Thread: Abandoning an interior well?

Client called with a question regarding a discovery a contractor made in her house (in a crawl space I couldn't get into because of piles of junk blocking the entrance). It seems there is the original well under the kitchen, which is not used because the house is on city water. Their contractor says he can fill it with a concrete slurry and cap it to abandon it in place. I'm just curious whether the slurry is necessary? Could it be enough just to seal the top of the well?

Maryland has some specific regulations pertaining to sealing un-used wells. The below is just an extract of the regulations to give you an idea. The main take away is that it depends on a variety of factors, and having a licensed well driller to accomplish the work would be in your clients best interests. If the caseing is not removed, chances are the entire well will be filled using a combination of sealing materials depending on the actual characteristics of the well in question.

General Requirements.

An abandoned well shall be filled and sealed in such a way that it will not:
(a) Act as a channel for the interchange of waters of undesirable quality with those whose quality is desirable; or
(b) Present a hazard to the safety and well-being of humans or animals.
Any well abandoned shall be sealed only by a well driller licensed by the Maryland State Board of Well Drillers or under the supervision of a master well driller or a representative of the Department or Approving Authority.
Abandonment Approval. When the Department or Approving Authority has reason to believe on the basis of local conditions that abandonment of a well necessitates close supervision, it may require the submission of sealing plans and specifications for approval before abandonment operations.

Sealing Materials.

(a) Concrete, Portland cement grout, sodium-base bentonite clay, or combinations of these materials may be used to seal a well.
(b) Used drilling muds are not to be used to seal a well.
(c) Concrete. Concrete may be used for filling the upper part of the well or water bearing formation, or plugging short sections of casing and filling large diameter wells.
(d) Portland cement grout is superior for sealing small openings, penetrating any annular space outside the casing, and for filling voids in the surrounding formation. Portland cement grout shall be composed of one bag of cement per 5 to 8 gallons of water. Two parts sand to one part cement may be added.
(e) Bentonite clay, when applied as a heavy mud-laden fluid under pressure, has most of the advantages of cement grout but under some conditions may be carried away into the surrounding formation. A bentonite clay mixture shall be composed of not less than 2 pounds of clay per gallon of water. Bentonite clay may not be used where it will come in contact with waters of a pH below 5.0 or total dissolved solids content greater than 1,000 mg/l or both.

Procedures for Sealing Wells.

(1) Preliminary Work.
(a) Before filling the hole, the well should be investigated to determine its condition, details of construction, and if there are obstructions which will interfere with the process of filling and sealing.
(b) If there are any obstructions, they shall be removed, if possible, by cleaning the hole or by redrilling.
(c) The casing shall be removed. If sidewall cave-in is likely to occur, the casing shall be removed gradually as the well is filled.
(d) In drilled wells, if it is not possible to remove the casing, the casing may be ripped or perforated to assure that sealing material fills all annular spaces and voids.
(2) Filling and Sealing Wells.
(a) A dug well exceeding 24 inches in diameter shall be filled and sealed by placing fill material (excluding clay or silt) in the well to a level approximately 5 feet below the land surface, and placing a 3 foot plug of sealing material above the fill. The remainder of the well shall be back filled with soil material.
(b) For other than dug wells, a well shall be filled with sealing material or a combination of sealing material and fill material as described below:
(i) A well in unconsolidated material in an unconfined ground water zone (Hydrogeologic Area 1) shall be filled and sealed by placing fill material in the well to the level of the water table, and filling the remainder of the well with sealing material. If the water table is at a depth greater than 40 feet, a minimum of 40 feet of sealing material shall be required.
(ii) Well Penetrating Several Aquifers or Formations.
(aa) A well penetrating several aquifers or formations (Hydrogeologic Area 2) shall be filled and sealed in such a way as to prevent the vertical movement of water from one aquifer or formation to another.
(bb) If the casing has been removed, sealing material shall be placed opposite confining formations, and from the surface down to the first confining formation. Sand and other suitable fill material may be placed opposite the producing aquifer. The driller has the option to fill the entire well with sealing material.
(cc) If the casing has not been removed, the entire well shall be filled with sealing material.

In MD there is a process to abandon the well which is basicly plugging the well and welding the cap. Techinically it has to be done by Lic driller and inspected with a permit. Usually for the public connection to be made the well has to be decommissioned as part of the process. This may vary from county to county I am not sure. Give the county a call.