When groundwater wells, both pumping and monitoring, are no longer being used, nor slated for future use, they are considered abandoned. These abandoned wells pose a potential threat to the groundwater quality as well as local children and wildlife if not decommissioned properly.
If there is an abandoned well on property you own, no matter the age of the well, you are responsible for the proper decommissioning of this well. If you do not have it properly sealed you are liable for any damage to person or property caused by this well.
An abandoned well is a direct route to the groundwater that is supplying the water for the surrounding area. Any surface contamination will be directly transported down the well to the aquifer. Runoff could carry excess chemicals such as fertilizer or weed killer into the well. Any small animal falling into the well could be killed and his decomposing body deposited into the groundwater. Animal feces being introduced into the groundwater table via an abandoned well was the cause of the Walkerton tragedy in 2000. https://en.wikipedia.org/wiki/Walkerton_E._coli_outbreak
Abandoned dug wells, while not posing as much danger to the local aquifer, represent a much larger risk to people and animals since they are usually 3 to 5 feet in diameter and represent a falling hazard.
Wells no longer in use should be plugged. They represent serious and potentially fatal hazards.
Simply covering the top of the well is not a solution. Wood can rot, dirt can wash away and concrete covers can break down over time, creating the danger of a collapse at a later date.
Backfilling the well with sand or gravel is also not an option. Many jurisdictions have guidelines on what may and may not be used to fill an abandoned well.
Plugging a Well
Most governments have guidelines and requirements that must be met when decommissioning a well. Check with a local well driller or government office for your regional requirements.
Before you can begin this process you must first define the parameters of the well. Heron Instruments Dipper-T http://www.heroninstruments.com/product/dipper-t is the perfect tool to obtain the necessary information such as well depth, head of water, or depth to water. It also has an optional “Well Casing Indicator Probe” which can help determine the dimensions of the casing.
Remove all equipment which may be in the well, such as pumps and disinfect the well by adding Chlorine to a concentration of 200 mg/L.
Remove the well casing if possible. If it cannot be removed, the casing must be cut off 0.5m (or 20”) below ground surface once the well is plugged.
Select the best material to plug this well. Cement grout and concrete may shrink after setting so bentonite is the preferred material to create the best seal. High yield Bentonite is a special type of clay that swells when wet to create an effective impervious seal. It can be purchased in a powder form to create a slurry which can be pumped into the well, or in pellet form which is poured into the well. The pellet form will swell to eight times it original volume when mixed with water leaving no space unfilled.
The material chosen to fill the well must be introduced from the bottom of the well. It is recommended that a licensed well contractor be employed to complete this as they have the equipment and experience to do it correctly. A well must be filled full length with impervious material.
The top 0.5m of the well can now be filled with native material with the material mounded so the area will blend in with the surrounding area and the land used as intended once the ground has settled.
In North America there are thousands of abandoned wells which have not been properly decommissioned. Prior to the 1900’s no well records were mandatory so their locations may be unknown and only found by accident. Some site surveys may indicate the presence of a well but not a history of the well. Some clues to the presence of an out of service well are a pipe sticking out of the ground, out of use windmills, depressions in the ground or concrete vaults.
In rural areas these can be found in fields and in out buildings. In more urban areas they may be under a garage, under a shed, under a porch, or even under an addition to a house in a basement or in a root cellar. Improperly filled or simply covered, these former wells present a risk of collapse if stepped on by an unsuspecting person. There have been many such cases of in the past few years with the case of 18 month old Jessica McClure in 1987 garnering worldwide attention even prompting a movie adaptation of her story. http://www.nytimes.com/1987/10/17/us/toddler-is-rescued-after-2-1-2-days-in-a-texas-well.html
It is extremely important that all wells be dealt with in a proper manner for safety sake. When out walking in remote areas, or even in your own backyard you can be at risk. The groundwater we rely on can be jeopardized by surface contaminants or foreign substances falling into an abandoned well. Proper decommissioning of all wells is imperative to maintain the security of our groundwater and way of life.
Safeguarding our groundwater should be a prime concern for everyone!! Always have decommissioned wells closed properly.