There are thousands of abandoned coal mines dotting the landscape of Pennsylvania, and many of them leak water tainted with toxic metals like iron and manganese, which seeps into streams and groundwater.

It’s been a long, expensive process for the state to clean up the acid mine drainage. But state environmental officials now say an alternative method of remediation -- constructed wetlands -- could remove iron and manganese from mine drainage at a much lower cost.

On Wednesday, members of the state’s Mining and Reclamation Advisory Board toured a constructed wetland built to purify water from two abandoned mines close to the Flight 93 National Memorial in Stoneycreek Township, Somerset County.

“This is a creative solution to a problem that is all too common in Pennsylvania,” said Patrick McDonnell, acting Secretary of the state Department of Environmental Protection, in a statement.

Water with heavy concentrations of iron and manganese is pumped out of the mines and into a series of pools, where iron settles and can be removed. Much of the remaining iron content is cleansed by the natural vegetation. Then, manganese is filtered out by bacteria and other microorganisms living in a 4-foot-deep bed of limestone gravel. Through the process, iron content is reduced by 77 percent and manganese levels drop by 95 percent. After it’s purified, the water joins Lamberts Run, which then flows into the Stoneycreek River and its much-used trout fishery.

According to the U.S. Geological Survey, the ongoing issue of acid mine drainage is contaminating more than 3,000 miles of the commonwealth’s streams, subduing ecosystems and costing roughly $67 million per year in potential economic activity from recreation.

Since coal companies aren’t held liable for acid drainage coming from mines that were abandoned before pollution controls were set in 1977, it’s largely been up to the state government to pump the water out of mines and treat it with chemicals. To remediate all of Pennsylvania’s abandoned mines this way would cost anywhere from $5 billion to $15 billion, according to USGS.

Malcolm Crittenden, watershed manager at the DEP’s Cambria office, said the Flight 93 memorial wetland was built about four years ago at a total cost just under $313,000, funded by a grant from the federal Office of Surface Mining.

Crittenden said the constructed wetland method could work just as well and just as cheaply for active mines as it does for abandoned ones.

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"A lot of your mine operators, they have to treat water,” Crittenden said. “It’s very expensive and it’s burdensome. But, if you have room for a manganese bed, you can do that same work with the biology removing the manganese.”

He said funding for remediation often comes from government grant programs that are funded by coal industry fees.