A spokesman for Akron-based FirstEnergy says the company plans to replace the 1,700-acre Little Blue Run dump in Beaver County with a new lined depository that will keep the pollutants from getting into the groundwater.
The current dump doesn't have a lining because that wasn't required when it opened in 1974.
A federal judge in Pittsburgh must still sign off on the agreement filed last week by the Pennsylvania Department of Environmental Protection and FirstEnergy.
The slurry is from the Bruce Mansfield coal-fired power plant about 35 miles northwest of Pittsburgh.
First Energy must also pay an $800,000 fine and clean up or supply new water to those living nearby.