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r r The perimeter of the site is not fenced and access to the site is unrestricted with the _ exception of the fenced 55-gallon and the chemical storage area (2,3,4). Two empty underground storage tanks (USTs) are located on the property; one within the airplane parking strip and the other east of the southern hangar. Three empty USTs Y- unearthed from a former gas station adjacent to the site are stored in an area south of the fenced 55-gallon drum storage area (4). _ Land uses surrounding the Trinkle & Boys site include scattered residences and the New Jerusalem School with a student and staff population of 223. The school is located on the eastern side of Highway 33 approximately 0.5mile southeast of the site. A farm field lies directly west of the site across Highway 33. Large surface water bodies within four miles of the site include the Banta Carbona Canal which is used solely for irrigation and the San Joaquin River (4,5). 3.0 Summary of Site Inspection Activities .� The Trinkle & Boys facility is not listed in the Resource Conservation and Recovery Act (RCRA) database printout list as of March 4, 1992. _ The Department of Health Services (DHS), presently, California Environmental Protection Agency, Department of Toxic Substances Control (Cal EPA-DTSC), is involved with unregulated pesticide wash down facilities and disposal of pesticide rinse water to the ground at aerial chemical application businesses in the Central Valley, including Trinkle & Boys. The Central Valley Regional Water Quality Control Board (RWQCB) collected soil and groundwater samples during an inspection of Trinkle & Boys in June 1986. Analysis of shallow groundwater samples at 1.5 feet below ground surface (bgs) ._ revealed contamination with pesticides including Endosulfan I at 36 parts per billion (ppb), Diazinon at 140 ppb, Di-Syston at 1,500 ppb, Fenthion at 67 ppb, chlorpyrifos at 210 ppb, malathion at 78 ppb, methomyl at 3,900 ppb, Furadan at 16,000 ppb, Diuron at 260 ppb, and Simazine at 48 ppb (2). r The RWQCB issued Trinkle & Boys a Cleanup and Abatement (C&A) Order No. 87-734 on October 27, 1987. Subsequent correspondence between the RWQCB and Trinkle & Boys resulted in the issuance of C&A Order No. 89-705 on March 8, 1989. Both C&A orders request Trinkle & Boys to clean up wastes and remediate shallow groundwater contamination that threatened to migrate to deeper parts of the aquifer. To meet the requirements of the C&A orders, Trinkle & Boys contracted Weston Consultants (Weston) to characterize the concrete pad and sump area (6). Results of the Weston investigation conducted in June 1989 indicated that soil from boring BC near the gravel rinse basin at 1 foot bgs is contaminated with the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) at 4.94 milligrams per kilograms (mg/kg). Analyses of soil from borings BA, BE ,BF, BG, and BH revealed DDT contamination at a range of 0.055 mg/kg to 3.24 mg/kg. See Figure 2 for Weston soil boring locations. Shallow groundwater samples taken from monitoring wells MW-1, MW-2, and MW-3 at 10, 9.4, and 8.5 feet bgs, respectively, showed trace amounts of Bromacil, carbaryl, and diuron. Weston recommended that Trinkle & Boys initiate an annual sampling program at three monitoring wells installed during the investigation. On May 7, 1990, the RWQCB requested that Weston clarify some of its findings, particularly, the possible differences in results between the data collected by RWQCB URS Consultants, Inc. Page 4