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ALAN M. BUEHLER <br />9340 <br />Alan M. Buehler, P.G. a_ <br />Engineering Geologist <br />sy3NAL G <br />OF CPO <br />Siebold Construction -2- 25 July 2017 <br />820 S. American Street <br />Stockton, San Joaquin County <br />flow direction since December 2015. Table 1 below presents June 2017 groundwater <br />data. <br />Table 1 — June 2017 Groundwater Data <br />WELL Screen Interval <br />(ft bgs) <br />TPHg <br />(ug/L) <br />Benzene <br />(ug/L) <br />MTBE <br />(ug/L) <br />TBA <br />(ug/L) <br />MW-2 30-50 750 14 28 <20 <br />MW-3 30-50 <50 <0.5 <1 <20 <br />MW-4 30-50 <50 <0.5 <1 <20 <br />MW-5 22-37 <50 <0.5 <1 <20 <br />MW-6 22-37 <50 <0.5 <1 <20 <br />MW-7 22-37 <50 <0.5 <1 <20 <br />MW-8 65-75 <50 7.0 1.9 <20 <br />TPHg=total petro eum hydrocarbons as gasoline; MTBE=methyl tert butyl ether; TBA=tert butyl alcohol; ft bgs=feet below <br />ground surface; ug/L=micrograms per liter <br />Based on June 2017 groundwater data, the Site meets LTCP Groundwater Specific <br />criteria by Scenario 1. The lateral and vertical extent of hydrocarbon impact to <br />groundwater has been defined. With only two (2) monitoring wells reported with <br />petroleum constituents, the extent of hydrocarbon impact to groundwater is less than <br />100 feet in length. Additionally, there is no free product, and no water supply wells are <br />present within 250 feet of the Site. <br />Based on 2011 soil gas sampling results, the Site meets LCTP Vapor Intrusion criteria <br />by Scenario 4.1. Soil gas concentrations are below LTCP residential and commercial <br />thresholds for where no bio-attenuation zone is present. <br />The Site does not meet LTCP Direct Contact and Outdoor Air Exposure (Direct Contact) <br />criteria. Evaluation of Direct Contact risk at the Site requires assessment of shallow soil <br />between 0 to 5 and 5 to 10 feet bgs. Historically, no soil samples have been collected at <br />the Site shallower than 15 feet bgs. As such, Central Valley Water Board staff request <br />that you collect shallow soil samples at the Site. By 22 September 2017, please submit <br />a Work Plan for the collection of a sufficient number of shallow soil samples to properly <br />assess hydrocarbon concentrations in soil between 0 to 5 and 5 to 10 feet bgs. <br />If you have any questions or concerns regarding comments in this letter please contact the <br />undersigned at (916) 464-4615 or by email at alan.buehler@waterboards.ca.gov . <br />cc: Song Her, State Water Resources Control Board, UST Cleanup Fund, Sacramento <br />Daniel O'Brian, DGS, Real Estate Division, 707 3rd Street, West Sacramento 95605 <br />Michael Keith, San Joaquin County Environmental Health Department, Stockton <br />Ryan Crawford, GHD Inc., 3831 N. Freeway Blvd #220, Sacramento 95834 <br />Christian Zamorano, 820 S. American Street, Stockton 95206