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14-104 Californiatgional Water Quality Control Board Central Valley Region ' ' =� Karl E. Longley,ScD, PE, Chair R s Linda S. Adams Arnold Secrerar'v for Fresno Branch Office Schwarzenegger Environmental 1685 E Street,Fresno,California 93706 Governor Prolection (559)445-5116• Fax(559)445-5910 litip://,Arww.waterboards.ca.gov/cejitralvalle}, To: Shelton R. Gray FROM: C. Dean Hubbard Senior Geologist Engineering Geologist DATE: 11 March 2008 SIGNATURE: SUBJECT: REVIEW- SOIL AND GROUNDWATER INVESTIGATION REPORT, TAOC TRACY GRAVEL PITS, TRACY, SAN JOAQUIN COUNTY I have reviewed the Soil and Groundwater Investigation, report, dated 22 February 2008 for the Tidewater Associated Oil Company (TAOC) Tracy Gravel Pits property located in southeast Tracy. The TAOC Tracy Gravel Pits property, located on Valpico Road, one-quarter mile west of MacArthur Drive, is jointly owned by Chevron and UPRR, and comprises approximately 34 acres. Geomatrix prepared the report for Chevron and Union Pacific Railroad (UPRR). The site is divided diagonally into three sections- northeast and southwest sections that are separated by a former gravel pit excavation (approximately 15 to 20-feet deep) that extends from the northwest to the southeast corners of the site. A temporary UPRR rail spur, situated within the excavation, was used to transport gravel quarried from the site and used elsewhere on other railroad tracks. The site is unimproved and presently enclosed by a perimeter fence. A summary of the historical documentation related to the site was previously provided in our letter to Chevron, dated 15 December 2006 which included a discussion of site activities conducted between 1989 and 2005. Our written response included a request for additional borings to obtain soil and groundwater samples for delineation and characterization purposes. Geomatrix submitted a workplan describing proposed activities and which was approved in our letter to Chevron dated 14 January 2007. We concurred that the affected soil at the site was partially delineated, generally located on the northeast portion of the site and within the former gravel pit excavation; however, additional characterization was needed. The southern portion of the site, south-southwest of the former gravel excavation does not appear to be affected. According to our requests outlined in the workplan, Geomatrix proposed the following scope of work: • Delineate the lateral and vertical extent of total petroleum hydrocarbons (TPH) in soil in the northeast part of the site; • Assess the metals concentrations in soil near the former railroad tracks; • Utilize sufficiently low method detection limits for polynuclear aromatic hydrocarbons (PAHs) so the values can be used in a future health risk assessment (HRA); California Environmental Protection Agency (p� RecYcled Paper