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(VATC A S S O C I A T E S I N C In order to assess potential receptors, ATC personnel performed a reconnaissance of the area surrounding the site, in March 1999 and March 2000. The site and surrounding area are primarily commercial; however, some areas north and west of the site contain residential properties. A residential property is present adjacent to the site across First Street, at a distance of approximately 100 feet to the north of the former UST. This residence was used as a potential receptor. The site is completely paved with new asphalt or concrete and the surfacing materials appeared to be in good condition. The only on-site structure located in the immediate vicinity of the former gasoline UST is the fire station building. This building has a concrete floor which appeared to be good condition with no open cracks observed. A garage is also present on site but is located over 30 feet from the former UST. Sensitive habitats, such as wetlands, were not observed in the immediate vicinity of the site during the reconnaissance. The Mormon Slough was observed approximately 0.3 miles to the north. A review of the above information indicates that, at present, there are no known completed exposure pathways at the subject site. However, there are several potential exposure pathways that exist at the project site which are described below: • Residual BTEX constituents and MTBE have leached to groundwater, adversely affecting designated beneficial uses, most notably that of a potable water supply; • In the event improvements are needed to the site in the immediate vicinity of the former UST, construction workers could be exposed to subsurface soil volatilization to outdoor air should deep soil excavation(>15 feet bgs)be required; • Subsurface soil or groundwater volatilization to indoor or outdoor air via underground utilities and/or vertical dispersion is possible for structures in the vicinity of the former gasoline UST. Although the above scenarios may appear highly unlikely, and perhaps do not warrant the need for further evaluation, this conservative approach may further assist in determining risk to human health and the environment. 6_2 RBCA Model V Using the RBCA Tier 1/ Tier 2 software (version 1.01) developed by GSI in cooperation with the ASTM committee, individual Site-Specific Target Levels (SSTLs) were calculated for each of the identified constituents of concern (COCs). The SSTLs are risk-based, site-specific corrective action target levels for constituents in question. The SSTLs represent upperbound constituent concentrations that, if achieved throughout the source zone, will prevent the exceedence of w:t62574.05\repofU\closu%-FS3.doc 8 V