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WORK PLAN FOR ADDITIONAL SUBSURFACE <br />INVESTIGATION AND WELL INSTALLATION <br />Public Works <br />1810 East Hazelton Avenue <br />Stockton, CA 95201 <br />June 19, 2017 <br />1.0 INTRODUCTION <br />This work plan was prepared by Condor Earth (Condor) to describe the proposed scope of work to <br />address additional investigation and remediation activities requested by the Central Valley Regional <br />Water Quality Control Board (Central Valley Water Board) in a letter dated July 27, 2016. The Central <br />Valley Water Board requested a work plan which includes: 1) a proposal for the collection of an adequate <br />number of groundwater samples to delineate the horizontal and vertical extent of groundwater impact <br />from the unauthorized release of petroleum hydrocarbons from the Site; 2) a proposal for additional <br />downgradient monitoring wells for transition and compliance zone monitoring related to proposed ozone <br />injection; 3) a proposal to collect an adequate number of soil samples from the surface to 10 feet bgs to <br />characterize the extent of hydrocarbon impact to shallow soil observed during ozone injection well <br />installation; and 4) preparation of at least two geologic cross sections oriented parallel to and <br />perpendicular to the groundwater flow direction showing subsurface lithology, depth to water, and <br />chemical data. <br />This work plan includes project background information, a description of the proposed field procedures, <br />laboratory analyses, reporting requirements, and anticipated project schedule. <br />2.0 PROJECT BACKGROUND <br />The Site is located at 1810 East Hazelton Avenue in Stockton, California as shown on Figure 1, Appendix <br />A. The Site serves as a motor pool facility and office complex for the San Joaquin County Facilities <br />Management Division. The Site currently houses two underground fuel tanks (USTs), associated <br />underground piping, and dispensers. Currently, the fueling system consists of one gasoline UST (UST <br />#1), one diesel UST (UST #2), and two dispenser islands. Additionally, five former tanks (USTs # 3, 4, 5, <br />6, and 7) were removed, and one former tank (UST #8) was abandoned in place. A municipal irrigation <br />well is located in Stribley Park, approximately 550 feet north of the fueling system. Key Site features are <br />presented on Figure 2, Appendix A. <br />Residual petroleum hydrocarbon constituents have been detected in soil and groundwater samples <br />collected at the Site during UST removal activities and during subsequent subsurface investigations <br />conducted at the Site. Notably, elevated gasoline constituents were detected in soil and groundwater <br />samples collected in June 1995 beneath a former 12,000-gallon gasoline UST (UST #3) that was located <br />just west of the existing dispensers (see Figure 2, Appendix A). Fisch Environmental over-excavated the <br />UST basin to a depth of approximately 27 feet and collected additional soil samples. The additional soil <br />samples collected at the base of the excavation also contained elevated concentrations of gasoline <br />constituents. Subsequent investigations conducted by various consultants included the installation and <br />sampling of two shallow hand augered soil borings (HA-1 and HA-2), two additional soil borings (B-3 <br />and SB-3), seven groundwater monitoring wells (MW-1 through MW-7), one soil vapor extraction test <br />well (SVE-1), and one combination soil vapor extraction test well/air sparge test well (AS-1/SVE-2). In <br />addition, Condor installed six ozone injection wells (OW-1 through OW-6) in May 2016 in anticipation <br />CONDOR