Ranking Hazardous-Waste Sites for Remedial Action (1994) / Chapter Skim
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5 DOD'S PRIORITY SETTING
5 DOD'S PRIORITY SETTING
Pages 135-176
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From page 135... ...
The DPM is a mathematical algo rithm or modes uses! to compute a nut merical score from 0 to 100 that repre sents the relative potential threat to human health and the environment posed by a contaminated site.
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From page 136... ...
groundwater pathways (e.g., by including floodwa ter transport, depth to grounc~water, ant! infiltration potentials; to improve the use of toxicity information to specifically address the relative potency of each significant contaminant; and to obtain better separation of scores by using a root mean square algorithm.
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From page 137... ...
The overall scoring methoc! of the DPM is based on a set of product algorithms that account for the exposure pathway, contaminant hazard, and receptors (human, animal, or plant)
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From page 138... ...
DOD's approach to priority setting. Source: Adapted from DOD, 199ib.
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From page 139... ...
5 2b and Table 5 1. The final normalized DPM score represents the relative potential threat that a contaminated site poses to human health and the environment.
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T o In o ~ {D 3 ._ ~ 1" 1 1 At, I I O In _ ._ ~ s an O 3 2 C of, l ~ O ,~ 3 cn ~ 1 C]
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From page 142... ...
RANKING HAZARDOUS WASTE SITES TABLE 5-1 Combining scores in the DPM Surface water = Surface human health water pathscore way score Surface water = Surface ecological water path score way score Groundwater human health score x Surface water x Surface water /10,000 human health human recephazard score tor score x Surface water x Surface water /10,000 ecological ecological re hazard score ceptor score = Groundwater x Groundwater x Groundwater /10,000 pathway human hearth human re score hazard score captor score Groundwater = Groundwater x Groundwater x Groundwater /10,000 ecological pathway ecological ecological re score score hazard score ceptor score Air/soil volatiles~ human health score Air/soil volatiles ecological score = = Air/soil vola- x Air/soil vola- x Air/soil vola- /10,000 tiles pathway tiles human tiles human score hearth hazard receptor score score Air/soil vola- x Air/soil vola- x Air/soil vola- /10,000 tiles pathway tiles ecolog- tiles ecologscore ical hazard ical receptor score score Air/soil dusts = Air/soil dust x Air/soil dust x Air/soil dust /10,000 human hearth pathway human hearth human re score score hazard score ceptor score Air/soil dusts eecological score = Air/soil dust x Air/soil dust x Air/soil dust /10,000 pathway ecological ecological re score hazard score ceptor score iThe higher of these two scores is used in the final computation. 2The higher of these two scores is used in the final computation.
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From page 143... ...
In Ski cd o v, ~ a cd a Cal ·C)
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From page 144... ...
.~= go u)
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In Id en Id cd 3 Cal ~U)
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From page 146... ...
Thus, for the surface water ant! groundwater pathways, the algorithm floes not consider the magnitude of the pollutant release rates or concentrations at the receptor site in arriving at the pathway scores.
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From page 147... ...
The pathway algorithm uses a summation formula, whereas theory suggests that a multiplicative formula or summation on a logarithmic scale would be the preferable approach for scoring the pathway poten tial. The DPM makes use of pathway algorithms that attempt to qualitatively capture the depenclence of the contaminant concen "ration, at a given distance from the source, on various physico chemical and transport parameters.
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From page 148... ...
The factors listed in Table 5 3 are used in the soil and air volatiles pathway algorithm. In the DPM, the following scoring algorithm is used: Score= [121`B' + 2T~ + 2R~8' + 2V~ + 2~` x [(We + Wq)
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From page 149... ...
Waste containment effectiveness factor | | [331 Waste quantity factor l 1~34, Air/soil volatiles pathway score = [31]
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From page 150... ...
on a simple treatment of transport phenomena fol lows. As a starting point, the development of a pathway potential model should focus on the probability of delivering a quantity of contaminated air (i.e., contaminant concentration)
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From page 151... ...
so that they are directly pro portional to the pathways factors. A summation algorithm could be devised by working in a logarithmic scale (such as taking the natural log of each sicle of the equation)
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From page 152... ...
This is especially important for aqueous waste containing sparingly wa ter soluble organics; Cs in the case of aqueous waste could be set to the interracial, liquid side concentration. This concentration is a function of the bulk chemical concentration in the aqueous phase, mass transfer coefficients for the liquid side ant!
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From page 153... ...
into the soil volatiles algorithm because it will negate, in part, the scoring for the grounc~water pathway. In summary, the above analysis demonstrates that use of a physical basis for the air soil volatiles pathway can leaf]
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score is assigned based on the values of hazard quotients defined as (1) the daily intake or acceptable daily intake of the contaminant or (2)
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involves a division of the total human daily intake by the HB. The measure of toxicity (the HB)
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From page 157... ...
However, because of their different BFs, the effect of the total human tinily intake for Zn is greatly magnified by the DPM relative to that of cyanide. The result is that the health hazard quotient is 32 for Zn ant!
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Ecotoxicological Concerns The current ecological scoring process emphasizes aquatic recep tors and is relatively unresponsive to broacler environmental threats to vegetation and terrestrial ecosystems. For ecotoxico logical concerns, the hazard scores for all but 45 chemicals are greater for human beings than for all other species.
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From page 159... ...
It is hard to hold the DPM developers wholly accountable for not considering the seven basic ecotoxicologic features (Neuholc!
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From page 160... ...
Obvi ously, provision of an alternative water supply only accounts for the consideration of human health risk and ignores needs for envi ronmental restoration. The lane!
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spe cies has been degracled by toxic releases appears to be of no conse quence to the scoring exercise. The restoration of the species, or even a reclucec!
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If the lane! were to be clecontaminatec3 and land use altered to civilian status, such as residential development, the ecological value of the area would be clegracled, so assigning a high ecological score to the site (and consequently a high priority for remecliation)
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, the DPM model ignores a key potential decision making variable: the value of lane! and exist ing structures if a site were remecliatecI.
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indicates that most of the population data were "estimated using personal knowledge of the scorer." Although the report notes! that it applied to a model earlier than Version 3.0 (DOD, 1990b)
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From page 165... ...
resiclents on those installations. SCORING METHODOLOGY AND AGGREGATION Overview The mathematical operations of the DPM are straightforwardly they involve substituting values into formulas ancI, in some cases following logical branching.
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From page 166... ...
Clear justification for various multipliers in scoring algorithms is not provident. Thus, it appears that the incliviclual pathway scores and their aggregation cannot be analyzes!
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From page 167... ...
as a result of the scoring or making a finer cletailec' ranking of the site scores. An appropriate validation study-comparing model results with what they should be-would involve perhaps 10 to 30 sites and the comparison of scores and rankings from the DPM with those from another approach, assumed a priori more likely to yield the right answer.
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From page 168... ...
SENSITIVITY AND UNCERTAINTY ANALYSES An important step in evaluating the performance and reliability of priority setting models is to determine through sensitivity and uncertainty analyses the magnitude of uncertainties in the moclel site scores and the implications of the uncertainties for site rank ing. Detailed sensitivity and uncertainty analyses are yet to be per formed on the direct model output (the DPM score)
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From page 169... ...
Highest-ranked site is Rocky Mountain Arsenal, which has a score of 64. Two sites, Riverbank Army Ammunition Plant E/P Ponds and Richards Gebaur Hazardous Waste Drum Storage Site 923, have a low DPM score of I
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From page 170... ...
subject to considerable variation. To implement the analysis, fifty simulations were performed by acicting random error values with the properly scaled variance to the T;Y 1991 DPM scores.
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Probability of inclusion among top-50 ranked sites as function of final Fiscal Year 1991 DPM score. Results based on 50 Monte Cario simulations.
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From page 172... ...
The uncertainty in site scores is shown to have a considerable impact on the composition of the top 50 list, although this impact is sensitive to the magnitude of the assumed site score uncertainty. The analysis demonstrates that the uncertainty in DPM scores could potentially limit the use of the model for setting priorities among sites for remectiation.
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From page 173... ...
it is not clear whether DOD addresses these issues through an evaluation process exter nal to the DPM. The DPM scoring scale is linear, anct results of DPM site scores reveal that the score intervals for the BY 1990 and BY 1991 sites are small.
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From page 174... ...
in DPM are fairly straightforward. However, the logic of the choices macle for particular operations and for combining quantities appears somewhat arbitrary.
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From page 175... ...
Specific DPM Technical Features Applicability to All Waste Sites: The DPM is broacily applica ble to essentially all DOD sites for which the model might be used. Allowance for Dynamic Tracking: The DPM has not been cle velopect as a tool for dynamic tracking.
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From page 176... ...
It is intentlecl only to provide a relative rank ing of sites based upon their relative threat to human health and the environment. The ranking provicled by DPM is to be used "along with adclitional risk information and other factors such as regulatory requirements and program efficiencies" to establish cleanup priorities among the DOD sites.
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