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A soil vapor extraction (SVE) system along with two air sparging wells (SWI and SW2) was installed in May 1994. The SVE system recovered petroleum hydrocarbon vapors using four vadose zone wells screened from 10 to 30 feet below ground surface (bgs). Due to an increase in groundwater elevation at the site, petroleum hydrocarbons trapped in soil below the water table have not been effectively remediated with the SVE system. In November 1996, a vacuum vaporizer well system, known as UVB (Underdruck Verdampfer ` Brunnen), was installed for groundwater remediation at the site. The installation of the UVB system consisted of overdrilling existing groundwater recovery well RW3 to install the dual- screen UVB well for groundwater extraction-injection, and the installation of adjacent ` monitoring wells UVB-MWI and UVB-MW2 to monitor system performance. The operational measurements of the UVB system show that it has reached the asymptotic stage of operation and has not achieved a significant migration control. The UVB system will therefore be shut down ` as referenced in ETIC's letter dated 29 October 2000. ` Groundwater monitoring and sampling was initially conducted in January 1987, and has been conducted on a quarterly basis since February 1989. The samples are submitted to a state certified laboratory and analyzed for benzene, toluene, ethylbenzene, and total xylenes (BTEX), ` and for Total Petroleum Hydrocarbons as gasoline (TPH-g). Groundwater samples have also been analyzed for methyl t-butyl ether(MTBE) since 1995. PLANNED ENVIRONMENTAL ACTIVITIES Risk Assessment ETIC will conduct a risk evaluation following ASTM RBCA methodology to assess environmental risks due to the presence of petroleum hydrocarbons at the site. The RBCA analysis will be based on ASTM E 1739-95 and San Francisco Regional Water Quality Control Board (SFRWQCB) vapor pathway guidelines, accounting for complete direct and/or indirect soil exposure pathways associated with future site residents and construction workers. r Additional data for the risk evaluation will be collected during a shallow soil and soil gas investigation. Eight soil borings will be installed to collect shallow soil and soil gas samples. One soil sample will be collected from each boring at approximately 2 feet bgs, and soil gas samples will be collected from each boring at approximately 3 and 6 feet bgs. Each soil sample will be analyzed for Total Organic Carbon (TOC) by SW9060, moisture content by D2216, and porosity by ASTM D854. Each soil vapor sample will be analyzed for TPH-g, BTEX, and oxygenates by EPA Method TO-14. The proposed depths and analyses for soil and soil gas samples are presented in Table 1. The borings will be driven by the direct push method, and the vapor samples will be collected in 6-liter Summa canisters or 1-liter Tediar bags. The proposed locations of the shallow soil borings are shown on Figure 1. The locations of the soil borings were chosen to assess the presence of hydrocabons in the vadose zone onsite. The results of this sampling and analysis will be used in the RBCA risk evaluation. F\Pmje u\73992\M STERMWP p1000\.ttd 2 V