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GERAGHTY & MILLER, INC 4 benzene (8 1 mg/kg and 0 29 mg/kg, respectively) were reported beneath the product lines Additional soil samples were collected by Geraghty & Miller during the remediation well tinstallation These results are presented in Attachment 2 DISSOLVED PETROLEUM HYDROCARBONS IN GROUNDWATER ' Maximum concentrations of etroleum hydrocarbons in groundwater detected during p ' the February 1997 sampling event were 27,000 micrograms per liter (gg/L) TPH as gasoline and 1,600 µg/L benzene in MW-1, the well closest to the former tank pit. MTBE has been included as an analyte beginning in June 1996 MTBE was detected in February 1997 in all ' monitoring wells except MW-5 and MW-7 The only well with a concentration of MTBE in excess of 100 µg/L was MW-9, which contained 1,200 µg/L MTBE The most recent ' groundwater monitoring report has been included in Attachment 3 for reference (Blaine Tech, March 25, 1997) The extent of TPH-as-gasoline contamination is defined to the west (upgradient) by ' MW-7 (historically nondetect for all analytes) and to the north by Monitoring Wells MW-3 and MW-4,with occasional detections near the method-detection limit for TPH as gasoline in both wells The southern boundary of the plume likely commingles with the northern boundary of the ARCO plume The farthest downgradient well, MW-8, had a TPH-as-gasoline concentra- tion of 200 µg/L in February 1997 ' SVE AND BIOS ARGING REMEDIATIO SYSTEM The remediation approach consists of on-site SVE for removal of petroleum hydro- carbons in the vadose zone and biosparging below the water table to address hydrocarbon mass removal within the saturated zone The purpose of these systems is to achieve sufficient source removal through volatilization and biological degradation to allow passive bioattenuation to ' address residual concentrations of petroleum hydrocarbons in the groundwater ' FEASIBILITY ANALYSIS GTI submitted an assessment report/feasibility study dated March 16, 1994. Four ' corrective action alternatives were presented in this report Project No RC0309.010