Ambient monitoring for naled and its oxidation product, dichlorvos, were performed in Tulare County during May and June of 1991. No application monitoring was completed in 1991 due to the substitution of another pesticide for naled at many fields in the study area. Application monitoring for these compounds was carried out by ARB personnel in Fresno County in 1992. The report for the application monitoring is in Appendix F. All data presented in the report for naled and dichlorvos have been determined and accepted subject to a rigorous quality assurance program.

Detectable levels of naled and dichlorvos were identified at four of the five monitoring sites, including the background site. At three of these sites (Sunnyside, Jefferson, and Kaweah), levels above the MDL generally occurred between May 20 and May 23,1991. Detectable levels were found at the background site between May 30 and June 4, 1991. Tables 1 and 2 present a summary of results for naled and dichlorvos, respectively.