What’s behind the (weird) colors of water
What is the color of water? That depends.
Colorless in its purest atomic form, water seen from another perspective can take on the hues of the minerals it contains, the biological matter that has dissolved in it or the chemical reactions occurring around it. Water can change its color based on its temperature and state of matter, and can reflect the colors around it without really changing at all.
In recent weeks throughout southwestern Pennsylvania, the colors of some streams have changed, causing concerned neighbors to suspect that upstream gas stations, waste dumps or septic tanks had become sources for pollution. But in most of those cases, it is believed the pollution originated decades or even hundreds of years ago.
On a database considered to be incomplete, the U.S. Office of Surface Mining Reclamation and Enforcement lists 139 abandoned mines in Allegheny County, about a third of the total abandoned mines in the United States.
“A lot of them aren’t even marked,” said Matt Gordon, a conservationist with the Allegheny County Conservation District. “There are several hundred years of industrial development underneath us, and the mines have been filling up with water. We just had the wettest February on record … [and] that’s flushing whatever is in [those mines] out to surface drainages.”
Sometimes the mineral additives temporarily discolor normally stable waterways. Pittsburghers of a certain age would recognize orange water as the complexion of iron oxide pollution, which was once pervasive throughout the region. Black water often contains traces of manganese.
Sometimes the colors are the result of complicated chemical processes.
Last week Montour Run, stocked with trout and bordering a popular biking-hiking trail, took on a greenish-white tinge from its headwaters near Pittsburgh International Airport to its confluence with the Ohio River at Coraopolis.
“The sulfur in the coal seam oxidizes when it’s exposed to air in the mine,” said Robert C. Dolence, a board member of the Montour Run Watershed Association. “When the oxidized sulfur meets water it creates dissolved iron particles and sulfuric acid, which dissolves aluminum and other minerals. The mine drainage including the dissolved aluminum mixes with alkaline, giving the discharge a milky appearance.”
Just east of the Squirrel Hill Tunnel, a different concentration of aluminum has altered the appearance of Nine Mile Run. From Frick Park to the Monongahela River, the creek has turned a pastel blue — one caller preferred “turquoise.”
“It’s a very interesting color — a bluish-green haze in the water,” said Lindsey-Rose Flowers of the Nine Mile Run
Watershed Association. “We don’t usually see that color in the stream.”
Dissolved organic matter can also color water. Wood and deciduous leaves stain water yellow or brown; coniferous needles give water a greenish tinge. Those colors are more common in warmer weather. Water is colorized as it diffuses through decaying plants at the surface, runs underground and emerges from springs.
The Allegheny County Health Department and state Department of Environmental Protection have examined the newly colored waters and issued no alerts. The Fish and Boat Commission hasn’t postponed stockings at this time but is monitoring Montour Run as the April 14 opening of the statewide trout season approaches.