California has proposed changes in the regulation of oil and gas injection wells to protect underground drinking-water supplies.

The injection wells are used to increase oil recovery and to safely dispose of fluid produced with oil and natural gas.

Steve Bohlen, head of the state Department of Conservation's oil and gas division, admitted that the proposed regulatory changes were "long overdue."

A review last year found that more than 2,500 underground injection wells had been permitted into aquifers that were supposed to be protected as current or potential sources of water for drinking and agricultural use.

According to the Associated Press, hundreds of state permits for oilfield injection into protected aquifers have been granted since 2011, despite the state facing one of the most severe droughts on record and warnings from the U.S. Environmental Protection Agency (EPA) about inadequate protection of aquifers in areas of oil and gas operations.

California's oil and gas regulators have now released a plan to bring the state back into compliance with federal drinking-water requirements. This includes a proposal to close by October up to 140 oilfield wells that state regulators had allowed to inject into protected drinking-water aquifers.

EPA spokeswoman Nahal Mogharabi, quoted by the Associated Press, said that the agency will review the state's proposals.

"EPA will then work with the state to ensure that the plan contains actions that will bring their program into compliance with the Safe Drinking Water Act," she said.

Last July, state officials ordered 11 injection wells that posed a threat to drinking-water supplies to immediately halt injection. They said that any additional such wells will also be shut down.

Tests of nine water supply wells near those injection wells have found no evidence of contamination related to underground injection.