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<br /> S E C ® R
<br /> July 1997 through December 1998—Tosco consultants performed the following tasks 1)
<br /> • conducted an underground utility search (ERI, October 6, 1997), 2) continued to perform
<br /> quarterly groundwater monitoring and sampling, 3) obtained access agreements to drill
<br /> soil borings at select properties located south and southwest of the site, 4) requested
<br /> Sequoia Analytical Laboratories (Sequoia) to review chromatograms of groundwater
<br /> samples collected during the September 1995 Geoprobe® investigation (Delta, February
<br /> 6, 1996) in order to estimate methyl tertiary butyl ether(MTBE) concentrations in
<br /> groundwater(ERI, March 2, 1999)
<br /> • February 1999—Tosco consultants advanced three off-site cone penetrometers (CPT1
<br /> through CPT3) and drilled three off-site soil borings (B8 through B10) (ERI, March 2,
<br /> 1999)
<br /> • April 1999—Tosco consultants installed nine off-site groundwater monitoring wells
<br /> consisting of three nested wells (shallow, intermediate, and deep) at each of three well
<br /> locations (ERI, June 9, 1999)
<br /> • May 1999—Tosco's consultant ERI submitted a report entitled Air Sparge/Soil Vapor
<br /> (AS/SVE) Extraction Test, dated October 18, 1999, presenting the data collected during
<br /> ERI's May 1999, ASISVE feasibility test
<br /> • December 28, 1999—Tosco's consultant ERI submitted a Corrective Action Plan (CAP)
<br /> Tosco received a letter from the San Joaquin County Public Health Services department
<br /> (the County) dated February 22, 2000, approving the remediation recommendations
<br /> provided in ERI's December 28, 1999 CAP as an Interim Remedial (IR)Action document
<br /> . • During second quarter 2000, Tosco consultant ERI installed one UST cavity well in t
<br /> general accordance with the CAP (ERI, December 28, 1999) Periodic purging of ,
<br /> groundwater from the UST cavity well and from groundwater monitoring well MW3 was
<br /> also initiated Groundwater purging was temporarily discontinued during third quarter
<br /> 2000 pending clarification from the County regarding water sampling and data collection
<br /> requirements Purging was resumed during January 2001, and continued through
<br /> January 2002, when it was terminated following installation and operation of the
<br /> microsparge remediation system Approximately 285,000 gallons of groundwater were
<br /> purged from the UST cavity well and well MW3 and transported to the Tosco refinery for
<br /> recycling during interim groundwater remediation efforts
<br /> • During June 2001, contractor Tracer Research Corporation 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, consultant ERI submitted an additional CAP, dated September
<br /> 25, 2001 The CAP included recommendations to install a microsparge system to
<br /> remediate MTBE impacted 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 ASS, AS7, ASS, and AS10, and nested
<br /> wells AS6SID and AS9SID), 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 (MWBS/IID
<br /> through MWI0SIIID) consisting of three wells nested at each location
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