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OZONE REMEDIATION PILOT TEST WORK PLAN San Joaquin County-Public Works 1810 E. Hazelton Avenue Stockton, California June 15, 2015 1.0 INTRODUCTION This Ozone Remediation Pilot Test Work Plan was prepared by Condor Earth Technologies, Inc. (Condor) to describe the proposed installation of an ozone injection system to remediate petroleum hydrocarbon impacted groundwater at San Joaquin County Public Works located at 1810 East Hazelton, Stockton, California (site), Figures 1 and 2, Appendix A. The State Water Resources Control Board Path to Closure Plan FY 1 2/1 3 as of 12/11/13 Step to Resolve Impediment 2-Step 1 indicated that a work plan to pilot test a technology to reduce benzene and methyl tertiary-butyl ether (MTBE) concentrations should be submitted. Condor prepared this work plan at the request of the County of San Joaquin General Services Department (property manager). All work conducted by Condor will be under the supervision of a California Professional Geologist. This work plan includes project background information; a description of the field, laboratory, and reporting procedures proposed to conduct the work; and a project schedule. 2.0 SITE BACKGROUND The Site is located at 1810 East Hazelton Avenue in the City of Stockton, California (Figure I, Appendix A). The Site is an active county motor pool and office complex with a gasoline and diesel fueling system as shown in Figure 2, Appendix A. Currently, the fueling system consists of one gasoline underground storage tank (UST #1), one diesel tank (UST #2), and two dispenser islands. Additionally, four former tanks (USTs # 3, 4, 6, and 7) were removed, and one former tank (UST #8) was abandoned in place. A municipal irrigation well is located in Stribley Park, approximately 600 feet north of the fueling system (Figure 2). Quarterly groundwater monitoring has been ongoing since April 1999. Comprehensive site background information is provided in Appendix B. 3.0 MASS FLUX OF CONTAMINANTS IN GROUNDWATER Soils encountered at the site during over-excavation and well installation were reported by Ramage Environmental in 2003 as primarily silty sand with three interbedded well graded sand layers. The 2003 Rarnage report is attached in Appendix B. The sand layers are at approximate depths of 33 to 37 feet below ground surface (bgs), 40 to 44 feet bgs, and 49 to 56 feet bgs. Historical groundwater gradients at the site are shown on Table B, Appendix B. Historical laboratory analytical data for groundwater samples collected from the monitor wells at the site are in Table A, Appendix B. Isoconcentration contours for total petroleum hydrocarbons quantified as gasoline (TPH-G) and MTBE in groundwater based on laboratory analytical results of groundwater samples collected during the first semi-annual 2015 groundwater monitoring event are shown on Figures 3 and 5, respectively, Appendix A. The depth to water at the site has ranged from 36.37 feet to 50.34 feet. If the contaminant plume is assumed to extend to a depth of 55 feet, then the thickness of petroleum impacted groundwater at the site is approximately 15 feet (55 feet total depth — 40 feet to the current water table = 15 feet). CONDOF4