Why a stream near Monroeville Mall is glowing bright blue

In the valley below Monroeville Mall, a small stream that starts in Penn Hills winds its way downhill alongside Stotler Road, before breaking southeast and following the road that bears its name, Thompson Run.

As the stream nears a bridge carrying Thompson Run Road over top, the water has an odd silvery-blue sheen to it. On the other side of the culvert, where it empties into a deeper pool, the water is a shockingly bright shade of blue, and there are no fish — or really, any aquatic life — to be seen.

It’s so bright, in fact, it can be spotted on a Google Maps satellite photo of the area.

The coloration comes from aluminum, which is picked up as stormwater passes through — and out of — any number of abandoned mines in the area. In the case of Thompson Run, local watershed officials say it likely comes from Oak Hill mines No. 4 and No. 5, operated by the Pittsburgh Coal Co. and O’Block Coal Co.

It is a common problem in the extensively mined hills of Southwestern Pennsylvania, and the fix typically comes with a massive price tag.

Thompson Run is part of the Turtle Creek Watershed, and the Turtle Creek Watershed Association is just one of several groups working on projects throughout its drainage area to mitigate the damage caused by acid mine water.

The association just completed a $70,000 grant-funded study on the entire watershed, according to association President Jim Brucker.

“We’re working on a project to clean the water in Brush Creek, which has one of the biggest acid mine drainage outbreaks in the state,” Brucker said.

Stretches of Brush Creek run bright orange rather than blue, owing to the presence of iron and sulfur draining from one of its tributaries, Tinker’s Run, which passes through Irwin before entering Brush Creek near Pacific Street. And just as with the “blue lagoon” as it’s commonly known, the water in Tinker’s Run is such a bright orange color, it can be spotted on Google Maps images.

Acid mine drainage occurs because the target ore in many mining operations is often surrounded by sulfide minerals. When those minerals are exposed to water and air, they form sulfuric acid, which can dissolve other harmful metals and metalloids, like arsenic, from the surrounding rock.

Depending on the level of pollution, some streams impacted by acid mine drainage can have a pH level of 4, equivalent to battery acid, according to environmental nonprofit Earthworks. In Great Britain, Earthworks officials said there are still ancient Roman mine sites from 2,000 years ago which continue to generate acid drainage today.

The Turtle Creek Watershed Association worked with Westmoreland County officials to purchase acreage near the Irwin Sportsmen’s Association in North Huntingdon to address the problem.

“The next phase there will be cleaning the property up,” Brucker said. “There are large coal spoil piles that the state has drilled through and examined. Three or four of them are pretty much just garbage, but one or two may have enough (viable coal) to sell and make some money.”

Eventually, the association wants to locate a mine water treatment plant on the site, which Brucker estimated will cost about $2 million.

“We also have to drill down into the mine to see what we’re dealing with,” he said. “We then either redirect Tinker’s Run through the filtration site, or we pump Tinker’s Run up to the treatment plant.”

The Turtle Creek association is just one of the groups working to get acid mine drainage out of the watershed.

Murrysville officials have worked with the Lyons Run Watershed Association and are considering seeking grant funding for a massive mine water treatment plant on property off Borland Farm Road. The plans come with an equally massive price tag of $5 million to $10 million.

Not far away, the Lyons Run association already has constructed a passive filtration system for drainage entering Lyons Run, another tributary to Turtle Creek.

Pennsylvania has the largest inventory of abandoned coal mines in the country, according to the Pennsylvania Department for Environmental Protection, and has received hundreds of millions of dollars in federal funding in recent years specifically to address the acidic water that drains from them.

In the case of the “blue lagoon,” Brucker said it is lower on the priority list than other, larger acid mine drainage areas targeted for mitigation.

“They generally get prioritized by how many miles of clean stream you can create with a remediation project,” he said.