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Alternatives for Ground Water Cleanup (1994)

Chapter: 6 Setting Goals for Ground Water Cleanup

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Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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6
Setting Goals For Ground Water Cleanup

The preceding chapters provide clear evidence that a range of conditions and complexities exist at waste sites where ground water contamination has occurred. While the conventional and innovative technologies described in this report provide approaches for restoring these sites, there are limits to how completely and how quickly existing technologies can remove contamination from ground water.

Historically, the goal of ground water remediation in the United States has been to protect public health and the environment. If the levels of remediation required could be achieved rapidly and at low cost with existing technologies, no conflict would exist between technology's capabilities and society's goals. However, in a number of cases, existing ground water cleanup goals cannot be met with current technologies. In other cases, achieving these goals will require extraordinary amounts of time (decades to centuries) and money (tens of millions of dollars). Thus, a public policy decision must be made about whether the goals of ground water treatment should be changed to reflect what can be achieved today.

The Committee on Ground Water Cleanup Alternatives discussed several questions relating to the goals of ground water cleanup. Should existing goals (which are usually drinking water standards) be changed to be consistent with the highest level of treatment technically achievable today? Should the goals be maintained and the objective kept at meeting the goals, irrespective of technologic capability, time needed, and cost?

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

Should the goals be made stricter and more consistent with a nondegradation approach in order to restore ground water quality to its fullest? Should the Environmental Protection Agency (EPA), in setting goals, consider other factors such as cost, fairness to all stakeholders, and comparative risks of exposure to contaminants in ground water relative to involuntary and voluntary risks people take in everyday life?

In exploring these questions, the committee defined its role as one of compiling and reviewing information on risks, benefits, costs, and uncertainties that surround the evaluation of these issues, rather than undertaking and contributing original research. The committee's main mission was to consider the degree to which technologies can restore contaminated sites. Nevertheless, technology does not operate in a vacuum: cleanup goals will have a significant impact on the type of remediation technology selected, on the design of the system, and, ultimately, on whether the effort is perceived as a success or a failure. Therefore, any review of the capabilities of ground water cleanup technologies would be incomplete without an assessment of cleanup goals driving the selection of technologies and of factors driving the selection of cleanup goals.

This chapter begins with a review of current U.S. goals for ground water cleanup and a discussion of alternative goals suggested by various interest groups. Next, the chapter discusses the public health and ecological risks that currently drive selection of cleanup goals. It then discusses what is known and not known about the costs of various cleanup options. Finally, it summarizes the committee's assessment of whether changes in ground water cleanup goals are warranted to reflect the limits of technology.

CURRENT CLEANUP GOALS

The two primary federal laws governing ground water cleanup are the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA, also known as the Superfund act because of the fund it established to clean up sites) and the Resource Conservation and Recovery Act (RCRA). Most commonly, ground water cleanup goals under CERCLA and RCRA are set at drinking water standards. However, although drinking water standards are the most commonly used cleanup goals, for any one chemical the cleanup goal may vary depending on the state in which the site is located and whether it is a CERCLA or a RCRA site. Table 6-1 shows a sampling of the range of concentrations that have been used as ground water cleanup goals under current policy.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

Cleanup Goals Under CERCLA

Technically, CERCLA governs any site where there is a release or threatened release of a hazardous substance. However, the EPA generally uses it to order cleanup of closed or abandoned waste sites. The goal-setting process for cleaning up ground water at CERCLA sites is detailed in an EPA regulation known as the National Contingency Plan. Central to this plan (and to the statute itself) is that ground water cleanup goals should meet chemical-specific ''applicable or relevant and appropriate requirements'' from other regulations, known as ARARs. Ground water that could be used for drinking must meet federal requirements under the Safe Drinking Water Act (known as maximum contaminant levels, or MCLs; see Table 6-1) or state drinking water standards, whichever are more stringent. In addition to meeting drinking water requirements, ground water that directly discharges to surface water must meet federal requirements under the Clean Water Act or similar state requirements. Furthermore, if states have antidegradation laws that prohibit the contamination of ground water with certain chemicals, these laws also apply (see the third column in Table 6-1). For example, 24 states have established background levels as the goal of ground water remedial actions; for organic chemicals, the background level is usually zero (EPA, 1991a).

If no ARAR exists for a particular chemical, the ground water cleanup goal is based on a site-specific risk assessment. In general, cleanup goals based on risk assessments must result in a risk level of 10-4 to 10-6 for carcinogens (Table 6-1 shows a few examples of 10-4 to 10-6 risk levels) and a hazard index of less than 1 for noncarcinogens. A cancer risk of 10-4 indicates a 1-in-10,000 (or 0.01 percent) risk of contracting cancer from chronic exposure to a certain substance, while a cancer risk of 10-6 indicates a 1-in-1 million (or 0.0001 percent) risk. A hazard index of less than 1 indicates that the level of contamination is less than that known to cause harm. (The hazard index is the ratio of the dose received to the dose known to cause health problems.)

For any one chemical, different cleanup goals are possible under CERCLA. Cleanup goals may be higher than MCLs if the aquifer is not usable for drinking. The EPA defines such unusable aquifers as those that (1) cannot supply drinking water to a well or spring sufficient for the needs of an average family; (2) are saline (containing 10,000 mg/liter or more of total dissolved solids); or (3) are otherwise contaminated from other sources beyond restoration using reasonable techniques (EPA, 1986, 1990b). Cleanup goals may also exceed MCLs if they are based on protecting a surface water body to which the ground water discharges rather than on protecting the ground water. Cleanup goals may be lower than MCLs for individual contaminants if multiple contaminants are present

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

TABLE 6-1 Comparison of Potential Ground Water Cleanup Levels (parts per billion)

Contaminants

Federal Drinking Water Standards (MCLs)a

Representative Range of State Cleanup Standardsb

RCRA Proposed Corrective Action Levela

Representative Examples of 10-4 to 10-6 Risk Range for Carcinogens or Reference Dose for Noncarcinogensc

Arsenic

50

BKG-50

50

0.046-4.6

Benzene

5

BKG-5

0.35-35

Benzo[a]pyrene/total polycyclic aromatic hydrocarbons

0.2

BKG-0.2

0.011-1.1

Cadmium

5

BKG-5

5

18

Carbon tetrachloride

5

BKG-5

0.3

0.2-20

Chromium VI

100

BKG-100

100

180

DDT

BKG-0.1

0.1

0.23-23

Ethylbenzene

700

BKG-700

4,000

1,300

Mercury

2

BKG-2

2

11

Methyl ethyl ketone

BKG-460

2,000

1,800

Pentachlorophenol

1

BKG-1

1,000

0.66-66

Phenol

BKG-6,000

20,000

22,000

Polychlorinated biphenyls

0.5

BKG-0.5

0.5

0.01-1

Tetrachloroethylene

5

BKG-5

0.7

1.3-130

1,1,1-Trichloroethane

200

BKG-200

3,000

1,300

Trichloroethylene

5

BKG-5

5

1.9-190

Vinyl chloride

2

BKG-2

0.023-2.3

Xylenes

10,000

BKG-10,000

70,000

12,000

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

a A "—" indicates that no standard has been established for this contaminant.

b BKG indicates the natural background level of the contaminant. This column is based on the summary of state cleanup goals in EPA 1991a, which indicates that goals range from background levels to drinking water standards or risk-based concentrations.

c The reference dose for noncarcinogens is the dose below which no adverse health effects are expected as reported in Smith, 1993. The risk ranges shown for carcinogens are from Smith, 1993, which regulators in EPA's Region III use as a risk-based screen for Superfund sites to determine whether further investigation is warranted. Smith's data are based on the assumption that a person drinks 1 liter of water per day from ages 1 to 6 years and 2 liters per day from ages 7 to 30 years.

SOURCES: Smith, 1993; EPA, 1991a.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

and the cumulative risk from all of them exceeds 10-4 for carcinogens or a hazard index of 1 for noncarcinogens. Cleanup goals may also be lower than MCLs if the state in which the site is located has state-mandated MCLs or cleanup standards lower than the federal MCLs. As an example, between 1982 and 1991 the EPA selected a cleanup goal of 5 µg/liter (the MCL) for the chemical trichloroethylene (TCE) at 99 Superfund sites, lower concentrations at 23 Superfund sites, and higher concentrations at 13 sites; at 32 sites, the goals were based on risk levels in the 10-4 to 10-6 range.1

Although a range of cleanup goals is possible, as a practical matter federal drinking water standards serve as ceilings for ground water cleanup goals at most sites for the contaminants for which MCLs have been developed. Of the approximately 300 ground water remedial actions selected in the Superfund program between October 1, 1987, and September 30, 1991, the cleanup goal was to achieve drinking water standards through pumping and treating at 270 sites (EPA, 1992). At the remaining sites, the most common alternative to drinking water standards was the provision of alternative water supplies.

Cleanup Goals under RCRA

RCRA provides for cradle-to-grave management of hazardous wastes. The EPA uses the statute in part to require ground water and soil cleanup at operating hazardous waste treatment, storage, and disposal facilities and at closed facilities that once operated under the RCRA program. The primary EPA regulation for implementing ground water cleanups under RCRA is known as the Corrective Action Rule (EPA, 1990a).2 The Corrective Action Rule has not yet been finalized, but the EPA is nevertheless using it to oversee ongoing work. More than two-thirds of the approximately 100 ground water cleanup remedies under the RCRA corrective action program have been finalized in the past two years (M. Hale, EPA, personal communication, 1994). There is therefore little basis upon which to evaluate the application of cleanup goals under this program.

Unlike cleanups governed by CERCLA, cleanups under the RCRA corrective action program have no requirement to meet ARARs from other laws. Nevertheless, the EPA intends that RCRA and CERCLA should establish a consistent approach for ground water cleanup. This internal consistency requirement is a key component of the EPA's long-term ground water strategy (EPA, 1991e). In keeping with the ground water strategy and with the proposed RCRA regulations, the agency anticipates that CERCLA and RCRA will arrive at similar solutions to similar environmental problems and that actions undertaken by one program will be

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

adopted by the other program in cases where the programmatic responsibility for a site shifts from one to the other. Therefore, under RCRA the EPA generally sets cleanup levels at MCLs, even though the proposed corrective action regulations do not require that cleanup goals correspond to ARARs.

Exceptions to Goals Based on Drinking Water Standards

Although ground water cleanups under CERCLA and RCRA usually require attainment of drinking water standards, the laws have provisions for allowing waivers to these standards even for potential drinking water sources. Both statutes attempt to balance the desirability of meeting health-based cleanup standards wherever possible with the constraints posed by technologic capability and cost. The basis for dealing with these practical considerations differs for the two statutes.

Under CERCLA, the EPA may waive health-based cleanup requirements where achieving them is "technically impracticable from an engineering perspective." However, the EPA has been criticized for making minimum use of CERCLA's statutory waiver provisions. Of the 945 sites for which cleanup remedies were selected between 1982 and 1991, only 13 included technical impracticability waivers.3

Because RCRA cleanups need not meet ARARs, the RCRA program is generally more flexible than the CERCLA program in allowing cleanup goals other than MCLs. Under RCRA, those responsible for the cleanup may apply for an "alternate concentration limit" (ACL) in place of drinking water standards as the cleanup goal. The ACL is based on a site-specific risk assessment. The key factor that the EPA considers in granting an ACL is whether it will protect public health at the point of exposure, i.e., whether contaminant concentrations will be reduced to ensure adequate public health protection at the nearest drinking water well.

The EPA is increasingly recognizing that attaining drinking water standards is not feasible at certain types of sites and has drafted a guidance document to clarify the policy regarding technical impracticability of ground water cleanup at CERCLA and RCRA sites (EPA, 1993b). The guidance document, discussed in more detail in the next chapter, describes the types of data necessary to demonstrate that the original cleanup goals for a site should be waived because of technical limitations.

ALTERNATIVE CLEANUP GOALS

Whether the nation's current emphasis on restoring contaminated

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

ground water to drinking water standards is appropriate is a matter of debate. On one hand, achieving MCLs may be impossible at many sites and may be extremely costly even when possible. On the other hand, even when strict cleanup goals are not technically achievable, their existence may provide an incentive against further pollution and may encourage development of cleanup technologies that better protect public health. In the debate over whether strict ground water cleanup goals are appropriate, given the limitations of technology and the high costs, various interest groups have advocated goals ranging from complete restoration to restricting use of the ground water, as shown on Figure 6-1 and explained below.

Unrestricted Use Goals

At the left end of the spectrum of possible goals in Figure 6-1 is cleanup to allow unrestricted use of the ground water. Many states have identified unrestricted use as the most beneficial use of ground water. Three possible cleanup goals that allow unrestricted use are (1) complete cleanup (i.e., cleanup to concentrations that may sometimes be below natural background levels), (2) cleanup to background levels measurable in uncontaminated areas (or to the detection limit for the contaminant), and (3) cleanup to health-based levels.

Complete Cleanup

Some groups have advocated complete cleanup—meaning removing the contaminants to zero concentration levels—as a ground water cleanup goal in order to keep the environment "pure" for ethical or moral reasons, to provide the private sector with a continuing incentive to exercise care in handling hazardous wastes, and to ensure that the most thorough cleanup possible occurs. However, the attainment of zero contaminant concentrations as an outcome for ground water remediation should be recognized as an unattainable goal no matter how far cleanup technologies advance in the future. Even pristine waters contain certain inorganic chemicals regarded as contaminants. In addition, it is impossible to prove zero concentrations, given limitations in analytical detection ability. Although the Safe Drinking Water Act established zero as the ultimate goal for carcinogens, the enforceable levels under the act are nonzero MCLs based on the capabilities of drinking water treatment technologies and the detection limits for the contaminants; the nonzero MCLs, rather than the ultimate goal of zero, serve as cleanup goals under Superfund and RCRA.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

FIGURE 6-1 The range of possible ground water cleanup goals.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×
Cleanup to Background/Detection Limits

As a more feasible alternative to zero contaminant levels, some have advocated the use of background concentrations or analytical detection limits as ground water cleanup goals. For example, 24 states use detection limits or background levels as the only acceptable cleanup goal (EPA, 1991a). Cleanup to background levels may be selected in cases where there is a naturally occurring background concentration of a contaminant; otherwise, analytical detection limits serve as cleanup goals. One benefit of using detection limits or background levels as cleanup goals is the elimination of the need for government agencies to define explicitly an "acceptable" risk level. Rather, using detection limits or background levels implies that cleanup is accomplished to the fullest extent measurable with today's technologies. A drawback is the high cost that can be associated with such cleanups; it is possible that such goals will achieve only a small additional benefit—at substantially higher cost—compared with cleanup to specific health-based goals. Another drawback is that detection limits change over time as analytical capabilities improve, meaning that cleanup standards will become outdated as technology advances.

Cleanup to Health-Based Levels

As discussed above, cleanup to health-based standards is the most common type of goal used today. There are two possible mechanisms for setting health-based goals: (1) using predetermined standards, such as drinking water standards and the other ARARs used at Superfund sites, and (2) using risk assessments at each site.

The advantages of using predetermined standards versus using site-specific risk assessments include speed and ease of implementation, consistency in the treatment of similar sites, usefulness for initial screening of contamination to determine its significance, elimination of incentives for industry to locate in the most environmentally lenient states, and avoidance of a need for technical expertise on the part of regulators in order to address toxicological and risk assessment issues on a case-by-case basis (Siegrist, 1989). The use of predetermined standards, if established based on "worst-case" assumptions, will also ensure adequate margins of safety for all sites. However, using predetermined standards also has important drawbacks. The most significant drawback is the inability to account for site-specific exposure patterns, which may result in higher expenditures than are necessary to protect public health at a particular site.

In lieu of using previously established standards as health-based

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

goals, formal risk assessments may be used to develop site-specific goals, as is done in some cases under the Superfund and RCRA corrective action programs. The site-specific approach allows flexibility in considering site conditions. It also ensures that the level of risk, which is based on exposure patterns as well as contaminant levels, will be the same at different sites. (When uniform cleanup standards are used, the level of risk may vary from site to site because of different exposure patterns, even if the contaminant concentrations are the same.) One major disadvantage of this approach is that it is time consuming and costly to implement. The site-specific approach requires that regulatory agencies have a technically trained staff large enough to evaluate individually the risk data for each site. Another major disadvantage is that by changing key exposure assumptions, the results can be easily manipulated.

It is important to realize that ground water remediation to assure a "safe" drinking water supply may not result in full restoration, because levels of contaminants may remain at concentrations greater than background levels. Further, contaminant levels designed to protect human health may not protect ecological receptors. Separate risk-based goals may be needed for ecosystem protection.

Partially Restricted Use Goals

Some who believe that the current ground water cleanup program is too costly have advocated using partially restricted use goals, shown in the middle of Figure 6-1. Under this scenario, cleanup goals would correspond to the expected use of the water. In some cases such goals are already used, such as when the goals are based on protecting a surface water body used for boating and fishing but not for drinking. Like health-based goals, partially restricted use goals can be based on predetermined standards, such as water quality criteria, or on site-specific risk assessments. The major drawback of such goals is that they may require institutional controls, such as well restrictions or fish advisories, to prevent excessive human exposure to the contamination. Some have expressed concern about whether it is possible to design policies and institutions capable of perpetually limiting people's use of contaminated water.

Technology-Based Goals

Many major environmental statutes applicable to media other than ground water use a technology-based approach to setting cleanup goals. For example, under the Clean Water Act municipal wastewater treatment plants are required to treat their effluent to a level achievable by what are known as "secondary treatment" systems (unless more strin-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

gent treatment is necessary because of local water quality considerations). Technology-based goals, shown in the middle of Figure 6-1, specify a remedial action to be taken rather than a concentration to be reached. The protectiveness of technology-based goals relative to health-based goals varies because the use of technology-based goals may result in risks that are greater than or smaller than those associated with health-based goals. For example, the best available technology may be unable to achieve concentrations based on health risk or may achieve concentrations below those necessary for public health protection.

Among the various cleanup options, technology-based goals are the only goals that fully account for the capabilities and limitations of technology that this report has emphasized. The technology-based approach avoids raising false expectations about what level of cleanup is possible. On the other hand, some contend that this approach eliminates the incentive to develop technologies capable of reaching health-based goals. Another drawback is that the approach, if too rigidly applied, may overlook important site-specific factors that could affect both implementation risks of that technology (for example, air pollution risks associated with incinerating soils) and the ability of the technology to actually achieve the desired remediation at a particular site.

Restricted Use: Degradation with Containment

Many critics of the current approach to ground water remediation have suggested establishment of areas in which ground water is permitted to remain degraded, as long as measures are taken to contain the contamination or to prevent public exposure by other means. Restricted use goals are the least costly approach to managing contaminated ground water. Such goals also account for the fact that in some cases containment may be the only technologically feasible option, as discussed in Chapter 3.

The major drawback of restricted use goals, like partially restricted use goals, is the requirement for measures to ensure that the public is not exposed to contaminated water. Restricting ground water use is especially problematic when the contaminated water serves as a drinking water supply, which is the case at a significant number of sites. Data indicate that at nearly one-third of Superfund sites, existing private, community, and public drinking water supply wells have been closed or restricted because of contamination (Wells, 1992). Three options are possible to prevent exposure in these situations: wellhead treatment, point-of-use treatment, and development of alternative water supplies (see Box 6-1 and Box 6-2). Each of these options has limitations, and whether any one of them will be possible or appropriate depends on site-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

BOX 6-1 OPTIONS FOR SUPPLYING DRINKING WATER WHEN GROUND WATER CONTAMINATION REMAINS IN PLACE

  • Wellhead Treatment Wellhead treatment involves upgrading the local drinking water treatment plant to remove contaminants from the water before it is distributed for drinking. Once contaminated water is pumped to the surface, treatment and removal of the contaminants prior to the water's distribution is generally possible. However, many water utilities in areas threatened by ground water contamination lack the specialized systems necessary to remove hazardous chemicals and would require an upgrade at substantial expense.

  • Point-of-Use Treatment When citizens whose drinking water has been contaminated are served by private wells rather than by public utilities, installation of special treatment units in individual homes is necessary. An example of this approach is in Elkhart, Indiana (see Box 6-2), where in-home granular activated carbon units and in some cases air strippers are being used for private wells contaminated with a variety of industrial solvents (Lykins et al., 1992). Using home treatment units where health-based ground water cleanup goals cannot be reached has two problems: maintenance requirements and high cost when many homes are affected. For example, in the Elkhart case frequent replacement of the carbon filters was necessary to maintain water quality (see Box 6-2). In addition, city officials decided that installing new water mains would ultimately be less costly than installing 800 individual home units.

  • Development of Alternative Water Supplies: In the simplest cases, alternative water can be obtained from an existing public water supply through expansion of the existing water delivery system, as in the Elkhart, Indiana, case described in Box 6-2. However, where there is no readily available existing alternative supply of adequate capacity, alternative water sources must be developed. Important obstades may limit this option. In some cases no readily available alternative supply exists. More commonly, alternative water sources exist but are of poor quality due to factors such as high salinity or high levels of dissolved solids. Finally, in some areas of the country, especially in the arid West, alternative water sources may already be allocated for someone else's use.

specific considerations such as the availability and size of a municipal water supply system, the number of residents affected, and the proximity to alternative water sources.

Comparing the Alternatives

If the capability of technology were the most important factor to consider in establishing ground water cleanup goals, then society might easily agree on a technology-based approach to remediation. Unfortunately, the decision is not so simple. The selection of ground water cleanup goals from among the variety of options discussed above is a political process involving debates about several factors, summarized in Table 6-2.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

BOX 6-2 POINT-OF-USE TREATMENT FOR TCE CONTAMINATIONELKHART, INDIANA

In 1984, a private citizen on the eastern side of Elkhart, Indiana, had his well water tested and learned that the water contained more than 200 µg/liter of the solvent TCE. Use of TCE and other chlorinated solvents is widespread in the town's industries, which include manufacturers of pharmaceuticals, recreational vehicles, and plastics. The citizen notified the county health department, which then notified the EPA, and the EPA and health department proceeded with an extensive sampling program on the eastern side of town.

The samples revealed that 80 wells had TCE levels above 200 µg/liter, with 15 of the wells exceeding 1,500 µg/liter and one sample containing 19,380 µg/liter. Investigators also found dichloroethylene, perchloroethylene, trichloroethane, and carbon tetrachloride. TCE at the levels found in the wells constitutes an immediate health threat from consumption, dermal absorption, and vapor inhalation. Therefore, the EPA and county health department temporarily placed 800 residents on bottled water.

In deciding on a long-term solution to the well water contamination, the county government decided that connecting most of the affected homes to the municipal water system would be more cost effective than maintaining in-home treatment units. The county connected 301 homes and 7 businesses on the east side of town to the municipal system, 11 homes that were not adjacent to the water main and where the contamination was relatively minor were given point-of-use treatment units. However, this was not the end of the town's TCE contamination problem.

In 1986, a private citizen, this time on the west side of town, found 800 µg/liter of TCE and 488 µg/liter of carbon tetrachloride in his water supply. The EPA tested 88 wells on the west side of town and found carbon tetrachloride at concentrations up to 6,860 µg/liter and TCE at concentrations up to 4,870 µg/liter. The EPA decided to install in-home activated carbon filters in 76 homes.

EPA tests revealed that the standard design calculations for these filters were unreliable for predicting filter life. Filters generally lasted half as long as expected (treating 490,000 liters instead of 850,000 liters) before contaminant breakthrough occurred. Researchers attributed the early breakthrough to competitive adsorption from multiple contaminants, bacterial colonization, and high influent levels. If the home treatment systems had not been carefully monitored by the EPA and the filters had been replaced according to the manufacturer's instructions, the homeowners would have incurred a significant health risk from contaminant exposure after the filters had exceeded their capacity.

SOURCE: Lykins et al., 1992.

Most of these factors have received far more consideration in policy debates than the capabilities of technology. Of the factors shown in Table 6-2, health risks and costs have received the most attention. Increasingly, policymakers are also recognizing the ecological risks of contamination as an important consideration. The following discussions focus on health and ecological risks of ground water contamination and the

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

TABLE 6-2 Site-Specific Factors Raised in Debates About Ground Water Cleanup Goals

Factor

Questions Raised

Public health risk

What levels of contamination create a public health risk?

Ecological risk

What levels of contamination cause damage to ecosystems?

Cost versus benefit

Will the benefits of cleaning up the contamination equal or exceed the costs?

Capabilities of technology

Are existing technologies capable of reaching the cleanup goal?

Time to reach the goal

How long will it take to reach the cleanup goal?

Risks associated with the cleanup technologies

Does implementation of cleanup using these technologies pose risks, such as breathing of contaminant vapors or construction accidents?

Impact on community

What will be the magnitude and duration of the visual disruption, noise, and traffic generated by constructing a remediation system?

Fairness to all stakeholders

Is the goal fair to all stakeholders, including nearby residents, responsible parties, regulators, and future generations?

costs and benefits of cleanup because these factors are at the center of national policy debates over cleanup goals. The chapter then addresses the question of whether current ground water cleanup goals should change, given the committee's conclusions about the capabilities of technology and the available evidence on health risks, ecological risks, and cleanup costs.

HEALTH RISKS OF CONTAMINATED GROUND WATER

Incidents such as that at Love Canal, in which homeowners were evacuated because the ground water and soil in their neighborhood were contaminated with hazardous wastes, have caused widespread public concern that subsurface contamination from hazardous waste sites poses serious risks to human health. Yet, determining the precise level of risk these sites pose—and what level of concern is warranted—is a task that is complicated by a high degree of uncertainty. Two general sources provide information on the potential for health effects from contaminated ground water: epidemiologic studies and animal studies. The evidence from each of these sources is uncertain and has been interpreted differently by different interest groups.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

Evidence from Epidemiologic Studies

Epidemiologic studies determine health effects by examining specific populations exposed to the contaminants. These populations may be either occupational groups exposed through the workplace or residents near contaminated sites. Studies of people living near contaminated sites are the more relevant approach because occupational groups are usually exposed at higher levels and through different pathways than populations exposed through contaminated ground water. However, there are serious limitations to undertaking epidemiologic studies at hazardous waste sites, undermining their ability to answer questions about health hazards.

Limitations of Epidemiologic Studies

The most important limitations of epidemiologic studies are the following:

  • Uncertain exposure: Without question, the single most perplexing problem in developing human health data related to hazardous waste sites is the assessment of exposure experienced by the study population. In many epidemiologic studies, individual exposures to contaminants are unknown, limiting the ability to establish linkages between exposure and disease. Direct evidence of exposure, such as residues in human tissues or fluids, is seldom available. Exposure is most often estimated from surrogate data such as place of residence; answers to questionnaires; employment records; and results of air, water, and soil monitoring. Exposure of individuals may vary greatly within the geographic areas studied, resulting in the misclassification of exposure status of individuals. The magnitude of exposure may also change over time, and determining past exposures may be difficult. Variation in exposure within a geographic area is an especially perplexing problem when ground water contamination is involved because populations quite distant from the waste site may be exposed if the water is distributed through a municipal supply system, resulting in a much larger exposed population than investigators would presume based on residential patterns near the site.

  • Latency: Frequently, the interval between exposure to a toxic chemical and the appearance of cancer or other chronic diseases is measured in decades. In the real world, however, epidemiologic studies frequently need to be undertaken before this latency period has elapsed. The likelihood of epidemiologic studies detecting adverse health effects is thus reduced.

  • Small size of study population: The populations studied in epidemi-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

Example of a containment suit worn by cleanup crews at hazardous waste sites. Courtesy of U.S. Environmental Protection Agency, R. S. Kerr Environmental Research Laboratory.

ologic investigations of hazardous waste sites are usually small, a situation that may result in risks going unobserved because the statistical power of the study is too low. While studying large populations would be preferable, communities surrounding waste sites are usually small. Loss of members of the population in the course of follow-up investigations adds to the difficulty of maintaining a large enough study population.

  • Inadequate control over comparison groups: To establish the baseline disease rate in the absence of contaminant exposure, an unexposed, or ''reference,'' population is necessary. However, it is difficult or impossible to be certain that the reference groups are not exposed to the chemicals under scrutiny unless direct exposure data are available for both the exposed and unexposed groups. When reference groups have also been exposed to the contaminants, excess occurrences of disease in the population under study may be impossible to detect.

  • Uncertain health effects of the contaminant: Epidemiologic studies

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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benefit from information about contaminant toxicity that can direct investigators toward specific types of toxic effects. Unfortunately, few measurable health effects are sufficiently specific to particular chemicals to allow establishment of a direct link between exposure and disease. In addition, toxicity data for many contaminants are limited, especially when these contaminants are not end products of a familiar commercial process but rather are residual, intermediate, or precursor substances from the process.

  • Presence of contaminant mixtures: Even less is understood about the toxic effects of complex mixtures of chemicals than about individual chemicals. Exposure to multiple contaminants is the rule rather than the exception at hazardous waste sites. Simultaneous exposure to many chemicals substantially complicates the determination of causality.

  • Confounding factors and sources of bias: The results of epidemiologic studies may be confounded by factors other than contaminant exposure that are themselves associated with the disease under study. For example, some hazardous waste sites may be located in industrialized and highly polluted areas. Individuals in the surrounding area may have been exposed to chemical pollutants while working for companies that created the waste, or they may have been exposed to air pollution from industrial or vehicular sources. In cases where waste sites are located in economically depressed areas, poor diet and absence of prenatal or other preventive medical care may also affect the study's outcome. In addition, population characteristics other than contaminant exposure that are linked with increased disease risks (for example, smoking) must be taken into account. Increased or differential recall of past health problems by residents near the site may also bias results of studies based on self-reported symptoms. For example, because they are concerned about possible exposure, residents near a site may be more likely to recall and report past problems than residents living in areas farther from the site. Conversely, residents near waste sites may be unwilling to disclose information about some types of medical problems, such as miscarriages.

Results from Existing Epidemiologic Studies

Isolated epidemiologic studies have provided positive links between exposure to ground water contaminants and certain diseases. One of the most notable studies was conducted in Hardeman County, Tennessee (Clark et al., 1982; Meyer, 1983; Harris et al., 1984). At this site, a chemical company buried pesticide production waste in unlined shallow trenches between 1964 and 1972. The location is rural, but many people built homes around the site in anticipation that the company would build a facility. By 1977, local residents were complaining of bad taste and

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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odor in their well water, which originated from ground water that extended under the area where the disposal trenches were located. The water from private wells was highly contaminated with chemicals known to cause liver damage and liver cancer in both animals and humans. A health survey was conducted in 1977 to determine if liver dysfunction was present in exposed populations. Epidemiologists found a dose-response relationship between measured levels of chemicals in the household water and an increase in liver function enzymes, a biochemical method for quantifying the effect of exposure. In addition, there was a significant difference in the presence of an enlarged liver between the exposed and unexposed controls, based on a clinical examination performed by a physician.

The Hardeman County study is important from an epidemiologic perspective for two reasons. First, direct measurements were taken to determine exposure to chemicals in individual households. This enabled determination of which families were heavily exposed and which were less severely exposed. Second, the chemical compounds detected are specifically related to the outcomes found. For example, carbon tetra-chloride is known to cause enlargement of the liver and elevated enzyme levels in humans.

Unfortunately, the ability to conduct conclusive epidemiologic studies at hazardous waste sites such as that in Hardeman County is extremely rare. As a result, when one analyzes the existing body of epidemiologic evidence as a whole, the public health implications of ground water contamination from hazardous waste sites are unclear. Many researchers have reviewed the evidence from existing epidemiologic studies and have provided cautiously worded, but nevertheless inconsistent, conclusions regarding the magnitude of human health risk associated with hazardous waste sites. Grisham (1986) reviewed 29 studies and concluded that "none of the investigations surveyed has provided sufficient evidence to support the hypothesis that a causal link exists between exposure to chemicals at a disposal site and latent or delayed adverse health effects in the general populace." Marsh and Caplan (1987) reviewed studies of 15 hazardous waste sites and concluded that "the exposure-health outcome linkages that were examined are, for the most part, weak or inconclusive." In both of these reviews the majority of community health studies revealed no adverse effects attributable to waste chemical exposure; the reviewers regarded the minority of studies that did report exposure-disease associations as inconclusive because the studies failed to meet the scientific standards of research in epidemiology. Likewise, in a review of 16 published studies of 8 hazardous waste sites, Upton et al. (1989) concluded that "[o]f the studies published thus far, few have been

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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sufficiently well designed and well conducted to yield meaningful re-suits."

A more recent review of health effects associated with hazardous waste sites by the National Research Council (1991) evaluated 22 published studies from 14 waste sites and concluded that the available epidemiologic literature on this subject is "scanty and not conclusive." Nevertheless, this report concluded that drinking water contaminated with certain chemicals is injurious to human health but that the magnitude of the risk is uncertain. As evidence, the report points to studies showing that trihalomethanes in surface drinking water are associated with an increased risk of bladder and other cancers (Cantor et al., 1987) and to a limited number of studies linking spontaneous abortion (Swan et al., 1989), low birth weight (Vianna and Polan, 1984), and birth defects to drinking water contamination.

Recent congressional testimony by the Agency for Toxic Substances and Disease Registry (ATSDR) describes studies by both the ATSDR and other researchers suggesting that reproductive problems may be associated with drinking contaminated water or living near hazardous waste sites (Johnson, 1993). Additional epidemiologic studies are under way to clarify these associations.

Evidence from Animal Studies

Regulators often lack sufficient data from epidemiologic studies of humans to determine the adverse consequences of ground water contamination. Therefore, in determining the human health risks of ground water contamination, regulators often must rely on animal studies. Animal studies provide estimates of the long-term human health effects of environmental contaminants based on the response of animals, usually rats and mice, to large doses of the contaminant over relatively short time periods (although the time period is long relative to the animal's life span). The use of animal studies is essential to a preventive approach to protecting public health because it avoids the ethically and medically unacceptable prospect of waiting for diseases to develop in human populations before taking action to protect public health.

Although essential in evaluating the health risks of exposure to ground water contamination, animal bioassays have several shortcomings. First, these studies must extrapolate effects observed in animals that are administered large doses of the contaminant to humans who will most likely receive much smaller doses. Second, different species may metabolize chemicals in different ways and therefore may be affected differently by chemical exposure. For example, a recent experimental study of the toxicity of mixtures of 25 ground water contaminants to rats

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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and mice revealed health complications in the rats at sufficiently high exposure levels but no effects in the mice (National Toxicology Program, 1992). Third, most animal studies to date have focused on single contaminants rather than on the mixtures most likely to be found at waste sites.

Because of such limitations, some scientists question whether health risks predicated on studies involving animals accurately reflect the likely magnitude and type of health impact on humans (Kimbrough, 1990). Nevertheless, those responsible for assessing the risks of ground water or other environmental contamination must often rely on experimental animal data. Although observations in humans are more relevant for predictions of risk in human populations, toxicologic data from animal studies are essential in quantitative risk assessment in circumstances where direct human information is not available which is the situation at the majority of hazardous waste sites.

Evaluating the Evidence: Risk Assessment

Epidemiologic and animal studies provide information about the types of health problems that may occur from exposure to hazardous chemicals, but they may be insufficient to determine the likelihood that health problems will occur in a given exposed population. To determine this likelihood, environmental regulators use a process known as risk assessment.

Many human activities, such as driving a car, carry some degree of risk. Many risks are known with a high degree of accuracy because data have been collected on their historical occurrence. For example, the risk of death in motor vehicle accidents in a given year can be determined from roadway data. However, the risks associated with activities that do not cause immediately observable forms of injury or disease cannot be as easily quantified. Exposure to hazardous chemicals in ground water is one area where determining the degree of risk is an uncertain process.

In assessing risks from activities such as chemical exposure, the National Research Council in 1983 defined four basic steps in the risk assessment process, as follows:

  • Hazard identification involves reviewing and critically evaluating data relevant to the toxicological properties of a substance and identifying the types of effects associated with exposure to the substance. For contaminated ground water, this step answers the question, "What types of health problems does chronic exposure to the contaminant cause?"

  • Dose-response evaluation involves determining the relationship between the magnitude of exposure and the probability that the adverse effects will occur. For contaminated ground water, this step answers the

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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Monitoring total hydrocarbons in the air for worker protection at a contaminated site. A network of pumping wells is visible in the background. Courtesy of the Johns Hopkins University, Department of Geography and Environmental Engineering.

question, "How is the probability of contracting health problems affected by a change in the dose of contamination received from ground water?"

  • Exposure evaluation involves identifying human populations that may be exposed to the substance and determining the potential magnitude and duration of the exposure. For contaminated ground water, this step answers the questions, "Who was exposed to the contaminants in the water, how frequently were they or might they be exposed, and for how long?"

  • Risk characterization involves integrating information on hazard, dose-response, and exposure to develop quantitative estimates of risk and of the uncertainties associated with the risk estimate. For contaminated ground water, this step answers the question, "What is the increased risk of health problems in a given population from exposure to the contaminants in the ground water?"

Table 6-3 shows the connection between the above four steps of the risk assessment process and information from epidemiologic research, animal studies, and field measurements.

Risk assessments of ground water contamination have several limitations. As discussed above, they often rely on hazard and dose-response

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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TABLE 6-3 Major Elements of Risk Assessment

Research Phase

Risk Assessment Phase

Observations from epidemiologic and toxicologic studies

Hazard Identification: What types of health problems does chronic exposure to the contaminant cause?

Information on methods for extrapolating from high to low contaminant dose, small to large animals, and animals to humans

Dose-Response Assessment: How is the probability of contracting health problems affected by a change in the dose of contamination received from ground water?

Field measurements of contaminant transport and estimated human exposures; characterization of exposed populations

Exposure Assessment: Who was exposed to the contaminants in the ground water, how frequently were they or might they be exposed, and for how long?

 

Risk Characterization: What is the increased risk of health problems in a given population from exposure to the contaminants in the ground water?

information obtained from studies in experimental animals, which is then extrapolated to human populations. The general lack of information on human exposures to chemicals is another limitation. In addition, risk may vary with age at exposure. For example, the National Research Council (1993) recently concluded that infants and children have markedly different risks from exposure to pesticide residues than do adults. Despite these limitations, risk assessment has formed the methodological basis for much public policy related to the regulation of ground water contamination (and other environmental problems) in the United States. For example, as discussed in this chapter, for chemicals for which no drinking water standard exists, cleanup goals at Superfund sites are based on a site-specific risk assessment.

Ideally, the characterization of risk (risk assessment) is separate from the subsequent process of deciding whether risks are sufficiently high to justify regulatory action and, if so, the types of action necessary (risk management). Risk management decisions are reached not solely on the basis of risk assessment but also on the basis of relevant statutory requirements, policy precedents, and societal values. For example, the decision that a 10-4 to 10-6 risk level is acceptable at Superfund sites is specified in the National Contingency Plan. Some argue that separation of risk assessment from risk management is difficult to achieve in prac-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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tice and that the increasing complexity of the advancing science of risk assessment has lowered public confidence in risk assessment (Silbergeld, 1993). Nevertheless, risk assessment remains an important tool in the regulatory process. In fact, the EPA is exploring the concept of "comparative risk assessment"—in which environmental problems would be ranked according to their relative risk—as a method for helping to establish environmental cleanup priorities (EPA, 1987; Science Advisory Board, 1990).

Uncertainty in the Evidence of Health Risks

In sum, existing evidence is insufficient to provide clear conclusions about the level of health risk posed by ground water and soil contamination from hazardous waste sites. Nevertheless, the absence of documentation of health risks cannot be used as proof that exposure and adverse health effects have not occurred. Given the scientific uncertainties associated with epidemiology and risk assessment, public policymakers should err on the side of caution in setting ground water cleanup goals.

ECOLOGICAL RISKS OF GROUND WATER CONTAMINATION

Until recently, ground water contamination was widely viewed as primarily a public health threat rather than a threat to ecosystems. Nevertheless, in recent years more attention has focused on this issue as regulators and the public have realized that ground water contamination can alter ecosystems in important ways. For example, at the Munisport landfill in Florida, the EPA required a $6.2 million remedial action because of a significant threat to aquatic organisms in an adjacent state mangrove preserve (EPA, 1990c). Because of salt water intrusion, the local ground water was not suitable for drinking; therefore, the cleanup goal was based on ecosystem protection rather than on human health protection.

Ground water contamination can damage three types of ecological receptors: organisms living in ground water and in the zones where streams connect with ground water; terrestrial plants that take up contaminated ground water through their roots; and organisms in surface waters that receive ground water discharges.

Impacts on Organisms in Ground Water

Ground water can support a diverse microbial community that functions as a biological filter for certain organic materials. Contaminated

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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ground water can adversely affect natural microbial communities by making the environment anaerobic and/or by direct chemical toxicity to the microbes. Studies of microbial adaptation and in situ biodegradation of contaminants in ground water are the primary sources of information on such effects (Madsen et al., 1991). There is also evidence that ground water contamination can damage the ecology of the hyporheic zone—the subsurface location near streams where the ground water and surface water are hydrologically connected. Hyporheic zones, which can extend as deep as 10 meters and as wide as several kilometers from the stream channel, in some locations serve as a refuge for important aquatic species of bacteria and benthos during drought or stress and consequently play an important role in the recovery of stressed systems (J. Stanford, University of Montana, personal communication, 1992).

Contamination may also affect organisms in limestone karst or conduit systems, such as areas of underground sinks, caverns, and streams that can be inhabited by fish, amphibians, and invertebrates (such as the cave crayfish). While these ecosystems represent only a fraction of a percent of the ground water in the United States, they are nonetheless important. Karst systems concentrate ground water flows and are therefore very important in influencing migration of ground water contamination.

Impacts on Terrestrial Plants

Contaminated ground water has been an issue of concern for some time in arid regions such as southern California, where ground water is used for crop irrigation. Highly saline and otherwise degraded sources of ground water can damage crops. There are also limited examples of phytotoxicity from ground water sources outside the context of irrigation. For example, researchers have reported that contaminated ground water has affected tree growth downslope from seepage basins at the Department of Energy's Savannah River site (LeBlanc and Loehle, 1990; Greenwood et al., 1990). At this site, trees in wetlands along Four Mile Creek began to show localized stress and mortality in the late 1970s. The researchers concluded that alteration of soil acidity and of soil aluminum, sodium, and heavy metal concentrations caused by ground water contamination likely predisposed trees to deteriorate, with severe drought acting as the final trigger for deterioration and tree death. In another example, involving a wetland, researchers observed direct and severe ecological effects as a result of ground water contamination with a highly alkaline leachate from an on-site lagoon at a Massachusetts hazardous waste facility. Impacts included decreased species diversity and

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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productivity, stunted growth, and altered life cycles of the wetland vegetation downgradient of the lagoon (EPA, 1989).

Impacts on Organisms in Surface Water

Contaminated ground water can discharge into surface water and can be a significant source of contaminant loading (EPA, 1991c). For example, the EPA and the New York State Department of Environmental Conservation estimated that in the late 1980s as much as 315 kg per day of toxic chemicals were migrating or had the potential to migrate into the Niagara River from ground water on the U.S. side and that 30 kg per day were migrating from the Canadian side (EPA and New York State Department of Environmental Conservation, 1993). In 1987, Canada and the United States signed an agreement to reduce these loadings, with the United States committing to cut its contribution to 4 kg per day by 1996 (EPA and New York State Department of Environmental Conservation, 1993).

Field reports have indicated that contaminants discharging from ground water can cause significant ecological damage to surface water. One example is the 64-ha South Macomb Disposal Superfund site in Michigan, which contains two inactive municipal landfills (EPA, 1991f). A small stream, the McBride Drain, runs along the western and southern boundaries of the site. Landfill leachate contaminated the ground water with benzene, toluene, phenols, arsenic, and chromium. Fish kills reported in the stream were attributed to landfill leachate seeping into the stream via ground water transport.

Probably the most comprehensive review of the ecological impacts of ground water contamination on surface water ecosystems is an EPA analysis of the nature and extent of ecological risks at Superfund sites (EPA, 1989). Of 52 Superfund sites evaluated, 30 (including 14 landfills and 16 surface impoundment lagoons) had seepage to ground water that discharged to surface water (EPA, 1989). Using a combination of laboratory tests of samples collected at the sites, in situ field tests, and correlations between chemical and biological monitoring programs, the EPA identified ground water contamination of surface waters (and wetlands) as a potential contributor to fish and shellfish kills, increased disease incidence, behavioral changes, reduced floral and faunal species diversity, and reduced aquatic productivity. The EPA determined that approximately 10 percent of the sites posed serious ecosystem threats and 10 percent represented minor threats, with the rest involving moderate threats typically confined to small areas.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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Importance of Ecological Impacts

In summary, at certain sites the ecological risks of ground water contamination can be significant. Given that nearly 60 percent of Superfund sites are located adjacent to a stream and 52 percent are adjacent to a river (EPA, 1991d), the ecological effects of ground water contaminants must be considered when alternative ground water cleanup goals are analyzed.

ECONOMICS OF GROUND WATER CLEANUP

In the debate over ground water cleanup goals, many have emphasized the high costs of attempting to reach health-based cleanup levels as a reason for making the goals less stringent. Changing cleanup goals can have a significant impact on cleanup costs. However, like the health and ecological risks of various levels of ground water contamination, the costs of reaching various cleanup goals are highly uncertain at both the national and site levels.4

National Cleanup Costs

A widely cited national study published by the University of Tennessee in 1991 concluded that the costs of cleaning up all hazardous waste sites nationwide could drop by approximately one-third if cleanup goals are made less stringent or could increase by approximately one-half if cleanup goals are made more stringent (Russell et al., 1991; Abelson, 1992). According to this study, the ''best-guess'' cost of cleaning up all hazardous waste sites nationwide under current policy will be $752 billion over the next 30 years. If cleanup goals become less stringent, shifting toward containment and isolation of wastes rather than full cleanup, the cost would decrease to approximately $484 billion. If cleanup goals become more stringent, minimizing the amount of contamination left in place, the cost would increase to approximately $1,177 billion.

The University of Tennessee report has been critiqued for presenting costs as raw cumulative values, not as present values (Congressional Budget Office, 1994). Table 6-4, developed by the committee, shows the cost estimates from the University of Tennessee study adjusted to present values by estimating a profile of annual costs over the 30-year time horizon used in the study and by converting these annual costs to present values. The table includes best-guess estimates of cleanup costs based on the Tennessee study, as well as upper and lower bounds, also based on the Tennessee study. As the table shows, the best-guess cost in present value terms under current policy is $280 billion. With more stringent

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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TABLE 6-4 Costs of Various National Policies for Hazardous Waste Site Remediation

 

Present Value of Resource Cost (billions of 1991 U.S. dollars)

National Policy

Lower Bound

Best Guess

Upper Bound

Current policya

180

280

390

Less stringent policyb

140

180

260

More stringent policyc

360

440

630

NOTE: This table is based on data from Russell et al. (1991). It converts the figures in Russell et al. to present value by assuming that costs are prorated equally each year for a 30-year time horizon and that the discount rate is 4 percent.

a According to Russell et al. (1991), current policy, means "the set of principles and practices for hazardous waste remediation that are inferred to be in place in the period 1988-91 when the experience base and data for this study were collected."

b According to Russell et al. (1991), less stringent policy means relying more on containment and less on full cleanup.

c According to Russell et al. (1991), more stringent policy means application of more intensive treatment technologies and reduced burden on future generations.

cleanup goals, the cost in present value terms increases to $440 billion. With less stringent cleanup goals, the cost decreases to $180 billion.

The University of Tennessee estimate encompasses all facets of hazardous waste site cleanup, including cleanup of media other than ground water (such as sediments and sludge) and cleanup of sites where the ground water is not contaminated. According to the EPA (1993a), an estimated 20 percent of CERCLA sites do not have contaminated ground water. Furthermore, at sites with contaminated ground water, not all of the costs are for ground water cleanup. Therefore, ground water cleanup costs account for less than 80 percent of the figures presented in Table 6-4. If one presumes that 70 percent of the total cost of hazardous waste site remediation represents ground water cleanup, then the best-guess cost in present value terms is $200 billion under current policy. If one presumes that 50 percent of the cost applies to ground water cleanup, then the best-guess cost is $140 billion under current policy.

Many assumptions underlie the cost estimates in the University of Tennessee report. As a result, some critics have argued that the estimates are too high, while others have argued that they are too low (Congressional Budget Office, 1994). Nevertheless, comparisons with other sources of information about cleanup costs indicate that the study probably provides a reasonable estimate of the order of magnitude of likely clean-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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up costs over the next 30 years. For example, in 1991 Carlin et al. (1991, 1992) estimated that in that year the nation would spend $29.7 billion complying with requirements under RCRA and CERCLA and that the level of spending would increase into the future. For comparison's sake, $30 billion per year for 30 years at a 4 percent discount rate yields a present value of approximately $520 billion, which is substantially above the $390 billion upper bound for current policy from the Tennessee study. Given the different approaches taken in the two studies5 and given that there are substantial uncertainties in both, these estimates should be viewed as only illustrative of the magnitude of cleanup costs.

Site-Level Cleanup Costs

Simple computations for a hypothetical site provide further indication of how changes in cleanup goals can affect cleanup costs. For this hypothetical illustration, consider an aquifer containing a 190-million-liter plume of the common contaminant TCE at an average concentration of 1,000 µg/liter.6 If the site will be cleaned Up using a conventional pump-and-treat system that will treat the effluent with an air stripper and a granular activated carbon filter, then Table 6-5 shows estimates for the time and cost required to achieve various cleanup goals, ranging from 80 to 99.99 percent TCE removal. As the table illustrates, the present worth cost of cleaning up the site increases substantially as the cleanup goal becomes more stringent—going from $2.8 million for 80 percent removal to $6.0 million for 99.99 percent removal. It is important to realize, however, that when a significant amount of contamination remains in place, additional costs will be incurred to construct and maintain a containment system, decreasing the cost differences shown in the table. The magnitude of the cost of the containment system is highly site specific, depending on factors such as the nearest sensitive receptor as well as on local hydrogeologic conditions.

Figure 6-2 compares present worth costs for various cleanup goals using different assumptions about discount rates. As can be seen, increasing requirements from 80 percent TCE removal to 99.99 percent removal would increase the present worth cost by approximately a factor of three for the low discount rate case. In contrast, using a higher discount rate such as the EPA uses in its cost estimates, the cost increase is substantially less.

Because this example is hypothetical and because the methods used to estimate cleanup cost are subject to substantial uncertainties, the numbers in Table 6-5 should not be cited as accurate values but rather as approximations of how changes in cleanup goals can affect cleanup costs. Further, while this example shows the general trend of how cleanup goals

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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FIGURE 6-2 Cost of operating a pump-and-treat system as a function of the cleanup goal. The curves begin at a goal of 80 percent contaminant removal. As the figure demonstrates, increasing the removal efficiency to 99.99 percent substantially increases cleanup costs.

can influence site-level costs, it is important to realize that costs vary widely depending on numerous factors at each site. Part of the variation in cleanup costs is due to local factors such as local construction costs, the types of equipment available, and whether extracted ground water can be discharged to publicly owned treatment works (which results in significantly lower treatment costs). At least as important, however, are the hydrogeologic conditions at the site and the treatment technology or sequence of technologies chosen.

As an illustration of how hydrogeologic conditions affect cleanup

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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TABLE 6-5 Impact of Cleanup Goal on Cost of a Conventional Pump-and-Treat System

Percent Removal Required

Calculated Years to Achieve

Present Worth

80

15

$ 2,800,000

90

21

$ 3,250,000

99

42

$ 4,750,000

99.9

63

$ 5,600,000

99.99

84

$ 6,000,000

NOTE: The following assumptions were made: the plume volume is 190 million liters; the pumping rate is 380 liters per minute; 1.05 pore volumes are pumped per year; the retardation factor for TCE is 4.8; the air stripper influent concentration for TCE is 1,000 µg/liter; the air stripper effluent concentration for TCE is 5 µg/liter; and the discount rate is 4 percent. The estimates include capital, operation, and maintenance costs. They were prepared using the Cost of Remedial Action software package (EPA, 1991b).

FIGURE 6-3 Cost of operating a pump-and-treat system as a function of the contaminant's retardation factor, which indicates its tendency to sorb to solid material in the aquifer. The figure illustrates that cleanup costs can increase substantially when contaminants sorb. This example assumes a pumping rate of 1 pore volume per year, initial capital costs of $650,000, initial operation and maintenance costs of $180,000, a 3.5 percent discount rate (reflecting 7.5 and 4 percent interest and inflation rates), and complete replacement of equipment every 25 years.

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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TABLE 6-6 Comparison of Costs for a Conventional Pump-and-Treat System and an In Situ Bioremediation System for Benzene Removal

 

Present Worth

 

Removal Efficiency

In Situ Bioremediation

Conventional Pump-and-Treat

90

$2,460,000

$3,200,000

99

$3,000,000

$5,020,000

NOTE: The assumptions for the conventional pump-and-treat system in this example are the same as those used in Table 6-5 except that the contaminant is benzene, for which the required effluent concentration is 1 µg/ liter and the retardation factor is 3.6. The hypothetical bioremediation system pumps at 190 liters per minute to supply oxygen and nutrients to stimulate biodegradation.

costs, Figure 6-3 shows the cost of cleaning up the TCE plume in the hypothetical example as a function of the tendency of soils at the site to sorb the TCE. In the figure, sorptive capacity is indicated by the retardation factor—the ratio of the total contaminant mass in the aquifer to the contaminant mass dissolved in the ground water. The greater the tendency of the contaminant to sorb (indicated by large retardation factors), the higher will be the cleanup costs, as illustrated by the figure. The cost difference between requiring 90 percent contaminant removal and requiring 99.9 percent removal ranges from approximately $1 million to more than $2 million, depending on the retardation factor.

As an illustration of how the cleanup technology chosen affects cleanup cost, Table 6-6 compares costs for a conventional pump-and-treat system and an in situ bioremediation system for benzene removal. As shown in the table, for 90 percent benzene removal, in situ bioremediation provides a substantial savings compared to the conventional pump-and-treat system. Increasing the percent removal to 99 percent, if this were achievable, would provide an even greater cost advantage for in situ bioremediation. (It is important to note that if the in situ bioremediation system cannot reach the required cleanup goal in the predicted time, its life cycle costs may increase to the point where the costs are similar to those associated with conventional pump-and-treat systems.)

These hypothetical computations show that changing ground water cleanup goals from 80 or 90 percent contaminant removal to nearly 100 percent contaminant removal can have a substantial effect on cleanup costs at the site level. However, the magnitude of the effect is influenced by local economic conditions, site hydrogeology, and the cleanup tech-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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nology chosen. Furthermore, it may be partially offset by the need to build and maintain containment systems when a significant quantity of contamination remains in place.

Benefits of Ground Water Cleanup

In considering costs for ground water cleanup under various scenarios, one must recognize that spending on cleanup yields benefits that have economic value. Benefits include reduced health risks, increased property values for uncontaminated land, and the knowledge that the ground water will be available for unrestricted use in the future. No studies have attempted to compare differences in the dollar value of benefits received for different national ground water cleanup goals. Further, at the time this report was prepared only one study assessing the total national economic benefits of restoring ground water was available, and this study was controversial. The study was carried out for the EPA by McClelland et al. (1992) at the University of Colorado as part of an effort to assess the economic impact of the proposed RCRA regulations.7 The study was controversial because it used an economic analysis method known as contingent valuation to estimate the benefits of clean ground water, and it was criticized by the EPA's Science Advisory Board (1993).

Contingent valuation is a method used to estimate what are known as the nonuse values of ground water. Nonuse values are those that individuals place on water unrelated to their own need to use it in the present or the future—values such as desiring to preserve the resource for future generations and desiring to preserve it because it is a unique natural asset. In contrast, use values are those that individuals place on the water to use it today or to have the option of using it for themselves in the future. While most use values can be approximated based on current water prices, nonuse values cannot be determined from observation of actual marketplace transactions. Consequently, economists devised the contingent valuation method to assign monetary worth to non-use values for natural resources. The method estimates nonmarket values by conducting surveys to ask individuals what they are willing to pay to maintain the resource (or what compensation they are willing to accept for its loss). In the EPA study, researchers surveyed a national sample of 900 people and asked, "What would a complete cleanup program be worth to your household, if you faced the hypothetical problem of 40 percent of your water supply coming from contaminated ground water as we have described?"8

The contingent valuation technique is controversial in part because of its short scientific life span and because flaws in the method are still being worked out. The first contingent valuation study of nonmarket

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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goods was completed by Robert K. Davis in the early 1960s (Davis, 1963). During the early 1970s, economists studied the method intensively for valuing atmospheric visibility in the Four Comers region of the southwest, but little research was carried out on its use for valuing other resources (Randall et al., 1975; Rowe et al., 1980). The studies of the 1970s showed that different contingent valuation studies with different designs yielded similar results, leading researchers to believe that the technique might be a useful approach for valuing nonmarket commodities in general (Rowe et al., 1980). However, the research also revealed distinct flaws in the method, including the following:

  • Results may vary depending on experimental design factors, such as whether individuals are surveyed over the telephone or in person and the amount and type of information the researcher provides to the individual (Rowe et al., 1980).

  • The fact that individuals are not actually required to pay their bid may affect the result of the study, although where there are well-defined related markets the magnitude of this bias seems small (Brookshire and Coursey, 1987).

  • Individuals may offer the same bid for cleaning up one hazardous waste site, all related hazardous waste sites, or all hazardous waste sites in a region (Kahneman and Knetsch, 1992), although some researchers have suggested that this problem can be overcome if the contingent valuation analysis is done correctly (Smith, 1992).

Despite these and other flaws, many economists believe the contingent valuation method shows promise. For example, Mitchell and Carson (1989) have said that the contingent valuation method may be "a powerful and versatile tool" for measuring the economic benefits of the provision of nonmarketed goods. More importantly, a recent panel convened by the National Oceanic and Atmospheric Administration and chaired by two Nobel Prize-winning economists concluded that the method may be used as a starting point for legal evaluation of nonuse values, as long as sufficient and elaborate scientific safeguards are taken (Arrow et al., 1993). However, other economists caution that the method has not reached a stage of scientific maturity sufficient to place confidence in the reliability and accuracy of the estimates it provides. In a recent general review, Cummings and Harrison (1992) concluded that "the present state of the art of the CVM [contingent valuation method] leads us to what we believe is an unavoidable conclusion: for uses that require that the term 'value' will imply some nexus with real economic commitments of people, it has yet to be demonstrated that the CVM as currently applied is up to the task." A National Research Council committee is currently review-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

TABLE 6-7 National Benefits of Ground Water Cleanup of U.S. dollars)

 

Present Value of National Benefits of Ground Water Cleanup (billions of U.S. dollars)

Discount Rate (real rate, percent)

10-year Time Horizon

Indefinite Time Horizon

2

76

420

4

69

210

6

63

140

8

57

110

10

52

85

NOTE: If the amount paid per year were assumed to continue indefinitely rather than stopping in 10 years, the present value of benefits would equal the amount in the second column. There is some evidence that respondents cannot differentiate between a 10-year payoff and an indefinite payoff date. This illustrates how sensitive contingent valuation measures are to exact specifications of the commodity.

SOURCE: McClelland et al., 1992.

ing this method to determine whether it is appropriate for assessing the future value of ground water.

In the EPA study of the national benefits of ground water cleanup, the 900 survey respondents indicated that, on average, they would be willing to add $7.08 to their monthly water bills for the next 10 years to clean up ground water.9 With approximately 100 million households in the United States, this estimate indicates an aggregate willingness to pay $8 billion per year for 10 years. Table 6-7 shows the present value of this annual willingness to pay using various discount rates for a 10-year period. Because there is some evidence that respondents cannot differentiate between a 10-year payoff date and an indefinite payoff date, also shown in Table 6-7 are present worth values assuming that people are willing to pay the $7.08 indefinitely. As shown in Table 6-7, based on the EPA study the benefits of ground water cleanup, like the costs, may range up to hundreds of billions of dollars.

Because of questions about the validity of the EPA study, one must view Table 6-7 with caution. The Science Advisory Board criticized the study because board members believed that the commodity "ground water cleanup" was not sufficiently well defined to allow a single interpretation of the respondents' answers to the survey. Whether this criticism is valid can only be proved or disproved by further scientific analyses. As an example of the study's possible limitations, the survey indicated a nonuse value component for ground water of $49.44 per

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

household per year—close to the nonuse values estimated for preserving visibility in the Grand Canyon and for cleaning up hazardous waste sites in Colorado as determined in other contingent valuation studies (Rahmatian, 1987; Energy Resource Consultants, 1986). That the value survey respondents placed on this "good cause" is similar to the measured values for other "good causes" may signal problems. The sum of values people express in independent studies of willingness to pay for all good causes may exceed the disposable income of any one respondent (Kahneman and Knetsch, 1992).

THE COMPLEXITY OF SELECTING CLEANUP GOALS

Selecting ground water cleanup goals is not a simple matter: it involves consideration of health risks, ecological risks, costs versus benefits, and a variety of other factors—all of which are difficult to quantify with certainty. Different people interpret this uncertainty in different ways. For example, some view the uncertainty in the health risks of ground water contamination as an indication that the risks are insignificant, while others view it merely as an indication that science is limited in its ability to quantify what they perceive as a major risk. Similarly, some view the inability to place a precise dollar value on the economic damage caused by ground water contamination as proof that the economic damage is not significant, while others view it as proof only of the limitations of economics to adequately value important resources. Thus, some view existing ground water cleanup programs as having high cost while providing society with little benefit, while others view the programs as barely adequate to address an important environmental problem. The national policy debate over ground water cleanup goals must resolve these two conflicting extremes.

The task of selecting ground water cleanup goals would be difficult enough without technologic constraints. However, as this report documents, present technologies will be unable to restore portions of a large number of sites. The limitations of technology, in the view of some people, provide added reason to reconsider whether current ground water cleanup goals are appropriate. Given the high level of uncertainty in the risks and economic damage created by ground water contamination, the committee believes that whether changes are needed in the policies for setting long-term cleanup goals can only be decided through policy debates; science can influence these debates, but value judgments must be the deciding factors. At the same time, however, the committee strongly believes that because existing ground water cleanup goals cannot be at-

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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tained at a large number of sites, short-term objectives should be established at these sites to temporarily supersede long-term goals.

Under the scenario the committee envisions, short-term objectives would be set based on the capabilities of current technologies at sites where long-term cleanup goals cannot be reached for the full site with current technology but the ability to reach them in the future cannot be ruled out. Access to portions of sites where contamination remains would be restricted or partially restricted. Periodically, the EPA would review whether technology had advanced to the point that the interim objective could be moved closer to the long-term goal. Short-term objectives would not be needed for the sites at which cleanup goals can be reached with current technology. In addition, short-term objectives might not be needed for another group of extremely complex contaminated sites where cleanup is highly unlikely even with new technologies; at such sites, technical impracticability waivers might be used to waive cleanup goals, as is done under current policy in the Superfund program. The next chapter explains the details of how policymakers would decide which sites should have interim objectives in addition to long-term goals.

The setting of short-term objectives in situations where long-term cleanup goals cannot currently be achieved has precedence in existing environmental policy. For example, the Clean Water Act set an unenforceable national goal of ''zero discharge'' of pollutants for surface water but used "interim" enforceable objectives that recognized that achieving zero discharge was not technically feasible at the time the act was passed. In the Clean Water Act and under the scenario the committee envisions for ground water cleanup programs, the long-term goal provides the vision for national policy, while the interim objectives reflect the reality that there may be technical constraints to reaching the goal. The committee believes that interim objectives prevent the expenditure of resources trying to reach goals that are not achievable with current technology and more accurately communicate to the public what is possible with current technologies. At the same time, interim objectives do not rule out the possibility that at some future time new technological breakthroughs may enable the achievement of existing cleanup goals. They preserve the values that public policymakers believed were important when the nation's ground water cleanup programs were first implemented.

CONCLUSIONS

Based on an assessment of current ground water cleanup goals in light of the capabilities of ground water cleanup technologies, along with a review of the risks, costs, and benefits associated with ground water

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
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contamination and cleanup, the committee reached the following conclusions:

  • Interim ground water cleanup objectives may be needed for portions of sites where health-based cleanup goals cannot be achieved with existing technology. The establishment of policies for setting long-term cleanup goals at sites requires consideration of many factors other than the capabilities of technology, including health risks, ecological risks, costs, benefits, and people's values. Changes in long-term cleanup goals therefore require debate in public policy arenas. However, the committee strongly advises setting short-term, technology-based objectives to temporarily supersede long-term goals at portions of sites where achieving the long-term, health-based goals is not possible with current technologies.

  • The health risks of ground water contamination from hazardous waste sites are uncertain, but this uncertainty does not provide justification for changing long-term cleanup goals. The inadequate documentation of health risks derives from the general absence of information on human exposure to contaminated ground water and lack of information on the adverse effects of ground water contamination on humans. Given this lack of information, the relative degree of public health protection offered by one ground water cleanup goal, such as drinking water standards, in comparison to another goal, such as contaminant levels higher or lower than drinking water standards, cannot be quantified with accuracy.

  • Ground water contamination can cause significant ecological damage at certain sites. Ground water remediation has generally focused on public health concerns. However, given the increasing evidence that ground water contamination can also damage important ecosystems, the ecological effects of unremediated contaminant plumes are important to consider when choosing a long-term ground water cleanup goal.

  • At the site level, ground water cleanup goals can substantially affect cleanup costs. Removing 80 or 90 percent of the contamination generally costs much less than attempting to remove all or nearly all of the contamination. The magnitude of the cost difference depends on local economic factors, site characteristics, the cleanup technology chosen, and whether a containment system will be necessary if contamination remains in place.

  • At the national level, the total benefits and the costs of existing ground water cleanup policies are both likely to be in the tens to hundreds of billions of dollars rangebut these figures are highly uncertain. Many assumptions underlie existing estimates of benefits and costs,

Suggested Citation:"6 Setting Goals for Ground Water Cleanup." National Research Council. 1994. Alternatives for Ground Water Cleanup. Washington, DC: The National Academies Press. doi: 10.17226/2311.
×

and there is no consensus on these estimates in the economics community. As a result, direct comparisons of the costs and benefits of various ground water cleanup policies must be used with caution.

NOTES

1.  

These numbers are based on the committee's analysis of the EPA's Record of Decision data base.

2.  

Similar but separate regulations apply to the correction of leaks from landfills.

3.  

This figure is based on a key word computer search of the EPA's data base containing Records of Decision issued from 1982 to fiscal year 1991.

4.  

Uncertainty increases substantially when one aggregates cleanup costs from the site level to state, regional, and national levels.

5.  

The Carlin et al. estimate excludes sites outside the Superfund and RCRA programs, while the University of Tennessee estimate includes all waste sites. On the other hand, the Carlin et al. estimate includes costs under Superfund and RCRA unrelated to ground water cleanup, such as waste disposal costs.

6.  

The plume volume is defined as the volume of ground water containing dissolved TCE at concentrations above the detection limit (0.5 µg/liter). For this example, all of the TCE is either dissolved or adsorbed to solid materials in the aquifer; none is present as a dense nonaqueous-phase liquid.

7.  

Under the Reagan administration, the Office of Management and Budget required economic analyses of all proposed new regulations.

8.  

In the hypothetical situation described in this survey, the contamination originated from a leaking public landfill. "Complete cleanup" refers to building a concrete wall around the landfill down to the rock layer beneath it and pumping and treating the water outside the containment zone.

9.  

The researchers who carried out this survey attributed $4.12 of the $7.08 to nonuse values.

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Next: 7 Policy Implications of a Technical Problem »
Alternatives for Ground Water Cleanup Get This Book
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There may be nearly 300,000 waste sites in the United States where ground water and soil are contaminated. Yet recent studies question whether existing technologies can restore contaminated ground water to drinking water standards, which is the goal for most sites and the result expected by the public.

How can the nation balance public health, technological realities, and cost when addressing ground water cleanup? This new volume offers specific conclusions, outlines research needs, and recommends policies that are technologically sound while still protecting health and the environment.

Authored by the top experts from industry and academia, this volume:

  • Examines how the physical, chemical, and biological characteristics of the subsurface environment, as well as the properties of contaminants, complicate the cleanup task.
  • Reviews the limitations of widely used conventional pump-and-treat cleanup systems, including detailed case studies.
  • Evaluates a range of innovative cleanup technologies and the barriers to their full implementation.
  • Presents specific recommendations for policies and practices in evaluating contamination sites, in choosing remediation technologies, and in setting appropriate cleanup goals.
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