ARCHIVED REPORTS XR0000211 - Laserfiche WebLink

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r SECTiONEIGHT Summary9FResultg The approach used in this nsk assessment was based on EPA, DTSC and ASTM guidance for 1 conducting human health nsk assessments The EPA cautions that these documents are intended to provide guidance only and that considerable professional judgement must be exercised m applying the guidance to site-specific human health nsk assessments This nsk assessment has incorporated conservative assumptions, in addition to site-specific information, in evaluating potential exposures so that potential health risks and potential impacts to groundwater would not be underestimated The following conservative assumptions were made for the nsk assessment and fate and transport analysis o No asphalt or concrete paving ' 0 Biodegradation half lives of 100,000 days for all CDCs o All drinking water used by potential receptors would be supplied only by the wells 0 Employees would be exposed for 25 years, residents for 30 years ' a VOCs that were detected infrequently m groundwater (1,2-dnchloroethane, naphthalene, styrene, chloroform, tetrachloroethene) were included at the highest detected concentrations for all scenarios o Groundwater table was assumed to be at the shallow depth to increase the leaching of chemicals into groundwater and to increase the volatilization emissions The risk assessment and groundwater impact analysis considered all potential chemicals of concern detected in soul and groundwater beneath the site Two primary receptor populations, occupational on- site and off-site residential, were evaluated The on-site occupational employee was assumed to ingest ' groundwater from either a well located 500 feet downgradient or from a well located 1,000 feet downgradient Conservative fate and transport modeling was performed to estimate potential groundwater concentrations at the two hypothetical wells It was also assumed that the asphalt and concrete paving were not present, so direct contact (dermal and soul ingestion) could occur on a daily basis Inhalation of VOCs from soil and groundwater were also included in the on-site occupational ' exposure scenano The pathways that had the largest nsk was direct soil contact from dermal and soil ingestion The nsk numbers were below levels of concern For the residential receptors located at 500 feet and 1,000 feet downgradxent of the site, the exposure pathways evaluated included groundwater ingestion from the two hypothetical wells and inhalation of VOCs and particulates from soul and groundwater at the site All nsk numbers were significantly below levels of concern using the conservative assumptions ® T11997W3009NA%STOCKTON REPORT%SHOREP01 DOC%&FE84M973009NA%SNA 8-1