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Assessing the Risk of Ground Water Contamination from Open Lot Management on Animal Feeding Operations (AFOs)

Ecological Sciences - Environment Technical Note Number MT-3

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Environment Technical Note Number MT-3 (PDF; 138 KB)

February 2006
by Tom Pick, Water Quality Specialist and Mike Garverich, Geotechnical Engineer

Introduction

Protecting ground water supplies is critically important in Montana. Ground water is a primary source of drinking water as well as providing lesser but crucial quantities for irrigation and industrial uses in Montana. Ground water provides 94 percent of Montana's rural domestic water supply and 39 percent of the public water supply for drinking water.

In a private well water testing program conducted by the Montana State University Extension Service in 1989, 43 percent of 1,400 water samples taken from private wells exceeded the federal limit of coliform bacteria (Montana State University, 1989). During this same test program, nitrate-nitrogen concentrations greater than the 10 parts per million drinking water standard were detected in about six percent of the private well waters tested. A more recent survey by the Montana Department of Agriculture of wells along the lower Yellowstone River valley detected nitrate in sixty-eight percent of the wells sampled with nitrate concentrations greater than the drinking water standard in nine percent of the wells tested. While no sources were positively identified during either study, concentration of animals in open feeding and holding lots can create waste accumulations that are potential sources of pollutants to ground and surface water supplies that also serve as drinking water sources.

Montana’s Water Quality Act limits discharges of pollutants to state waters (including ground water) without a Montana Pollutant Discharge Elimination System (MPDES) or a Ground Water Pollution Control System (MGWPCS) Permit. Specific information about either permit is available from the Montana Department of Environmental Quality online at: Water Quality Discharge Permits.

Montana’s Water Quality rules (MCA-75-5-605) prohibit construction of a new waste treatment or storage facility within a 500-foot distance of existing water wells. The Department of Environmental Quality’s (DEQ) Circular 9 Montana Standards for Concentrated Animal Feeding Operations (CAFOs) currently in draft form (01/19/06), specifies that producers utilizing land application of animal waste shall maintain a 100-foot setback or 35-foot vegetated buffer from any down gradient sinkholes, agricultural well heads or other conduits to surface waters. Additional considerations relative to MPDES design requirements can be found in the NRCS National Engineering Handbook and Agricultural Waste Management Guide located in each field office.

Often, the major or primary emphasis of the NRCS assistance with open lot treatment and animal waste management is to eliminate the potential for surface water contamination via interception or elimination of overland transport. Yet in all cases, a secondary - but no less important objective - should be to eliminate ground water contamination where this pollution potential exits. The risk for ground water contamination first must be evaluated in order to assess the need for specific ground water conservation practices.

While surface water contamination and transport vectors such as topography, proximity to open water, presence of gullies and pipes, and other physical features are usually readily visible, factors related to ground water risk are far less obvious. As opposed to waste application areas where nutrients are theoretically applied at agronomic rates and off-site runoff is controlled, the feedlot surface itself is subjected to nearly continuous application of wastes where cumulative deep leaching is possible over time. This technical note will serve as a format to provide a consistent and thorough approach to the evaluation and assessment of ground water contamination risk on open lot Animal Feeding Operations (AFOs). The approach may also aid in evaluation of risk factors for field application of animal waste.

Summary

Sites receiving ‘high risk’ ratings for two or more individual criterion should receive more intensive investigation. This may involve additional geologic or engineering investigations and/or the use of monitoring wells installed to sample upgradient and downgradient water quality parameters (see Section C. Site Investigation for a more detailed discussion). Sites that receive four or more high risk ratings may not be suitable for AFOs. Existing feeding operations with several high-risk factors should be investigated further (Section C) to include the use of monitoring wells (Section D) to document current and future water quality conditions.

References

Devinny, J. S., et al. Subsurface Migration of Hazardous Wastes. Van Nostrand Reinhold. New York, 1990.

Gonzáles, W.G. and K. Sankaran. Environmental Sampling and Monitoring Primer, Ground Water Monitoring Wells. Virginia Tech, 1997. September 22, 2004.

MSU (Montana State University). Reports of Nitrates in Montana Drinking Water Wells Increase. News Release from Montana State University Communication Services, Bozeman, Montana, 1998.

NDEQ (Nebraska Department of Environmental Quality). Guideline for Ground Water Monitoring Plans at Livestock Waste Control Facilities. Guidance Documents, December 2003. September 22, 2004.

NRCS General Manual.

U.S. Army Corps of Engineers. Unified Soil Classification System. U.S. Army Technical Memorandum No. 3-357 Vols. 1 and 3, March 1953.

USDA, Soil Survey Division Staff. Soil Survey Manual. Agricultural Handbook 18. Issued October 1962. Revised and expanded October 1993. Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

If you have any questions, please contact:

Tom Pick, Water Quality Specialist
Phone: (406) 587-6947
Email: Thomas.Pick

Mike Garverich, Geotechnical Engineer
Phone: (406) 587-6830
Email: Michael.Garverich

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Last Modified: 08/18/2008