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N URS Ms.Lori Duncan Page 2 San Joaquin County Environmental Health Department July 5,2002 On July 30, 1996, BC drilled and installed one 2-inch groundwater monitoring well (MW-1 shown on Figure 1, Attachment I) near the southwestern dispenser island to a depth of 25 feet bgs. Laboratory analysis reported total xylenes in all three soil samples analyzed with concentrations ranging from 0.0064 mg/kg to 0.0089 mg/kg. No other hydrocarbons were detected. BC sampled well MW-1 on July 30, 1996, November 15, 1996, and March 19, 1997. Laboratory analysis reported concentrations of methyl tert-butyl ether (MTBE) of 35 micrograms per liter(gg/L), 8 pg/L, and 19 pg/L, respectively, during those sampling events. TPHg and BTEX were not detected in any of the three sampling events. Depth to groundwater ranged from 8.89 feet to 12.37 feet bgs. On August 4, 1997, the California Regional Water Quality Control Board — Central Valley Region (CRWQCB-CVR) issued the site "No Further Action Required" status. Between 1997 and 1999, well MW-1 was abandoned. On November 24, 1999, Delta Environmental Consultants, Incorporated (Delta) performed oversight and soil sampling during facility product piping and dispenser upgrade activities. Ten soil samples were collected beneath the product piping lines and eight soil samples were collected beneath the product dispensers. Toluene,ethylbenzene, xylenes, and MTBE were reported in several soil samples. On February 21, 2002, three soil borings (SB-1, SB-2, and SB-3) were completed at the site by Delta. The soil borings were advanced to a depth of approximately 20 feet bgs. Grab groundwater samples were collected from each of the borings. Analytical results for these samples indicated that TPHg was not detected in any of the samples; however, MTBE was detected in all three samples at concentrations ranging from 3.7 gg/L in SB-2 to 68 gg/L in SB-1 (Figure 1,Attachment 1). SUBSURFACE CONDITIONS In previous soil borings conducted at the site, sand was encountered from ground surface to approximately 6 feet bgs. Beneath the sand, clayey silts and silty clays were present to a depth of approximately 20 feet bgs (Delta, 2002). Groundwater was encountered in clayey silt at approximately 12 to 13 feet bgs. SCOPE OF WORK URS proposes to install three groundwater monitoring wells to monitor MTBE concentrations in groundwater associated with the product lines. This work plan includes discussion of permitting, drilling, sample collection, and report preparation requirements. ICA0U5MWorkPh n.doc