Class III underground injection wells are regulated by an authorized agency typically through the state. The wells are used for mineral extraction of salts, sulfur, and extracting copper, gold, and uranium. The well only allows injected fluids to go into an authorized injection zone and does not allow it to migrate to other areas. Monitoring wells must be placed around the body of ore to detect any horizontal migration of the solutions used in the mining process.
Best Practices for Class III Underground Injection Wells
• Requires a permit prior to construction from the proper authorizing agency including information on casing and cementing, financial assurances, maximum operating pressure to avoid causing or increasing fractures that would allow the fluids to enter the underground safe drinking water supply, monitoring and reporting requirements, demonstration of mechanical integrity, pressure test when the system has been disturbed, and plans for plugging and abandonment of the well.
• Sample the injection fluid and make sure that it meets the appropriate specifications.
• Observe the injection pressure, flow rate, or volume at least twice a month and record the information.
• Perform a mechanical integrity test on the well at least once every 5 years. Notify the authorizing agency 30 days prior to the event.
• Determine the results of the testing of required groundwater monitoring wells and advise the US EPA if problems are occurring.
• Notify the authorizing agency 45 days before starting the plugging and abandonment of a well.