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v 7J%TC ' A S S O C I A T E S I N C feet bgs which contained only trace or nondetectable concentrations of petroleum hydrocarbons Total lead was detected at 5 5 mg/kg in the soil sample collected from SB 1 at 25 5 feet bgs ' Neither benzene, fuel oxygenate additives, nor VOCs were detected above laboratory method detection limits in any of the soil samples analyzed Soil analytical results are summarized in Table 1 ' Petroleum hydrocarbon constituents, including TPHg and BTEX, were detected in initial groundwater grab samples collected from borings SB 1 and SB2 Only benzene, which was ' reported at concentrations of 7 6 ug11 and 12 ug/l, exceeded California's Maximum Contaminant Level (MCL) for drinking water In correspondence dated October 9, 1998, San Joaquin County Public Health Services, Environmental Health Division (PHD/EHD) requested additional work be performed at the ' project site On June 15 and 16, 1999, a total of three soil borings (MW 1 through MW3) were advanced at the site in the vicinity of the"closed" or former underground storage tanks (USTs) to evaluate the ' lateral extent of petroleum affected soil and groundwater Following soil sample collection the borings were completed as groundwater monitoring wells The initial sampling of the on-site wells indicated that only low levels of petroleum hydrocarbons were present in MW1 This work is summarized in ATC's Summary Report of Supplemental Subsurface Investigation dated October 15, 1999 Since the installation of the groundwater monitoring wells in June 1999, three quarterly groundwater monitoring events have been performed at the site Concentrations of petroleum ' hydrocarbons have been consistently nondetect or very low The groundwater gradient has been predominantly east-southeast during these monitoring events Groundwater elevation data is summarized in Table 2 and copy of a gradient map representative of site conditions is included as Figure 3 2.0 SUBSURFACE CONDITIONS 1 2_1 Ge•lory ' The site is situated at an approximate elevation of approximately 43 feet above mean sea level, in the Great Valley geomorphic province The Great Valley province is a north-south elongated ' structural trough filled with sediment from marine and continental sources The continentally derived sedimentary deposits comprise the upper portion of the valley fill, and were deposited in fluvial, alluvial, and lacustrine environments 1 The site is situated on level terrain The soils at the property have been mapped by the United States Department of Agriculture (USDA), Soil Conservation Service as Archerdale Clay Loam This nearly tlevel map unit is formed in alluvium derived from mixed rock sources A few areas have been noted to w 114885V"rlslNFA-Request doc 2