The Department of Pesticide Regulation began addressing pesticide contamination of ground water in the early 1980s, spurred by the discovery of contamination of ground water from the legal applications of the fumigant dibromochloropropane (DBCP). Reports of additional pesticides in ground water led to the passage of the Pesticide Contamination Prevention Act (PCPA) in 1985. The purpose of the PCPA is to prevent further pollution by agricultural pesticides of ground water used for drinking water supplies. It established a program to identify pesticides that have the potential to pollute ground water, requires sampling to determine if those pesticides are present in ground water, directs DPR to maintain a database of all wells sampled by all agencies for pesticides, and requires DPR to conduct a formal review to determine whether the use of the detected pesticides can be modified to protect ground water.
Mitigating pesticide contamination
Beginning in the late 1980s, DPR adopted regulations to protect ground water from detected pesticides. Some uses of these pesticides were prohibited and other uses were regulated in sensitive areas, called pesticide management zones (PMZs). PMZs were pesticide-specific. To apply detected pesticides in PMZs, users were required to get a permit from the county agricultural commissioner. To get the permit, users were required to obtain a ground water protection advisory written by a pest control adviser who had been trained by DPR in ground water protection. These advisories described management practices that users could voluntarily adopt to protect ground water. This regulatory approach was limited since it only regulated pesticides after they contaminated ground water.
In subsequent years, DPR scientists identified soil, climate, and depth-to-ground-water conditions that were associated with ground water contamination. In addition, DPR identified pathways of contamination (such as leaching and runoff) and mechanisms of movement to ground water (such as over-irrigation and rainfall) that were used as the scientific basis for developing mitigation measures.
In 2004, DPR adopted regulations to identify new sensitive areas, called either leaching ground water protection areas (GWPAs) or runoff GWPAs, depending on the predicted pathway to ground water. The GWPAs are either based on detections (and include all PMZs) or on soil characteristics and depth to ground water. This increased the size of regulated areas from 333,000 acres to 2.4 million acres. To use a pesticide regulated as a ground water contaminant in a GWPA, users must obtain permits for use from county agricultural commissioners that specify the enforceable management practices required in each type of GWPA. Additional statewide restrictions apply to pesticides applied in canals, ditches, and artificial recharge basins and by chemigation. Wellhead protection measures were also adopted. This new approach is designed to not only stop continued contamination but also to prevent future contamination. DPR samples a network of wells to determine the effectiveness of these regulations.
Using computer modeling to predict pesticide behavior
DPR uses computer modeling to evaluate the contamination potential of new pesticide active ingredients and of new uses of current active ingredients. That information is used to help determine whether a pesticide should be registered for use and what management practices should be required to protect ground water.
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