(Richmond, Va.) (AP) — Dominion Energy has released a report that details the cost of recycling some of Virginia’s toxic coal ash and moving the rest to lined landfills.

Dominion said that one company could do the work for as little as $2.8 billion. Costs would grow to as much as $5.6 billion if multiple companies are hired.

Coal ash is heavy metal-laden waste left over from burning the fossil fuel to produce electricity. It’s been stored in landfills or in ponds. But leakage and spills have fueled environmental concerns in various states.

Virginia lawmakers had mandated Wednesday’s report. They’ve also halted Dominion’s plan to close its largest coal ash ponds by leaving them in place and putting a cover over them. Company officials said that plan’s costs top out at $1.9 billion.