Agricultural Practices

Agriculture accounts for 73 percent of the land use in the basin. The use of best management practices (BMPs) can help protect groundwater resources. The UW-Extension and the Department of Agriculture Trade and Consumer Protection (DATCP) provide assistance in the application of agricultural BMPs.

Animal Feedlots

Animal feedlots are outdoor areas where animals are concentrated for feeding or other management purposes. The principal groundwater pollutants originating from feedlots are nitrates, chlorides, bacteria, oxygen demanding materials, and phosphorus. Water percolating through soil into groundwater may also carry a bad odor and taste.

The potential for groundwater pollution from feedlots depends on the design and construction of the lot as well as characteristics in the immediate area and the depth to groundwater. Abandoned feedlots/barnyards contribute more nitrate to groundwater as soil permeability increases. Surface permeability is low as long as livestock are trampling or compacting the surface soils.

Factors that may inhibit or increase the occurrence of groundwater contamination are:

• Soil characteristics of the feedlot
• Geology at or near the lot (e.g. depth to bedrock, depth to groundwater)
• Runoff control practices present
• Waste handling practices
• Rainfall
• Number of animals
• Spreading waste on snow-covered and sloping terrain that results in runoff to streams and groundwater

Livestock Waste Storage

Livestock wastes stored or disposed of improperly can seriously affect surface and groundwater. For example, many farm operators do not have adequate livestock waste storage facilities. During the winter months, many farms pile waste until spreading it prior to spring cultivation. Rainfall and snowmelt on unprotected manure stacks can generate runoff that degrades surface and groundwater quality. Potential pollutants from livestock wastes are nitrates, chlorides, bacteria, oxygen-demanding materials, and phosphorus.

In general, properly designed, located, operated and managed livestock waste storage facilities have little potential for causing groundwater and/or surface water pollution. The UW-Extension and DATCP provide materials and assistance with proper management of feedlot and livestock waste storage facilities.

Land Spreading Of Livestock Waste

Animal waste land spreading practices can result in groundwater and surface water pollution. The most common poor practices are:

• Spreading waste on shallow permeable soils.
• Spreading waste at rates that exceed crop needs or the soil's ability to attenuate nitrogen.
• Not crediting nitrogen from livestock waste when calculating crop fertility needs.
• Spreading livestock waste upgradient from a potable well, allowing runoff to carry wastes to the well. Polluted runoff may infiltrate along the well casing if the casing is not properly grouted.
• Spreading in areas of bedrock outcrops or known sinkholes.

Fertilizer Application, Storage, and Handling

The over-application of nitrogen-based fertilizers to cropland leads to fertilizer leaching to groundwater. Nitrate leaching usually occurs in coarse permeable soils with low water holding capacity. To minimize groundwater contamination originating from fertilizer application, several factors must be considered. Before fertilizers are applied, a soil test should be performed to determine the nutrient needs of the crop to be planted in a given year. The form of fertilizer applied should also be considered. For example, ammonia is a less soluble and less mobile form of nitrogen than nitrate and may be more suitable for areas with highly permeable soils. Ammonia will nitrify to nitrate and then leach. Crediting of nitrogen in manure and crop residues should be credited. Finally, fertilizers should be applied during times of greatest nutrient uptake.

Groundwater contamination by fertilizers often occurs at fertilizer storage and transfer stations. Spills of bulk fertilizer can cause significant surface water and groundwater pollution problems. Carelessness and faulty equipment are the primary causes of such spills.

Pesticide Application, Storage, and Handling

Pesticides types and application rates should be determined only after considering soil, geologic, hydrologic and agrichemical characteristics. Significant surface and groundwater contamination by pesticides occurs as a consequence of over application, as well as poor practices in the storage, transport, mixing and loading of pesticides. Illegal disposal of pesticides and containers also contributes to pollution.

In 1990, DATCP conducted a pesticides usage survey. This survey showed which pesticides and herbicides were most widely used and which are of most interest in the context of groundwater pollution. Atrazine was, and still is, the most commonly found pesticide in groundwater. The UW Extension technical bulletin Nutrient and Best Management Practices for Wisconsin Farms provides general guidance for pesticide and nutrient management in Wisconsin. It provides a review of recommended practices for pesticide applications and handling. There is still a critical need for more funding for research on pesticide transport, degradation pathways and toxicity of metabolites (breakdown products).

Atrazine prohibition areas are established under the authority of DATCP under AG 30. The prohibition on use of atrazine is instituted in response to groundwater standards of 3 milligrams/liter or parts per billion being exceeded. Pesticide sampling has shown several areas prone to atrazine contamination. Atrazine prohibitions areas have been established within the basin: two areas are in Rock county in the southern part of the town of Lima. In all of the basin in Columbia County and all but the eastern edge of Dane County, atrazine use is prohibited.

Irrigation

Irrigation contributes to groundwater contamination in two ways. First, irrigation water percolating down may carry pollutants such as fertilizers and pesticides through the soil to the groundwater. Second, the malfunction or lack of back-siphoning valves on the irrigation wells may permit contaminated water to flow back into the well, affecting groundwater directly. Studies conducted in the heavily irrigated Central Sands Region of Wisconsin have identified higher concentrations of nitrogen in the soil and groundwater relative to levels in non-irrigated areas. It also found increased levels of pesticide residues in ground and surface water as a result of irrigation. Irrigated agriculture is not very common in most of the basin. The exceptions is on outwash plains south of the terminal moraine in Rock County.

Numerous agricultural management strategies and practices have been developed and/or suggested to minimize groundwater contamination. These strategies are addressed in publications from the UW-Extension's Environmental Resource Center, Agricultural Management Practices to Minimize Groundwater Contamination (1987) and Nutrient and Pesticide Best Management Practices for Wisconsin Farms (UW-Extension and DATCP 1989).

Forestry

Forestry is limited in the basin. Logging operations can have adverse affects on groundwater by altering infiltration and recharge rates. Best Management Practices for Water Quality (PUB-FR-093 95) has been developed to assist loggers and landowners in minimizing impacts of logging operations on water quality. It is available from the WDNR Bureau of Forestry. WDNR provides training on the use of best management practices for forestry at sites around the state. Information on the training schedule can be obtained from the Bureau of Forestry by calling (608) 264-9247.

For more information on groundwater, visit the WDNR - Drinking Water and Groundwater Program