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Revised Work Plan for Additional Groundwater-Investigation j Quik Stop Market No. 132 I 3555 West Hammer Lane Stockton, California BTEX (at least one constituent) was present in at least one soil sample obtained from B-1, B-2, o. B-3, B-5 and MW-1. The maximum TPHg concentration was 460 milligrams per kilograms (mg/kg) in the soil sample obtained from B-3 at a depth of 15 feet below ground surface (bgs). The maximum benzene concentration was 3.9 mg/kg in the soil sample obtained from B-3 at a depth of 15 feet bgs. TPHg was present in the groundwater sample obtained from MW-1[320 micrograms per liter (ug/L)]. BTEX (at least one constituent) was present in the groundwater samples obtained from MW-1 and MW-2. The maximum benzene concentration was 34 ug/L in p7 the groundwater sample obtained from groundwater monitoring well MW-1. The locations of soil u borings and groundwater monitoring wells are shown on Figure 2. Review of the site geology.indicates that two separate groundwater bearing zones may exist beneath the site. The upper groundwater bearing zone appears to be present from approximately 14 to 19 feet bgs, and the lower groundwater bearing zone appears to be present from approximately 20 to 30 feet bgs. Consequently, on October 3, 1990, Exceltech abandoned groundwater monitoring well MW-1 due to the concern that this groundwater monitoring well could possibly connect the two groundwater bearing zones. �! On April 2, 1991, Exceltech completed an additional site assessment consisting of the installation of two additional groundwater monitoring wells (MW-IA and MW-5). The soil and groundwater samples (from new and existing groundwater monitoring wells) were analyzed for TPHg and BTEX in accordance with EPA test methods 8015 and 8020, respectively. TPHg and BTEX were not present in any of the soil borings. TPHg was present in the groundwater sample L obtained from MW-5 (210 ug/L). Benzene (3.4 ug/L) and xylenes (2.1 ug/L) were present in groundwater sample obtained from groundwater monitoring well MW-5. The locations of groundwater monitoring wells are shown on Figure 2. On December 9, 1992, RESNA Industries Inc. (RESNA) completed an additional site assessment consisting of the installation of two additional off-site groundwater monitoring wells (MW-6 and Lj MW-7). The soil and groundwater samples (from new and existing groundwater monitoring I•j wells) were analyzed for TPHg and BTEX in accordance with EPA test methods 8015 and 8020, respectively. TPHg and BTEX were not present in any of the soil borings. TPHg was present in a groundwater sample obtained from MW-5 (350 ug/L). BTEX (at least one constituent) was ` present in groundwater samples obtained from MW-2 and MW-5. The maximum benzene • concentration was 0.66 ug/L in the groundwater sample obtained from groundwater monitoring well MW-2. The locations of groundwater monitoring wells are shown on Figure 2. In March 1996, groundwater samples obtained from groundwater monitoring wells MW-1R, MW-2, MW-5, MW-6 and MW-7 were first analyzed for methyl tert-butyl ether (MTBE) in accordance with EPA test method 8020. MTBE was present in groundwater samples obtained from MW-1R, MW-2 and MW-5. The maximum MTBE concentration was present in a 14SI groundwater sample obtained from MW-5 (1,100 ug/L). MTBE concentrations in MW-5 subsequently decreased steadily for five quarters until September 1997, when the MTBE . Cconcentrations rose back to 1,100 ug/L. 1\flecwnlan hNM.r...,vwako \WORr3LAN(Oeopmo )2.d 2 I p t