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  <br /> <br />Central Valley Regional Water Quality Control Board <br />7 December 2021 <br />Bill Doerr <br />The Newark Group <br />33878 Drifting Sands Circle <br />Thousand Palms, CA 92276 <br /> <br /> <br />RESPONSE TO LOW THREAT CLOSURE EVALUATION, DOPACO AREA CASE #3, <br />800 WEST CHURCH STREET, STOCKTON, SAN JOAQUIN COUNTY, <br />LUST CASE# 391193, GEOTRACKER GLOBAL ID #T10000006482 <br /> <br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br />reviewed the August 2021 Groundwater Sampling and Low-Threat Underground <br />Storage Tank Closure Policy Evaluation (Report) dated 11 November 2021. AECOM <br />submitted this document on your behalf for the Dopaco Area Case #3 (Dopaco) <br />underground storage tank (UST) petroleum release case at 800 Church Street in <br />Stockton (Site). In the Report, AECOM presents August 2021 Site groundwater <br />sampling data, and evaluates Site conditions against criteria established in the State <br />Water Resources Control Board’s Low-Threat Underground Storage Tank Case Closure <br />Policy (LTCP). AECOM identifies impediments to closure and data gaps related to <br />shallow soil and soil gas and recommends proposing a scope of work to address these <br />gaps. AECOM also recommends discontinuing total petroleum hydrocarbons as diesel <br />(TPHd) analysis as part of the groundwater sampling analytical suite due to the overall <br />stable and decreasing nature of TPHd concentrations at the Site. <br /> <br />Central Valley Water Board staff has the following comments: <br /> <br />1. In the Report, AECOM states that TPHd should no longer be analyzed due to <br />stable and declining concentration trends. However, while TPHd concentrations <br />do appear to be stable and declining, they remain above water quality objectives. <br />As such, Central Valley Water Board staff does not concur. Please continue to <br />analyze TPHd in collected Site groundwater samples. Please continue to <br />perform routine groundwater sampling on a semi-annual basis during 1st and 3rd <br />quarters, with groundwater monitoring reports due by the first day of the second <br />month following the end of each calendar quarter (1 May and 1 November). <br /> <br />2. In the Report, AECOM identifies historical soil shallow soil samples which exceed <br />the LTCP Petroleum Vapor Intrusion to Indoor Air Media-Specific threshold of <br />100 milligrams per kilogram (mg/kg) for combined total petroleum hydrocarbons <br />as gasoline (TPHg) and TPHd, or Total TPH. AECOM concludes that these