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 SanrnJoaquin Valley as a part of the East San Joaquin Water Quality Framework during and afterrn2 storm events in December 2005 and February/March 2006, and twice during the irrigationrnseason in June and August 2006. Parameters measured included 11 organophosphate pesticides,rn4 pyrethroid insecticides, 6 herbicides, and 3 metals, as well as nutrients and general waterrnquality parameters such as TDS, pH and temperature. Concentrations of all detected parametersrnwere compared to conservative screening thresholds based on ecotoxicity, human health, orrnagricultural standards. During the stormwater season, diazinon was detected in 28% ofrnstormwater samples, with 16% of the samples exceeding the screening threshold (based on thernlowest TMDL objective for chronic toxicity). No diazinon was detected in surface water duringrnthe irrigation season. This is consistent with pesticide use trends in the region, as diazinon isrnprimarily used as a dormant spray during the winter. In contrast, chlorpyrifos was detected inrn13% of the samples during the irrigation season but only 2% of samples during the storm season,rnagain consistent with pesticide use trends as the highest use of chlorpyrifos occurs during thernsummer. One other OP pesticide (methyl parathion) and one pyrethroid (cypermethrin) wererneach detected once above the screening thresholds. Diuron was the only herbicide detected abovernthe initial screening threshold. Copper and zinc were detected above screening thresholds atrnmultiple locations during both storm and irrigation seasons, but selenium was never detectedrnabove screening threshold.