Decommission Abandoned Wells

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 of Saskatchewan have been abandoned due to floodwaters, 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.  Wolverine Drilling Inc. will be very accommodating and will to what we can to assist with this situation and attempt to keep costs low while ensuring it is done properly so it does not put your new well at risk of contamination. 

ABANDONED WELLS CRITICAL INFORMATION:

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 E.coli from one contaminated zone into another aquifer that did not have E.coli. 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 neighboring 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.

Additional Notes When Working with Abandoned Wells

SMALL DIAMETER WELL DECOMMISSION INFORMATION (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 INFORMATION (BORED)

These LD (large diameter ) 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.

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