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amec <br /> HPP-BTR TAOC <br /> Tracy Rail Yard Off Site South Area <br /> May 9, 2012 Work Plan <br /> Project OD11161140.05.**** <br /> Mr. Dean Hubbard <br /> Engineering Geologist <br /> California Regional Water Quality Control Board - Central Valley Region <br /> 1685 E Street <br /> Fresno, California 93706 <br /> Subject: Addendum to July 2011 Work Plan <br /> Tracy Rail Yard —Off Site South <br /> Tracy, California <br /> Dear Mr. Hubbard: <br /> As discussed at our March 29, 2012, meeting, Chevron Environmental Management Company <br /> (CEMC) proposes to conduct additional investigation south of the Tidewater Associated Oil <br /> Company(TAOC) 6th Street Tracy Rail Yard ("Off Site South Area") in Tracy, California, to <br /> further delineate the lateral extent of petroleum hydrocarbons in soil and groundwater <br /> associated with the former TAOC pipeline. <br /> On behalf of Chevron, AMEC Environment& Infrastructure (AMEC) conducted a site <br /> investigation in October 2011. Stained soil was observed in boring SOUTH-1(Figure 1); <br /> therefore, a groundwater sample was not collected from this boring. Analytical and petroleum <br /> hydrocarbon fingerprinting results indicate that soil at this location is impacted with petroleum <br /> hydrocarbons. Therefore, AMEC plans to advance one additional boring (SOUTH-13; Figure 1) <br /> to delineate soil and groundwater impacts downgradient of boring SOUTH-1. <br /> During the October 2011 investigation, stained soil was also observed at borings SOUTH-5 and <br /> SOUTH-11 (Figure 1). Based on the results of petroleum hydrocarbon fingerprinting, impacts <br /> observed in soil in borings SOUTH-5 and SOUTH-11 are not petroleum hydrocarbons but are <br /> fatty acids and a polypropylene glycol-type polymer. Therefore, petroleum hydrocarbon <br /> impacted soil has been delineated upgradient of the former pipeline. AMEC plans to advance <br /> one additional boring (SOUTH-12; Figure 1) to delineate groundwater impacts upgradient of the <br /> pipeline (south of borings SOUTH-5 and SOUTH-11). <br /> Borings SOUTH-12 and SOUTH-13 will be advanced to a depth of approximately 25 feet bgs <br /> using a Geoprobe direct push rig operated by PeneCore Drilling. Drilling, sampling, analytical, <br /> and borehole destruction methodology described in the July 2011 Work Plan will be employed. <br /> AMEC Environment&Infrastructure, Inc. <br /> 2101 Webster Street, 12th Floor <br /> Oakland,California 94612-3066 <br /> USA <br /> Tel (510)663-4100 <br /> Fax (510)663-4141 <br /> amec.com <br />