Idaho Growers


In 1999 and 2000, Oust® herbicide was sprayed on more than 50,000 acres of rangeland in South Central Idaho. Subsequently, from late 1999 through spring 2001, dust contaminated with Sulfometuron methyl (the active ingredient of Oust®) was resuspended and transported by high winds and deposited over agricultural fields, injuring Idaho farmers’ crops.

Litigation was filed in 2002 after an investigation by the Idaho State Department of Agriculture of what was described as the largest agricultural disaster in the history of the state.

EnviroComp’s Role

We were retained by the attorneys representing the farmers whose crops had been damaged. We collaborated with Exponent, Inc. which was also retained by the plaintiffs’ side. Our main role was 1) to simulate the transport and deposition of contaminated dust particles during a series of dust episodes in 1999-2001; and 2) to calculate the deposition amounts of Oust® in dust that originated from different area sources during various high-wind episodes. To perform our simulations we used the CALPUFF modeling system, which is listed as a preferred/recommended model by the US EPA for long range transport and complex terrain.

Some of our results are presented in the maps below: Oust® depositions for the June 12-13, 2001 dust episode, with 20-mph threshold (Figure 1) and Total Oust® deposition for the second growing season of October 2000 – June 2001 (Figure 2).

Our work was presented at trial and contributed to achieving a jury verdict in favor of the farmers. Our technical report is available here.


Figure 1 Figure 2