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ERI 205512 R01 Tosco Facility 5886Stockton California A nl 22 2002 • . Advancement of 21 soil borings, which included collecting soil and groundwater samples from the borings using a Geoprobe® sampling system (Delta, February 6, 1996) Completion of a water-supply well survey within a one-quarter-mile radius of the site The survey identified 10 wells located within the survey area These wells are located northeast to southeast of the site and are apparently used as cathodic protection or irrigation wells (Pacific Environmental Group, Inc [PEG], June 24, 1996) • Drilling four additional soil borings, and constructing groundwater monitoring wells (MW1 through MW3) in three of these borings (Delta, December 5, 1996) • Advancement of three off-site cone penetrometers (CPT1 through CPT3) and drilling of three off-site soil borings (B8 through 1310) (ERI, March 2, 1999) • Installation of nine off-site shallow (S), intermediate (1), and deep (D), groundwater monitoring wells (MW8SII/D through MWIOSII/D) nested in three soil borings (ERI, June 9, 1999) • Submittal of the report entitled Air Sparge/Soil Vapor Extraction (ASISVE) Test, dated October 18, 1999, presenting the data collected during ERI's May 1999 ASISVE feasibility test Submittal of a Corrective Action Plan (CAP) for the site (ERI, December 28, 1999) Tosco received a letter from the County dated February 22, 2000, approving the remediation recommendations provided in ERI's December 28, 1999, CAP as an interim remedial action Installation of one UST cavity well in general accordance with ERI's December 28, 1999, CAP, and periodic purging of groundwater from the UST cavity well and from groundwater monitoring well MW3 • Quarterly groundwater monitoring, sampling, and reporting Based upon data collected during ongoing quarterly groundwater monitoring and sampling, dissolved hydrocarbons are effectively delineated both laterally and vertically in the vicinity of the site However, dissolved hydrocarbons continue to be detected in groundwater beneath the site and are concentrated near and downgradient of the UST cavity(Plate 2) PRESENT WORK Scope of Work ERI previously submitted a CAP, dated September 25, 2001, to the San Joaquin County Environmental Health Division Public Health Services(the County) The County approved the CAP in a letters dated October 2 and November 6, 2001 (Attachment A) As proposed in the CAP, ERI drilled ten soil borings (AS I through AS 10) and installed AS wells AS 1 through AS5, AS7, AS8, and AS 10 in the respective borings, and nested AS wells AS6 shallow/deep (SID) and AS9SID in borings AS6 and AS9, respectively ERI obtained a well installation permit from the County prior to performing the field . work A copy of the permit is provided in Attachment B ERI performed field work in general 2