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• A S S O C I A T E S I M C mg/kg) The petroleum hydrocarbons appear to attenuate rapidly with depth as indicated greatest by soil samples from 5131 at 45 5 feet bgs and S132 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 SBI 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 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 • GROUNDWATER MONITORING AND SAMPLING ATC performed quarterly groundwater monitoring and sampling on March 14, 2000 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 14, 2000 from monitoring wells MWl through MW3 The water table elevation has increased an average of 3 86 feet in the monitoring wells since the last monitoring event in December 1999 Groundwater beneath the site flows in an easterly direction at an average gradient of 0 003 ft/ft, or approximately 16 feet/mile Historically, groundwater beneath the site generally flowed in a southeasterly direction Groundwater monitoring data are summarized in Table 1 A groundwater gradient map for the March 2000 monitoring event is shown on Figure 3 Groundwater samples were collected from wells MW 1 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 PHS/EHD 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 following the discharge of approximately 160-gallons of water Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Argon Laboratories, Inc , (DHS Certification No 2359) Samples were analyzed W 11488Slreportsl4gtr1999 doc 2