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� E C 0 R <br /> and southwest of the site, and requested that Sequoia Analytical Laboratories (Sequoia) <br /> review chromatograms of groundwater samples collected during the September 1995 <br /> Geoprobe® investigation (Delta, February 6, 1996)and provide an estimate of methyl <br /> tertiary butyl ether(MTBE) concentrations in groundwater(ERI, March 2, 1999) <br /> • February 1999—Tosco advanced three off-site cone penetrometers (CPT1 through CPT3) <br /> and drilled three off-site soil borings (158 through B10) (ERI, March 2, 1999) <br /> • April 1999—Tosco installed nine off-site groundwater monitoring wells, consisting of three <br /> nested wells (shallow, intermediate, and deep)at each of three well locations <br /> (ERI, June 9, 1999) <br /> • April 1999—Tosco submitted the Work Plan for Supplemental Evaluation <br /> (ERI, April 16, 1999)to the County <br /> • May 1999 - ERI submitted the report entitled Air Sparge/Soil Vapor(AS/SVE) Extraction <br /> Test, dated October 18, 1999, presenting the data collected during ERI's May 1999, ASISVE <br /> 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 (IR) <br /> action <br /> • During second quarter 2000, ERI installed one LIST cavity well in general accordance with <br /> the CAP (ERI, December 28, 1999)and Tosca initiated periodic purging of groundwater from <br /> the UST cavity well and from groundwater monitoring well MW3 Groundwater purging was <br /> temporarily discontinued during third quarter 2000 pending clarification from the County <br /> regarding water sampling and data collection requirements Purging was resumed during <br /> January 2001, and continued through January 2002, when it was terminated following <br /> installation and operation of the microsparge remediation system Approximately 285,000 <br /> gallons of groundwater were purged from the UST cavity well and well MW3 and transported <br /> to the Tosco refinery for recycling during interim groundwater remediation efforts <br /> • During June 2001, Tracer Research Corporation (TRC) performed an enhanced leak <br /> detection test on underground storage systems to evaluate the system integrity According <br /> to Tosco, the results of the enhanced detection test indicated that the underground storage <br /> systems are functioning within acceptable parameters <br /> • During third quarter 2001, ERI submitted a CAP, dated September 25, 2001 The CAP <br /> included recommendations to install a microsparge system to remediate MTBE impacted <br /> groundwater beneath the site <br /> • During first quarter 2002,the microsparge remediation system was completed and ERI <br /> performed system startup and initiated monthly operation and maintenance (O&M)of the <br /> system <br /> Currently, there are ten on-site AS wells (ASI through AS5, AS7, AS8, and AS10, and nested wells <br /> AS6SID and AS9S/D), three on-site, single-casing groundwater monitoring wells (MW1 through <br /> MW3), four on-site, dual-casing groundwater monitoring wells (MW4S/D through MW7S/D), one on- <br /> site UST cavity well, and nine off-site groundwater monitoring wells (MW8S/I/D through MW 10S/l/D) <br /> consisting of three wells at each nested well location as shown on Plate 2 and the On-Site Well <br /> Locations (Plate 3) <br />