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�� tl S E C 0 R Atlantic Richfield Company ARCO Service Station 4932 September 22, 2003 Page 3 Also in 2001, SECOR performed a utility survey to evaluate whether nearby off-site utilities or other underground Improvements may act as potential conduits for migration of petroleum hydrocarbons Since depth to water at the site is approximately 27 feet bgs and no underground improvements or utilities were Identified near this depth, It is unlikely that any subsurface utilities or other unknown underground Improvements are preferential migration pathways for petroleum hydrocarbon-Impacted groundwater SECOR concluded that higher potential exists for vapor-phase contaminant migration through these areas (SECOR, Additional Site Assessment Report, dated November 9, 2001) As a result of the discovery of LPH in wells MW-4 and SVE-1 during the third quarter 2001 sampling event on July 20, 2001, weekly Interim groundwater remediation was Initiated on October 29, 2001, which consisted of the removal of LPH and petroleum hydrocarbon-Impacted groundwater from the wells with a bailer Interim GWE continued for approximately six weeks until measurable LPH was no longer present Between October 29, 2001 and December 17, 2001, approximately 10 to 15 gallons of LPH had been removed from the wells As a result of the continued presence of elevated concentrations of petroleum hydrocarbons and MtBE in on-site wells, Interim GWE was reinitiated on March 18, 2002 utilizing a vacuum truck Between March 18 and August 2, 2002, approximately 23,350 gallons of LPH and petroleum hydrocarbon-Impacted groundwater had been removed from beneath the site On March 14 and 15, 2002, West Hazmat Installed one deep groundwater monitoring well (DMW-1) and one GWE well (EW-1) DMW-1 and EW-1 were completed at 81 feet bgs and 44 feet bgs, respectively Stabilized groundwater levels In wells DMW-1 and EW-1 were measured at 29 and 28 feet bgs, respectively TPHg was detected in four of the ten samples at a maximum concentration of 780 mg/kg (EW-1, 27 5') Benzene was detected In six of the ten samples at a maximum concentration of 51 mg/kg (EW-1, 275') MtBE was detected in eight of the ten samples at a maximum concentration of 290 mg/kg (EW-1, 27 5') On April 2 through 4, 2002, a step drawdown pumping test, constant rate drawdown pumping test, and aquifer test were completed Results were as follows • Capture zones of approximately 31 feet and 48 feet were calculated In the downgradlent and cross-gradient directions, respectively The capture zone was calculated using the Javandel and Tsang method • A pumping rate 4 and 6 gallons per minute was used for the constant rate drawdown pumping test The well Installation and aquifer pumping test Is documented In SECOR's report titled, Site Assessment and Aquifer Testing Results, dated June 7, 2002 On June 10 through 13, 2002, two monitoring wells (MW-10 and MW-11), two deep monitoring wells (DMW-2 and DMW-3), and one extraction well (EW-2) were Installed at the site by West Hazmat (Figure 2) Monitoring wells MW-10 and MW-11 were completed at 40 feet bgs, and were Installed with a 2-Inch PVC well casing screened from 20 to 40 feet bgs These wells are located off-site to the north, MW-10 is in an alley off El Dorado Street and MW-11 is on the corner of EI Dorado Street and Sperry Avenue Deep monitoring wells (DMW-2 and DMW-3) were completed at 82 feet bgs, and were Installed with a 2-inch PVC well casing screened from 77 to 82 feet bgs Extraction well (EW-2) was completed at 43 feet bgs, and was Installed with a 6-Inch PVC well casing with a stainless steel wire-wrap screen extending from 20 to 40 feet bgs Wells DMW-2, DMW-3, and EW-2 are located off-site north across E Harding Way from the site In August 2002, SECOR submitted a Problem Assessment Report (PAR), which evaluated various remedial alternatives for the site SECOR recommended the Installation of a groundwater extraction (GWE) and soil vapor extraction (SVE) system The recommendation included the Installation of five 11ARC0149321ReporlsVemedial well start-up doc