ARCHIVED REPORTS XR0000211 - Laserfiche WebLink

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SECTION S IEVEN 91neerteintles and umitallons days for xylenes) for all COCl, 95% UCL concentrations, high porosity to groundwater, no paving, and seasonal high groundwater used for inhalation exposures 7.3 EXPOSURE ASSESSMENT UNCERTAINTIES Risk assessments require assumptions in order to assess potential human exposure This risk assessment includes assumptions about general characteristics and potential patterns of human exposure of the population in the vicinity of the site which were based upon 0 Limited site-specific information o EPA Guidance(EPA 1989b)and the EPA Exposure Factors Handbook(EPA 1989a) ' o Professional judgment In this risk assessment, reasonable maximum exposures were calculated to provide some measure of the range and uncertainty to potential exposures The reasonable maximum case is developed to provide an upper bound on exposure Because reasonable maximum exposure estimates are based on a combination of conservative assumptions, the estimates are highly unlikely to reflect exposures that are generally encountered at the site Specific conservative assumptions that tend to overestimate actual site risks are listed below r0 It was assumed that occupational employees would ingest 100 percent of the average daily water amount from either the hypothetical well located at 500 feet or 1,000 feet downgradient, and not from other sources, like home and restaurants 0 For adult and child residential exposures it was assumed that 100 percent of all ingested water would come from the hypothetical groundwater wells located at 500 feet and 1,000 feet ' downgradtent and not other sources 0 It was assumed that paving did not exist at the site which increases the amount that can volatilize and increases the amount of precipitation that will infiltrate 7.4 TOXICITY ASSESSMENT In general, the available scientific information is nnsuffictent to provide a thorough understanding of all the potential toxic properties of chemicals to which humans are potentially exposed Consequently, ' varying degrees of uncertainty surround the assessment of adverse health effects to exposed populations Source of uncertainty related directly to toxicity data include 0 Use of dose-response data from experiments on homogeneous, sensitive animal populations to predict effects to heterogeneous human populations with a wide range of sensitivities � � ® T%1997W73009NA%STOGKTOMREPORrSHOREPOI D0GW-FEB4W73009NA1.SNA 7-3