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<br /> S EC ® R
<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
<br /> and sampling, obtained access agreements to drill soil borings at select properties
<br /> located south and southwest of the site, and requested that Sequoia Analytical
<br /> Laboratories (Sequoia) review chromatograms of groundwater samples collected during
<br /> the September 1995 Geoprobe® investigation (Delta, February 6, 1996) and provide an
<br /> estimate of methyl tertiary butyl ether(MTBE) concentrations in groundwater(ERI, March
<br /> 2, 1999)
<br /> February 1999—Tosco advanced three off-site cone penetrometers (CPT1 through
<br /> CPT3) and drilled three off-site soil borings (B8 through 610) (ERI, March 2, 1999)
<br /> April 1999--Tosco installed nine off-site groundwater monitoring wells, consisting of
<br /> three nested wells (shallow, intermediate, and deep) at each of three well locations
<br /> (ERI, June 9, 1999)
<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,
<br /> AS/SVE feasibility test
<br /> December 28, 1999 - ERI submitted the report entitled Corrective Action Plan (CAP)
<br /> Tosco received a letter from the County dated February 22, 2000, approving the
<br /> remediation recommendations provided in ERI's December 28, 1999 CAP as an interim
<br /> remedial (IR)
<br /> action
<br /> • During second quarter 2000, ERI installed one UST cavity well in general accordance
<br /> with the CAP (ERI, December 28, 1999) and Tosco initiated periodic purging of
<br /> groundwater from the UST cavity well and from groundwater monitoring well MW3
<br /> Groundwater purging was temporarily discontinued during third quarter 2000 pending
<br /> clarification from the County regarding water sampling and data collection requirements
<br /> Purging was resumed during January 2001, and continued through January 2002, when
<br /> it was terminated following installation and operation of the microsparge remediation
<br /> system Approximately 285,000 gallons of groundwater were purged from the UST cavity
<br /> well and well MW3 and transported to the Tosco refinery for recycling during interim
<br /> 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
<br /> According to Tosco, the results of the enhanced detection test indicated that the
<br /> underground storage 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 (AS1 through AS5, AS7, AS8, and AS10, and nested
<br /> wells AS6S/D and AS9S/D), three on-site, single-casing groundwater monitoring wells (MW1
<br /> through MW3), four on-site, dual-casing groundwater monitoring wells (MW4S/D through
<br /> . MW7S/D), one on-site UST cavity well, and nine off-site groundwater monitoring wells (MW8S/IID 3
<br /> through MW10S/I/D) consisting of three wells at each nested well location as shown on Plate 2
<br /> and the On-Site Well Locations (Plate 3)
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