Well abandonment or decommissioning of abandoned wells is the process used to permanently close wells that are not in use or are left alone due to different reasons.
What are the reasons behind well abandonment?
Water wells may be removed from service due to the following reasons.
- Construction of a new well
- The well fails to provide safe and healthy water
- Well goes dry
- Destruction of the property where the well was used
- Availability of municipal water system
What are the benefits of well abandonment?
The basic purpose of well abandonment is to stop the vertical movement of water in an unused well. Proper decommissioning and closure of the well will provide the following benefits.
- Prevent contamination of nearby groundwater sources through abandoned wells
- Prevent physical hazards
- Stop water contamination from waste disposal
- Conserve and protect the aquifers in the area
- Prevent mixing of potable and non-potable water
What is the criterion for well abandonment?
- Construction was stopped before the well could be completed
- The well owner notifies the local board of health or well management department that the well will not be used again
- The well is out of use for at a certain time (check state laws for the exact number of years)
- The well water is unhealthy and can’t be made consumable through water treatment units or disinfection
- The well is a risk for underground water sources contamination
Who is responsible for decommissioning?
It is the well owner’s responsibility to decommission the well. Most states require you to hire a licensed contractor to carry out the decommissioning.
Make sure you have the well completion report with you. It contains information that helps during the sealing process.
The contractor must also check the well for any debris or sediment deposits that may interfere in the sealing process. The water well must be disconnected from the plumbing system, and all the treatment units or appliances must be removed.
The next step is to measure the static water level in the well to calculate the volume of grout for sealing. The volume of sealing material (grout) must be equal to or more than the volume of the casing of the borehole being sealed. This information is available in the well completion report. You can also calculate it using the cylindrical volume calculation formula, πr2h. The volume calculated will be different for each well. Once the volume has been calculated, the number of bags can be calculated by dividing the volume by the cubic feet of material produced per bag.
Your contractor will discuss the sealing materials with you before starting the process. Make sure you only use an approved material for sealing purposes. The acceptable and commonly used materials are:
- Bentonite cement grout
- Bentonite chips
- Sand cement grout
- Neat cement grout
The above materials can be divided into two groups; bentonite and cement. The advantages and disadvantages of each are mentioned below.
- Do not shrink
- Have a low density
- Don’t need too much curing time
- Permeability is suitable with high-solid grouts
- They are difficult to mix
- Each bentonite grout has different instructions
- They swell very fast, and hence it is difficult to pump them
- Post-sealing equipment cleaning is very difficult
- Can be washed out in fractured bedrocks
- They can be easily mixed and pumped.
- Applicable to most of the geologic formation
- Their properties can be molded by adding additives.
- Last for decades
- They need a high curing time.
- Prompt post-sealing equipment cleaning is needed.
- Prone to shrinkages
The contractor is responsible for submitting a decommissioning report within 10-30 days after completing the sealing process. (Exact time varies from one state to another). It contains information about the owner and property, the reason for decommissioning, contractor, well depth, sealing materials, and the sealing procedure. Once the report is approved, it is the contractor’s responsibility to send a copy to the well owner.