More and more producers today are asking how to properly plug — or decommission — old, unused water wells on their farms to avoid costly water contamination issues.

At the same time, the decommissioning of water wells is a relatively new field of technical knowledge. The positive side is that specialists are discovering new ways to make decommissioning projects more effective. On the flipside, they are also finding new ways things can go wrong if a well is not decommissioned properly.

For this reason, technical assistants (TAs) generally recommend that producers hire a professional to do the job. A professional will know what's involved in fully decommissioning a well so it no longer presents a contamination threat. They will also have the necessary tools to do the job right.

Pulling or perforating

Regulations do not say that the well casing has to be perforated. However, in cases where casings have become either stuck or too corroded to pull, the casing must be filled full-length with suitable material. This is particularly important if there is some evidence of water movement in the annulus, the space between the drill hole and the outer edge of the casing.

Plugging process

Steps involved in properly decommissioning a well.

1.) Consult with a professional. Whether they are completing a project by themselves or not, producers should still consult with a professional in advance. Because every well situation is unique, professionals can act as a key resource in helping producers understand the specific parameters of a decommissioning project.

2.) Remove pumping equipment from the well. Thoroughly flush the well using a bailer or air compressor.

3.) Measure total depth and diameter of the well and non-pumping water level. This information may be available in the driller's report, if it exists. However, even with the actual report it's a good idea to measure the well's depth to confirm whether or not the well is open to its original depth.

4.) Choose the plugging material. Although grout, concrete and uncontaminated clay are all acceptable materials for filling in a well, high-yield bentonite - a special type of clay that swells when wet to create an impervious seal – is considered to be the best option. Bentonite comes in pellet or granular form which, when mixed with water, will swell up to eight times its original size and form a watertight plug.

5.) Disinfect the well. If there has been some bacterial contamination of the well, this is the last chance to deal with it. Add chlorine to bring the water standing in the well to a chlorine concentration of 200 mg/L. For every 450 litres (100 gallons) of water in the well, add 2 litres (0.5 gallons) of household bleach.

6.) Remove the well casing. If removing the casing isn't possible, use a casing ripper to go down into the well and tear holes in the casing and liner so the sealant can get through.

If the casing is left in place, dig around the top of the casing and cut it off to a minimum of 0.5 metres (20 inches) below the ground surface. After plugging the well this area will be backfilled and mounded to accommodate settling and prevent water from ponding on top of the old well site. Use appropriate material for the intended use of the land.

7.) Place plugging material into the well. Regulations require that the plugging material be introduced from the bottom of the well and placed progressively upward to the ground surface. The only exception to this rule is when the plugging material being used is bentonite pellets, which have been designed and manufactured for pouring into the well from the ground surface.

"Filling from the bottom means a lot better chance of getting a really good seal and fill of the old well," says Ken Williamson, a water specialist with Alberta Agriculture and Food (AF).

8.) Record the details. Complete AF worksheets that include details such as name, well location, total depth, casing diameter, type and amount of plugging material. Records of the fill are critical, says Williamson. Filing these records with the Alberta Environment Groundwater Information Centre in Edmonton is a courtesy to the next owner of your property.

Assistance available

Information and assistance on casing perforation, as well as a number of other on-farm environmental practices, is available through a strong network of technical assistants (TAs).

Information on water well decommissioning is also available in Water Wells That Last for Generations (Agdex 716(A10)). It is made available through AF and Agriculture and Agri-Food Canada / Prairie Farm Rehabilitation Administration (AAFC – PFRA).

The information on this website is available for reprint with credit to "The Alberta Environmental Farm Plan, www.albertaEFP.com".
Article development courtesy of The Alberta Environmental Farm Plan Company