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CHRONOLOGY Unocal #6981 4707 Pacific Avenue Stockton, CA 95207 05/12/88 Notification of Hazardous Waste Discharge and Unauthorized Release Report were filed this date following the discovery of petroleum hydrocarbon contaminated soil during piping replacements. 05/13/88 Soil samples were collected from test pits around the two dispenser island areas. Eight samples were collected at 4' bsg; one was collected at 8' bsg. See Applied GeoSystems report Preliminary Report of Soil Contamination Investigation and Removal of Underground Storage Tanks dated July 8, 1988, available on microfiche. 05/20/88 Additional excavation was done in the same areas around the dispenser islands. See the above referenced Applied GeoSystems report. 06/14/88 Three Underground Storage Tanks removed this date; the EHD provided inspection. Soil samples for laboratory analysis were collected from beneath the tanks. The tank pit was subsequently overexcavated to between 17 and 22 feet bsg. See the above referenced Applied GeoSystems report. 12/15/88 Soil vapor samples collected from borings onsite. See Applied GeoSystems Site Investigation Report dated January 12, 1989, available on microfiche. 01/31/90 Five soil borings and five groundwater monitoring wells, MW's 1-5, were installed onsite. See Applied GeoSystems report available on microfiche. 03/10/92 Three groundwater monitoring wells, MW's 6-8, and four soil vapor extraction wells, VW's 1-4, installed onsite. See Resna's Environmental Investigation Status Report and Work Plan Addendum dated July 9, 1992, available on Questy's. 08/10/92 Five groundwater monitoring wells, MW's 9-13 and one groundwater extraction well, PTW-1 were installed beginning this date. An aquifer test was conducted on PTW-1. See Resna's Problem Assessment Report dated December 16, 1992, available on Questy's. 12/10/93 Two soil vapor extraction wells, VW's 5-6, were installed onsite. See Resna's Letter Report Well Installation dated January 18, 1994, available on Questys. 09/22/94 Soil Vapor Extraction system started operation this date. See GeoStrategies, Inc. dW>" Soil Sampling and System Startup Report dated November 28, 1994 available on _ 15 Questy's. 05/03/96 Wells MW-3, MW-10, MW-12 and MW-13 were destroyed at the request of the City of Stockton to allow for a road construction project. No report of this work has been found; inspector generated field notes are available in the LOP site file. 08/16/99 Three groundwater monitoring wells, MW's 14-16, one air sparging well, VW-7, and one soil boring, VW-9, were installed. See Gettler-Ryan Well Installation and Soil Boring Report dated November 18, 1999, available on Questy's.