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FR1 205513 QSR15 Tosco Service Station 5886Stockton Califorma January 25 2001 <br /> • September 1996 - Unocal drilled four additional soil borings, and constructed groundwater <br /> monitoring wells in three of these borings (Delta, December 5, 1996) <br /> • March 1997 -Tosco submitted a Work Plan for Supplemental Environmental Investigation <br /> (ERI, March 28, 1997) to the County <br /> • April 1997 -Tosco submitted an Addendum to Work Plan (ERI, April 3, 1997) to the County <br /> • April 1997 -Tosco performed a soil and groundwater investigation at the site The investigation <br /> included hand-auguring three soil borings adjacent to catch basins, drlllmg four soil borings, and <br /> constructing dual-completion groundwater monitoring wells (MW4SID through MW7S/D) at <br /> discrete depths in the borings (ERI, June 3, 1997) <br /> 1 • July 1997 -Tosco submitted a Work Plan for Supplemental Environmental Investigation <br /> (ERI, July 14, 1997) to the County <br /> • August 1997 -Tosco submitted the Addendum to Work Plan (ERI, August 8, 1997) to the County <br /> • July 1997 through December 1998 - Tosco performed an underground utility search <br /> ' (ERI, October 6, 1997) (Plate 2), continued to perform quarterly groundwater monitoring and <br /> sampling, obtained access agreements to drill soil borings at select properties located south and <br /> southwest of the site, and requested that Sequoia Analytical Laboratories (Sequoia) review <br /> chromatograms of groundwater samples collected during the September 1995 Geoprobe® <br /> investigation <br /> (Delta, February 6, 1996) and provide an estimate of methyl tertiary butyl ether (MTBE) <br /> concentrations in groundwater (ERT, March 2, 1999) <br /> • February 1999 -Tosco advanced three off-site cone penetrometers (CPT1 through CPT3) and <br /> drilled three off-site soil borings (138 through B10) (ERI, March 2, 1999) <br /> • April 1999 -Tosco installed nine off-site groundwater monitoring wells, consisting of three nested <br /> wells (shallow, intermediate, and deep) at each of three well locations (ERI, June 9, 1999) <br /> • April 1999 -Tosco submitted the Work Plan for Supplemental Evaluation (ERI, April 16, 1999) to <br /> the County <br /> • May 1999 - ERI submitted the report entitled Air Sparge/Soil Vapor Extraction Test, dated <br /> October 18, 1999, presenting the data collected during ERI's May 1999, AS/SVE feasibility test <br /> • December 28, 1999 - ERI submitted the report entitled Corrective Action Plan (CAP) Tosco <br /> ' received a letter from the County dated February 22, 2000, approving the remediation <br /> recommendations provided in ERI's December 28, 1999, CAP as an interim remedial action <br /> 2 <br />