Yellowstone River Valley Project - 2005
Summary of Pesticide and Nitrate Monitoring in Ground Water and Surface Water in 8 counties in the Yellowstone River Valley
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. For this monitoring effort, ground water samples were collected from shallow alluvial aquifers along the Yellowstone River from Stillwater County, west of Billings, to Richland County on the North Dakota border.
A total of 44 ground-water samples were collected from 22 wells and analyzed for 83 pesticides (47 herbicides, 24 insecticides, nematicides, and fungicides, and 12 metabolites) and nitrate/nitrite. Of these 22 wells, seven were monitoring wells maintained by the MDA as part of its ambient ground-water monitoring program and 15 were private domestic wells.
Laboratory analysis of the water samples indicated the presence of at least one pesticide compound in 17 of the 44 samples and at 10 of the 22 sampling sites (45%). Multiple pesticide compounds were detected in 4 of the 44 samples and 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 MDA has compiled pesticide and nitrate data for both ground water 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.
Yellowstone River Valley Agriculture
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. For the year of 2002 the U.S. Department of Agriculture’s National Agriculture Statistics Service (NASS) reports that for the eight counties listed above there was 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 ground water 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.
Contacts:
Amy Bamber
Program Manager
Phone: (406) 444-5400
E-mail: agr@mt.govRick Mulder
Groundwater Hydrologist
Phone: (406) 444-5400
E-mail: agr@mt.gov
