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A-C2 4. This site is a very old airport which has had aerial pesticide applicator use sporadically over the past 40 years. At some time, a wash pad incor- porating a French drain (vertical leachfield) was installed at the facil- ity. It was reported that in the 1960' s, Pacific Gas and Electric utilized the site for equipment storage and partially excavated the French drain to increase infiltration. No operator is currently based at the facility, but due to the past disposal practices and site geohydrology, there is a potential for adverse water quality impacts. Water samples were collected from an unused hand-dug well , approximately 200 yards from the wash pad and from two residential domestic wells approximately 300 yards from the facility. Analyses for all 6 classes of pesticides revealed low levels of 3 compounds. A second set of samples was collected from the two residential wells and atrazine and DDT/DDE were confirmed at approximately 3 and 0.04 ppb respectively. The source of the pesticides is unclear; atrazine is not usually applied by aerial appli- cators and has been shown to move into ground water in areas where it is used to control weeds on roads. DDT was used extensively in the area in the past, perhaps on the soils through which the wells were constructed. The old French drain will need to be closed in such a manner that there is no further threat to water quality. Additional sampling and hydrogeologic investigation will be necessary as part of the closure procedure and to evaluate the French drain as the potential source of pesticides in the residential wells. 5. This aerial applicator facility consists of two adjoining concrete wash pads sloped to a ditch which was constructed to retain all pesticide rinse water on the facility property. The ditch has been in use over twenty years . A composite sample was collected at 0-6" from 5 sites along approximately 100 ' of the ditch adjacent to the wash pads. Two 18"-24" samples were collected from the drain, one downgradient from the rinse water input from each wash pad. There was a flooded rice field adjacent to the ditch at the time of sample collection. The holes resulting from sampling to 24" filled with water soon after sampling (this indicates a high perched water table -- probably the result of rice culture in the area) . Site soils are heavy clay. Analysis of the 0-6" composite revealed several - pesticides from five classes (no phenoxy herbicides were detected) . DDT and metabolites were detected at 36 parts per million (ppm) total . Molinate (Ordram) and endosulfan were present at high levels . Analyses of the two 18"-24" samples revealed that all materials detected at 0-6" experienced high attenuation. DDT and metabolites total was 0.35 ppm; molinate and endo- sulfan were similarly reduced to low levels. The attenuation noted reduces the concern for any impact on ground water from past rinse water disposal practices at this site, although the effect of the high perched water table as it affects leaching of pesticides is unknown.