface water

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Risk Screening Findings

EPA also screened for potential risks to human health through indirect pathways that were not considered in the risk analysis and for potential risks to ecological receptors. The objective of the screening was to determine the worst case potential for wastes of concern to cause harm.

Indirect pathway hazards can occur when humans ingest foods that have been contaminated indirectly by surface impoundment releases. For example, constituents can evaporate, move by dispersion through air, and then deposit on nearby crops and contaminate food sources. EPA's methodology resulted in estimates of potential indirect pathway hazards that were ranked categorically. Approximately 6 percent of the facilities fell into the highest category, indicating that this group of facilities has the greatest potential to result in an indirect risk of concern. However, this analysis does not confirm that facilities in this group actually have indirect risks of concern.

Industrial wastes managed in surface impoundments may potentially cause adverse effects on nonhuman organisms and natural systems. Many impoundments are located near waterbodies and are freely accessible to wildlife. For this study, EPA assessed the potential for impoundments to pose risks to populations and communities of ecological receptors that live in and near surface impoundments both during their operation and in the event that the impoundments were closed with exposed wastes remaining in place. EPA estimates that approximately 29 percent of facilities may have localized ecological impact during their operation or after closure if ecological receptors inhabit the impoundment area or the nearby areas affected by undiluted impoundment runoff.

The results of the risk analysis and risk screening are presented in Chapter 3 of this report. Appendix C describes the methodology and more detailed findings.

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Evaluation of Existing Federal and State Programs


The LDPFA requires EPA to assess the various federal and state regulatory and nonregulatory programs that address potential risks from surface impoundments and evaluate the adequacy of such programs. In addition, the EDF consent decree requires us to determine the need for a RCRA air characteristic to address potential air pathway risks from the studied surface impoundments.

Our general approach for the regulatory coverage analysis included a detailed review of applicable federal and state regulatory and nonregulatory programs. The regulatory coverage analysis and identification of gaps in this coverage focused on the potential for risks as determined by our human health and ecological risk screening analyses. The regulatory analysis addresses each of the health pathways of concern and potential risks to ecological receptors. We divided our analysis into two parts: (1) regulatory coverage of direct air inhalation risks, and (2) regulatory coverage of all other "nonair" risks.

To evaluate regulatory coverage and potential gaps for direct air inhalation risks, we reviewed two federal statutes: RCRA, that is, the hazardous and nonhazardous waste programs under this act, and the CAA. The CAA analysis involved three interrelated elements: (1) a waste management unit analysis to identify CAA provisions that can address surface impoundments; (2) a constituent coverage analysis, which focused on the constituents of concern from the risk assessment; and (3) an industry coverage analysis, which focused on the industry categories that were within the scope of this study. We then evaluated possible regulatory coverage by state programs. For potential nonair pathway risks posed by nonhazardous wastes in surface impoundments, we (1) identified constituents of concern from the groundwater and groundwater to surface water pathways, (2) identified federal regulations and programs that may address such risks, and (3) assessed coverage by state programs.

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Regulatory Analysis Findings

Overall, the study shows that regulatory and nonregulatory coverage of potential air risks is extensive and that any gaps in coverage appear to be limited to specific industry sectors, individual facilities that meet certain CAA exemptions, or specific air pollutants. The primary regulatory program that addresses potential air risks from industrial surface impoundments is the CAA National Emission Standards for Hazardous Air Pollutants program. Pursuant to section 112 of the CAA, all source categories that emit hazardous air pollutants and pose risks to human health should be regulated when the maximum achievable control technology program is fully implemented. There also are several other existing regulatory and nonregulatory programs that, to varying degrees, address air releases from industrial surface impoundments. These programs include the RCRA Corrective Action Program, the CAA Criteria Air Pollutant Program, state regulations pursuant to State Implementation Plans, the Voluntary Industrial Waste Management Guidance Program, and federal and state waste minimization programs.

For groundwater, the study shows that regulatory and nonregulatory coverage of potential groundwater risks is extensive, but may still have some limited gaps. Potential groundwater risks from industrial surface impoundments, including the groundwater to surface water pathway, are addressed primarily through state regulatory and nonregulatory programs. Based on our available information, most states have one or more programs that include provisions for controlling or addressing groundwater releases from industrial nonhazardous waste surface impoundments. The level of regulatory control or ability to address these releases, however, varies from state to state. These state regulations may be implemented under either general solid and industrial waste management authority or under water program authority, for example, a state National Pollutant Discharge Elimination System (NPDES) program. Additionally, there are RCRA, CWA, and Safe Drinking Water Act (SDWA) programs that also, to varying degrees, address groundwater releases or assess the susceptibility of drinking water sources to contamination. These programs, for example, include the SDWA Source Water Assessment Program, SDWA Wellhead Protection Programs, RCRA Corrective Action Program, the Voluntary Industrial Waste Management Guidance Program, NPDES program, and federal or state waste minimization programs.

The results of EPA's regulatory analysis are presented in Chapter 4 of this report. In addition to identification of potential regulatory "gaps," EPA discusses the limitations of the analysis and existing and future regulatory or nonregulatory tools that may be used to address identified gaps.

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Study Conclusions

Today's study satisfies both the requirements of the EDF consent decree and the LDPFA with regard to evaluating the risks and regulatory programs for surface impoundments receiving "decharacterized" wastewaters and never characteristic wastewaters. In both cases, EPA has conducted an extensive analysis of the impoundment universe to understand the risks that may be posed and the extent to which risks are addressed by current and emerging federal and state programs.

In conducting the study pursuant to the EDF consent decree, EPA obtained the information necessary to determine whether a rulemaking to promulgate a hazardous waste characteristic should be initiated. Specifically, EPA examined the universe of impoundments that manage nonhazardous wastewaters. In addition, EPA characterized the pollutants of concern, likely releases, and pathways from these impoundments and assessed potential risks to human health and environment. Little risk has been found, and any risk found is not widespread, but may exist at a facility-specific level. Further, EPA examined the regulations that may apply to impoundments under a variety of federal and state authorities and found that coverage is extensive, but may not be complete in all cases. EPA identified a number of tools (for example, CAA, RCRA, state programs) that can be used effectively to mitigate risks as alternatives to a new hazardous waste characteristic.

In conducting the study pursuant to the LDPFA, EPA completed a study of "decharacterized" wastewater that characterizes the risks to human health or the environment associated with such management. The completed surface impoundment risk study will be undergoing a formal peer review process by EPA's Science Advisory Board expected to begin in early summer. In light of the planned peer review, any technical data in the report should be used with appropriate caveats and cautions. Further, EPA examined existing federal and state programs to evaluate the extent to which risks are adequately addressed under those programs and looked at whether the risks could be better addressed under such laws or programs. EPA concluded that there are some limited gaps in regulatory coverage, but did not find any serious risks that are unaddressed by existing programs. The Agency has not yet determined whether any specific regulatory actions are appropriate to mitigate the potential risks identified in the study.

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1. Congress, in the LDPFA, also required that EPA conduct a study of nonhazardous injection wells. The results and findings of that study are reported in U.S. EPA, Office of Groundwater and Drinking Water, 2001, Class I Underground Injection Control Program: Study of the Risks Associated with Class I Underground Injection Wells, Washington, DC.

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