ST. PAUL, Minn. (AP) — State pollution regulators on Thursday issued the last major state permits sought by the developers of the planned PolyMet copper-nickel mine in northeastern Minnesota, leaving only one major federal permit still pending.

The Minnesota Pollution Control Agency announced its approval of the air and water quality permits for the project and a certification of the company's plan to mitigate the mine's impact on wetlands. The only remaining major permit is a wetlands permit from the Army Corps of Engineers.

"Issuing these permits comes after a years-long process that saw the most thorough environmental review any construction project has ever had in Minnesota," MPCA Commissioner John Linc Stine said in a statement. "We are confident the requirements in these permits will protect the environment and human health over the long term."

PolyMet would be the state's first copper-nickel mine. Thursday's announcement follows a decision by the Department of Natural Resources last month to grant PolyMet several major permits, including the key one — a permit to mine.

Critics of the planned open-pit mine near Babbitt and processing plant near Hoyt Lakes cite the risks of acid mine drainage and concerns about the safety of the dam for its tailings basin. The vast but untapped reserves of buried copper, nickel and precious metals in northeastern Minnesota are locked up in sulfide minerals that can leach sulfuric acid and other pollutants when exposed to air and water.

Several environmental groups sued the DNR last month to challenge its permit decisions, saying the mine would threaten water quality downstream from Polymet as far as Lake Superior for centuries.

Polymet says it can operate without harming the environment while providing hundreds of jobs. President and CEO Jon Cherry said in a statement that Thursday's decision "represents the culmination of many years of hard work." He said the company expects to get the federal permit soon, and then it can start working to secure financing.

Company spokesman Bruce Richardson said the company hopes to begin major work in the 2019 construction season.

Altogether the DNR and MPCA have issued 17 permits and other approvals, though a few minor permits remain pending.