Unplugged Abandoned Wells Are a Safety, Health & Environmental Threat
- They are a safety hazard. Each year the Michigan Department of Environmental Quality (DEQ) receives reports of people, mostly children, falling into old wells. Injury or death can result.
- They pose a health concern by acting as conduits for contaminants to move from the surface, through the earth's protective formations, into deeper aquifers. Drinking water contamination has been caused by abandoned wells.
- They threaten the environment. Deteriorated well casings or open, uncased boreholes allow movement of water between previously separated aquifers. This can degrade water quality. Abandoned wells have also been used for illegal waste dumping.
The DEQ and Monroe County Health Department recommend that property owners hire registered well drilling contractors to plug abandoned wells. Registered well drillers have the specialized training and equipment necessary to properly plug abandoned wells.
Examples of Abandoned Wells That Must Be Plugged
- Wells that are not operational.
- Wells that are disconnected and taken out of service at the time connection is made to the municipal water system.
- Any inoperable or abandoned well which is not properly sealed which can be a safety or environmental hazard.
- For more information on abandoned wells, please visit the State of Michigan website.
Remove All Obstructions
Pumps, drop pipe, pump rods, packers, wire, check valves and all other debris or obstructions must be removed from the well before plugging.
Well type and site geology affect the requirements for plugging abandoned water wells. Each well type has specific plugging requirements:
- Dug wells: These large (12-to 48-inch diameter) wells are made of cement crock, brick, stone, or tile. A 6-inch layer of bentonite chips or pellets shall be placed at the bottom of the well. The remainder of the well shall be plugged by placing clean soil backfill* layers that are not more than 10-feet thick, with a 6-inch layer of bentonite chips between backfill layers. The upper 3-to 4-feet of stone, brick, cement crock, or curbing must be broken up and removed. A final 6-inch layer of bentonite must be placed 3-feet below finish grade, then the remainder of the hole backfilled and crowned in a manner that will prevent settling or ponding of water over the old well site. (*Clean, dry soil backfill may be loam, clay, silt, or sand obtained from commercial sources or from the site. Clean backfill may not contain trash, wood, roots, sod, construction debris, or chemical contaminants.)
- Drilled Wells in Sand or Gravel Formations: Bentonite grout slurry, neat cement slurry*, or dry bentonite chips or pellets may be used to plug wells with screens in sand and gravel formations. All slurry grouts must be placed using a "tremie" pipe which runs to the bottom of the well. The slurry may be pumped or poured using a funnel into the tremie pipe. The tremie pipe should be removed after or during the plugging process. (*Neat cement slurry is a mixture of one 94 pound bag of Portland cement and not more than 6 gallons of water.)
- Wells in Bedrock Formations: Neat cement must be used to plug bedrock wells. A pump and tremie pipe, which runs to the bottom of the well, is necessary. The tremie pipe should be removed as the neat cement is pumped into the well or after cement appears at the surface. Bedrock wells should be plugged by registered well drilling contractors.
- Hand-driven Point Wells: These small diameter wells (normally 1¼ inch diameter) may be plugged by carefully dropping bentonite chips or pellets into the top of the well casing, or by pouring a slurry of neat cement through a funnel and tremie pipe extending to the bottom of the well.
- As bentonite chips are poured into the well casing, a hardware cloth screen (with ¼ inch mesh) should be used to remove any fine bentonite powder. These particles swell upon contacting water and can bridge in the upper part of the well. When using dry bentonite chips or pellets, periodic tamping with a pipe will help prevent bridging.
- Flowing Wells: Because of their unique characteristics, flowing wells should be plugged by registered well drilling contractors.
- Neat cement must be used to plug flowing wells. Its heavy slurry weight is needed to overcome the artesian pressure of flowing wells and to provide a permanent seal.
Abandoned Well Volume
|Well Diameter||Volume Per Feet of Depth "Cubic Feet (CF)"||Volume Per Feet of Depth "Gallons"||Feet of Well Plugged Neat Cement||Feet of Well Plugged Bentonite Chips|
|1.24 Inch||0.01 CF||0.07 Gallon||118||70|
|2 inches||0.02 CF||0.17 Gallon||51.3||32|
|4 inches||0.09 CF||0.066 Gallon||13.4||8|
|5 inches||0.14 CF||1 Gallon||8.5||5|
|6 inches||0.20 CF||1.50 Gallons||5.9||3.5|
|48 inches||12.56 CF||94.0 Gallons||0.1||9 Bags per 6-Inch Layer|