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r CHRONOLOGY San Joaquin County Agricultural Commissioners Office 503 East Tenth Street Tracy CA 95376 10/28/88 Three 1,000-gallon underground storage tanks were removed this date. Two of the tanks stored weed oil, one contained unleaded gasoline. Soil samples collected from beneath the tanks were reported positive for petroleum hydrocarbons. 10/28/88 Notification of Hazardous Waste Discharge #88-199 filed this date. 11/03/88 Unauthorized Release Report filed this date. 03/20/95 Notice of Reimbursement letter sent this date to San Joaquin County General Services and site placed in Local Oversight Program. 12/19/97 Site investigation began this date with the advancement of ten Geoprobe soil borings and the collection of soil and grab groundwater samples for analysis, See Ramage_.En.vironmenta"Sit----lF�vestigation-Report" bated-- 01-/23J9&.------ The 1123f9&.--- -- The soil near the former UST area and all groundwater samples had reported petroleum hydrocarbon contamination. 10/28/98 Three groundwater monitoring wells were installed this date, see Ramage Environmental "Monitoring Well Installation & Groundwater Sampling Report" dated 01127199. Well MW-2, located northeast (down gradient) of the former UST area reported a detection of 140 micrograms per liter of total petroleum hydrocarbons as diesel (TPHd). A sensitive receptor survey was included in the report; The California Department of Water Resources (DWR) records indicate six wells were located within 2,000 feet of the site, but a site reconnaissance was performed and only four wells were located. Properties in the area are provided city water. 02/18/99 The three groundwater monitoring wells were sampled for a second time, all results were reported as non-detect. 07/08/99 Date of Revised Residual Hydrocarbon Mass Calculations that estimates 813 pounds of total petroleum hydrocarbons remaining in the soil. 01/18/06 Quarterly monitoring and sampling of the three groundwater monitoring wells resumed on this date. A detection of 238 micrograms per liter of TPHd was reported in well MW-2. Routine quarterly groundwater monitoring and sampling continued from this date. 04/30/08 Soil vapor samples for laboratory analysis were collected on this date to evaluate the potential risk to indoor air posed by the remaining onsite contamination. 08/29/08 "Soil Vapor Sampling and Human Health Risk Assessment Report" was submitted this date by Ramage Environmental, Inc. which included a current sensitive receptor survey. The Report concludes the contamination remaining at the site poses no risk to human health or the environment.