Ranking Hazardous-Waste Sites for Remedial Action (1994) / Chapter Skim
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8 COMPARING FEDERAL RANKING MODELS
8 COMPARING FEDERAL RANKING MODELS
Pages 225-250
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From page 225... ...
The committee re viewed these processes, specifi cally in an attempt to uncler stand where each agency's model fits into their overall priority setting process. Much less writ ten information was available to the committee about the overall prioritization processes them selves than about the ranking models used in the processes.
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From page 226... ...
EPA is requires! by fecleral law to be responsible for aban cloned and active hazardous waste sites, unclergrounc3 storage tanks, a variety of other hazardous waste programs, and the inte "ration of environmental laws, such as the Resource Conservation and Recovery Act (RCRA)
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From page 227... ...
EPA directly to the development of a relatively simple mathematical screening model, the Hazard Ranking System (HRS) , which is user!
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From page 228... ...
resources to devel op a priority setting method that requires extensive data gathering collection at every step in the process for its most hazardous sites. Because each site may contain mixtures of extremely toxic and radioactive as well as other types of wastes, DOE needs much in formation to make sounc!
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From page 229... ...
EPA must contend with all of the diverse interest groups when it makes decisions. For many of the major sites, DOD and DOE have signed legal contracts with the states and EPA that mandate specific targets for cleanup of these selected sites.
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From page 230... ...
concerned citizens in their decision making process, but their mandate to consult with other interested parties is not nearly as strong as it is for EPA. COMPARATIVE SCORING EXERCISE OF FEDERAL RANKING MODELS Objective ant!
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From page 231... ...
to produce similar relative rankings when applied to the same set of hazardous waste sitesthat is, to give the same indication of which sites produce the higher health risk. Each agency was provider!
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From page 232... ...
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From page 233... ...
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From page 235... ...
, and DOE's Multimedia Environmental Pollutant Assessment System (MEPAS) Pathway Air vegetation HRS DPM MEPAS No No Yes Soil vegetation No -- a Yes Water aquatic biota Yes Yes Terrestrial animals No Yes Air water No Yes Yes Water air No Yes Yes Air soil Yes Yes Yes Water sediment No No Yes Sediment water No No Yes Soil water Yes Yes Yes Soil groundwater Yes Yes Yes Groundwater soil No No Yes Groundwater surface water `!
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From page 236... ...
largely undocumented. A vertical trench cirain located on one corner of the site was used from 1969 to 1978 to dispose of approximately 29,000 gallons of liquid hazard ous waste, including various organics, waste oil, diesel fuel, hero sene, and fluids containing polychlorinated biphenyls (PCBs)
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From page 237... ...
The drums contain inorganic and organic waste sludge that was collected from a re tension basin and holding pond. The outside of the strums show signs of internal corrosion.
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From page 238... ...
Next to the waste pits (no longer in use) is a burn pit that was used for disposal of chemicals and other combustible waste.
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From page 239... ...
to visual comparison of the outputs. TABLE 8 3 Results from Scoring Five Sites Using DOD's Defense Priority Model (DPM)
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From page 240... ...
The three moclels clo not agree as to which site of the five poses the highest hazard. ("Hazard" is a generic term for all three models; "hazard level" corresponds to the magni tulle of the site scores that are used for screening, priority setting for cleanup, or inclusion on the NPL)
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From page 241... ...
, and DOE's Multimedia Environmental Pollutant Assessment System (MEPAS) a Site's Hazard level DPM HRS MEPAS Very high High Moderate~high Moderate medium 2, 5 Moderate low Low Very low ,, ,, b ,, 1 ,, 3 4 ,, 1, 2, 5 i, 3 3,4,5 4 Numbers refer to site identification.
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From page 242... ...
Since the general site ranking protocol embedclecl in each moclel is basically the same, as noted in the separate chapters on each mod el, this congruent behavior is to be expectecl. Although there is congruence of the DPM and MEPAS scores, MEPAS uses cle tailed transport and fate algorithms while DPM and HRS use a simpler structureclvalue approach to model transport and fate elements in arriving at scores.
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From page 243... ...
Conversely, DPM relies heavily on observed con centrations of contaminants in the air, surface water, groundwa ter, or soil near the waste site to be scored. If no sampling has been clone at the site, DPM assumes a worst case approach by as suming all chemicals in the inventory have contaminated the grounc~water and surface water pathways, but not for the pathways of atmospheric transport.
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From page 244... ...
site ~ The DPM and MEPAS evaluations of Site 1 cliffer in that MEPAS identifies the atmospheric transport pathway as the path way producing the highest risk, whereas DPM identifies the groundwater pathway as the pathway contributing most to the site score, followed closely by the atmospheric pathway. The high groundwater score of DPM can be attributed to the fact that DPM iclentifiec3 and scored the site using groundwater contaminants that were not iclentifiec3 in the MEPAS source term.
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From page 245... ...
DPM consid ers grounc~water recharge of surface water in the groundwater pathway rather than in the surface water pathway. Neither model run identified the surface water pathway as a significant contribu tor to the overall site risk.
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From page 246... ...
this site using sampling data that iclentifiect potentially hazardous contaminants that were not iden tiffed by the users of MEPAS as part of the contaminant inven tory. This discrepancy explains why the surface water pathway was more significant in the DPM scoring than in the MEPAS scoring.
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From page 247... ...
Despite this similarity, the moclels differ in the proportion of risk attributed to each contaminant transport pathway. The DPM score is driven by the grounc~water pathway, whereas MEPAS identifies low but roughly equal risks from both the grounc~water and atmospheric pathways.
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From page 248... ...
MEPAS iclentifiect the surface water pathway as the pathway contributing the highest risk, whereas the DPM iden tiffed the grounc~water pathway as the primary contributor to the overall site score. HRS scored the grounc~water pathway low since sampling data did not indicate that contaminants had actually reached the target and no large drinking water supply well was near the site.
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From page 249... ...
use of ciata to weight different environmental transport pathways also reacts to a discrepancy in the differences in site scores. Even when relatively consistent site scores are proclucect, the dominant risk producing contaminants and transport pathways usually differ between models.
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From page 250... ...
RANKING HAZARDOUS WASTE SITES jective criteria for these comparisons, however, are needled both in a relative sense (comparing one site with another)
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