Study GW15: Groundwater Protection List Monitoring for Bentazon
Abstract
The Department of Pesticide Regulation’s (DPR) Environmental Monitoring Branch (EM) Groundwater Protection Program (GWPP) staff sampled 32 wells between October 2015 and October 2017 to determine if current agricultural uses of bentazon were resulting in contamination of groundwater. For this study, wells were sampled in high-use sections of Modoc, Monterey, San Luis Obispo, Santa Barbara, and Siskiyou counties. Bentazon was detected in four wells in Modoc County; two of the wells had quantifiable detections of 0.139 and 0.199 parts per billion (ppb) and two had trace detections below the reporting limit. All bentazon concentrations are well below human health levels for drinking water. Based on these detections, it is recommended that DPR establish sections 25M47N05E10 and 25M47N05E15 as Ground Water Protection Areas.