An iron-orange acid water discharge from a long-abandoned coal mine discolored the Monongahela River for a four-mile stretch along the Allegheny County-Washington County border over the weekend, raising public concern but causing no problems for public water suppliers downriver.

The discharge from the Boston Gas Mine, its volume boosted by recent rains, enters the river in the small Sunfish Run tributary at Sunnyside, in Forward, 34 river miles from Pittsburgh’s Point. Beginning Saturday evening and continuing through Sunday, it was visible flowing downriver in a 75-foot wide plume that hugged the east bank until blending into the river near New Eagle.

“It was orange, and it had to be an enormous amount of water to color the Mon,” said Janet Roslund, a resident of Monongahela, where she viewed the plume. “Something about that is just not right.”

Neil Shader, a spokesman for the Pennsylvania Department of Environmental Protection, said the plume likely contained iron, aluminum and manganese, and the department is continuing to take water samples. “At this time there is no concern for drinking water, and water systems have systems in place to remove the contaminants,” he said.

The Ohio River Valley Water Sanitation commission notified all downriver water suppliers on the Allegheny and Ohio rivers, but the closest, Pennsylvania American Water, with intakes 10 miles down the Mon in Elrama and 18 miles downriver at Becks Run, reported no water quality problems.

“We’ve been monitoring the intakes for the past 40 hours and have found no impacts to the water supply,” Gary Lobaugh, a water company spokesman said Monday. “We’ve increased our sampling of source water to every hour but seen nothing impacting our water quality.”

According to Joe Donovan, a geologist at West Virginia University who studies abandoned mine discharges in the Mon Valley, the abandoned Boston Gas mine is a large mining complex that has approximately eight outcrop discharges along the river between Donora and Monongahela. The one on Sunfish Run that created the orange plume in the river is the largest, he said.

“Nothing new here,” he said. “(The) flow may be up this time of year, especially right after a precip event.”

Don Hopey: dhopey@post-gazette.com, 412-263-1983, or on Twitter @donhopey

First Published: January 31, 2017, 5:00 a.m.