Ranking Hazardous-Waste Sites for Remedial Action (1994) / Chapter Skim
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4 EPA'S PRIORITY SETTING
4 EPA'S PRIORITY SETTING
Pages 85-134
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From page 85... ...
with it, the authority to identify the most serious abandoned hazardous waste sites for attention under the feet eral Superfuncl program. As part of this authority, EPA must determine criteria for inclusion on the National Priorities List (NPL)
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From page 86... ...
with implementa lion 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 Envi ronmental Response, Compensation, and Liability Act (CERCLA)
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From page 87... ...
CERCLA Ji] require EPA to establish "criteria for determining priorities among releases or threatened releases [of hazardous substances]
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From page 88... ...
air contamination; effects through the human food chain; and better risk assessments for large volume wastes, inclucI ing 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 clict not occur until Decem her 1990 (Federal Register, 1990~.
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From page 89... ...
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 macle by EPA. Through February 1991, only 79 sites hac]
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From page 91... ...
With more than 1,200 sites now on the NPL the HRS score has been the principal mechanism for determining whether candiciate sites are nominated and incluclect. 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.
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From page 92... ...
= same as H a = initial HRS score ~ 25.0 b = QA initial score c28.5 c = region adjusted score 28.5 d = proposed score ~ 28.5 e = final score >28.5 | Back to region for more/better | | data; HRS score adjusted I t 1 t I HRS a HQ Review/ Proposed Scoring ~ Contractor d for NPL NFRAP Other Final NPL Programs Site NFRAP {no further remedial action planned) = sites with no reasonable potential to score above 28.50.
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From page 93... ...
AS part of the calculations, separate scores are computed for each of four exposure pathways: · grounc~water migration pathway (Sg`,) ; · surface water migration pathway (Ssw)
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From page 94... ...
The surface water migration pathway considers drinking water intakes, human foot! chain impacts, ant!
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From page 96... ...
oo It ~ s <~' JO x o 3 ~ J ~, o ~ C W o ' ~Z .
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From page 100... ...
Previous reviews have been macIe for the original HRS (e.g., Wu and Hilger, 1984~; some of their comments have been acictressed in the recent revisions, others remain pertinent. Likelihood of Release Component The likelihood of release component accounts for observed re leases and the potential for a contaminant to be released.
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From page 101... ...
travel time for contaminated grounc3wa ter to discharge to the surface water. For the soil exposure path way, only observed contamination is considered.
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From page 102... ...
The toxicity factor for the hazardous substance and the hazardous waste quantity are common to all the pathways, except for the surface water pathway, which treats ecosystem toxicity sep arately. The persistence and mobility factors are pathway specific and are consiclerec3 in the more cletailec!
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From page 103... ...
This coulc! be corrected by selecting the hazardous substance used to represent each pathway to be the one yielding the greatest waste characteristic score, rather than the substance with the highest toxicity or combined factor value.
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From page 104... ...
The product of the toxicity factor and the hazardous waste quantity factor, which is a "hazard scaled" mass of the substance or waste present, is assignee! a second scaling factor according to the logo of the product.
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From page 105... ...
from regula tory limit concentrations anct screening concentrations. Chemical properties such as mobility and persistence are considered w~th toxicity to clescribe the waste characteristics.
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From page 106... ...
The equivalent cancer risk for a noncarcinogen at the RfD is thus near Iy four orciers of magnitude lower in the targets factor category than in the Waste Characteristics factor category (1 x lob vs.
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From page 107... ...
This results in assigned toxicity factor values of 100 and 1000, respectively, showing Cct to be worse than CN. At this close, CN iS at 0.2 times its ED50 ant!
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From page 108... ...
The lack of separate subscores indicative of chemical toxicity and of exposure likelihood and magnitude makes it difficult to assess how the HRS conceptually compares to a quantitative risk assessment. Groundwater Pathway A grounc~water migration pathway subscore is calculates!
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From page 109... ...
Although one might argue that it is sufficient for the present purpose to use net precipitation without accounting for runoff, such detail is inclucled in other parts of the calculations. Specifi cally, soil hydrological groups and rainfall runoff values are used in Section 4.~.2.~.2.~.2 of the final HRS rule for the surface water component of the scoring.
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From page 110... ...
Thus, it is inap propriate to adjust the grounc~water mobility factor values clown ward from ~ for liquic! wastes when the Kit value is >10 mVg.
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From page 111... ...
plain, would be consistent with similar distributions as signed elsewhere in the procedure. Persistence factor values for substances in surface water are determined as the greater of the values determined either by the half life or the logarithm of the
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From page 112... ...
Because exposure is assumed to occur when individuals visit the site, there are no considerations of fate and mobility contributing to the soil pathway score. Air Pathway The air migration pathway score is based on the exposure of ~2
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From page 113... ...
in the scoring twice for substances with lower vapor pressures. The maps pro viclecl to determine the particulate migration potential factor vat ues anti the particulate mobility factor values are different from each other and also cliffer from maps delineating areas of actual (Plaster, 1985)
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From page 114... ...
Double counting for factors influ encing mobility is evident in the grounc~water and air migration pathways. Since the score is based on just one substance for each pathway, it is critical that the most appropriate substance be se lectecl.
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From page 115... ...
A range of sensitive environments is considered for the air pathway, with special em phasis on large wetland areas. An important issue in unclerstanding and comparing the stiffer ent priority setting and ranking moclels for hazardous waste sites is the relative weights applier!
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From page 116... ...
in Chapter 9, the com mittee believes that it would be clesirable for a national model to have adjustable value weights to reflect local preferences, perhaps on a state by state basis. Socioeconomic Factors in the HRS Potential economic benefits from remediating hazardous waste sites include reduction of community damage, appreciation of property, increased productivity of lancI, creation of jobs, ant!
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From page 117... ...
The environmental resource targets (in adclition to sensitive environments) include commercial farming, food preparation, recreational areas, and drinking water supplies.
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From page 118... ...
Additional issues in model development and use include the level of field testing and peer and public review of the moclel prior to its release for general use, the clegree of user friendliness, its transparency, and the quality of the documentation that guicles the ciata collection and scoring steps. In the development of the original and the revised HRS model, EPA, in conjunction with the MITRE Corporation, undertook extensive field testing programs (Chang et al., 1981; Caldwell and Ortiz, 1989; Zaragoza, 1990~.
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From page 119... ...
Many site evaluators will collect the data necessary to push the HRS score above 28.5, then stop. Once the score passes this threshold, the site will be on the NPE, ant!
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From page 120... ...
studies provide the only cur rent comparisons of HRS scores to more detailed site hazard esti mates, and based on these more objective and rigorous measures of risk and threat, it is likely that the FIRS floes yield a significant number of false positives (sites includes! on the NPL that shoulc!
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From page 121... ...
scores being significantly different (higher) at many sites from the HRS scores ultimately determined with PA ant!
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From page 122... ...
outside the long term scope of the NPL process. Ac3ctitions to the model includes} · a new exposure pathway for contact with contaminated soils; · consideration of chronic noncarcinogenic toxicity; · expansion of the ecological components of the model, allow ing for consideration of a wicker range of sensitive environments; · consideration of the potential for air emissions; · a groundwater to surface water migration pathway; · use of concentration data in determining waste quantity; and · higher weights for actual exposure and for potential exposure closer to the site.
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From page 123... ...
complexity of the re vised HRS might diminish as regular EPA scorers gain experience with the model, it is apparent that the model is now less accessible to other users than was previously the case. A related concern with the revised HRS is that the im provements in the coverage ant!
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From page 124... ...
~ Ail, ~ if, 54 Site ove 2 .5 i . _ I 72 Sites Above 13 5 20 40 60 Original HRS Score FIGURE 4-4 Scatter plot of site scores for the original and revised HRS.
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From page 125... ...
and feasibility study (FS) priority setting process and the remedial action (RA)
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From page 126... ...
The RA priority setting process is somewhat more formal, but still 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.
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Motivated largely by the criticism it received through the early years of Superfund, EPA has modified the Superfuncl process to encourage quicker progress along the path towards final remectia lion ant! closure.
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IncleecI, as cliscussec! above, many think that the increased data neecis of the revised HRS now re quire information beyond the typical PA and S} effort.
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From page 129... ...
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 user! to re fleet ordinal differences in sites, and not cardinal or continuous differences in absolute risks.
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From page 130... ...
Application Clearly Defined Purpose The HRS model has a well defined purpose within the Superfund process site selection for the NPWanc3 a specified user population made up of those responsi ble for site scoring. The priority setting processes for the later stages of SuperfuncI are similarly well clefinect.
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From page 131... ...
However, the often ad hoc procedures for determining the factor anct category scores, and the chemical and site factors that combine source, transport, ant! exposure toxicity into single measures, make it difficult to inter pret the resulting HRS score in any absolute sense.
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From page 132... ...
However, the revised HRS is too complex for routine use by lay citizens. The committee is unaware of any interactive com puter implementation of the HRS.
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From page 133... ...
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 selectee!
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