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Ranking Hazardous-Waste Sites for Remedial Action 4 EPA's PRIORITYSETTING The U.S. Environmental Protection Agency (EPA) has primary responsibility for environmental management and regulation in the United States, and with it, the authority to identify the most serious abandoned hazardous waste sites for attention under the federal Superfund program. As part of this authority, EPA must determine criteria for inclusion on the National Priorities List (NPL) for Superfund sites and the pace at which sites continue along the administrative path from identification to remedial action and closure. The principal priority setting step occurs when a site, following preliminary assessment (PA) and site inspection (SI), is scored using the Hazard Ranking System (HRS) model. The score (ranging from 0 to 100) determines whether the proposed site is included on the NPL and remains under the continued auspices of the federal Superfund program. Other scoring and ranking systems are used by EPA in other phases of the Superfund program, although as shown later, they are considerably less formal and rigorous.
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Ranking Hazardous-Waste Sites for Remedial Action In this chapter, the background and history of the HRS are presented, and the model's approach and structure are characterized and evaluated. The evolution of the HRS is traced in the context of the legislative mandate and management pressures that have guided and constrained EPA's administration of the Superfund program. The strengths and drawbacks of the HRS are discussed, with particular focus on changes that occurred with implementation of the revised HRS in December 1990. BACKGROUND AND HISTORY With the realization of the magnitude and potential impact of hazardous-waste contamination that occurred following the Love Canal incident in 1978, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. That law granted EPA the authority to respond to current or potential releases of hazardous waste that could threaten "public health or welfare or the environment." It established the principle of strict, joint and several liability whereby all potentially responsible parties (PRPs) identified at a site are liable for the costs of addressing and removing the hazardous threat. A multi-billion dollar fund was established through taxes on petroleum and chemical feedstocks to pay the costs of response action and remediation in cases where viable PRPs were not present or in cases where immediate federal action was deemed necessary. This Superfund, administered by EPA, has since provided the name by which the entire CERCLA process and the sites themselves have become known. The initial CERCLA legislation was debated and passed under highly charged conditions, and many of the involved parties, including EPA, were primarily concerned with establishing their position at the forefront of this new and powerful tool for harness-
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Ranking Hazardous-Waste Sites for Remedial Action ing public concern and anger over environmental contamination (Landy et al., 1990). Many practical issues of implementation, such as methods for setting site priorities, were largely ignored in the development of the legislation. CERCLA did require EPA to establish "criteria for determining priorities among releases or threatened releases [of hazardous substances] through the United States for the purpose of taking remedial action." Furthermore, the "criteria and priorities . . . shall be based upon the relative risk or danger to public health or welfare or the environment" (emphasis added) (CERCLA, 1980, Section 105(8)(A)). These criteria were to take into account the following considerations as much as possible: the population at risk; hazard potential of substances at the facilities; potential for contamination of drinking water supplies; potential for direct human contact; and potential for destruction of sensitive ecosystems As highlighted above, the initial criteria and priorities were to consider public health, the environment, and public welfare. The HRS, however, is designed to focus solely upon human health and the environment, with socioeconomic impacts considered only in an indirect manner. To determine which candidate sites would be included on the NPL, EPA contracted for the development of the original HRS model. The HRS model was developed by the MITRE Corporation to meet EPA's need for a multimedia environmental assessment model (Chang et al., 1981). At that time, multimedia assessment procedures were unavailable, and although pollutant transport and fate models had been developed for some of the individual pathways considered, those models were not connectable or comprehensive. Furthermore, methodologies for environmental and health risk assessment were just beginning to be devel-
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Ranking Hazardous-Waste Sites for Remedial Action oped. The multimedia risk approach of the HRS model was thus very innovative for its time. Following scientific review and public comment, formal adoption of the HRS occurred with passage of the National Oil and Hazardous Substances Pollution Contingency Plan (40 CFR 300), which indicated that the original HRS would be "used to assess the relative threat associated with actual or potential releases of hazardous substances at sites" (Appendix A, 40 CFR 300). Through the 1980s, dissatisfaction with the HRS, motivated in part by a desire to provide a more accurate representation of relative risks, particularly at large coal and other mining facilities, led to the push for modifications of the HRS. The requirement for modifications was included in the Superfund Amendments and Reauthorization Act (SARA) of 1986 which instructed EPA to amend the HRS to ensure, "to the maximum extent feasible, that the hazard ranking system accurately assesses the relative degree of risk to human health and the environment" (SARA, 1986, Section 105(C)(1)). It is noted in SARA that, given the need for expeditious site identification, the revised HRS is not required to be equivalent to a detailed risk assessment, but rather should be as accurate as possible using the screening level information usually available at the preliminary assessment (PA) and site inspection (SI) phases of the Superfund process. Further requirements of the mandated revisions included the need to consider potential and observed air contamination; effects through the human food chain; and better risk assessments for large-volume wastes, including the quantity, toxicity, and concentration of wastes and their potential for release to the environment. The target date given in 1986 for SARA-mandated revisions was October 1988; however, final promulgation of the revised HRS did not occur until December 1990 (Federal Register, 1990).
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Ranking Hazardous-Waste Sites for Remedial Action ROLE OF THE HRS IN THE SUPERFUND PROGRAM The primary function of the HRS is to serve as the screening mechanism for determining which candidate sites are included on the Superfund NPL. The major steps in this process are summarized in Figure 4-1. A site where hazardous-waste problems are known or suspected is first placed on the CERCLA Information System (CERCLIS), which is the master list of hazardous-waste sites in the United States. A PA and SI are conducted to provide a screening evaluation of the site and to gather the necessary information for scoring the site with the HRS. The sites are scored under the auspices of a regional EPA office by designated contractors or state agencies and submitted to that office for review. The site is proposed for placement on the NPL if the final HRS score is greater than or equal to 28.50; if the score is below 28.50, the site is designated as "no further remediation action planned (NFRAP)" under the federal Superfund program. The selection of the 28.50 cutoff score was initially made in 1982; it was chosen to meet the CERCLA mandate (CERCLA, Section 105(8)(B)) that at least 400 of the approximately 700 CERCLIS sites first scored at that time would be included on the NPL. The cutoff number thus had no apparent significance in terms of an absolute level of environmental or human health risk. Sites proposed for the NPL as a result of their HRS score undergo a period of public comment, after which the final decision for inclusion on the NPL is made by EPA. Through February 1991, only 79 sites had been proposed but rejected for inclusion on the NPL, in most cases because their revised HRS score was below 28.50 or because the site was reclassified as a Resource Conservation and Recovery Act (RCRA) facility (EPA, 1991a). Other mechanisms are also available for placement of a site on the NPL. States are each allowed to nominate one high priority site irrespective of its HRS score. As of 1992,
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Ranking Hazardous-Waste Sites for Remedial Action FIGURE 4-1 The Superfund process and the role of the Hazard Ranking System
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Ranking Hazardous-Waste Sites for Remedial Action approximately two-thirds of the states had proposed sites in this manner (EPA, 1991b). In addition, a site can be placed on the NPL as a result of a health advisory from the Agency for Toxic Substances Disease Registry (ATSDR). Five sites have been proposed through this mechanism. With more than 1,200 sites now on the NPL, the HRS score has been the principal mechanism for determining whether candidate sites are nominated and included. This score thus serves a critical role in determining the priority and level of attention that a site will receive in the EPA Superfund program. The steps shown in Figure 4-1 provide an idealized and highly simplified representation of the Superfund site-selection process and the role that the HRS plays in it. In actual practice, the process is more involved, as summarized in Figure 4-2. As shown near the bottom of the diagram, the HRS scoring must undergo review by EPA headquarters and a quality-assurance (QA) review by a contractor before the decision for nomination to the NPL. Furthermore, simplified screening versions of the HRS have evolved to allow sites to be prescored following the preliminary assessment (PA). The PA method is based upon the full HRS, but uses conservative default values for factors that are still unknown at the conclusion of the preliminary assessment phase of the analysis (EPA, 1991c). The PA method is designed to result in a score that is at least as high as the subsequent HRS score, and can therefore serve as a screening mechanism. The intent is to avoid, where possible, the expenditure of time and resources on sites where the potential for eventual inclusion on the NPL is low or nonexistent. The development of screening steps designed to eliminate false positives along the site-selection process has been largely motivated by the difficulties EPA has encountered in attempting to process the large number of CERCLIS sites under consideration for the NPL. As discussed later in this chapter, management considerations of this type, rather than environmental evaluation, have often been the driving factors in the evolution
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Ranking Hazardous-Waste Sites for Remedial Action FIGURE 4-2 More detailed steps in the HRS scoring process and National Priorities List development. Source: OTA, 1989.
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Ranking Hazardous-Waste Sites for Remedial Action of the Superfund site-selection process and have subsequently affected the role of the HRS in this process. In addition to its formal role in the NPL selection process, the HRS model has been used by others for various purposes. Some states use the HRS score to set priorities for sites under their jurisdiction that do not qualify for the NPL. Many states implemented their own site-scoring systems, which were often similar to the original HRS model. The HRS score is used by EPA regional offices as a starting point in their subsequent remedial investigation and feasibility study (RI/FS) priority process, discussed later in this chapter. A positive correlation between the HRS score and the pace of subsequent Superfund actions has been found by Hird (1990). Finally, the HRS score has been proposed as a general mechanism for quantifying risks from hazardous-waste sites and measuring the risk reduction achieved in subsequent remediation (Wilson, 1991; Butler and Jones, 1992). MODEL STRUCTURE AND COMPONENTS The HRS is a structured-value model in which various characteristics of the site, wastes, and surrounding environment are combined through use of a numerical algorithm to compute an overall score. As part of the calculations, separate scores are computed for each of four exposure pathways: groundwater migration pathway (Sgw); surface water migration pathway (Ssw); soil exposure pathway (Ss); and air migration pathway (Sa). The overall score is determined as the root mean square average of the four pathway scores:
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Ranking Hazardous-Waste Sites for Remedial Action That score and each of the individual pathway scores range from 0 to 100, with higher scores reflecting higher degrees of threat. A schematic summary of the major components and calculations of the revised HRS model is presented in Figure 4-3. The algorithm is structured to include the effect of three factor categories: likelihood of release or exposure; characteristics of the wastes present at the site; and characteristics of the target population or environment. The score for each pathway is calculated as the product of its three factor category scores. The likelihood of release is determined based on the presence of an observed or potential release. Observed releases are verified with site monitoring data. The potential for release depends on pathway characteristics that either restrict or promote transport at or near the site. The waste characteristics are chemical-specific and are intended to represent the properties of the chemical that indicate the likelihood of exposure and potential health hazard. The waste characteristics considered across all pathways include the toxicity, persistence or mobility, and hazardous-waste quantity. The bioaccumulation potential is considered in the surface water migration pathway for human food chain and environmental impacts. The environmental and human health targets considered in the HRS vary across pathways. The groundwater migration pathway includes water supply wells, groundwater resources, and wellhead protection areas. The surface water migration pathway considers drinking water intakes, human food chain impacts, and sensitive environments. Calculations for the soil exposure pathway include potential health impacts to residents and workers on-site and
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Ranking Hazardous-Waste Sites for Remedial Action
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Ranking Hazardous-Waste Sites for Remedial Action industry (Zaragoza, 1990). To support the evaluation, EPA compared original and revised HRS scores at 110 test sites (Zaragoza, 1990). The revised HRS scores tended to be somewhat lower, with fewer of the 110 sites scoring above the 28.5 threshold with the revised model (see Figure 4-4). However, based on a qualitative assessment of risks at selected sites (and given the administrative and legal difficulties that could result from a change in the threshold value), EPA did not feel there was sufficient cause to lower the threshold value to maintain a risk equivalency. The 28.5 threshold for inclusion on the NPL was thus maintained. FIGURE 4-4 Scatter plot of site scores for the original and revised HRS. Results were obtained from an EPA study to evaluate the 28.5 cutoff. Source: Wells et al., 1990). Reprinted with permission; copyright 1990, Hazardous Materials Control Research Institute, Rockville, Md.
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Ranking Hazardous-Waste Sites for Remedial Action PRIORITY SETTING AT LATER STAGES OF SUPERFUND A backlog of unremediated sites developed as a result of the unexpectedly large number of sites listed on the NPL as well as the significant time and effort required to complete detailed site studies and reach agreement on appropriate plans for remedial action. Such a backlog dictated that EPA develop procedures for priority-setting activities in the later stages of the Superfund process. These procedures include the regional remedial investigation (RI) and feasibility study (FS) priority-setting process and the remedial action (RA) priority-setting process. These processes are not mandated by law and are considerably simpler and less formal than the HRS. However, they do affect the priority assigned to different Superfund sites for remediation and thus need to be considered in this review of alternative priority-setting methods. The regional RI/FS priority-setting process is not a formal model, but rather a systematic procedure that individual EPA regions must establish to determine priorities for RI/FS projects. The process is applicable to sites and individual operating units and is based on a "worst-first" principle that allocates resources so as to have the "greatest impact on human health and the environment." (EPA, 1990c). The method is applicable only to sites where the costs of the RI/FS could be covered by the Superfund budget; sites where no Superfund dollars are spent, such as federal facility activities or state-initiated enforcements, are exempt from the policy. In addition, other management considerations can be evoked by the regional office to override the evaluation of priority level, including enforcement considerations such as the presence of a willing and financially viable potentially responsible party, or the desire to push forward in-house projects for training, operating unit projects needed for site completion, or projects for sites with multiple, interdependent operating units. State involvement in the priority-setting process is also encouraged.
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Ranking Hazardous-Waste Sites for Remedial Action To implement the worst-first principle, regions are directed to use the HRS package as a starting point and to consider additional information using "standard environmental criteria." These criteria, also used to determine remedial action priorities, include: the risk of contaminants (nature of principal threats), the stability of contaminants, whether human populations are exposed, and threats to significant environments. The result of the priority-setting process is to classify projects which are candidates for RI/FS into three tiers: highest, next-highest, and relatively low priority. The RA priority-setting process is somewhat more formal, but stir quite simple compared with the HRS. Regions determine scores for the standard environmental criteria and for program management considerations, based on questionnaires and a panel review. The scores are combined in a structured-value model, using the weights shown in Table 4-2. Based on this result, remedial action starts are classified into three categories: Priority 1: Immediate or imminent threat. Priority 2: Threat from current situation. Priority 3: Threat from future situation. The RA priority-setting process incorporates aggregate, subjective evaluations, but it is simple and quite transparent, so that the reasons for a particular site receiving a given score are clear. This type of model is appropriate for an internal, administrative function, but lacks the formality and replicability of a priority-setting process required by law, such as the NPL selection process wherein the HRS is used. PROPOSALS FOR IMPROVING SUPERFUND SITE SELECTION AND PRIORITY SETTING Several suggestions for improving the Superfund site-selection
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Ranking Hazardous-Waste Sites for Remedial Action TABLE 4-2 Weights for Remedial Action Priority Setting Criteria Score Weight Maximum Score Risk of contaminants 1-5 × 5 25 Stability 1-5 × 5 25 Population exposed 1-5 × 4 20 Significant environment 1-5 × 3 15 Program management 1-5 × 3 15 100 Source: D. Evans, EPA, unpublished data presented to the committee, April 10, 1991. process have been put forth in recent proposals by OTA and other sources. The OTA report, "Coming Clean, Superfund Problems Can Be Solved," (OTA, 1989), notes that many of the features of the site-selection process have been motivated by institutional management constraints rather than environmental or cost-benefit considerations for society as a whole. As mentioned previously, the initial selection of the HRS cutoff value of 28.5 was not based on any inherent environmental-risk threshold or cost-benefit trade-off, but rather the desire at the start of the program to allow an administratively manageable number of sites onto the NPL. The number of sites on the NPL has since grown considerably; however, the HRS cutoff of 28.5 has remained, reflecting the reality that regulatory criteria, once in place, are difficult to change. Motivated largely by the criticism it received through the early years of Superfund, EPA has modified the Superfund process to encourage quicker progress along the path towards final remediation and closure. The need to demonstrate better administrative progress and control, mandated in part by SARA, has also provided a motivation for EPA to limit the number of sites in the selection pipeline. Fewer sites entering the NPL allow for a better record of progress on those sites that do enter. OTA believes that
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Ranking Hazardous-Waste Sites for Remedial Action this motivation has discouraged EPA from undertaking an active-site discovery program, which might lead to hundreds of thousands of sites being placed on CERCLIS, but would avoid future problems that otherwise would occur as these sites are discovered in a delayed and random manner, often by (unpleasant) surprise. Similarly, the motivation to demonstrate progress has encouraged EPA to implement the prescreening evaluations shown in Figure 4-2 (such as the PA method) to further trim the number of sites in the pipeline. Although these decisions are a logical result of the administrative pressures placed on EPA, they do not necessarily encourage environmentally sound decisions. In particular, the strong push to avoid false positives can potentially lead to an increase in the rate of false negatives. Two of the recommendations put forth by OTA to improve the administration of Superfund directly concern the use of the HRS in site selection. The first is to eliminate the 28.5 score as an exact threshold for inclusion on the NPL. Instead, two HRS scores, one higher and one lower, would be used to classify the candidate sites into three groups. Those above the high score would be selected for immediate inclusion on the NPL. Those below the low score would be deleted as NFRAP cases. Those with scores in the range between the low and high score would then be subject to further review by an expert panel with authority to make the final recommendation for NPL nomination. This procedure would help to eliminate both false positives and false negatives, by allowing more careful evaluation of those sites where selection errors are most likely to occur. The second OTA recommendation is to combine the PA and SI and RI/FS phase of the Superfund process into a single site-evaluation step, which would then be followed by the HRS scoring. This recommendation, intended to streamline and expedite the overall process, would provide a higher level of site information for use in the HRS scoring. Indeed, as discussed above, many think that the increased data needs of the revised HRS now require information beyond the typical PA and SI effort.
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Ranking Hazardous-Waste Sites for Remedial Action Additional proposals to reform the Superfund process have appeared recently in studies by the MIT Center for Technology, Policy and Industrial Development (MIT, 1992) and by Putnam, Hayes, & Bartlett, Inc. (Butler and Jones, 1992) for the Coalition on Superfund. The MIT study recommends the development of special assessment and remediation procedures for sites with common characteristics, such as landfills, and earlier categorization of sites into immediate action versus no-action but monitor pathways. The Putnam, Hayes, & Bartlett study goes further, and specifically recommends setting priorities for individual actions across sites, rather than setting priorities for the sites themselves, and the identification of early actions that might be taken at sites to significantly reduce risk, even before the NPL decision is made (Butler and Jones, 1992). Both studies recommend that the HRS should be rescored as remediation actions are implemented and that, as warranted, the rescored sites should be deleted from the NPL. The Putnam, Hayes, & Bartlett study specifically recommends that predicted reductions in HRS scores associated with alternative remedial actions be used to assign priority to these actions (Butler and Jones, 1992). This use of HRS score differences to reflect risk reduction benefits runs counter to the committee's scientific assessment that the HRS scores can only be used to reflect ordinal differences in sites, and not cardinal or continuous differences in absolute risks. EPA has recently responded to the recommendations discussed above as well as others by considering new approaches, such as the Superfund Accelerated Cleanup Model (Inside E.P.A., 1992). That plan would combine the site-screening and risk-assessment studies for the preremedial, removal, and remedial phases into a single study. This change would allow elimination of the distinction between EPA's early removal and long-term remedial programs and encourage expedited progress through the Superfund time frame. Whatever the outcome of this particular proposal, it is likely that further efforts will be made to compress the Superfund timeline. Those efforts, consistent with recommendations of
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Ranking Hazardous-Waste Sites for Remedial Action the OTA and others recommendations, suggest that more data could be available when the HRS scoring is performed. Again, the issue arises of whether a structured-value model such as HRS should be used, in contrast to a formal risk assessment, when these additional data are available. However this issue is resolved, current statutory requirements make it probable that the HRS will remain a key part of the EPA priority-setting process for NPL selection. SUMMARY EVALUATION OF EPA PRIORITY SETTING FOR HAZARDOUS-WASTE SITES To provide a summary evaluation of the EPA priority-setting process, the evaluation criteria identified in Chapter 2 are examined with the primary focus upon the current (revised) version of the HRS model. General Issues in HRS Model Development and Application Clearly Defined Purpose: The HRS model has a well-defined purpose within the Superfund process—site selection for the NPL—and a specified user population made up of those responsible for site scoring. The priority-setting processes for the later stages of Superfund are similarly well defined. Credibilities and Acceptability: Although certain technical limitations to the HRS model have been identified by the committee and others, including particular aspects of the likelihood of release or exposure category for certain pathways, and questions on the handling of the toxicity component of the waste characteristic category, the committee finds that, in general, the HRS
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Ranking Hazardous-Waste Sites for Remedial Action model is (within the context of a structured-value model) generally consistent with accepted scientific understanding and knowledge of the environment. Extensive scientific peer review, public participation, and public comment have been included as part of the model development process. Appropriate Logic and Implementation of Mathematics: The HRS model includes a combination of additive and multiplicative calculations to obtain pathway and total site scores from the individual factor scores. The calculation of pathway scores as the product of the contaminant release (or exposure), chemical characteristics, and target receptor category scores is patterned according to the multiplicative model for risk. However, the often ad hoc procedures for determining the factor and category scores, and the chemical and site factors that combine source, transport, and exposure-toxicity into single measures, make it difficult to interpret the resulting HRS score in any absolute sense. This problem, endemic to structured-value models, precludes the use of the FIRS for evaluating risk-reduction benefits obtained from a proposed or completed remedial activity. Model Documentation: The documentation for the HRS model is generally adequate, though little guidance has been provided to ensure consistent sampling and collection of input data. This need is being addressed in the HRS guidance document being developed by EPA. Model Validation: The HRS model has been compared in a number of studies with more detailed site assessments based on risk analysis or expert panels. The degree of correlation with these other estimates has generally been low to modest. Model Sensitivity and Uncertainty Analysis: A number of studies have been conducted by EPA and others to evaluate the sensitivity of the model to various factors and factor categories. In practice, the scoring outcome is quite sensitive to the overall effort exerted in data collection at the site, with a potential for manipulation of this effort by interested parties.
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Ranking Hazardous-Waste Sites for Remedial Action Specific HRS Technical Features Applicability to All Waste Sites: The HRS model is broadly applicable to the range of hazardous-waste sites encountered. Allowance for Dynamic Tracking: Proposals have been made to use the HRS model at various stages of the Superfund process to set priorities and track alternative remedial actions. While this could provide a useful administrative tool, such use is not consistent with the ordinal (non-absolute) nature of the HRS normalized score. Discrimination between Immediate- and Long-Term Risk: The model is intended for long-term risk (greater than 20 years), because immediate threats have been addressed by EPA prior to the NPL-listing decision. The recent EPA plan to remove the sharp division between immediate response and long-term remediation, if implemented, would dictate the need to reintroduce immediate threats to the HRS model. Inclusion of Cost Estimates of Remediation: The HRS model does not consider costs or timing issues associated with remediation. These issues are considered in the priority-setting procedures for later stages of Superfund. Transparency: The original HRS model was relatively transparent, but the recent revisions have made the model significantly more difficult to understand. The effective weights for human health versus ecological impacts are difficult to assess. User-Friendliness: The model is presented in a straightforward manner that should be relatively easy to follow for regular site scorers. However, the revised HRS is too complex for routine use by lay citizens. The committee is unaware of any interactive computer implementation of the HRS. Appropriate Security: The hard-copy format for HRS Scoring and the quality-assurance checks provided by EPA and a contractor limit the potential for security problems.
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Ranking Hazardous-Waste Sites for Remedial Action The HRS model has been described as providing a consistent, expedient format for site-scoring and site-setting priorities consistent with legislative mandate (Wu and Hilger, 1984). However, some of the particular features of the model are subject to challenge, and the overall appropriateness of a structured-value approach is questioned, given the availability of risk- assessment procedures. This question might continue to be raised as more detailed site study and evaluation procedures are performed earlier in the Superfund process. To the extent that EPA remains committed to an early decision for inclusion on the NPL, the HRS model may remain the best alternative available. Modifications to allow for more detailed review of sites with intermediate scores could, however, help to reduce the number of false positive and false negative decisions. Subsequent EPA Priority-Setting Process The HRS represents a critical, first step for remediation priority setting: deciding which sites to place on the National Priority list. Sites that are placed on this list then are subject to subsequent priority setting to determine which ones to investigate first through the Remedial Action/Feasibility Study (RI/FS) process, following which sites are selected for remedial action (RA). The steps in these priority-setting processes are well defined and open to public comment and scrutiny, though the selections themselves are generally not open to outside review. The RA process is somewhat formal and involves a structured-value model with weighted consideration of the risk of contaminants, stability, population exposed, significant environments, and program management. The process is well defined, relatively simple, and transparent. It is consistent with an administrative program which is not mandated by law, but still needed to ensure effective management of the Superfund program.
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Representative terms from entire chapter: