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.„„ Water Boards Central Valley Regional Water Quality Control Board 23 April 2018 Mr. David Atwater Van De Pol Enterprises, Inc. P.O. Box 1107 Stockton, CA 95201 RECEIVED APR 3 0 2013 ENV/ROAMENTAL HEALTH PERMIT/SERVICES Soil Vapor Investigation Work Plan, Pacific Pride, 3147 South El Dorado Street, Stockton, San Joaquin County Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff reviewed the Soil-Vapor Investigation Report (Vapor Report) dated 22 November 2018, and the Groundwater Monitoring Report— Fourth Quarter 2018 (4Q2018 Report) dated 13 March 2018, both submitted on your behalf by Advanced GeoEnvironmental, Inc. (AGE). The Pacific Pride property is located at 3147 South El Dorado Street in Stockton (Site). In October 2017, AGE installed and sampled two soil gas wells, SV-1 and SV-2. Soil samples were collected at 5 feet below ground surface (bgs) from each boring, and soil vapor samples were collected from approximately 5 feet bgs. AGE detected petroleum hydrocarbons in vapor samples at maximum concentrations of 6,300 micrograms per cubic meter (ug/m3) total petroleum hydrocarbons as gasoline (TPH-G), 15 ug/m3 benzene, 16 ug/m3 ethylbenzene, and 15 ug/m3 naphthalene. AGE did not detect the leak detection compound, xxx, in either of the soil gas samples. Percent oxygen was 0.88% in sample SV-1 and 0.48% in sample SV-2, indicating that a bio-attenuation zone does not exist at the Site. Petroleum hydrocarbons were not detected in soil samples from the SV wells, with the exception of one detection of TPH as diesel (TPH-D) in SV-2 at 8.6 milligrams per kilogram. AGE recommended performing a second soil vapor monitoring event to verify soil vapor concentrations at the Site. AGE stated that they have tentatively scheduled a second sampling event in April 2018. During the fourth quarter 2017, ATC detected petroleum hydrocarbons at maximum concentrations of 200 ug/L TPH-G, 170 ug/L TPH-D, 2.7 ug/L benzene, 4.3 ug/L methyl tert butyl ether (MTBE), and 2.6 ug/L 1,2-Dichloroethane (1,2-DCA). Central Valley Water Board staff have the following comments: Central Valley Water Board staff concur with AGE's recommendation to perform a confirmation soil gas sampling event. Please submit the results by 30 June 2018. TPH-G and TPH-D concentrations in well MW-1 have increased since shut-down of the remedial system in February 2016. The groundwater gradient during the fourth quarter ;AP. L L01,.:1_ • SoC.), P.E. PAFALLf.C. (..;REEDO:, P.E.., EiCEL. EXU.,;.1 71020 c nLLTh', 420C. Rancho ,orciovi.,. GA 9557C ! www.waLerboard4.ce.govIcentralvalliOy PA