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510 420 1707; <br /> Nov-9-99 16:32; Page 27,29 <br /> Metals <br /> Aluminum (groundwater only) <br /> Lead (soil and groundwater) <br /> Manganese(groundwater Only) <br /> Exposure point concentrations for chemicals of potential concern included for further evaluation are <br /> shown in Tables 7A and 7B. The maximum concentration was used in conducting the human health <br /> screening. Note that only the maximum cunutmtration of soil data collected during verification <br /> sampling after operation of the soil vapor and groundwater extraction system were included in the <br /> human health screening analysis for samples collected near the former Shell Station; soil data <br /> collected from this area of the site prior to operation of the Ireatrrient systems were excluded from <br /> the screening analysis. Also, the maximum concentration of groundwater samples collected from <br /> the past four groundwater monitoring events only for each of the Shell wells were evaluated for <br /> inclusion in the human health screening assessment for on-site groundwater, as approved by DTSC <br /> (Cambridge and Lile, 1999). All grab groundwater samples collected in the Phase II investigation <br /> (including one off-site hydropunch boring)and groundwater sampling data from the adjacent ARCO <br /> site were also considered in the selection of maximum groundwater concentrations and calculation <br /> of risks and hazards from off-site groundwater. Physical constants for chemicals evaluated as <br /> COPCs are included in Appendix C. <br /> EQUATIONS AND MODELS <br /> Groundwater, Soil, and Ambient Air <br /> Risks and hazards were calculated for exposure of adults and children to contaminants in <br /> groundwater during showeringlbathing, and by ingestion. Volatilization of contaminants into <br /> household air during water usage was accounted for in these calculations. Risks and hazards were <br /> calculated for exposure of adults and children to contaminants in soil from incidental ingestion and <br /> dermal contact with soil,assuming the site is unpaved. Risks and hazards for exposure of adults and <br /> children to contaminants in ambient air from soil were also calculated;note that these calculations <br /> do not include contributions to ambient air fmm groundwater contamination. Risks and hazards <br /> from exposure to contaminants in ambient air also assume that the site is entirely uncapped, <br /> permitting vapor migration and exposure to particulates in air. Site redevelopment activities include <br /> substantial paving of the site with concrete and/or brick. <br /> Risks and hazards were calculated using equations provided in the DTSC PEA guidance manual <br /> using default conservative assumptions. These calculations assume the site is or would be used for <br /> a residential setting;this is considered a conservative assumption since the pmposed redevelopment <br /> of the site is not residential,and potential exposures to future users of a water squareipublic meeting <br /> area are expected to be less than residential site uses where humans are assumed to be living on the <br /> site. See Appendix C for calculations for grouridwater, soil,and ambient air. The results of these <br /> calculations are described in the Risk Characterization section below. <br /> 97369stk.peA.wp4-1 PN99 21 <br />