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i i,24 150 Big ME a - A. FrTE ASSeSSMENT MOf1ItORNG WELL iNSTALLATM"RESULTS FAUK)Fif 420 W.KcMa.an.Ladl.California r-' Additional information regarding adjacent land uses,tank storage products, , niderg underground - accident history, site and regional geology and hydrogeology, structures and site description are presentedin Section 2 0 of Aegis' "Pre-Tank and "Pre-Tank Replacement Site Assessment Work Plan" (Aegis, Replacement Site Assessment Results Report', (Aegis, October 1989) submitted to the SJCPHS. 2.1 Previous Subsurface Soil [Hues#i ation Results In September 1989, a total of fifteen soil borings were drilled at the site ("Pre-Tank Replacement Site Assessment Results Report" (Aegis, 1989)) ranging in depth from 11-1h to 21-1/E feet bg. Four berings were drilled adjacent to the existing tank basin, three borings adjacent to the existing dispenser islands, and eight borings within the formerly proposed new underground storage tank basin vertical�ntervals and selected samples were ure 2). The borings were screened in-field with a PID at approximately five-foot forwarded to a state-certified laboratory for the required analysis. In-field screened samples had PID readings of zero. Low concentrations of toluene and total xylenes were detected in baring B-1 adjacent to the existing underground storage tanks at 15 feet bg. Laboratory analysis of the soil samples for the remaining borings adjacent to the existing dispenser islands and underground storage tanks were below detection limits. Low concentrations of toluene were detected in soil borings B-7 and B-10 at approximately five T, feet bg in the formerly proposed tank basin. Boring eight (B-8}, also located in the the highest petroleum constituent concentrations. Total proposed tank basin, contained µ Petroleum Hydrocarbons as gasoline (TPH as gasoline)was present at 1,060 ppm 10 feet bg. The source may have resulted from the removal of liquid trapped in the 'Thief Port" of the Stage ll Vapor Recovery lines. ystem allows vapors to be captured at the nozzle of the The Stage ll Vapor Recovery S s._. dispenser through a secondary boot and then allows the heavier petroleum particles to drain back to the underground storage tanks under the farce of gravity due to the fall of the Stage II lines to the tanks. The island parallel to Hutchin Road was not high enough to allow for adequate fall in the vapor lines; therefore, the vapor line was installed with a vertical t,ep allowing liquids to collect and vapors to step up to an elevation creating to enhance gravity flow. The station operator would enough tall in the vapor lines moving collected liquid gasoline, so as not to impede periodically '"Thief them Dry," by re vapor flow. The "Thieving," or removal of the liquids, from this trap has a high potential for spillage. F 89-013A.RPT -