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]0_ Trinkle and- Boys Ag Flying Service. San Joaquin County T This facility has been utilized by three aerial applicator businesses over last 40 nears. The current operators acquired the facility from their parents and implemented changes in rinse water disposal practices. One chance, made a few months before our inspection, was to install a sump, a submersible pump., and an above-ground tank for rinse water. Prior disposal was onto a paved rsrea (part of which had numerous cracks) or into a small pit from where it probably infiltrated. The first sampling site selected was a gravel area adjacent to the runway at the end where the wash area is located. The sampling site was approxi- ma te I y pproxi- mately 50 f eet from the old pit in the wash area; the separating area is oaved with asphalt.. At approximately 6 inches depth, an underlying fill of larae gravel was encountered. The large gravel was discolored and had a -' pesticide/hydrocarbon odor. Free water was encountered at 1.8 inches. Samples of the discolored gravel and of the water were collected. Two soil composite samples were taken from areas adjacent to other portions of the runway. One composite was from 1"-6" at five sites (surface debris was removed prior to sampling) , and the other sample was from 18-24" at two sites. A water sample was collected from a faucet supplied by an on-site well . Analyses revealed that the gravel contained several pesticides at fairly h,gh levels, including DDE at 22 ppm, DDD at 15 ppm, disulfoton (Di-Syston) at 2.50 ppm, and carbofuran at 38 ppm. The free-water sample also contained numerous pesticides. but generally at low levels. Carbofuran, however, was at. 16 ppm. The -6" cr_0l composite contained seven pesticides including ethion at 110 ppm and ethy? parathion at 48 ppm_ The 18"-24" soil com- posite showed only one pesticide, 2,4-D at 0.16 ppm. No pesticides were detected in the well water sample. It is possible ghat -the discolored gravel is part of an old leach field to disperse water trom the pit in the wash area. In any event, some miti- gation will be necessary to prevent the off-site movement of pesticides in the shallow ground water. Some mitigation may also be necessary in areas where surface soils have significant pesticide residues, but additional sampling is necessary to define the areas, and a review of site soils and hydrogeology is necessary to determine the degree of protection afforded by site specific conditions.