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CLEARWATER <br /> G R O U P I N C <br /> Environmental S,,r­s <br /> addendum to the workplan,dated December 10, 1998 was submitted in response to EHD comments The <br /> Workplan and addendum were approved by the EHD on December 15,1998 <br /> In January 1999, Clearwater supervised the installation of three additional groundwater monitoring <br /> wells (MW-4 through MW-6) to delineate the extent of dissolved-phase contamination The results of <br /> the investigation indicated that the extent of sorbed-phase contamination was delineated and existed <br /> from approximately 10 to 25 feet bgs near the former USTs Results of the groundwater samples <br /> indicated that the extent of dissolved-phase contamination remained undelineated downgradient from <br /> v the former UST system However, high contaminant concentrations in cross-gradient position of wells <br /> suggested that off-site sources may be contributing to contamination detected beneath the site Initial <br /> inquiries suggest that there may be a former or existing fuel transport lune in the area if the site Based <br /> on these results, Clearwater recommended additional investigation along South Fresno Avenue to better <br /> understand the distribution of contamination and possible contribution from potential off-site sources <br /> The results of this phase of investigation were presented in Clearwater's Well Installation and <br /> Groundwater Monitoring Report-First Quarter 1999 <br /> GROUNDWATER MONITORING AND SAMPLING ACTIVITIES <br /> Date of groundwater sampling September 21, 1999 <br /> Wells gauged MW-1 through MW-4, and MW-6 <br /> Wells purged and sampled MW-1 through MW-4, and MW-6 <br /> Analytes tested TPHg/BTEX (EPA Method 8015M/8020), <br /> MTBE and Fuel Oxygenates (EPA Method 8260) <br /> Laboratory Entech Analytical Labs, (Sunnyvale, CA), <br /> Remarks None <br /> GROUNDWATER MONITORING AND SAMPLING RESULTS <br /> Depth to groundwater 9 99 to 10 61 feet below top of casing <br /> Flow direction Southeast at 0 0025 ft/ft <br /> TPHg concentration range 56 pg/L (MW-2) to 5,800 pg/L(MW-1) <br /> Benzene concentration range 0 50 pg/L(MW-2)to 55 lig/L(MW-1) <br /> MTBE concentration range <5 0 pg/L (MW-1, MW-2, MW-3, MW-4, MW-6) <br /> Fuel Oxygenates No other Fuel Oxygenates (TBA, ETBE, DIPE,TAME) were detected <br /> Remarks During recent paving and construction activities on-site, both MW-2 and MW-5 were <br /> damaged The well box and top of casing of MW-2 were damaged, so the depth to water in this well <br /> was not used in calculating a groundwater elevation MW-5 was damaged beyond repair and will <br /> require proper abandonment and re-installation Once MW-5 is re-installed, all the wells will be re- <br /> surveyed prior to the next monitoring event <br /> • <br /> C-178 3Q99 GW Mon Rpt 2 October 1, 1999 <br />