Appendix B Technical Appendix to supplement Section 7: Application of Emission Ratios, Gaussian Plume Functions, and Meteorological Data in the Analysis of Use Concentration Relationships of 1,3-Dichloropropene

Abstract

Alachlor, a preemergent herbicide, was registered in California in 1977. It is primarily used in the production of corn (human consumption and forage) and beans (dry and succulent). Alachlor’s physical and chemical properties indicated that it was persistent and mobile so it was placed on the California Department of Pesticide Regulation’s (DPR) Groundwater Protection List as required by Title 3, California Code of Regulations section 6800(b). DPR has currently analyzed 406 samples from 253 wells for the presence of alachlor. While alachlor has not been detected in ground water, its ethanesulfonic and oxanilic acid degradates (AESA and AOXA, respectively) have been detected. These residues range in concentrations from 0.05 to 1.38 parts per billion (ppb) in 29 wells. DPR’s monitoring results for alachlor, AESA, and AOXA are consistent with detection patterns nationwide.

There have been four groups of adjacent detections located in San Joaquin, Solano, and Stanislaus Counties in areas of either corn or bean production. Alachlor has been used in the vicinity of these adjacent detections. These detections are likely due to legal agricultural use of alachlor.