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Bob Black,
USGS Hydrologist,
934 Broadway,
Suite 300
Tacoma, WA 98402

(253) 552-1687
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Ground-Water Pesticide

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9722-9EW - Development of Methods to Assess the Vulnerability of Ground Water to Pesticide Contamination in Washington State - Completed FY2003

Introduction - The Environmental Protection Agency (EPA) is developing a rule requiring States to have a Pesticide Management Plan (PMP) for the pesticides atrazine, simazine, alachlor, metolachlor, and other pesticides if found at levels of concern. Under the proposed rule, if a State does not have an approved plan, these pesticides can no longer be used in the state. The Washington State Department of Agriculture, the lead agency for the PMP in Washington, has submitted a draft generic management plan to EPA for review. At some future time, a final plan will be required. Completion of the plan requires an assessment of ground-water vulnerability to pesticides in agricultural areas of the state.

Objectives - Designate agricultural areas in the State that need to be considered for pesticide management planning.

Develop a process-based modeling approach to help delineate areas of high, medium, and low vulnerability of ground water to pesticides in the management areas.

Evaluate the feasibility of using the process-based model for determining vulnerability of ground water to pesticides by testing it in one or two of the management areas were vulnerability can be assessed using statistical methods.

Relevance and Benefits - The results of this study will provide the Washington State Department of Agriculture with the information needed to develop the PMP. The Federal interest lies in helping to develop a tool that can be used to address the needs of those charged with protecting the nation's water resources. The modeling approach used could have high transferability to other parts of the nation.

Approach - Identify agricultural areas in the state to be considered for pesticide management planning by using crop statistics, information about pesticides used on crops, and other data, such as depth to ground water.

Modify the input to PATRIOT/PRZM, an existing process-based model, so that model output can be mapped to the intersection of GIS data layers, including soils, approximate depth to ground water, surficial geology, and estimates of pesticide application rates.

Compare model results against results of statistical analyses and/or observed concentrations of pesticides in ground water in the test areas. Based on this comparison, evaluate if the model, or a modified version of the model, can be used in other management areas.

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