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ti CLEAKWATER • n R O S P $nveronmertf of Services In January 1999, Clearwater supervised the installation of three additional groundwater monitoring wells (MW-4 through MW-6) to delineate the extent of dissolved-phase contamination and performed a sensitive receptor survey The results of the investigation indicated that the extent of sorbed-phase contamination was delineated and existed from approximately 10 to 25 feet bgs near the former USTs Results of the groundwater samples indicated that the extent of dissolved-phase contamination remained undelineated downgradient from the former UST system However, high contaminant concentrations in cross-gradient position of wells suggested that off-site sources may be contributing to contamination detected beneath the site Initial inquiries suggested and was later confirmed that there is existing fuel transport line in the area if the site, and that it is currently filled with nitrogen gas Based on this information, Clearwater recommended additional investigation along South Fresno Avenue to better understand the distribution of contamination and possible contribution from potential off-site sources The results of this phase of investigation were presented in Clearwater's Well Installation and Groundwater Monitoring Report - First Quarter 1999 In March 2000, Clearwater supervised the completion of one hydropunch, six soil borings, the destruction of MW-5, and three of the borings were converted into monitoring wells (MW-5B, MW-7, and MW-8) All three wells were placed on the downgradient portion of the plume to help determine the downgradient extent of contaminants The hydropunch was performed in the former UST location to assess the vertical extent of groundwater contamination at 36 feet bgs Three soil bongs were performed to define the lateral extent of soil and groundwater contamination on the northeastern portion of the site and assess possible off-site sources A total of three soil samples and one groundwater sample were analyzed from each boring Soil concentrations of TPHg and BTEX were only detected in boring MW-5B The highest soil concentration of TPHg (1,000 mg/kg) was detected at 25 feet bgs in MW-5B This sample was also analyzed for TPH as Jet Fuel and contained 55 mg/kg Detectable concentrations of BTEX were present in soil samples collected from boring MW-5B at 25 feet and 35 feet bgs MTBE was not detected by EPA method 8260 in any of the soil samples analyzed Groundwater concentrations of TPHg and BTEX were detected in bongs SB-9, MW-5B, MW-7 and MW-8 The highest groundwater concentration of TPHg (9,700 µg/L) was detected in MW-5B MTBE was not detected by EPA method 8260 in any of the groundwater samples analyzed GROUNDWATER MONITORING AND SAMPLING ACTIVITIES Date of groundwater sampling May 30,2001 Wells gauged MW-1 through MW-8 Wells purged and sampled MW-1 through MW-8 Analytes tested TPHg/BTEX/MTBE(EPA Method 8015M/8020) Laboratory Entech Analytical Labs, (Sunnyvale, CA) Remarks None GROUNDWATER MONITORING AND SAMPLING RESULTS Depth to groundwater 8 86 (MW-2) to 10 94 (MW-8) feet below top of casing Flow direction Southeast at 0 005 ft/ft TPHg concentration range < 50 gg/L (MW-2, MW-4) to 15,000 gg/L(MW-5B) Benzene concentration range <0 50 lig/L (MW-2, MW-4) to 2,600 µg/L (MW-5B) MTBE concentration range <5 0 gg/L (MW-2,MW-3,MW-4,MW-7) to 42 gg/L (MW-1) ZB 178C-2QTOI 2 June 8, 2001