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Pesticides

Pesticides in Groundwater

Groundwater Law

Under Wisconsin’s groundwater law (ch. 160, Stats.), the Department of Natural Resources (DNR) adopts numerical standards for contaminants in groundwater. DNR adopts an enforcement standard (“red light”) and a lower preventive action limit (“yellow light”) for each contaminant substance. These standards are contained in Wisconsin Administrative Code chapter NR 140. Standards are based on public health recommendations. The standards include a required safety factor, and are often set at very low levels (expressed in parts per million, or parts per billion).

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) regulates pesticide use in Wisconsin. DATCP reviews groundwater monitoring data, and acts to prevent pesticide contamination of groundwater. If pesticide contamination exceeds the enforcement standard (“red light”) at any location, DATCP must ordinarily prohibit applications of that pesticide at that location.

If contamination does not exceed the enforcement standard, DATCP may not ordinarily prohibit pesticide applications unless DATCP finds that lesser actions will not effectively control groundwater contamination. But DATCP must take other regulatory steps that are designed, to the extent technically and economically feasible, to minimize pesticide contamination and maintain compliance with the preventive action limit (“yellow light”).

Pesticide Rules

DATCP has adopted rules to regulate atrazine and other pesticides found in groundwater. Atrazine is the most widely used agricultural herbicide in Wisconsin. It has been found in more than 7,500 wells throughout the state, with over 430 wells having levels above the enforcement standard. DATCP has prohibited atrazine use on approximately 1.2 million acres in Wisconsin, and has cut labeled use rates in half elsewhere. (See
Wisconsin Administrative Code chapter ATCP 30.) Atrazine contamination levels have fallen since DATCP adopted these rules.