EAST SAN JOAQUIN WATER QUALITY FRAMEWORK 2005/2006 WATER QUALITY MONITORING RESULTS

摘要

Surface water quality was measured in irrigation supply and drainage canals in the East San Joaquin Valley as a part of the East San Joaquin Water Quality Framework during and after 2 storm events in December 2005 and February/March 2006, and twice during the irrigation season in June and August 2006. Parameters measured included 11 organophosphate pesticides, 4 pyrethroid insecticides, 6 herbicides, and 3 metals, as well as nutrients and general water quality parameters such as TDS, pH and temperature. Concentrations of all detected parameters were compared to conservative screening thresholds based on ecotoxicity, human health, or agricultural standards. During the stormwater season, diazinon was detected in 28% of stormwater samples, with 16% of the samples exceeding the screening threshold (based on the lowest TMDL objective for chronic toxicity). No diazinon was detected in surface water during the irrigation season. This is consistent with pesticide use trends in the region, as diazinon is primarily used as a dormant spray during the winter. In contrast, chlorpyrifos was detected in 13% of the samples during the irrigation season but only 2% of samples during the storm season, again consistent with pesticide use trends as the highest use of chlorpyrifos occurs during the summer. One other OP pesticide (methyl parathion) and one pyrethroid (cypermethrin) were each detected once above the screening thresholds. Diuron was the only herbicide detected above the initial screening threshold. Copper and zinc were detected above screening thresholds at multiple locations during both storm and irrigation seasons, but selenium was never detected above screening threshold.