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1 • AR[AD]S GERAGHTY&MILLER ' due to rising groundwater which submerged the impacted soil targeted for mclusion to the Feasibility Study ' In May 1997, GSI conducted a search of Department of Water Resources files in Sacramento, California for domestic and municipal supply wells located within a 0 5-mile radius of the subject site GSI identified twelve sites with wells within the ' area searched Six sites were identified as domestic water supply wells, four sites as municipal water supply wells, and two sites as industrial water supply wells The nearest downgradient well (classified use is municipal) was reported to be located ' approximately 1,580 feet from the subject site Well search data were included in GSI's Well Installation Report(No 482721-2,October 21, 1997) As reported in the same document (Well Installation Report (No 482721-2, GSI, October 21, 1997), GSI installed off-site groundwater monitoring well U-9 in an attempt to delineate the downgradient edge of the dissolved plume (Figure 1) ' Petroleum hydrocarbons were not detected in the three soil samples from thewell boring that were submitted for analysis The groundwater sample from the well initially contained TPHg(990 ppb),benzene(130 ppb),and MTBE(12 ppb) Drilling and well mstallabon data are presented in GSI's Well Installation Report(No 482721- 2), dated October 21, 1997 Recent groundwater monitoring data indicate that monitoring well U-9 is nondetect for TPHg,BTEX and MTBE Quarterly monitoring and samplmg of the groundwater monitoring wells began in August 1994. At the time wells U-1 through U-3 were installed in August 1994, groundwater was measured at approximately 48 feet bgs Groundwater m well ' U-9 is currently measured at approximately 32 to 33 feet bgs (August 31, 1997),a rise of 15 to lb feet Groundwater flow direction during this period has been to the northeast The SICPHS indicates that depth to water has been as deep as 70 feet bgs ' Dissolved concentrations of TPHg or benzene have been detected in wells U-I through U-4 and U-7 through U-9 The most recent groundwater monitoring analytic data indicate that wells U-1 and U-3 contain dissolved concentrations of TPHg and ' benzene, but wells U-5 through U-9, which encompass upgradient, side gradient, and downgradient locations, were nondetect for TPHg and benzene (First Quarter, 1998, Groundwater Monitoring&Sampling Report,Gettler-Ryan Inc,March 26, 1998) ' PROPOSED SCOPE OF WORK ARCADIS Geraghty & Miller developed this scope of work to vertically delineate dissolved-phase petroleum hydrocarbon impact in groundwater The scope of work includes installation of one soil boring, collection of depth-discrete groundwater samples from the saturated zone, completion of a nested piezometer beneath the current level of groundwater, and preparation of a Corrective Action Plan