Abandoned wells are wells that are no longer in use
Over the years, many wells and test holes around homes and farms throughout the province have been abandoned due to flood waters, or owners moving off the farm site without being properly sealed and decommissioned. Abandoned wells or improperly decommissioned wells can pose a serious threat to groundwater quality for the entire aquifer and can also be a safety hazard. All abandoned wells should be properly plugged from bottom to top with a tremie line to prevent contamination and casing dug out and capped to eliminate any safety hazards. When a replacement water well is drilled, the old well should be decommissioned. Speak to your driller when they are on site. We are very accommodating to assist with this, keep costs low, and ensure it is done properly so it does not put your new well at risk of contamination.
- May allow surface runoff to enter an aquifer, contaminating the aquifer and potentially contaminating nearby wells.
- May permit cross-contamination of different aquifers encountered by the well bore. (Examples: bring ecoli from one contaminated zone into another aquifer that did not have ecoli. Essentially linking the two sources by a zone of exposure.
- Maybe a physical safety threat, because they are not often marked or covered properly or easily lifted or pushed open. Posing a risk for people, or pets or live stalk to fall into them.
- Is a liability risk, if the source of the contamination is linked from your site to the neighbouring wells, or if the abandoned well still exists at the time of property resale. Banks don’t like to grant loans for properties that have such environmental hazards.
General Decommission STEPS:
- Removal of Well Equipment (pumps, drop pipe, wiring, etc.)
- Well Characterization – We try to refer to registered drill reports as much as possible to understand the depth, diameter and non-pumping (static) water level of the well should be recorded. This information is used to calculate the amount of materials required to decommission the well. Comparing the original depth to the current depth of the well and determine if a portion of the well has collapsed or if an obstruction exists within the well column. If an obstruction does occur within the well, it should be removed prior to sealing the well whenever possible.
- Disinfection – enough chlorine should be added to bring the standing water in the well to a chlorine concentration of 250 mg/L. The amount of chlorine to be added will depend on the casing size and the amount of water in the well. Follow the recommended formula on the well shock. We tend to chlorinate very heavy to ensure no cross contamination occurs at our end.
- Remove Casing – the casing should be removed prior to plugging the well whenever possible, but only if the integrity of the borehole will not be affected. Sometimes the casing integrity is already so significant. Removing the casing in domestic wells that have been in place for a substantial period is often very difficult. Sask water encourages any casing that is left in place should be cut off three meters (9.85 ft) below ground surface after the well is sealed. We try to remove the entire top length of casing usually about 15-20ft.
- Filling and Sealing – the most preferred materials for sealing wells are low permeability materials that prevent the vertical movement of water, from top of well to bottom of well. Generally, the best product for this purpose is a manufactured bentonite product (chips, pellets or grout). Pressurized feed using a tremie line is best. However, in some cases it may be acceptable to use a combination of bentonite, clay and granular material mixed into a pumpable liquid that swells once inside the well. The top portion is capped with natural clay.
- It is the client’s responsibility to provide equipment to assist with the casing removal. Depending on the casing size and length determines the equipment best to preform the removal.
- We then submit the required Water Well Decommission Worksheet to the Sask. Water Authority.
- It is the responsibility of the home owner to call for underground lines to be located prior to any excavation.
Small Diameter Well Decommission (drilled)
Small diameter wells should be decommissioned with a pumped grout seal. The grout must be introduced at the bottom of the well and placed progressively upwards to ground surface. The use of a grout pump and tremie pipe is the preferred method for placing the grout. This is the only method that is currently accepted for Decommission Grants. This will ensure the displacement of water in the well and minimize dilution or separation of the grout. The tremie pipe should be removed as the well is grouted. We use and internal pipe cutter to sever the pipe about 15ft below surface.
Large Diameter Well Decommission (bored)
These LD wells are usually 0.3 meters (12 in.) to 1.2 meters (48 in.) in diameter and less than 30 meters deep.
A 0.3-meter (12 in.) layer of bentonite chips/pellets should be placed at the bottom of the well. The remainder of the well should be backfilled to a depth 3 meters (120 in.) below the ground surface with layers of uncontaminated coarse sand/ gravel not more than 3 meters (120 in.) thick, with a 0.15 meter (6 in.) layer of bentonite chips between backfill layers.
- Remove casing and capping – casing that was left in place before sealing the well should be removed to a depth 3 meters (120 in.) below ground surface. We tend try to remove the last casing segment if possible. The excavation should be backfilled with local uncontaminated clay, compacted and mounded to prevent water from ponding near the abandoned well site. It is the owner’s responsibility to provide uncontaminated clay and uncontaminated course sand / gravel. We will provide the bentonite chips. The client is responsible to provide equipment necessary for the excavation.
Artesian Well Decommission
Flowing wells have unique characteristics and should only be decommissioned by an experienced water well contractor. If not done properly, the artesian well can undermine material around it and the annulus and create a dangerous wash out or underground cavern. Well decommission procedures may differ for each circumstance, which is why it is important that the person responsible for performing the well decommissioning be knowledgeable about well construction, have a variety of equipment and products available and on hand.
Improperly Decommissioned Wells
There are several ways that abandoned wells and improperly decommissioned wells may allow for the contamination from surface into aquifers. Wells can act as a pathway for surface runoff to directly enter the aquifer. Bacteria such as e-coli can enter the well from cattle run off or septic pump out and contaminate the well, thus permitting cross contamination of different aquifers along the length of the borehole. Nearby wells that are completed in the same aquifer may also eventually become contaminated.
Wolverine Drilling Inc. is dedicated to working with you through out the decommissioning process to ensure clear and concise measures are taken for both liability and safety, We are experienced water well contractos and have a long history decommissioning wells within Saskatchewan. Please contact us directly to discuss your options and the best process to follow for the decommissioning of your water well.