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b � A S S O C I A T E S I N C by soil samples from SB 1 at 45 5 feet bgs and SB2 at 55 5 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 Petroleum hydrocarbon constituents, including TPHg and total petroleum hydrocarbons as gasoline (TPHg), and benzene, toluene, ethylbenzene, and xylenes (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 parts per billion (ppb) and 12 ppb, exceeded California's Maximum Contaminant Level (MCL) for drinking water On June 15 and 16, 1999, a total of three soil borings (MW1 through MW3) were advanced at the site in the vicinity of the "closed" or former underground storage tanks (USTs) to evaluate determine 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 only low levels of petroleum hydrocarbons were present in MW-1 On October 26, 2001, ATC submitted a request for closure The San Joaquin County Environmental Health Department (SJEHD) requested that an additional monitoring event be performed GROUNDWATER MONITORING AND SAMPLING ATC performed quarterly groundwater monitoring and sampling on March 17, 2003 Field work included measuring the depth-to-water in wells MW1 through MW3 and purging and sampling the water from these wells in addition to the site's domestic well (Domestic Well) The samples were analyzed for the presence of dissolved petroleum hydrocarbons Depth to water measurements were collected on March 17, 2003 from monitoring wells MW1 through MW3 The water table elevation has decreased an average of 1 58 feet in the monitoring wells since the last monitoring event in November 2001 Groundwater beneath the site generally flows in a northeasterly direction at an average gradient of 0 0016 ft/ft, or approximately 8 6 feet/mile Historically, groundwater beneath the site generally flows in a southeasterly direction Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the March 2003 monitoring event is shown on Figure 3 Groundwater samples were collected from wells MW1 through MW3 after purging and stabilization of physical parameters (pH, electrical conductivity, and temperature) The monitoring wells were purged and sampled according to ATC's Field Procedures on file with SJEHD Monitoring well purge logs are included in Attachment 1 Furthermore, ATC collected a water sample from the sampling port of the on-site Domestic Well w U48851reportsl1gtr2003 doc 2