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v <br /> TC <br /> A S S O C I A T E S I N C <br /> J <br /> •-- groundwater and the subsequent transport of the constituents in groundwater. All three of these <br /> transport mechanisms are viable at the site. <br /> Exposure Pathways <br /> V Three complete exposure pathways are possible for the site: <br /> • potable use of groundwater; <br /> • inhalation of outdoor vapor; and <br /> • inhalation of indoor vapor. <br /> `,,, To assess the likelihood that groundwater in the vicinity of the site is being used and/or will be <br /> used for potable water, personnel from ATC performed a groundwater receptor survey for the <br /> subject site as previously discussed. Results of this survey indicate that there is one municipal <br /> well within a 2,000-foot radius of the site. The municipal well was visually located about <br /> 1,600 feet northeast of the site in a hydraulically downgradient direction. The closest surface <br /> water to the site is Mormon Slough, approximately 0.3 miles to the north. <br /> These findings suggest that shallow groundwater in the vicinity of the site is not presently being <br /> used for drinking water. Municipal supply wells are rarely screened in the shallowest aquifer and <br /> `-� construction logs for other by California Water Service Co. wells in the vicinity indicate <br /> perforations start at depth no shallower that 140 feet. It is, therefore, highly unlikely that shallow <br /> groundwater in the immediate vicinity of the site would be used in the foreseeable future for <br /> potable water. The use of shallow groundwater as a current potable water source is, therefore, <br /> not considered a complete pathway. However, to address the State's water quality objectives as <br /> delineated in the Central Valley Region's Water Quality Control Plan (Basin Plan) for the <br /> y Sacramento River and San,Joaquin River Basin (RWQCB, 1998)the use of shallow groundwater <br /> as a potential potable water source warrants evaluation. <br /> V <br /> The inhalation of vapor volatilized from the subsurface soils and from the dissolved groundwater <br /> plume at the site are also the potential exposure pathways that were evaluated. Even though the <br /> estimated extent of hydrocarbons in soil and groundwater do not extend beneath the building on <br /> site, inhalation of both indoor and outdoor vapor were evaluated. <br /> The next step in evaluating complete exposure pathways is identifying potential on-site and off- <br /> site receptors. <br /> L- Potential Receptors <br /> The location of the former gasoline UST is south of the site's fire station building, underlying <br /> asphalt pavement. Chemical analytical data indicate residual soil contamination at the site is <br /> limited to within 15 feet of the former UST to the north and east. Vertically, the residual soil <br /> contamination is generally limited from 16 feet to 28 feet bgs. <br /> tow <br /> w:t62574.05\rcpoiUa-losuro-FS3.doc 7 <br /> v <br />