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Pesticide Rinse Water Disposal Sites -2- In May 1985, staff completed a survey of 160 sites which handled pesticides and/or fertilizers. Review and ranking of these sites was completed in April 1986, and 130 sites identified where pesticide rinse water disposal practices needed to be evaluated. Due to a lack of technical information on rinse water disposal sites, it was decided to collect samples from selected disposal areas, primarily those representative of sites considered to have the greatest poten- tial to affect water quality (the MAD sites were not selected on this basis). At some sites, water from on-site or adjacent wells was sampled when regional hydrogeology, well construction parameters , and waste disposal practices indicated a potential for impact on ground water. SAMPLE COLLECTION AND ANALYSES As indicated above, most pesticides used in the study area fall into six chemical classes . All classes may not be used by an applicator. Mosquito abatement districts in particular usually utilize only •one class of pesticides (OPs) . None of the sites studied had any historical discharge of soil fumigants such as DBCP or EDB, and hence analyses for volatile organics were not con- ducted. Laboratory test procedures are available for each class and can be run on soil or water samples. Generally, eight ounces of soil or two liters of water are sufficient sample for analyses covering all six classes of pesticides. Appendix B describes the collection procedures used and lists the pesticides that could be detected in each class. Note that some pesticides in current use are not included in the lists. FINDINGS Forty-four samples were collected at thirteen . facilities during this inves- tigation. The individual facilities and sampling results are discussed in Appendix C; analytical data is presented in Appendix D. A summary of the findings is presented below. The results obtained during this investigation are generally consistent with current scientific thought on the behavior of pesticides in the environment. In particular, three basic observations can be made: 1. At facilities with histories that included the use of persistent OC pesticides , detectable levels of OC pesticide and breakdown products remained at rinse water disposal sites. In particular, DDT and its metabolites were encountered at most sites that were in use prior to 1973. The finding of DDT is consistent with findings of DDT in agricultural fields that had been treated with DDT and in drains that receive runoff from such fields.1,2 1. "Agricultural Sources of DDT Residues in California' s Environment" , California Department of Food and Agriculture, September, 1985. 2. DDT in the Salinas Valley" , California State Water Resources Control Board, Report No. 86-2-WQ. Lam'