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V � . A S S O C I A T E S I N C In 1997 GHH Engineering removed fuel pipelines, three 12,000-gallon gasoline underground storage tanks(USTs), and one 3,000-gallon diesel UST The highest total petroleum hydrocarbons as diesel (TPHd) concentration was detected at 5,000 mg/kg in the soil sample collected beneath the diesel fuel dispenser The highest TPHg concentration was detected at 4,800 mg/kg in the soil sample collected beneath the gasoline USTs Benzene was detected at up to 4 2 and 6 4 mg/kg in the soil samples collected beneath the USTs and dispensers, respectively Methyl tertiary butyl ether (MTBE) was detected at up to 28 and 18 mg/kg in the soil samples collected beneath the USTs and dispensers, respectively Approximately 400 yards of soil excavated during UST and associated pipeline removal was disposed of offsite at a licensed landfill GHH Engineering estimated the mass of residual gasoline at the site to be approximately 1065 GHH Engineering performed quarterly groundwater monitoring and sampling from July 1997 to September 2002 The historic groundwater gradient direction has ranged from northeast to the southeast GROUNDWATER MONITORING Water level measurements were collected from wells MW-1P through MW-6P, MW-1 and MW-2 • on May 28, 2003 Depth to water levels ranged from 60 95 to 61 89 feet below the tops of the well casings There was an average increase of 0 65 foot for groundwater elevations from the previous quarter The water level data were used to develop the groundwater elevation contour map (Figure 3) The average hydraulic gradient on May 28, 2003 was calculated to be 0 0015 ft/ft or approximately 7 9 ftlrrule, and flowed generally towards the southeast A summary of groundwater monitoring data is presented in Table 1 SAMPLING ACTIVITIES On May 28, 2003, ATC personnel collected groundwater samples from monitoring wells MW-1P through MW-6P, MW-1, and MW-2 The locations of the morutoring wells are shown on Figures 2 and 3 Prior to collection of groundwater samples, the depth to water, pH, electrical conductivity, and temperature were measured in the monitoring wells and recorded Aquifer parameters were allowed to stablilize and a minimum of three well casing volumes were purged from each well pnor to sampling The wells were allowed to recover and samples were collected from each well using dedicated disposable bailers Purged well water was contained on site in DOT approved 55-gallon drums and labeled for disposal pending receipt of laboratory results The groundwater samples collected from each well were submitted to Argon Laboratories, a state-certified analytical laboratory (FLAP cert no 2359) located in Ceres, California, for analysis Laboratory analysis consisted of total petroleum hydrocarbons as gasoline (TPHg) utilizing EPA method 8015, benzene, toluene, ethyl benzene, total xylenes (BTEX) utilizing EPA • Method 8020, and oxygenate fuel additives MTBE, ethyl tertiary butyl ether (ETBE), di- isopropyl ether (DIPE), tertiary butyl alcohol (TBA), tertiary amyl ether (TAME), 1,2- S lenvuonmental12591210003-StwktonlQuartlyl2QR-2003 dw 2