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- - - Nip- C1 A S S O C I A T E S I N C 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 SB1 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 (NMI 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 GROUNDWATER MONITORING AND SAMPLENTG ATC performed quarterly groundwater monitoring and sampling on December 20, 1999 Field work included measuring the depth-to-water in wells NMI 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 December 20, 1999 from monitoring wells MW 1 through MW3 The water table elevation has decreased an average of 2 49 feet in the monitoring wells since the last monitoring event in June 1999 Groundwater beneath the site generally flows in a westerly direction at an average gradient 0 0007 Rift, or approximately 3 9 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 December 1999 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 Collected groundwater samples were placed on ice and transported under chain-of-custody to State-certified Argon Laboratories, Inc , (DHS Certification No 23 59) Samples were analyzed for BTEX by EPA method 8020, TPHg by EPA method modified 8015, and oxygenate fuel additives by EPA method 8260 w 114885Vepo=isl4gtr1999 dw 2