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EDMUND O.BROWN JR. <br /> GOVERNOR <br /> �Wo <br /> C A l I I O R N 1 A Me"THRW RORDRN)UEI <br /> WaterBoards ltl� FNVIRONI/EN1Al PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 16 November 2015 <br /> Chevron Environmental Management Company <br /> and Phillips 66 (L&M Group) <br /> c/o Dan Schreiner <br /> Stantec Consulting Services Inc. <br /> 3017 Kilgore Road, Suite 100 <br /> Rancho Cordova, CA 95670 <br /> WORK PLAN FOR ADDITIONAL METHANE AND VOC SOIL VAPOR SURVEY, LBM OPERABLE <br /> UNIT, STOCKTON, SAN JOAQUIN COUNTY <br /> Central Valley Water Board staff has reviewed the 21 October 2015 Response to California Regional <br /> Water Quality Control Board Letter dated June 15, 2015 and Request for Additional Methane and Soil <br /> Gas VOC Investigation (Work Plan) prepared by Stantec Consulting Services Inc. on behalf of <br /> Chevron Environmental Management Company and Phillips 66 (L&M Group)for the L&M Operable <br /> Unit site in San Joaquin County. The Work Plan was submitted pursuant to discussions during our <br /> meeting on 24 September 2015. <br /> The Work Plan includes a section at the beginning that responds to comments in our 15 June 2015 <br /> letter that approved the previous soil vapor investigation work plan. The responses include a proposal <br /> for analyzing carbon ranges of gasoline in soil vapor for which toxicity data are available and <br /> comparing those results to risk assessment numbers for these carbon ranges. The responses also <br /> include a proposal for reducing the frequency of soil vapor monitoring from quarterly to semiannual <br /> beginning in 2016. Central Valley Water Board staff concurs with this proposal at this time; however, <br /> frequency of monitoring may be reassessed depending on the outcome of future monitoring and <br /> proposals to address any threats to human health. <br /> The Work Plan proposes to conduct shallow soil vapor sampling to profile impacts in the upper 6 feet <br /> at 12 locations as shown on Figure 2 of the Work Plan. The locations focus on areas with higher <br /> methane and total petroleum hydrocarbons (TPH) as gasoline, as well as areas near probes with <br /> elevated naphthalene or benzene. At each location, soil vapor samples will be collected at 1 foot <br /> intervals from 1 to 6 feet below ground surface and analyzed for methane, carbon dioxide, and <br /> oxygen to assess the existence and depth of an aerobic bioattenuation zone. At least one sample <br /> from each location will also be analyzed for volatile organic compounds by US EPA Method TO-15 full <br /> scan including TPH as gasoline, BTEX compounds, and naphthalene. Individual carbon ranges of <br /> gasoline will not be evaluated during this survey, but will be included in future sampling from the <br /> existing soil vapor probes. <br /> KARL E. LONGLEY SCD, P.E.,CHAIR 1 PAMELA C. CREEDON P.E., BCEE,EXECUTIVE OFFICER <br /> 11020 Sun Center Drive 0200.Rancho Cordova,CA 95670 1 www.waterboards.ca.gov/controlvalley <br /> ILA RECYCLED PAPER <br />