Borehole Abandonment and Decommissioning
What is Borehole Abandonment and Decommissioning?
Borehole abandonment and decommissioning refers to the permanent closure of a borehole or well that is no longer needed, unsafe, non-productive, or environmentally at risk. This process is designed to protect groundwater resources, prevent surface water infiltration, and eliminate safety hazards associated with open or deteriorated boreholes.
It is a regulated activity and must be done following local environmental and health standards (e.g., EPA, provincial/state groundwater guidelines, CSA Z129.1, AER Directive 020 in Alberta).
When Is a Borehole Decommissioned?
- After environmental investigations are complete (e.g., monitoring wells no longer needed)
- When production wells (water, oil, gas) become dry, damaged, or inactive
- Following geotechnical drilling programs where boreholes cannot be repurposed
- As part of site closure, redevelopment, or remediation
Borehole Abandonment Process
1. Planning & Regulatory Approval
- Identify borehole/well depth, construction, stratigraphy, and groundwater zones
- Obtain permits or notify regulators as required
2. Well Preparation
- Remove all equipment, pumps, tubing, screens, or instruments
- Clean out sediment, debris, and obstructions
3. Sealing/Backfilling
- Install approved sealing materials:
- Bentonite chips, pellets, or slurry
- Neat cement or cement-bentonite grout
- Sand/gravel backfill in screened zones (only if permitted)
- Seal from bottom to top in stages to prevent bridging and voids
- Pressure grouting may be used in deep or artesian wells
4. Surface Restoration
- Cut casing below grade (e.g., 0.3–1 m)
- Cap and seal (if not removed)
- Backfill and regrade with native soil
- Re-vegetate or restore surface to match surroundings
5. Documentation & Reporting
- Submit closure logs, grout volumes, depth intervals, and photographic evidence
Provide as-built decommissioning drawings if required
Purpose of Borehole Abandonment
| Objective | Explanation |
| Protect groundwater | Prevents contamination via open borehole paths between aquifers or to surface |
| Ensure surface safety | Eliminates physical hazards (collapse, trip/fall risk, open casing) |
| Comply with regulations | Meets closure requirements under permits or site remediation plans |
| Control fluid migration | Seals boreholes to stop cross-contamination or uncontrolled water movement |
Special Considerations
| Scenario | Additional Actions |
| Artesian wells | Controlled sealing to avoid blowouts; surface venting may be required |
| Contaminated boreholes | Use chemically compatible grout; prevent spread of contamination |
| Multi-aquifer wells | Use interval seals to isolate zones and prevent mixing |
| Uncertain construction records | Conduct downhole camera inspection or geophysics to confirm geometry |
Common Materials Used
| Material | Purpose |
| Bentonite chips/pellets | Swelling clay that forms a tight seal in low-pressure settings |
| Cement grout | Durable seal, especially in deeper or high-pressure zones |
| Cement-bentonite slurry | Flexible, low-permeability seal for groundwater protection |
| Sand/gravel backfill | Used in screened zones (only when allowed and properly sealed above/below) |
Regulatory Guidelines (Examples)
| Jurisdiction | Guideline |
| Canada (CCME, CSA Z129.1) | National guidelines for monitoring well abandonment |
| Alberta (AER Directive 020) | Specific procedures for energy sector well decommissioning |
| Ontario Regulation 903 | Groundwater well abandonment and sealing codes |
| U.S. EPA & state agencies | Require closure reporting and certified contractors in many states |
Summary
| Attribute | Details |
| Definition | Permanent closure of a borehole or monitoring well |
| Purpose | Protect groundwater, eliminate safety risk, ensure regulatory compliance |
| Steps Involved | Cleaning, sealing with bentonite/cement, casing cut-off, site restoration |
| Regulated By | Environmental and health authorities (provincial/state/federal) |
| Critical Consideration | Prevent vertical migration of contaminants or groundwater between zones |
Proper borehole decommissioning is a key part of environmental stewardship, ensuring that once a borehole’s purpose is complete, it leaves no lasting risk to public health, safety, or groundwater systems.