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'I!,\ EDMUND C 8RU111 JR. <br /> ti. l.(IVCnli Ufi <br /> Op <br /> MAT I HEW RgDR1UUE[ <br /> Water Boards <br /> Central Valley Regional Water Quality Control Board <br /> TO: Shelton R. Gray <br /> Senior Engineering Geolog�isl_ j <br /> C <br /> FROM: C. Dean Hubbard <br /> Engineering Geologist <br /> DATE: 26 March 2012 <br /> SUBJECT: REVIEW— SOIL AND GROUNDWATER INVESTIGATION REPORT, TRACY <br /> RAIL YARD OFFSITE —WEST AREA, TRACY, SAN JOAQUIN COUNTY <br /> Chevron Environmental Management Company (Chevron) submitted a Soil and Groundwater <br /> Investigation Report (Report), dated 30 August 2011, for the Tidewater Associated Oil Company <br /> (TAOC) Tracy Rail Yard Offsite—West Area (Site). The Report was prepared on behalf of Chevron by <br /> AMEC Geomatrix, Inc. (AMEC). Previously, Central Valley Regional Water Quality Control Board <br /> (Central Valley Water Board) staff concurred in a 6 January 2011 letter to Chevron, that an additional <br /> soil and groundwater investigation was needed. <br /> I have reviewed the Report and related investigation reports completed since about 2005 provided by <br /> Chevron and my comments are provided below. Historical information is available in the project files. <br /> Earlier investigations determined that impacted soil and groundwater on the original Site were likely <br /> associated with leaks from the historical TAOC crude oil pipelines, previously located within what is <br /> now a residential neighborhood. The-former crude oil pipelines crossed the approximate center of the <br /> Site from southeast to northwest. Earlier findings indicated that the lateral and vertical extent of crude <br /> oil affected soil and groundwater was not delineated and additional characterization was needed. <br /> The purpose of AMEC's investigation was to drill offset soil borings and collect samples for analysis, to <br /> define the lateral and vertical extent of affected soil and groundwater within the residential <br /> neighborhood. To evaluate the lateral extent of affected groundwater downgradient, offset borings <br /> were advanced on a vacant property a few hundred feet to the north of the residences. <br /> According to the Report: <br /> • In April 2011 twelve borings were drilled as offsets to earlier boring locations, to collect soil <br /> samples for petroleum hydrocarbon analysis. Three of the borings were drilled at one location <br /> to collect deeper groundwater samples. <br /> • Total petroleum hydrocarbons as crude oil (TPHc) was detected in 19 of 22 soil samples with <br /> concentrations ranging from 1.1 milligrams per kilogram (mg/kg) to 850 mg/kg. The highest <br /> concentration was in a sample from five feet below ground surface (bgs), TPH impacted soil <br /> was not observed in this boring but pieces of asphaltic material were noted in the drill cuttings. <br /> AMEC concluded that the detection was associated with the asphaltic material and not related <br /> to crude oil from the former pipelines. Deeper samples from 9 to 18 feet bgs in the same boring <br /> reported TPHc concentrations of 1.7 to 4.1 mg/kg. <br /> KARL E. LONGLEY ScD, P.E., CHAIR I PAMELA C. CREEDON, E%ECUINE OFFICER <br /> 1685 F 31reel.Fresno.CA 93706 www.walerbbarOB.Ca.gowcen;ralvalleY <br />