Strategy of an Agricultural Coalition to Meet the Diazinon and Chlorpyrifos Total Maximun Daily Load in the Lower San Joaquin River, CA

ABSTRACT STRATEGY OF AN AGRICULTURAL COALITION TO MEET THE DIAZINON AND CHLORPYRIFOS TOTAL MAXIMUM DAILY LOAD IN THE LOWER SAN JOAQUIN RIVER, CA by © Stephanie A. Henderson 2011 Master of Science in Environmental Science: Professional Science Master Option California State University, Chico Spring 2011 The San Joaquin River Watershed is one of the two major fresh water sources that drain into the Sacramento and San Joaquin Delta and San Francisco Bay, which supports an extremely productive and environmentally significant aquatic ecosystem. However, organophosphate pesticide runoff from the profitable agricultural industry of the San Joaquin River Valley is contributing to water quality impairments that are causing population declines of several aquatic organisms in the watershed. To address impairments due to two organophosphate pesticides, the Chlorpyrifos and Diazinon Total Maximum Daily Load for the Lower San Joaquin River was established. All agricultural coalitions discharging to the Lower San Joaquin River under the Irrigated Lands Conditional Waiver were required to enact a surveillance and monitoring program to collect information necessary to assess compliance with seven monitoring objectives. The East San Joaquin Water Quality Coalition initiated such a program. The data generated during January through September 2010 revealed that the growers represented by the Coalition failed to comply with water quality objectives (10 exceedances), San Joaquin River loading capacity (one non-compliant load), and load allocations of tributaries (nine non-compliant loads). Concentrations of chlorpyrifos caused all impairments; diazinon was not detected within the watershed. In addition, other pesticides are present in the waterways of the Coalition‘s region and chlorpyrifos may interact with other agricultural contaminants to cause toxicity. However, the Coalition recently reported decreases in exceedances of water quality objectives in tributaries where intensive grower outreach and education have occurred. Chlorpyrifos remains a major concern for the Coalition region and remains the focus of Coalition outreach and education to growers. Through continued outreach, the Coalition believes it will be able to address impairments due to chlorpyrifos within its region. Through continued monitoring at an appropriate magnitude and frequency—which may need to be adjusted from the Coalition‘s present design—the Coalition can determine where, when, and which agricultural constituents are impairing water quality and can adjust its actions accordingly to achieve optimum water quality within the San Joaquin River Watershed.