WW-06265-GO Reviewed 2008
Copyright © 2002 Regents of the University of Minnesota. All rights reserved.
Agricultural Drainage Wells (ADWs)--also known as shallow injection or dry wells--have been used in some farming situations as a way to carry excess water from surface or subsurface drainage systems directly into deeper layers of the ground. ADWs threaten groundwater quality because they allow agricultural runoff and the pollutants it may contain to feed directly into the groundwater. Normally, natural filtering of runoff takes place as water seeps slowly through several layers of fine- and medium-textured soil before it reaches the groundwater. This natural filtering is bypassed when an ADW is used, potentially polluting the groundwater.
For landowners the presence of an ADW on one's property:
The State of Minnesota has given high priority to identifying and sealing ADWs to protect groundwater quality. There are many resources available to help landowners accomplish this in a way that causes as little financial hardship as possible. It is in a landowner's best interest to cooperate in this effort because it is usually far less expensive to identify and properly seal an ADW in compliance with state law than to correct or pay punitive damages for polluted groundwater.
Agricultural drainage wells (ADWs)--also referred to as shallow injection or dry wells--were dug to allow water from subsurface drainage systems or surface water to drain deeper into the ground. They were used to receive irrigation tailwaters, other field drainage, and barnyard runoff or to remove excess water from potential crop land in areas where it was difficult to do so using streams or ditches. Similar drainage wells have been used to accept water from roadways, septic systems, and urban land.
Agricultural drainage wells were usually constructed in relatively flat low areas where the removal of excess water through surface drainage or tile lines was difficult, and where underground layers that would accept water existed. Some are buried and others are open to the surface. There are several hundred ADWs known to exist in a region of north central Iowa and many are thought to exist in south central Minnesota as well.
An ADW may drain anywhere from a few acres to several hundred acres. Some ADWs consist of a collection cistern that empties into a well at the bottom. The well has a smaller diameter than the cistern and may be capable of accepting large volumes of water. Other ADWs may exist simply as wells that open to the surface. In either case, water travels down the well and enters permeable underground layers of gravel or fractured rock. Water in these underground layers may be a source of drinking water.
Water from runoff or from drainage tile may contain nutrients, sediment, organic debris, pesticides, and bacteria. When this drainage water slowly seeps through a fine- or medium-textured, deep soil to the groundwater, it is somewhat purified by physical, chemical, and biological processes that absorb or break down many contaminants. Drainage water that flows into an ADW does not pass through much (if any) soil and it can carry contaminants deep into the ground. Drainage water can then make the groundwater unfit for human consumption. Nitrate, pesticides, and bacteria are the major contaminants that are of concern. Once the groundwater is contaminated, cleanup is usually difficult or practically impossible.
Contaminants that enter groundwater through ADWs can pose a health threat to people who use that water for drinking and can limit the future use of that groundwater. Minnesota State law prohibits the discharge of "sewage, industrial waste, or other waste" into groundwater or into the ground if that discharge would cause groundwater to be polluted. "Other waste" would include sediments, nutrients, and pesticides that are carried in runoff and drainage from agricultural lands.
Diagram of an agricultural drainage well (ADW). Based with permission on Glanville, P.D., 1985, Agricultural Drainage Wells In Iowa, Iowa State University Publication PM-1201.
The State of Minnesota has given high priority to sealing ADWs to help protect groundwater quality. If you have an ADW on your property, you should check with the proper agencies (listed in this publication) to get technical and financial assistance to seal it. If you are concerned about your liability, it is important to know that:
Sealing an ADW is the process of permanently filling the well with cement or a special clay to prevent the well from contaminating groundwater or posing a safety hazard. State law requires that sealing be done by a licensed well contractor or licensed well sealing contractor. Sealing begins by clearing the ADW of any obstructions, debris, or equipment that might prevent an effective seal. Then, in the most commonly used method of sealing, a special cement mixture called grout is pumped through a pipe from the bottom of the well to within two feet of the surface. The remaining hole is filled with soil. If the ADW is in a pit, the pit may be filled with native soil. Other procedures are specified in the well sealing rules if the well is large in diameter or if there are special geologic conditions.
The final step in sealing an ADW is the submission of a sealing report by the licensed well contractor to the Minnesota Department of Health (MDH). This report is the official documentation and your guarantee that the ADW has been properly sealed and no longer constitutes a real or potential pathway for contamination to enter the groundwater. A copy of the well sealing report should be kept with your other important property ownership papers.
The economic impact of sealing an ADW includes more than paying for the seal itself. It also includes the cost of developing alternative methods for handling drainage water and/or alternative ways to use land that can no longer be drained as thoroughly as it had been. It is important that sealing an ADW cause as little adverse economic impact on individual landowners as possible, and this can only happen if all the alternatives for drainage and /or land use are carefully examined and compared.
In cases where the ADW drained cropland, for example, it may be difficult--though not impossible--to find reasonable ways to provide alternative drainage so that the land can continue to be used as it had been. Installing a tile line or constructing a drainage ditch to divert water to a nearby water body may be feasible but is likely to be expensive. It may be possible to direct the drainage water into a constructed impoundment area and pump the water to a nearby drainage ditch or stream. ADWs were often built in low areas that did not have adequate surface drainage for the very reason that installing these surface drainage structures was not cost effective. A further barrier to surface drainage alternatives is wetland designation. If the area around the ADW is classified as a wetland, there may be regulations that limit the ability of the landowner to make these changes.
In cases where the ADW received barnyard runoff, it might be necessary to change the management of animal waste and install structures to divert and contain runoff.
Depending on how wet the area becomes without the ADW, it may still be used for agricultural production. The cropping system may need to be altered to include crops that are more tolerant of poorly drained conditions. For example, the affected area may be useful for forage production or as rangeland. However, the risk of crop failure may be increased.
If large amounts of drainage water are entering an ADW, sealing the well and the tiles leading into it may cause the area to become too poorly drained to be used for cropland. Restoring the wetland may be the best option. Funds are available through the Reinvest in Minnesota (RIM) Reserve Wetland Restoration Program for landowners interested in sealing an ADW and restoring a wetland. The funding would offset well-sealing costs and lost cropland revenue. The RIM Reserve Program is administered locally by Soil and Water Conservation Districts (SWCD). Interested landowners should contact their local SWCD office.
The following materials provide additional information on ADWs and groundwater contamination:
Injection Wells--An Introduction to Their Use, Operation and Regulation, Groundwater Protection Council, 1-800-762-0190
Agricultural Drainage Well Research and Demonstration Project Annual Report 1993, Iowa Department of Agriculture and Land Stewardship, 1-515-281-3963
Below is a list of agencies that can provide more information on ADWs:
New Ulm Office:
Hwy. 15 South, Box 756
New Ulm, MN 56073-0756
St. Paul Office:
155 South Wabasha, Suite 104
St. Paul, MN 55107
St. Paul Office:
Gretchen Sabel, MPCA
520 Lafayette Road
St. Paul, MN 55155
St. Paul Office:
Agronomy Services Division
90 West Plato Blvd.
St. Paul, MN 55107
Well Management Unit
925 S.E. Delaware Street
P.O. Box 59040
Minneapolis, MN 56459-0040
St. Paul Office:
Dan Zwilling, DNR
500 Lafayette Road
St. Paul, MN 55155
L. M. Busman
South Central Minnesota Water Quality Educator
Minnesota Extension Service
University of Minnesota
Technical assistance and partial funding for this publication was provided by the Minnesota Board of Water and Soil Resources, the Minnesota Pollution Control Agency, the Minnesota Department of Agriculture, the Minnesota Department of Health, and the Minnesota Department of Natural Resources.
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.