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Toyota Town - 2 - 22 February 2017 610 North Hunter Street Stockton, San Joaquin County In the Revised Work Plan, ATC proposes the advancement of five (5) soil borings. Soil is to be collected between 0-5 and 5-10 feet bgs in all five proposed boring locations. ATC indicates that the former UST basin was over-excavated to a depth of 22 feet bgs in 1988, and thus proposes to collect a soil sample from 25 feet bgs in the vicinity of the former waste oil tank. Soil from 25 feet bgs in the boring nearest the former waste oil tank will be analyzed for total petroleum hydrocarbon as gasoline, (TPHg), TPH as diesel (TPHd), volatile organic compounds (VOCs), semi-VOCs (SVOCs), polychlorinated biphenyls (PCBs), and Title 22 metals (collectively waste oil constituents). Additionally, soil will be collected from 25 feet bgs and analyzed for Title 22 metals in the two of the five borings that are furthest upgradient from the former USTs, for the purpose of establishing background concentrations. In two emails dated 17 January 2017, Ms. Jeanne Homsey of ATC provided a historical Site map showing the location, size, and contents of each former tank, as well as historical San Joaquin County Environmental Health Department (SJCEHD) files indicating that the former tank basin was over-excavated to a depth of 21 feet bgs. It appears that the proposed waste oil tank soil boring is actually located between the former 1,000-gallon fuel tanks. The location of this soil boring should be moved to the northeast, closer to the location of the former waste oil tank. While ATC has proposed collection of a soil sample from 25 feet bgs, the lithology in this boring should be continuously logged, and the soil sample collected from the shallowest observed native soil. In addition to the analysis proposed, the collected soil sample should be analyzed for total oil and grease (TOG) and polycyclic aromatic hydrocarbons (PAHs). Please provide the results in the Assessment Report due 5 May 2017. In the Revised Work Plan, ATC proposes the installation and sampling of four (4) permanent soil gas wells, as requested in my 18 November 2016 letter. The placement and installation and sampling methodology of the proposed soil gas wells are appropriate. However, no groundwater sampling has occurred since 2012, and no soil sampling has been performed shallower than 10.5 feet. In an effort to conserve the remaining Cleanup Fund budget, the soil gas wells should not be installed and sampled until the Vapor Intrusion risk is confirmed by the proposed shallow soil sampling and current groundwater sampling data. Therefore, at this time staff do not concur with installation and sampling of the four (4) proposed soil gas wells. In the Assessment Report due 5 May 2017, please include an evaluation of risk to indoor air due to vapor intrusion, based on comparison of collected soil and current groundwater data to LTCP screening criteria. If you have any questions or concerns regarding comments in this letter please call me at (916) 464-4615 or contact me by email at alan.buehler@waterboards.ca.gov . Alan M. Buehler, P.G. Engineering Geologist cc: Sriram lyer, State Water Resources Control Board, UST Cleanup Fund, Sacramento Nuel Henderson, San Joaquin County Environmental Health Department, Stockton Jeanne Homsey, ATC Group Services LLC, Modesto