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, <br />�,anepa`s ;;ar Vvash Pacifi- - _ - 2 December 2020 <br />6230 Pacific Avenue <br />Stockton, San Joaquin County <br />Central Valley Water Board staff have the following comments.- <br />1. <br />omments: <br />1. By 18 December 2020, please submit a report presenting the location and <br />results of collected UST removal soil samples. <br />2. As completion of the Pilot Test is delayed until the completion of the Site <br />redevelopment, by 18 December 2020, please submit a schedule for the <br />anticipated completion of the redevelopment activities. <br />3. Starting 31 December 2020, please submit monthly Site redevelopment <br />progress updates at the end of each month. <br />4. Remaining concentrations of petroleum hydrocarbons in groundwater are <br />summarized in Table 1 below. While the Pilot Test may be postponed until after <br />completion of the Site redevelopment activities, routine semi-annual groundwater <br />sampling of Site wells should be performed during 1St and 3rd calendar quarters <br />until case closure is granted, with Groundwater Monitoring Reports (GMRs) <br />submitted within 30 days of the end of each semi-annual calendar period <br />(30 April and 30 October, respectively). Recently, the frequency of groundwater <br />sampling events has been inadequate. Only two groundwater sampling events <br />have been performed since 2012: during 1St quarter 2017 and 1St quarter 2019. <br />Please perform the next groundwater sampling event during 1St quarter 2021 and <br />submit a GMR by 30 April 2021. <br />Table 1 — Maximum February 2019 Groundwater Concentrations (ua/I ) <br />Depth <br />No. of Screen <br />Interval <br />Zone <br />TPHg <br />Wells <br />B <br />T <br />E <br />X <br />MTBE <br />TBA <br />Range <br />(ft bgs) <br />Shallow <br />12 6-49 200,000 <br />49,900 <br />22,900 <br />3,480 <br />9,300 <br />50,600 <br />3'000A <br />nter- <br />mediate <br />7 45-70 9,970 <br />1,480 <br />60.5 <br />622 <br />118 <br />3,690 <br />256 <br />LWater Quality Objectives 50 1.0 , 150 1 300 1 1,750 1 13 12 <br />TPHg= total petroleum hydrocarbon as gasoline, BTEX= benzene, toluene, ethylbenzene, <br />xylenes; MTBE= methyl tert butyl ether; ug/L= micrograms per liter; ft bgs= feet below ground <br />surface <br />A= February 2019 concentration was below the elevated reporting limits of 10.000 ug/L. The <br />March 2017 concentration was 3,000 ug/L. <br />