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California .gional Water Quality Cor, A Board <br /> Central Valley Region og <br /> Karl E. Longley,ScD, P.E.,Chair ,� r <br /> Linda S.Adams 1685 E Street,Fresno,California 93706 Arnold <br /> Secretaryfor (559)445-5116•Fax(559)445-5910 Schwarzenegger <br /> Environmental Protection htip://www.waterboards.ca.gov/centralvalIcN Governor <br /> �YEW <br /> SEP 0) 4 2008 <br /> 3 September 2008 ENVIROI�t Eir T HEALTH <br /> PER,MIT/SERVECES <br /> M. Scott Mansholt <br /> Chevron Environmental Management Company <br /> 6111 Bollinger Canyon Road, Rm 3432 <br /> San Ramon, CA 94583 <br /> REVIEW—WORKPLAN, ADDITIONAL INVESTIGATION PROPOSAL, TIDEWATER <br /> ASSOCIATED OIL COMPANY (TAOC) TRACY GRAVEL PITS, TRACY, SAN JOAQUIN <br /> COUNTY <br /> Regional Water Board staff reviewed the workplan dated 14 August 2008, prepared for <br /> Chevron Environmental Management Company (Chevron) and Union Pacific Railroad (UPRR) <br /> by AMEC Geomatrix, Inc. (AMEC). The TAOC Tracy Gravel Pits site, jointly owned by <br /> Chevron and UPRR, is on Valpico Road, west of MacDonald Road in south Tracy. <br /> Previously, AMEC submitted a February 2008 report that summarized the findings of a soil and <br /> groundwater investigation conducted in June and August 2007. In a 12 March 2008 response <br /> letter to Chevron and UPRR, Regional Water Board staff summarized the findings of the <br /> investigation and requested a workplan for an additional investigation. The purpose was to <br /> further delineate the extent of total petroleum hydrocarbons (TPH) in soil and groundwater. <br /> Additionally, we requested sampling of an industrial water supply well identified on an adjacent <br /> property, northwest of the site. <br /> The workplan proposes to excavate up to 19 exploration trenches to a depth below visually <br /> affected soil to define the lateral and vertical extent of affected soil. Samples will be collected <br /> for analysis of TPH as diesel, TPH as motor oil, and polynuclear aromatic hydrocarbons. In <br /> the event the extent of affected soil is not determined, an additional nine step-out trench <br /> locations are proposed. <br /> Two of the trenches will be excavated to at least 11 feet below grade surface within an area <br /> where a layer of oily debris was observed. Five samples from each of the two trenches will be <br /> collected and analyzed for metals in accordance with Title 22. All trenches will be backfilled <br /> and compacted using the original excavated soil. <br /> AMEC will attempt to locate the property owner of the industrial water supply well to obtain <br /> permission to sample groundwater. AMEC proposes to implement the workplan as soon as <br /> possible. <br /> California Environmental Protection Agency <br /> C5 Recycled Paper <br />