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Extension > Agriculture > Crops > Agricultural drainage > Technical, planning & design > Identifying and sealing agricultural drainage wells

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Identifying and sealing agricultural drainage wells

L. M. Busman


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.

What is an agricultural drainage well?

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.

How do ADWs threaten groundwater quality?

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.

What is a landowner's responsibility?


Figure 1. 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.

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.

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:

  1. The State of Minnesota is more interested in sealing ADWs to prevent further groundwater pollution than in being punitive toward landowners who report and seal ADWs on their property.
  2. Your greatest liability is from the continued existence of an ADW on your property.
  3. Properly sealing an ADW eliminates a source of pollution and protects you from further liability. You are not liable for contamination of groundwater by a well that occurs after the well has been sealed in compliance with Minnesota law.

Seeing an agricultural drainage well

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.

Economic impact and land use

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.

Alternative drainage methods

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.

Changing land use

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.

Wetland restoration

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.

For more information

The following materials provide additional information on ADWs and groundwater contamination:

Below is a list of agencies that can provide more information on ADWs:

Your local Soil and Water Conservation District (SWCD) office for information on

The Minnesota Board of Water Soil Resources (BWSR) for further information on

Your local Natural Resources Conservation Service office for information on

The Minnesota Pollution Control Agency (MPCA) for information on

The Minnesota Department of Agriculture for information on

The Minnesota Department of Health (MDH) Well management program for information on

The Minnesota Department of Natural Resources (DNR) for information on

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.

WW-06265-GO Reviewed 2008

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