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<br /> <br />Central Valley Regional Water Quality Control Board <br />31 January 2022 <br />Bill Doerr <br />The Newark Group <br />33878 Drifting Sands Circle <br />Thousand Palms, CA 92276 <br /> <br /> <br /> <br />RESPONSE TO ASSESSMENT WORK PLAN, DOPACO AREA CASE #3, <br />800 WEST CHURCH STREET, STOCKTON, SAN JOAQUIN COUNTY, <br />LUST CASE# 391193 <br /> <br />Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff <br />reviewed the Soil and Soil Vapor Sampling Work Plan (Work Plan) dated 27 January <br />2022. AECOM submitted this document on your behalf for the Dopaco Area Case #3 <br />underground storage tank (UST) petroleum release case at 800 West Church Street in <br />Stockton (Site). In the Work Plan, AECOM proposes the assessment of soil and soil <br />gas in the vicinity of the former UST area. <br /> <br />Central Valley Water Board staff concurs with AECOM’s proposal and has following <br />comments: <br /> <br />1. AECOM proposes to install temporary soil gas wells at 5 feet below ground <br />surface (bgs). However, Section 3.1.3 of the July 2015 joint-agency guidance <br />Advisory – Active Soil Gas Investigation (Guidance) states that soil gas samples <br />collected from shallower than 5 feet bgs are prone to breakthrough of ambient <br />air. As such, the top of the filter sand should be placed no shallower than 5 feet <br />bgs. The Guidance states that the probe tip should be placed midway in the filter <br />sand with at least 6 inches of sand above and below the tip. As such, the top of <br />the probe tip should be placed no shallower than 5.5 feet bgs. <br /> <br />2. AECOM proposes to collect soil and soil gas samples from each borehole. In <br />each boring, AECOM will (1) collect soil samples to the total depth of the soil gas <br />well via hand-auger, (2) install the soil gas well, (3) wait a minimum of 48 hours, <br />(4) collect a soil gas sample, (5) remove the soil gas well construction materials <br />to total depth of the well, and (6) collect soil samples below the well via direct <br />push. Incorporating Comment 1 above, AECOM’s proposed soil and soil gas <br />sampling is summarized in the Tables 1 and 2 below. <br />