Hazardous Waste Site Management Water Quality Issues (1988) / Chapter Skim
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3. SOME APPROACHES TO SETTING CLEANUP GOALS AT HAZARDOUS WASTE SITES
3. SOME APPROACHES TO SETTING CLEANUP GOALS AT HAZARDOUS WASTE SITES
Pages 34-66
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From page 34... ...
As illustrated in Figure 3-1, human and nonhuman exposure to soil contaminants can occur through a variety of pathways. Also, because hazardous waste sites usually contain large numbers of toxic substances with a wide combined spectrum of adverse effects, cleanup standards must be sensitive to this multiple route/multiple agent exposure pattern.
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From page 35... ...
GROUND WATER +: WATER A A PLANT CROP ~ Ale A,; _ FOLIAGE _ ~ I'm ANIMAL .; ~` I WATER ~14~ , I HYDRO SOIL ' :FILTER/ BOTTOM FEEDER .,, ~ B -VAPOR)
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From page 36... ...
" at hazardous waste sites. The paper focuses on the general concepts that are used as well as on specific methods.
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From page 37... ...
Critical Toxicity Value This is a property of toxic substances that reflects the quantitative relationship between daily dose and magnitude of adverse effect of that substance. Three types of critical toxicity values are used: ~ Acceptable intake for subchronic exposure (AlS)
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From page 38... ...
. The projected human intake of a chemical averaged over a short period of time, expressed as mg/kg x day.
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From page 39... ...
= LTCx,y x human intake factory, where SDIX y and CDIX y are subchronic and chronic daily intakes of chemical X by route Y; STCx y and LTCx y are short- and long-term concentrations of chemical X in a medium associated with route of exposure Y; and the human intake factor of the medium is associated with route of exposure Y This is illustrated below for two routes and three media: SDIX,inha~ = STCX'air x human intake factorair, CDIX,inha~ = LTCX,air x human intake factorair, and SDIX,ora~ = STCX~wa~er x human intake factorwa~er + STCX,fi~h x human intake factoring.
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From page 40... ...
The value of lifetime risk is later used to determine cleanup levels for the site. Daily intake values for chronic and subchronic exposure, as well as carcinogenic risk, are calculated for specific exposure conditions and are therefore specific for each site.
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From page 41... ...
The total carcinogenic risk for multiple substances and multiple routes is: m n Cancer risk = ~ ~ CDIij x carcinogenic potency factorij. i=1 j=1 Only chronic, 70-year exposure duration conditions are used for calculating cancer risks.
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From page 42... ...
Step 4 requires knowledge of critical toxicity values such as acceptable intake for subchronic exposure (AlS) and carcinogenic potency factors.
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From page 43... ...
For chemicals with noncarcinogenic toxic effects, the target concentration is defined as that at which (1) chronic daily intake does not exceed the acceptable intake for chronic exposure for individual substances/routes; and/or (2)
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From page 44... ...
From human or animal toxicologic dose-response curves. The derivation of MELs from toxicologic dose-response curves follows a classic method of acceptable daily intake (ADI)
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From page 45... ...
uncertainty factor 45 where NOAEL is a no observed adverse eject level and body weight is 70 kg for an adult. The NOAEL can be derived either from human epidemiologic data, which are preferable but rarely available, or from animal laboratory data.
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From page 46... ...
= . x PF, intake factor where the intake factor is the average daily intake of the medium.
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From page 47... ...
Thus, n ~ AAt < 1. i=1 Multiple Agents with the Same Toxic Action/Multiple Media In this scenario, both the total dose from each medium (a sum of media-specific doses)
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From page 48... ...
(mg/kg x day) , is a dose of toxic substance, per kilogram of body weight, that is not expected to produce significant adverse health effects in a population upon chronic exposure.
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From page 49... ...
guidelines) to DTS requires application of daily intake factors (transfer factors)
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From page 50... ...
Derivation of Single-Pathway Prellm;nary Pollutant Limit Values SPPPLVs are calculated from DTS using the following formula: body weight SPPPLV (medium) = DT X transfer factor x K K is the partition coefficient or the product of intermedia partition coefficients between the medium from which an agent originated and that through which the actual human exposure occurs (for example, when a substance is deposited in the soil but human exposure occurs through ground water or through fish from contaminated surface water)
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From page 51... ...
It is also recommended that, for multiple sources of a particular pollutant, the cleanup level must meet the DT X body weight value. The document does not specify whether the cumulative DT X body weight value is calculated by addition or multiplication.
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From page 52... ...
For carcinogenic substances the healthbased acceptable daily intake is that which corresponds to an excess lifetime risk of 10-6. For noncarcinogens, it is equivalent to ADIs published in EPA water quality criteria documents.
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From page 53... ...
Determination of Cleanup Levels According to the methodology, site assessment is conducted in two steps. In Step 1, indicator compounds are selected on the basis of the total score, using the following formula: Score = relative amount score + toxicity score + volatilization score + leachability score + persistence score + bioaccumulation score + aquatic toxicity score In Step 2, ASCEs for indicator compounds are derived for each environmental pathway (soil, ground water, and surface water)
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From page 54... ...
for defining levels of cleanup at hazardous waste sites reveals that their key goal is the protection of public health. Implicitly or explicitly, all assume that chemicals deposited in the primary medium, soil, will migrate into secondary environmental media according to their properties and those of the media.
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From page 55... ...
Once a site investigation indicates that human exposure to toxic materials present at the site is likely, the goal of each cleanup action is to prevent significant adverse health ejects in the exposed population. In each of the five methods the goal of the cleanup is defined through a set of mediaspecific numerical permissible concentrations of toxic substances at the points of human exposure to them.
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From page 57... ...
Army and New Jersey methods may be overly simplistic and stringent, the EPA and California approaches are narrower in scope. Derivation of Media-Specific Numerical Criteria As stated earlier, in each of the five methodologies reviewed here, media-specific numerical criteria play an essential function in defining cleanup levels at hazardous waste sites.
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From page 59... ...
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From page 60... ...
Second, because these numbers are meaningful only when applied to a particular substance in a particular medium, they can not be used to address the multiple media/multiple chemical exposure scenarios that are prevalent at many hazardous waste sites. Third, the number of chemicals for which air and water standards, guidelines, or criteria have been developed is small.
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From page 61... ...
The New Jersey method relies only on intake factors to convert numerical criteria into allowable daily doses. (See Tables 3-1 and 3-2 for a list of the uncertainty factors used in the California and U.S.
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From page 62... ...
These are 95 percent statistical upper bounds estimates, extrapolated to humans and extrapolated to Tow doses using the one-hit model. Given the above differences one may expect that carcinogenic risks calculated by each method for the same substance/exposure conditions may differ by one or more orders of magnitude.
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From page 63... ...
SUMMARY AND CONCLUSIONS Hazard management at waste sites is more complex than at other locations because it involves multiple pathways of exposure. All of the methods reviewed in this paper focus on the protection of public health from the adverse effects of exposure to single toxicants as well as their mixtures, through single or multiple routes of exposure.
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From page 64... ...
1982. An Environmental Fate Model Leading to Preliminary Pollutant Limit Values for Human Health Effects.
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From page 65... ...
Yet most sites can be managed to minimize health and environmental impacts without spending tens of millions of dollars to clean them up to background levels. Contaminated portions of aquifers will never be developed by the waterworks industry as potable water supplies anyway, and further contamination of ground water and surface water sources can be prevented.
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From page 66... ...
During these delays, plumes of contamination increase in size as does, proportionately, the ultimate cost of the cleanup. In conclusion, ~ am not advocating no action, but ~ am proposing source control and the treatment of contaminants with the principal objective of protecting what is left and reaching achievable cleanup goals over a reasonable length of time.
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