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MAY _'. 8 <br /> •u r°n x u Menlrcw Reoxmucr <br /> Water Boards `/ ° <br /> Central Valley Regional Water Quality Control Board <br /> 26 May 2015 <br /> Ms. Georgia Rooks <br /> STAND Affordable Housing <br /> 1209 east 8th Street <br /> Stockton, CA 95206 <br /> SOIL GAS INVESTIGATION, CASA DE OASIS, 1700 SOUTH EL DORADO STREET, STOCKON, <br /> SAN JOAQUIN COUNTY, <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water Board) staff <br /> reviewed the Soil-Vapor Survey Work Plan (Work Plan), dated 7 May 2015, submitted by Advanced <br /> GeoEnvironmental Inc. (AGE[) on behalf of STAND Affordable Housing (STAND). We understand STAND is <br /> currently considering purchasing the property at 1700 South EI Dorado Street in Stockton (Casa De Oasis), for <br /> use as an adult (senior) apartment complex with a community center. <br /> In January 2015 a Phase 6 Environmental Assessment was conducted by AGEI on behalf of STAND and <br /> reported five underground storage tanks (USTs), identified in 1991, in the City of Stockton sidewalk adjacent to <br /> the proposed community center. Evidence of a fuel dispenser was found inside the community center. The <br /> USTs and associated piping were removed on 11 December 1991. Petroleum hydrocarbons or volatile <br /> organic compounds were not detected in the soil samples collected at this time of the tank removal activities. <br /> On 16 September 1992, the San Joaquin County Department of Public Health Services issued a closure letter <br /> to the City of Stockton for the UST case. <br /> In March 2015 a Phase II Site Assessment Report was prepared by AGEI. AGEI reported the results of seven <br /> soil vapor samples collected at five and ten feet below ground surface (' bgs). Naphthalene was detected in <br /> the sample collected in the sidewalk near the former USTs. Naphthalene concentrations of 1.2 micrograms <br /> per Liter(ug/L) in SV3-5, exceed the California Human Health Screening Level (CHHSLs) developed by the <br /> Office of Environmental Health Hazard Assessment of 0.032 ug/L for residential exposures. Toluene and <br /> xylenes were detected in SV3-5 and also in SV4-5 (150'from the USTs) but results did not exceed the <br /> California Human Health Screening Levels (CHHSLs) for residential exposures. AGEI recommended <br /> additional soil vapor sampling and submitted the May 2015 Soil Vapor Survey Work Plan proposing <br /> construction of additional soil borings for the purpose of collecting additional soil vapor samples. <br /> In the Work Plan, AGEI proposed installation of twelve (12) soil borings along EI Dorado Street and 3rd Avenue <br /> and within the adult senior apartment complex, but showed seven (7)soil borings in Figure 2 of the Work Plan. <br /> Based on Figure 2, AGEI proposed two (2) soil borings advanced to 5 feet below ground surface(' bgs), and <br /> five (5) soil borings to 10' bgs. Temporary vapor probes are proposed to be installed in the borings to <br /> investigate potential for petroleum vapors to migrate into indoor air. A mobile laboratory is proposed to be <br /> used to analyze soil vapor samples for volatile organic compounds (VOCs) by USEPA Method 82608 on a <br /> same day turn around. A tracer compound(isopropyl alcohol or 1,2-diflouroethane) will be used to check <br /> sample probe and piping integrity. A Min-RaeTm photoicnization detector will measure total VOCs from the <br /> KARL E. LONOL6Y SOD, P.E., mwm I PAMGLA C. CnEE00x P.E., BCEE, cxccuT=orr,em <br /> 11020 Sun Center Drive 0200.Rancho Cordova,CA 95670 1www.weterboarde.ca.pov/cenValveliey <br /> r^.nee.cao rnren <br />