The aerial spraying of pesticides is a point source and requires a National Pollutant Discharge Elimination System (NPDES) permit. That's a recent ruling out of the 9th Circuit U.S. Court of Appeals (League of Wilderness Defenders/Blue Mountains Biodiversity Project v. Forsgren).

The USDA Forest Service annually sprays insecticides over 628,000 acres of national forest in Washington and Oregon. Environmental groups sued, claiming the Forest Service needed to obtain a NPDES permit and provide a more adequate Environmental Impact Statement (EIS). A lower court held for the Forest Service on both issues but was reversed by the appeals court.

The 9th Circuit ruled that the insecticides in question meet the definition of pollutants under the Clean Water Act and that an airplane fitted with tanks and spraying apparatus is a point source. A NPDES permit is required even though EPA regulation and guidance exclude spraying in forests as a point source. 7932/cc