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• f ' Pesticide Rinse Water Disposal Sites -3- 2. Soil attenuation of most pesticides was evident at all the facilities where it was evaluated. As previously noted, this investigation did not include sites where soil fumigants (several of which have demonstrated poor atten- uation in some soils ) were discharged. Also, except for one MAD site and one lined pond site, the disposal sites were not located on sandy soils. The data which indicates soil attenuation is presented in Table 1. 3. There were no high levels of carbamate or OP pesticide residues that would cause disposal site soils to be classified as ' hazardous waste' based on the calculated L050 (i .e. , based on mamalian toxicity) . This situation is attributable to two factors. First, most aerial pesticide applicators have ceased washing out pesticide tanks on the ground and instead apply rinsate back onto the treated fields. Only exterior rinse is discharged to ground at the airport, and pesticide levels in such rinsate are relatively low. Secondly, the half-lives of most OP and carbamate -pesticides are relatively short in the surface soil environment. The generally "heavy" soils at the disposal sites and the number of warm, dry, sunny days in the study area during the application season should contribute to breakdown of OP and carbamate pesticides. Disposal practices at some facilities did not comply with CVRWQCB guide- lines (Appendix A) . In particular, sites# 2, 4, and 10 utilized disposal pits which promoted wastewater infiltration. Several other sites did not have test data to indicate if the 1x10-8 cm/sec permeability requirement was met at disposal areas. In addition, two other observations were made that raise concern for ground water protection. One, backflow prevention devices were not in use on wells or hose bibs used for equipment washing. Under certain cir- cumstances, a direct waste discharge to ground water could therefore occur. Two, at sites #6 and #8, wash water is generated or collected adjacent to wells. Pesticides that were detected in well water from site #6 are possibly a result of infiltration via the well borehole. With respect to the primary reason for conducting this investigation, i .e. , to develop information on the potential water quality impacts from past and present rinse water disposal practices, it is necessary to recognize that wastes below the ' hazardous' level can affect water quality. Such wastes are called 'desig- nated waste ' . The designated waste levels are site specific and take into account factors such as soil properties, depth to ground water, etc. A CVRWQCB staff report3by Or. Jon Marshack presents a procedure for determining desig- nated waste levels, and Appendix 3 of the report uses some assumed site factors to calculate example designated waste levels for several pesticides. Dr. Marshack's report was considered in making the following findings: 3. "The Designated Level Methodology for Waste Classification and Cleanup Level Determination", October 1986.