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Environmental groups on Thursday filed a suit in federal appeals court challenging provisions in the Environmental Protection Agency’s recently updated wastewater limits for coal-fired power plants that they say don’t go far enough.

Our groups strongly support the new rule’s zero-discharge requirements for the largest power plant waste streams, which once implemented will protect our drinking water and the health and safety of our waterways,” Thomas Cmar, a senior attorney with Earthjustice, said in an email.

However, the EPA’s rule, or “effluent limitation guidelines,” exempts power plants that promise to retire by 2034, placing a burden on downstream communities for another decade, according to Cmar.

Also, the new rule’s weaker standards for certain categories of power plant leachate fall short of what the Clean Water Act requires, he said.

The rule was part of a package of rules affecting power plants the EPA released in late April, including one rule that limits greenhouse gas emissions from coal-fired and new gas-fired power plants.

The effluent rule sets more stringent limits for flue gas desulfurization wastewater, bottom ash transport water and combustion residual leachate. Power plant owners must meet the new requirements by Dec. 31, 2029.

The agency estimates the wastewater rule will cut pollution from coal-fired power plants by more than 660 million pounds a year and produce $3.2 billion in annual benefits. It said the rule could lead to about 5,780 MW in power plant retirements by 2035.

Earthjustice filed the petition in the U.S. Court of Appeals for the District of Columbia Circuit on behalf of Clean Water Action, Sierra Club, Diné Citizens Against Ruining Our Environment, Waterkeeper Alliance and the Natural Resources Defense Council. They were joined in the petition by Environmental Integrity Project, PennEnvironment and Prairie Rivers Network, Cmar said.

The Center for Biological Diversity filed a separate lawsuit on May 23 in the 9th U.S. Circuit Court of Appeals challenging the exemption for power plants that retire before 2034. The environmental group argues the exemption violates the Clean Water Act and Endangered Species Act.

Meanwhile, utility company American Electric Power has said it is also considering suing the EPA over the effluent limitation guidelines, while Oklahoma Gas and Electric said it intends to comply with the rule, according to the companies’ most recent quarterly financial filings with the U.S. Securities and Exchange Commission.

The U.S. coal-fired power plant fleet is in decline, in part because of the cost of complying with environmental regulations, plant owners say. There was 208 GW of coal-fired generation, making up 16.2% of the total U.S. generating fleet, at the end of last year, down from 266 GW making up 22.2% of the fleet in 2018, according to the Federal Energy Regulatory Commission. The agency expects 22 GW of coal capacity to shutter between the start of this year and the end of 2026.