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CALIFORNIA REGIO .N iNATER QUALITY CONTROL BOARD Cal/EPA <br /> _ CENTRAL VALLEY REGION <br /> b *... b <br /> 3443 Routier Road, Suite A <br /> tw!w. <br /> war Sacramento,CA' 95827-3098 t> qf J`4 ( <br /> AX Phone(916)255-3000 "'-� <br /> FAX 916 255-3015 i. Pete Wilson Governor <br /> i! <br /> 19 May 1998 <br /> qjq1 <br /> Mr. Ronald Nunan E' <br /> 651 Gateway Boulevard 4790 ,,. <br /> PL <br /> South San Francisco, CA 94080 4 ``' <br /> REVIEW OF`�iMENDE%D-WORKPLAN FOR AN ADDED SUBSURFACE-ENVIR4N1ViENTAI." <br /> INVESTIGATION, TOWN AND COUNTRY CHEVRON, 13336 HWY 88, LOCKEFORD, SAN <br /> JOAQUIN COUNTY <br /> In response to your submittal of the 20 March 1998 amended.workplan for additional investigation at the <br /> above site, Board and San Joaquin County Environmental Health�staff, after reviewing this workplan <br /> and the case files, have the following comments. Please include tY em in your site work. <br /> Page 2, paragraphs I and 2 of the amended workplan state that a borehole will be advanced to 40 feet <br /> below ground surface (ft bgs), and extended to greater depths, if obvious contamination is still evident <br /> during the drilling and sampling process. The borehole will be sampled from 20 to 40 ft bgs. In <br /> addition to collecting soil samples at 5 ft intervals, samples will be'collected at lithologic soil changes or <br /> where obvious staining is noted. Therefore, a minimum of five soil samples will be collected and <br /> analyzed for total petroleum hydrocarbons as gasoline (TPH-g), b�ehzenea toluene, eth ]benzene, and. <br /> xylene(BTEX) and methyl tertiary-butyl ether(MTBE) constituents and Toxicity Characteristic <br /> Leaching Procedure (TCLP) leachability. The goal is to establish a decreasing trend in benzene <br /> concentrations with depth so that the deepest sample confirms a rion-detectable concentration. <br /> In the 15 July 1997 Workplan for a Subsurface Environmental Investigation, Frank Goldman, the <br /> '�`� FRk- . '-1'i! 'X <br /> cozisultant,"states that'tlie regionaY ground water depth is 90 to 120 ft bgs. Information'froin nearby sites <br /> shows ground water is encountered at approximately 75 ft bgs; sol the depth to ground water at this site is <br /> possibly 75 ft bgs. <br /> The goal of this-investigation is to determine the vertical extent of contamination for all constituents in <br /> soil and to verify the depth of ground water. If ground water is impacted, the lateral and vertical extent <br /> of contamination must be determined at this site. Therefore,'the `workplan is approved, but the following <br /> changes need to.be implemented during the investigation. In addition to collecting soil samples at <br /> 40 ft bgs, as stated in the workplan, the collection and analysis of soil samples for TPH-g, BTEX, <br /> MTBE and the other oxygenates using EPA Method 8260 most continue as long as these contaminants <br /> are detected. Ifno contamination is detected at 40 ft bgs, soil samples need to be collected and analyzed <br /> for petroleum constituents for the next 10 ft to verify that contaminated soil is not present. This <br /> sampling is needed, because contamination meanders through the soil rather than being continuous like a <br /> plume in ground water. If any contamination is detected between 40 to 50 ft bgs, then the boring must <br /> Recycled Paper Our mission is to preserve and enhance the quality of California's ivater resources,and <br /> ensure their proper allocation and efficient use for the bene ft of present and,future generations. <br />