Is EPA’s National Priorities List correct?
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By Carolyn B . Doty and Curtis C . Travis The Comprehensive Environmental Response, Compensation, and Liability Act of 1980 mandated that EPA prioritize the hazardous waste sites in the United States according to their potential to cause harm to human health and the environment. Criteria to be taken into account were: the population at risk, the hazard potential of the hazardous substances present, the potential for contamination of drinking water supplies, the potential for direct human contact, and the potential for the destruction of sensitive ecosystems. In response to this requirement, EPA developed the Hazard Ranking System to rank the worst hazardous waste sites for placement on the
National Priorities List (NPL), thereby making the sites eligible for Superfundfinanced remedial action. To date, more than 1200 sites have been placed on the NPL, with estimated cleanup costs ranging from $32 billion to $80 billion (1). Although the placement of sites on the NPL is a critical step in EPA’s environmental restoration process, the HRS has not proved to be an adequate screening tool for prioritizing sites. The HRS has been revised recently to include more comprehensive criteria for evaluation, but the new system will not affect the sites that have already been listed. Our analysis indicates that most of the sites placed on the NPL pose little or no risk to human health. Moreover, once placed on the NPL, most are remediated. Conversely, one may suppose that sites
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exist that pose significant health and environmental risk but are not on the NPL.
HRS scores and risk Evaluations of the original Hazard Ranking System have indicated that the contaminant migration scores derived using the system are not adequate indicators of risk. Bpth false positives (sites with no significant risks and high HRS scores) and false negatives (sites with significant risk and low HRS scores) have occurred. A study conducted by EPA showed poor correlation between HRS scores and potential danger at sites and indicated that false negatives are more common than false positives (2). A recent assessment of the inclusion of hazardous waste sites in poor rural areas on the NPL (3) reveals that rural sites
0013.936w9010924-1778502.5010 0 1990 American Chemical Society
Carolyn Do@
one would expect a correlation between future (potential) risk levels and HRS scores if not for current risk levels. Our analysis indicates, however, that no significant correlation exists between HRS scores, and total baseline risk levels for either current or future scenarios and suggests that both false positives and false negatives have occurred (Figure I). Because groundwater constitutes the primary pathway of exposure at Superfund sites and groundwater scores have driven the HRS scoring process in the past, one would expect a greater correlation. However, groundwater HRS scores are no better indicators of risk than are total scores. The failure of the original HRS system to adequately assess relative risk can be attributed to both the inadequacy of the model itself and the lack of information necessary to rank sites based on a preliminary site investigation. The lack of differentiation between actual
and potential exposures, the assignment of higher priority to heavily populated areas over sparsely populated areas without considering groundwater use, and the lack of i n f d o n as to whether groundwater is confaminated at a site result in the inadequate assessment of risk fmm groundwater contamination. The following cases illustrate the lack of consistency between information used to assess groundwater use and contamination early in the investigation process and information used to make a fmal decision regarding the need for remediation. California Gulch, CO. EPA's Site Inspection Report indicated that groundwater is potentially contaminated. However, the HRS scoring data indicated that it is not contaminated. Four years later, the Agency for Toxic Substances and Disease Registry (ATSDR) Health Assessment indicated that it is contamnated. The Record of Decision (ROD), however, stated that the groundwater is
FIGURE 1
EPAs Hazard Ranking System scores compared with formal risk assessments of NPL. sites
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Total baseline risk
__..."Travis are underrepresented. The study identitied 21 rural sites involving actual human exposure to contaminated groundwater that have not been listed on the NPL. An indicator of false positive results is the range of risk levels at Superfund sites. A previous analysis of risk levels at NF'L sites indicates that 70% of sites had current total baseline risk levels in the lo4 to 10.' range, the same range that EPA targets as acceptable after remediation (4). In addition, only 11.5% of NF'L sites involve actual or potential current exposure to contamination (A. Susten, Agency for Toxic Substances and Disease Registry, personal communication, 1990). The remaining sites fall in the gray mea of posing potential risks. Sites are often designated as such because of the lack of information needed to determine that the site does not pose a risk; therefore some of these sites may not pose significant risks, and thus were placed on the NF'L erroneously. We studied the correlation between HRS scores (5)and both current and future public health risk levels at B group of NPL sites where formal risk assessments have been conducted (4). Although the HRS has not differentiated between actual and potential exposures,
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not contaminated, although it had been in the past. Brown Wood Preserving, FL. The HRS scoring data indicated that groundwater is contaminated and is used as a drinking water source by more than 10,000 persons. The ROD, however, stated that the groundwater is not contaminated. Sapp Battery, FL. The HRS data stated that groundwater is not contaminated; an ATSDR Health Assessment stated that groundwater contamination is unknown. The ROD indicated that groundwater is contaminated and is used as a source of drinking water by more than 1000 people. Newsom BrotherslOld Reichhold, MS. EPA’s Site Inspection Report revealed potential groundwater contamination. The HRS data stated that the groundwater is used as a source of drinking water by 11,500 persons and no contamination exists. Both the health assessment and ROD, however. reported that the groundwater is contaminated. West Virginia Ordnance, WV. The HRS scoring data stated that the groundwater is used as a source of drinking water by 5000 people and is not contaminated. However. a health assessment and two RODS indicated that the groundwater is contaminated but is not used as a drinking water source 13).
Revised hazard ranking system The Superfund Amendments and Reauthorization Act of 1986 (SARA) required EPA to amend the HRS to more accurately reflect the relative degree of risk to human health and the environment posed by sites in need of evaluation. SARA specified that modifications include the consideration of damage to natural resources that may affect the human food chain, current or potential contamination of ambient air, and current or potential contamination of surface waters used for recreation or as drinking-water supplies. Another primar y requirement is the assignment of a high priority to sites where the release of hazardous substances has resulted in the closing of drinking-water wells or has contaminated a principal drinkingwater supply. The HRS has been revised to include an on-site pathway analysis and more detailed scores for groundwater and surface water pathway analyses. The revised HRS also assigns a higher value to target populations where actual exposures exist (6). Discussion Thus far, the challenge of establishing well-defined priorities for the Superfund program has not been met, and money is being spent with no guarantee that the
program is proviaing aaequate protection of public health and the environment. The decision-making process has reflected an ambiguous approach to using risk assessment as a priority-setting tool, and thus the program suffers from a lack of clear priorities in deciding which sites to clean up. The majority of resources are being directed toward the remediation of sites involving only potential risk, while other sites that involve more urgent health threats may be unaddressed. The effectiveness of the new HRS remains to be seen. Its usefulness as a priority-setting tool will depend largely on the accuracy and comprehensiveness of information used to score sites. Because the new system will not address the hundreds of sites that are already in the pipeline as a result of the old system, a key element of improving the Superfund decision-making process will involve identifying ways to effectively prioritize sites that are currently on the NPL.
References (1)
(2)
(3) (3) (5)
(6)
“Impact Analysis of RCRA Corrective Action and CERCLA Remediation Programs”; Chemical Manufacturers Association: Washington, DC, 1988. “HRS Revisions Support: SARA Studies on HRS Scores and Remedial Actions, HRS Scores and Potential Dangers, and the Effect of the 28.5 Cutoff Score”; U.S. Environmental Protection Agency: Washington, DC, November 1987. “Hazardous Waste Sites and the Rural Poor: A Preliminary Assessment”; Clean Sites, Inc.: Washington, DC, March 1990. Doty. C. B.; Travis, C. C. J . Air Waste Manag. Assoc. 1989, 39(12), 1535-43. “National Priorities List: Final and Proposed Sites, Route Scores”; US.Environmental Protection Agency: Washington. DC. February 1990. Caldwell, S.; Ortiz. A. J . Air Waste Manug. Assoc.. 1989, 39(12), 8 0 1 4 7 .
Carolyn B. Doty is on the research staff at Oak Ridge National Laboratory’s Office of Risk Analysis. She holds B.S. and M . A . degrees from the University of Tennessee. Among other topics, her research concerns hazardous waste policy issues and risk assessment.
Curtis C . Travis is the director of the Office of Risk Analysis at the Oak Ridge, National Laboratory in Oak Ridge, TN. He has a Ph.D. in mathematics from the University of California-Davis.
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To improve the system’s reliability, a cyclone was installed between the kiln and the SCC to remove particulates from the gas stream. A wet electrostatic precipitator (WEP) was installed to remove particulates downstream of the SCC, in place of the CHEAF, and a Monarch CPI separator was added to remove the suspended particulate matter in the process water stream. In addition, a Hauptmann conveyor was installed to improve the ram feed system. Selection of the OCS by FWEI was based on its ability to produce low flame temperatures compared to other pure oxygen burners. This allowed the burners to achieve lowered NO, levels, which reduced slagging tendency and the potential for kiln distortion. These modifications proved successful. The feed rate of soils increased from 2000 Ib/h to 4000 lbh. Because of the cyclone and the reduced volume of air, particulate buildup in the SCC was almost eliminated. The WEP proved successful in particulate removal and required little maintenance. Fuel savings of more than 60% were achieved for soil processing during the operation of the improved MIS with the OCS incorporated. Shakedown tests during 1987 revealed that a mist eliminator was required to control particulate emissions, especially for feeds containing high halogen levels. The incineration of materials from the Denney Farm site and other southwest Missouri dioxin sites continued. In addition, a trial bum was made in the summer of 1987 with these objectives: first, to demonstrate the capability of the MIS to simultaneously destroy liquid and solid wastes regulated by both the Toxic Substances Control Act and RCRA; and second, to qualify the MIS to incinerate dioxin-contaminated brominated sludge from southwestern Missouri sites. As a result of the trial bum, the unit was allowed to process brominated sludge. Destruction and removal efficiencies (DREs) exceeding 99.9999% were achieved for PCBs. DREs exceeding 99.99% were demonstrated for hard-to-destroy compounds such as carbon tetrachloride and hexachloroethane. Gopal D. Gupta is a vice-president of Foster Wheeler Enviresponse, Inc. He has a B.S. degree from the Indian Institute of Technology, Kanpur, India, and a Ph.D. from Lehigh University, Bethlehem, PA. He is a registered engineer in New Jersey, has authored more than 80 technical articles, and was an assistant professor in the Department of Mechanical Engineering at Lehigh.
