The Sierra Club has dropped a lawsuit against South Carolina’s environmental agency after the department moved to curtail discharges of toxic metals that for years have drained into rivers in three parts of the state.

Environmentalists sued state regulators last summer, accusing them of letting pollution permits expire, a failure that conservation groups say endangered waterways near Columbia, Georgetown and Moncks Corner.

The Sierra Club said Friday it has settled the suit because the S.C. Department of Health and Environmental Control agreed to issue updated pollution permits for Santee Cooper and Dominion Energy.

The updated permits are expected to place tighter pollution limits on the power companies than the ones that expired nine to 11 years ago, said Dori Jaffe, an attorney with the Sierra Club. Water discharge permits, which are supposed to control unchecked pollution, are supposed to be renewed every five years.

Leslie Lenhardt, an attorney working with the Sierra Club on the settlement, said the legal action forced DHEC to do its job.

“This is great news for our waters, wildlife and communities,’’ Lenhardt said in a news release. “We have achieved our goal of forcing DHEC to render decisions on these coal plant applications after years of the agency’s extensive inaction. This settlement ensures the applications will be evaluated without further delay and under the correct regulatory standards, thereby protecting public health from unlawful and toxic contamination.”

The dispute examined power company discharges, but DHEC was targeted because it failed to act, instead of the companies.

Contaminants legally released into water from the plants include arsenic and mercury, but discharge permits limit how much can be released because those pollutants are toxic. In this case, the issue revolves around how strict those permits should be regarding the amount of pollutants that can be released.

Arsenic once was used in ancient times as a poison. Mercury can cause nervous system disorders in people who eat fish contaminated with the metal.

Dominion’s coal plant in Richland County discharges to the Wateree River; Santee Cooper’s plant in Georgetown discharges to a creek that flows to the Sampit and North Santee Rivers; and Santee Cooper’s Cross plant discharges to a diversion canal at Lake Moultrie north of Charleston.

According to the Sierra Club’s news release and the settlement, DHEC plans to issue new permits for Dominion’s Wateree coal plant southeast of Columbia on July 1 and for Santee Cooper’s Winyah station in Georgetown and Cross Station near Moncks Corner on Oct. 1.

The permits would be on public notice, so a final decision is not expected immediately.

DHEC issued a statement Friday afternoon saying it was “ pleased to have reached an agreeable timeline’’ for processing the wastewater discharge permits.

“The Department will be engaging in a public participation process once permitting decisions have been made and looks forward to continuing to work with Sierra Club and any other interested parties during the this process,’’ the statement said.

The Sierra Club’s action follows years of disputes involving utilities, state and federal regulators and environmentalists over the cleanup of coal ash waste ponds. Many of those disputes have been resolved with agreements by utilities to clean out lagoons. The Sierra Club suit focused other discharges from power plants.

It targeted an area that environmental agencies have been criticized for: allowing water pollution discharge permits to expire without updating them. That often allows the industry to continue to discharge at the same levels, even if federal rules on releases have been tightened.

“Utilities and power plants need to have permits that are accurate and in line with current regualtions,’’ Jaffe said. “That is not what was going on. We are seeing this across many states.’’

“Sometimes it takes a lawsuit to get them to do their jobs.’’

At this point, it’s appears likely that the South Carolina permits will include tighter limits, but the question is how much.

The Trump Administration scaled back tougher discharge rules enacted under the Obama Administration. But the Trump rules are still tighter than they were in the past. Environmentalists have sued to stop the Trump rules, so that the Obama limits take effect.

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