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Mr. Jeff Whitworth - 2 - 2 August 2006 <br /> oil (TPHc) ranges will be analyzed using EPA Method 8015. Benzene, toluene, ethylbenzene, <br /> and xylenes (BTEX) will be analyzed using EPA Method 8260B. <br /> Soil samples will be collected from three locations beneath the former pipeline where previous <br /> investigations reported a range of TPH concentrations in soil. Soil samples will be analyzed <br /> for TPHd and TPHc using EPA Method 8015. Selected soil samples for which TPH is <br /> detected will be tested for leachability using Soluble Threshold Limit Concentration (STLC) <br /> methodology utilizing de-ionized water. <br /> A written report will be submitted summarizing the investigations findings and providing <br /> recommendations for additional work, if warranted. The soil vapor data will be compared to <br /> California Human Health Screening Levels for soil vapor in a residential setting as established <br /> by the California Office of Environmental Health Hazard Assessment. The groundwater data <br /> will be utilized to evaluate whether dissolved petroleum hydrocarbons are related to releases <br /> from the former pipeline or are naturally occurring. STLC data from the soil samples wil! be <br /> used to evaluate TPH concentrations that may pose a threat to groundwater quality. <br /> Regional Water Board staff concurs with the activities proposed in the Work Plan with one <br /> clarification request. There was no rationale given for selecting soil samples for laboratory <br /> analysis, either through visual or olfactory indications, sample vapor headspace monitoring, or <br /> some other means. A written statement addressing this issue should be provided in the final <br /> report. It is our understanding that the field investigation began on 10 July 2006. Based on <br /> the two-phase nature of soil sample analyses, the report for the proposed scope of work is due <br /> to this office by 15 September 2006. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4719 or <br /> mclardy@waterboards.ca.gov. <br /> Mark W. Clardy, P.G. <br /> Engineering Geologist <br /> Private Sites Cleanup Unit <br /> cc: Mr. Michael Hurd, Scientific Applications International Corporation, Oakland <br /> Mr. Mike Infurna, San Joaquin County Environmental Health Department, Stockton <br /> Ms. Eileen Nottoli, Allen Matkins Leck Gamble & Mallory LLP, San Francisco <br /> Ms. Ileana Rhodes, Shell Global Solutions (US) Inc., Houston, TX <br /> Mr. David Corliss, Golden State Developers, Walnut Creek <br /> MWC/W.\slit—dod\AustinStaff\Mark\Shell-Hansen&Schulte Rd\6-26-06 GW-SG work plan.doc <br />