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GEOMATRIX <br /> SECOND SEMIANNUAL 2002 GROUNDWATER MONITORING <br /> ' (JULY — DECEMBER) AND ANNUAL PROGRESS REPORT <br /> Corral Hollow and Grant Line Roads Site <br /> ' Tracy, California <br /> ' Geomatrix Consultants,Inc. (Geomatrix), has prepared this report on behalf of Chevron <br /> Environmental Management Company (ChevronTexaco) describing the second semiannual <br /> ' 2002 groundwater monitoring event(July—December) conducted at the Corral Hollow and <br /> Grant Line Roads site located in Tracy, California(Figure 1). This report also includes an <br /> ' annual progress summary for 2002. Groundwater monitoring was conducted in accordance <br /> with the California Regional Water Quality Control Board—Central Valley Region (RWQCB) <br /> ' Monitoring and Reporting Program Order No. 96-814 (MRP), as revised in subsequent <br /> RWQCB letters (RWQCB, 1998 and 2002). <br /> ' 1.0 BACKGROUND INFORMATION <br /> ChevronTexaco operates an underground refined fuel pipeline that runs parallel to Grant Line <br /> Road and adjacent to the subject site, which is located at the northwest intersection of Corral <br /> Hollow and Grant Line Roads in Tracy, California (Figure 2). In 1987, the pipeline was <br /> ' compromised by the City of Tracy during the installation of dewatering wells, which resulted in <br /> a petroleum release. Immediately following the release, ChevronTexaco repaired the pipeline <br /> and excavated and disposed of approximately 100 cubic yards of petroleum-affected soil. <br /> ' Site investigation and/or groundwater monitoring activities have been conducted at the site <br /> since 1987, and active remediation (dual-phase groundwater and vapor extraction) was <br /> conducted from June through November 1997. A human health risk assessment(HHRA) <br /> ' prepared by Geomatrix in 1998 was submitted to and approved by the California Department of <br /> Toxic Substances Control (DTSC)in their January 26, 1999, letter to the RWQCB. <br /> Groundwater monitoring activities have been conducted at the site since 1989; the wells still <br /> existing on the site (MW-5, MW-6, MW-7,MW-8, and MW-12)have been monitored since <br /> ' 1991. The extensive monitoring data show that petroleum hydrocarbon concentration trends <br /> are stable and/or declining, indicating a stable and shrinking plume. <br /> In 2000, site conditions were evaluated within the context of the RWQCB's 1996 Low-Risk <br /> • Guidelines (the Guidelines) with respect to protection of the environment and restoration of the <br /> potential beneficial uses of groundwater(Geomatrix, 2000a). Conditions at the site conform to <br /> 1:11'&OJEC112000s124631DOCUMEN112463 12-02 MIAm I <br />