The Missouri Public Service Commission unanimously approved Ameren Missouri’s plan to build a coal ash landfill for its Labadie power plant, leaving final approval of the project in the hands of the Missouri Department of Natural Resources.

The decision Wednesday came three months after the utility regulator took days of testimony from Ameren and environmental groups who have opposed the Franklin County landfill for years. Passions have run high at the state and local levels, as Ameren sought to win regulatory approval while local residents and environmental groups fought it at every turn.

“This is an order that has kept me up at night,” Commissioner Daniel Hall said during a webcast of the Wednesday meeting. “I’m concerned about where the facility is being built. At the same time, I don’t think it’s our role to micromanage this issue.”

Opponents warn that Ameren’s plan to put the landfill in the Missouri River floodplain near its plant could pose a risk to groundwater, endangering the drinking water. A severe flood, they say, could wash coal ash into the river, contaminating a source of water for thousands in the St. Louis region. Critics cite Duke Energy’s coal ash spill earlier this year, which fouled about 70 miles of the Dan River in North Carolina, as an example of what could happen.