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INTERIM REMEDIAL ACTION TEST REPORT AND ADDITIONAL SUBSURFACE ASSESSMENT WORK PLAN at Former Unocal Service Station No 0187 437 East Miner Avenue Stockton, California Report No 240042 09-1 INTRODUCTION This report presents the evaluation of an interim remedial action performed by Gettler-Ryan Inc (GR) at the above referenced site The work was performed at the request of Unocal Corporation (Unocal) to evaluate the effectiveness of using an ozone microsparging system to decrease levels of petroleum hydrocarbons in groundwater beneath the subject site The scope of work performed included installing the ozone supply panel and connecting it to the previously installed sparge wells,collecting and analyzing groundwater samples from nearby monitoring wells during the system's operation, evaluating nearby underground storage tank (UST) sites to determine to what extent they may have contributed to the dissolved hydrocarbon plume downgradient of the subject site, and preparing a report that documents the work performed, evaluates the systems performance, and makes recommendations regarding future use of the system as well as the need for additional subsurface assessment work This work was requested by San Joaquin County Public Health Services Environmental Health Division (SJCPHS-EHD) and the San Joaquin County District Attorney in an August 30, 2000 meeting Work performed was proposed in GR's Work Plan For Additional Subsurface Assessment And Feasibility Study (report #240042 08, dated September 14, 2000), and approved by SJCPHS-EHD in a letter dated September 27,2000(Appendix A) SITE DESCRIPTION The subject site is a vacant lot situated on the northwest corner of East Miner Avenue and California Street in the city of Stockton, California, as shown on the Vicinity Map (Figure 1) The site is situated in an urban area of retail shops and hotels Topography in the site vicinity is flat lying, at an elevation of approximately 15 feet above mean sea level (MSL) Surface water in the vicinity of the site includes McLeod Lake and the Stockton Deep Water Channel, situated approximately one-half mile to the west The site was an operating Unocal service station from 1922 until 1992 Most recently the station consisted of a three-bay station building, three product dispenser islands (D-1 through D-3), and two gasoline and one waste oil USTs in a common excavation All station facilities have been removed and the site is currently an unpaved vacant lot Locations of former site features are shown on Figure 2