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CLEAR-WATER cr r. 0 L P I \ C Er—ronmentu! Serr ices 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 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 contamunation 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 suggest that there may be a former or existing fuel transport lute in the area if the site Based on these results, 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 InstaIIation and Groundwater Monitoring Report - First Quarter 1999 GROUNDWATER MONITORING AND SAMPLING ACTIVITIES Date of groundwater sampling June 21,1999 Wells gauged MW-1 through MW-4, and MW-6 Wells purged and sampled MW-1 through MW-4, and MW-6 Analytes tested TPHg(EPA Method 8015M), BTEX/ MTBE (EPA Method 8260 Laboratory Entech Analytical Labs, (Sunny ale, CA), KIFF Analytical (Davis, CA) e �mrkL As requested by Lori Duncan of the San Joaquin County Environmental Health Division, (ni'd MTBE were analyzed by EPA Method 8260 GROUNDWATER MONITORING AND SAMPLING RESULTS Depth to groundwater 8 94 to 9 34 feet below top of casing Flow direction Southeast at 0 002 ft/ft TPHg concentration range 66 pg/L (MW-2) to 5,600 pg/L (MW-1) Benzene concentration range 0 69 pg/L(MW-2) to 290 lig/L (MW-1) MTBE concentration range <0 50 nig/L (MW-1, MW-2, MW-3, MW-4, MW-6) Remarks During recent paving and construction activities on-site, both MW-2 and \M-5 were damaged The well box and top of casing of MW-2 were damaged, so the depth to water in this well was not used in calculating a groundwater elevation MW-5 was damaged beyond repair and will require proper abandonment and re-installation Once MW-5 is re-installed, all the wells will be re- surveyed prior to the next monitoring event PROJECT STATUS&RECOMMENDATIONS The EHD responded to Clearwater's Well Installation and Groundwater Monitoring Report - First Quarter 1999 in a letter dated June 25, 1999 The EHD concurred with the recommendations for additional assessment of groundwater contamination downgradient of the former UST s-,stem As CGI C-178 2Q99 2 August 24, 1999