The Montana Department of Agriculture received a grant from the Environmental Protection Agency (EPA) to perform ground water monitoring for pesticides and nitrate along the Yellowstone River Valley. A total of 44 groundwater samples were collected from wells in shallow alluvial aquifers along the Yellowstone River from Stillwater County, west of Billings, to Richland County on the North Dakota border. (Map)
Laboratory analysis of the water samples indicated the presence of at least one pesticide compound in 10 of the 22 sampling sites (45%). Multiple pesticide compounds were detected in 4 of the 44 samples collected at 2 of the 22 sites. The most common pesticide compound detected was atrazine and atrazine metabolites, which were detected in 15 of the 17 samples that tested positive for pesticides.Other pesticides detected included imazapyr (three detections from two wells), bentazon (two detections from one well) and nicosulfuron (one detection). Pesticide concentrations were very low with the maximum concentration being 0.77 parts per billion of bentazon. None of the pesticide concentrations exceeded drinking water standards or lifetime health advisories, where such standards exist. Nitrate was detected in 27 of the 44 samples (61%) and at 15 of 22 sites (68%). Nitrate concentrations exceeded the maximum contaminant level (MCL) for public drinking water supplies of 10 parts per million (ppm) in four of the 44 samples and at two of the 22 sampling sites. Nitrite was detected in one sample but did not exceed the drinking water standard of 1 ppm.
In addition to the ground-water monitoring, the department has compiled pesticide and nitrate data for both groundwater and surface water from the U.S. Geological Survey (USGS), the Montana Bureau of Mines and Geology (MBMG), and the Montana Department of Environmental Quality (DEQ), Public Water Supply Division. By combining the department water sampling data with previously collected data we hope to give a fairly comprehensive picture of the water quality of the Yellowstone River Valley as it relates to pesticides and nitrate.
The valley bottom created by the Yellowstone River in central and eastern Montana is productive cropland. For the counties of Stillwater, Yellowstone, Treasure, Rosebud, Custer, Prairie, Dawson, and Richland the most common crops grown are hay, corn, small grains, and sugar beets. Because of the proximity of the Yellowstone River these crops are generally irrigated, with flood/furrow irrigation techniques being the predominant irrigation method. The USDA's National Agriculture Statistics Service reports that in 2002 the eight counties had a total of 264,074 acres of irrigated land with 122,300 acres of irrigated hay, 84,900 acres of irrigated corn, 53,200 acres of irrigated small grains, and 40,130 acres of sugar beets. While some of this irrigated acreage is located in the major tributary valleys like the Clarks Fork, Powder, and Tongue, and some of the irrigated acres are in outlying areas, most of the irrigated acreage in these counties is along the Yellowstone River.
Because of the shallow water table and the high permeability of the alluvial aquifer along the Yellowstone River Valley as well as the pesticides and irrigation techniques used, the groundwater below the Yellowstone River Valley has a high potential of being impacted by pesticide and fertilizer use. Flood irrigation techniques tend to be inefficient and water is commonly lost below the root zone of the crop. The water that seeps below the root zone can leach pesticides and fertilizers down to ground water. Because ground water in the alluvial aquifers along the valley floor is generally shallow, this makes it particularly vulnerable to the leaching of pesticides and fertilizers. The shallow alluvial aquifer is also the predominant source of drinking water for most of the rural residents living and working on the valley floor.
Map of Sampling Area (PDF)
Map (Larger file in JPG format)
Published: Mon Nov 08 15:52:00 MST 2010.
Last Modified: Thu Dec 29 10:47:24 MST 2011