Thiobencarb monitoring was off to a rough start with nine exceedances of the 1.5 µg/L (parts per billion) performance goal in the agricultural drains. The performance goal, established in 1991, is set in the Central Valley Water Board Basin Plan. Our concern was the exceedances began the second week of monitoring rather than the typical mid-season timing coordinating with Memorial Day.
Fortunately, we have had no detections in the river, which is the point of compliance for the Central Valley Water Board. The water quality objective in the river is 1.0 µg/L at the city drinking water intakes. The water quality objective is set at a level to mitigate nuisance from taste and odor from thiobencarb elevated levels.
The monitoring season will extend until July 16. We are positive the monitoring results through June 18 will continue through the end of the season.