Well Abandonment and Plugging
An abandoned well is a direct conduit from the surface to the aquifer. Plugging restores the geologic barrier, removes a physical hazard, and prevents mixing of good and poor-quality water. Michigan requires plugging by a licensed driller, with a record filed.
Sequence of work
- Remove pumps, drop pipe, and obstructions; the hole must be clear for the seal to reach its full depth.
- Disinfect the well before and during plugging.
- Fill the full length with an approved material: neat cement, concrete, cement-bentonite, or bentonite in the casing and borehole. Sand or gravel alone is not an acceptable seal across a contaminated interval.
- Where the casing is removed, pull or perforate it and fill the resulting void; otherwise cut it off below grade so the plug is covered by soil.
- Flowing wells need a cement plug placed to control the flow before the upper section is finished.
Worked example
A 120-ft well has 6-in. inside-diameter casing. Casing capacity is about 0.196 ft2 times 120 ft, or 23.6 ft3. At 1.18 ft3 per sack of neat cement, that is about 20 sacks, and the driller orders extra for loss into the screen and formation. Grout is tremied from bottom to top, the casing is cut off below grade, and the plugging is entered on the well record.
Traps
- Filling the casing with sand and stopping there.
- Leaving casing standing above grade as a future hazard.
- Plugging only the top 20 ft while the screen below still connects aquifers.
- Skipping the plugging record, which leaves the owner and the state with no documentation.