EB1716

Surface water is any body of water whose surface is visible, that is, ponds, lakes and streams. Groundwater is any water beneath the surface of the land. This includes precipitation or irrigation water in the crop root zone. Once the soil profile is full, any excess water percolates through soil, subsoil, or layers of rock and gravel to the underlying aquifers. Aquifers are bodies of underground water that can yield usable amounts of water via a well. The recommendations in this bulletin provide general information on agricultural practices that may help protect groundwater. Washington State University, the USDA Natural Resources Conservation Service (NRCS) and local Conservation Districts are evaluating specific practices that will protect groundwater while continuing to protect surface water quality.

The Environmental Protection Agency's (EPA) National Water Quality Inventory completed in 1990 indicates that nitrate and pesticide contamination of groundwater is a concern in 42 states. In 1989, Ecology's Nonpoint Source Pollution Assessment and Management Program reported pesticides in groundwater samples from at least one location in 11 different Washington counties. Similarly, Ecology reported nitrate contamination in 23 counties.

Both point and nonpoint sources can contaminate water. Point source contamination originates from a specific place, such as a discharge pipe. On the other hand, nonpoint source contamination results from many small sources spread over a wide area or from unspecified locations. While each single source of contamination may be minor, a number of small sources can add up to a large groundwater problem. Agricultural pesticides, fertilizers, petroleum products, and animal wastes can contribute to nonpoint source water contamination through runoff or leaching. Agricultural activity accounts for some groundwater contamination.

Laws Require Protection

Federal and state laws require that farm operators protect groundwater. In Washington, the groundwater standards appear in Chapter 173-200 of the Washington Administrative Code. Within the groundwater quality standards is an antidegradation policy that protects present and future uses of Washington's groundwater.

The EPA defines the standard for evaluating any enterprise's efforts to protect groundwater as the use of AKART or "all known, available and reasonable methods of prevention, control, and treatment." AKART implies that managers are to prevent or minimize releases of potential contaminants. For agriculture, AKART is the appropriate combination of best management practices (BMP) for each operation. Ecology defines BMPs as agronomic, managerial or structural techniques for controlling nonpoint source contamination where it is generated. BMPs outline appropriate practices for each field, farm or crop.

In Washington, the soil, topography, climate, farming practices, and cropping systems differ from farm to farm. Therefore, land managers often must combine appropriate practices as a complete BMP system. Copies of Section 208 BMPs and some additional farming practices for protecting surface water quality are available through local Conservation Districts and the NRCS. Discuss effectiveness of these BMPs for groundwater quality protection with the local WSU Cooperative Extension, NRCS, or Conservation District office. The Washington State Water Quality Guide provides information on BMP effects on water quality. The table below shows general practices identified as having a positive effect on protecting groundwater quality. Evaluate each practice for a particular farm or field.

Structural Practices for Groundwater Protection

Irrigation systems. Washington groundwater standards allow farm managers to apply agrichemicals, including fertilizers, if they manage the irrigation system to prevent leaching to groundwater below the crop root zone. Switching from furrow irrigation to sprinkler irrigation applies water more evenly, reducing the chance of leaching agrichemicals below the crop zone. If furrow irrigating, use surge flow techniques to apply water more evenly.

Antibacksiphon devices. Wells provide the most direct route for contamination of groundwater. Antibacksiphon devices, required by law for chemigation, prevent direct introduction of agrichemicals into aquifers.

Animal waste storage and handling. Proper handling and storage of animal wastes prevent leaching of concentrated nutrients, salts, and bacteria into the aquifer below. Long-term seasonal storage allows managers to avoid runoff and leaching by delaying application of manure to fields until the growing season. In addition, when applying animal waste as fertilizer, managers should adjust the application rate to fit the crop, soil, and climatic conditions. Do not apply more nutrients than the crop or acreage requires.

Subsurface (tile) drainage reduces the amount of nitrate transported to deeper groundwater zones by reducing soil saturation in the crop root zone and maintaining a separation between the root zone water and underlying water table. Since pesticides typically leach less readily than nitrate, tile drainage may not remove all pesticides. Be sure you know what effect agrichemical laden drainage water will have on surface water quality before installing a drainage system to move it.

Wellhead protection. Federal law mandates wellhead protection programs for public drinking water systems. Wellhead protection also is important for private well users. To protect the well from contamination, mix pesticides, load sprayers and store pesticides and petroleum products at a safe distance from the wellhead. Locate livestock pens and septic tanks at least 100 feet away from the wellhead. In sandy or gravelly soils, you may need 200 feet of separation for these structures and activities. Protect farmstead wells with antibacksiphon devices when mixing pesticides and loading sprayers with water directly from the well.

To prevent groundwater contamination, state law requires land owners to cap temporarily unused wells and to plug abandoned wells according to code.

Cultural Practices for Groundwater Protection

Grassed waterways. In addition to slowing erosion and protecting surface water, grassed waterways protect places in fields where water infiltrates into the ground. They provide living filters that keep silt and some attached heavy metals and pesticides from contaminating surface or groundwater resources. The grass also will use some of the nitrate from infiltrating water.

Cover cropping. You may need to plant cover crops before heavy fall and winter precipitation, when erosion and leaching are greatest. By taking up mobile nutrients like nitrate, cover crops protect groundwater. Plowing or incorporating the cover crop into the soil before planting releases the nutrients for the next crop. If you use cover crops, run soil tests before adding additional nitrogen to avoid overfertilizing.

Low input farming protects groundwater by reducing the use of agrichemicals, including pesticides and fertilizers. Various combinations of legume cover crops, manure, and sludge can reduce off-farm purchases of nitrogen. As in conventional farming, run soil tests before adding any amendments to prevent overuse of nitrogen and subsequent nitrate losses to groundwater. Crop rotations that interrupt pest cycles may reduce the need for some pesticides.

Management Practices for Groundwater Protection

Integrated pest management (IPM) practices are designed to protect the crop with minimum adverse effects on the environment.

• Use pest resistant crop cultivars.
• Scout fields to determine pest levels before using pesticides.
• Use biological pest control and predator enhancement.

IPM also incorporates careful selection of pesticides when necessary, and spot or border spraying.

Nutrient management. Test soil to determine the fertilizer needs of crops. Time applications accurately, split applications, or use proper placement to ensure better fertilizer use by the crop. If applying animal waste, analyze the nutrient content of the waste, then determine the correct amount to apply. These methods help place needed nutrients in the crop root zone, while minimizing nutrient losses. It is economically and environmentally beneficial to keep the nutrients in the crop root zone where the plants can use them.

Pesticide management. Whenever possible, use the least persistent, least leachable alternative. WSU Cooperative Extension and the NRCS have information available to help determine vulnerability to leaching of individual pesticides on different soils. The Washington State Water Quality Guide and an NRCS computer program called WRAP can evaluate the leachability of pesticide and soil combinations before application. Safe handling and mixing, as well as accurate pesticide application, help reduce pesticide contamination.

Irrigation management. Manage irrigation water applications to keep water, plant nutrients and pesticides in the crop root zone. WSU's Washington Irrigation Forecaster computer software and the Public Agricultural Weather System can help forecast crop water needs and plan irrigations. Use water applications to leach built up salts at a point in a crop rotation when leachable agrichemicals are reduced or absent.

Partial funding for this publication was provided by the Ecology Centennial Clean Water Fund administered by the Washington Department of Ecology.

By Edward B. Adams, Ph.D., Washington State University Eastern Washington Water Quality Coordinator, WSU Spokane.

in cooperation with WASHINGTON STATE DEPARTMENT OF ECOLOGY

Issued by Washington State University Cooperative Extension and the U. S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Published August 1992. Subject code 376 A EB1716