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;a EDMUND G.BROWN JR. <br /> ••• GOVERNOR <br /> C A O P N I A MATTHEW RODRIQUEZ <br /> SE CR RR <br /> WaterBoards ENVIRONMENTAL PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 16 February 2018 <br /> Mr. Jason Cashman <br /> Environmental Manager <br /> Port of Stockton <br /> P.O. Box 2089 <br /> Stockton, California 95201 <br /> UST DATA GAP INVESTIGATION WORK PLAN, ROUGH AND READYISLAND, PORT OF <br /> STOCKTON, STOCKTON, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff, has reviewed the Draft Underground Storage Tank(UST) Data Gap Investigation <br /> Work Plan (Work Plan) received 19 January 2018 and prepared by Anchor QEA, LLC for the Port <br /> of Stockton. Central Valley Water Board staff's comments are provided below. <br /> COMMENTS <br /> 1. At UST 517, a single sample was proposed at a depth of 6 feet below ground surface(bgs)for <br /> analysis of naphthalene. Please collect the sample from the 0 to 5 feet bgs depth interval. The <br /> Total Petroleum Hydrocarbon (TPH) results from the sample collected at 9.5 feet bgs from <br /> adjacent boring 517-MW5 (1.7 milligrams per kilogram TPH) are considered sufficient to show <br /> naphthalene concentrations between 5 and 10 feet bgs are less than the 9.7 milligrams per <br /> kilogram (mg/kg) threshold value in the Low Threat Underground Storage Tank Case Closure <br /> Policy (LTCP) for volatilization to outdoor air. <br /> 2. At UST 605, sampling was proposed at depths of 13 and 16 feet bgs, as was requested in the <br /> Water Board letter dated 26 September 2017. Upon further review, naphthalene data from the <br /> depth intervals of 0 to 5 and 5 to 10 feet bgs would better enable comparison to the threshold <br /> concentrations provided in the LTCP. However, the historical TPH data from 7.5 feet bgs (3.1 <br /> mg/kg TPH as diesel) indicate the naphthalene concentrations are less than the threshold <br /> value of 9.7 mg/kg (i.e., evaluation of the 5 to 10 foot interval is not required). Please modify <br /> the work scope to include testing of naphthalene in the 0 to 5 foot bgs interval. <br /> 3. At UST 817B, benzene sampling was proposed at two locations where historically, benzene <br /> concentrations exceeded the LTCP media-specific criteria for direct contact and volatilization to <br /> outdoor air. It is also necessary to also comply with the LTCP media-specific criteria for <br /> petroleum vapor intrusion to indoor air. As specified in the LTCP, this can be accomplished by <br /> either 1) collecting TPH data, in addition to the benzene data, to demonstrate that TPH <br /> concentrations in the upper five feet of soil have attenuated to less than 100 mg/kg; or 2) <br /> collecting soil vapor data to demonstrate compliance with the threshold values provided in <br /> KARL E. LONGLEY SCD, P.E., CHAIR I PAMELA C. CREEDON, EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200,Rancho Cordova,CA 95670 1 www.waterboards.ca.gov/centraIvalley <br /> C'J RECYCLED PAPER <br />