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Heather@AspenJournalism.org
Colorado’s mountains are pockmarked with orange tailings piles, adits, tunnels and rusted tramways, the remnants of a historic mining industry often blamed for fouling the state’s waterways.
But a recent study points the finger at a different culprit as the cause of increasing metal concentrations in Colorado’s high mountain streams: climate change. And these findings have implications for local ecosystems and the water supplies of mountain communities.
Scientists from the U.S. Geological Survey and the University of Colorado Boulder analyzed water chemistry data over the past 40 years for 22 stream sites throughout Colorado’s mountains. They found that concentrations of zinc and copper have doubled over the past 30 years, with melting of previously frozen ground being a likely major cause.
“These trends are concerning because, even at low concentrations, dissolved metals can negatively affect downstream ecosystem health and the quality of water resources,” reads the paper, which was published in Water Resources Research in late April.
Tanya Petach, a climate scientist at the Aspen Global Change Institute, worked on the study. She said the trend of increasing metal concentrations is relatively steep and widespread across Colorado’s mountains.
“There’s this theory that those increases in metal concentrations in these streams are really driven by a climate change signal,” Petach said. “We are really used to tying increases in metals to anthropogenic activities, but in this case, we’re just seeing a climate response.”
The process that causes metals to leach into streams can be both naturally occurring and caused by mining activities. In both cases, sulfide minerals in rock come in contact with oxygen and water, producing sulfuric acid. The acid can then leach the metals out of the rock and into a stream, a process known as acid rock drainage. As temperatures warm, rock that has long been encased in ice becomes exposed to weathering.
“These high-elevation streams, some of them have mean annual air temperatures right around freezing,” Petach said. “So you go from having permafrost to melting that permafrost. Once you lose the ice, you’ve created a phenomenal conduit for new water and oxygen to come into contact with sulfide minerals that have been blocked for centuries, if not millennia.”
Diane McKnight, an environmental engineering professor at CU Boulder’s Institute of Arctic and Alpine Research, has been measuring the pH levels of the upper Snake River in Summit County for decades. On a recent trip with students, a stream that usually had a pH level of about 4 measured 2.75, meaning the acidity had greatly increased.
“I said: Wait, the probe must be wrong, the probe must be broken,” McKnight said. “Guess what, the probe was not broken. … The public should be aware the world is changing and there are surprises.”
The study says declining streamflows also contribute to increasing metal concentrations, but not as much as the increase in acid rock drainage caused by climate change.
These findings on the Snake River and other sites in Colorado are important for the members of a workgroup trying to figure out how to address increasing metal concentrations in Lincoln Creek above Aspen. Although Lincoln Creek wasn’t one of the sites included in the study, the conditions in Lincoln Creek mirror many of the headwaters study sites.
“Lincoln Creek is very intriguing because it matches a similar pattern,” Petach said. “The Lincoln Creek system seems fairly similar to a lot of these other high-elevation headwaters catchments where this occurs.”
Water quality issues in Lincoln Creek have been a concern for years and have been getting worse. A November report by the U.S. Environmental Protection Agency showed that metal concentrations in Lincoln Creek are high enough to be toxic to fish and aquatic life. The creek above Grizzly Reservoir exceeds state water quality standards for aluminum, cadmium, copper, iron, lead, manganese and zinc, and aluminum and copper concentrations were higher than standards set by the Colorado Department of Public Health and Environment in multiple locations.
“The public should be aware the world is changing and there are surprises.”
The report found that the vast majority of the contamination was coming from a “mineralized tributary” to Lincoln Creek and not from the nearby Ruby Mine, where prospectors in the early 1900s dug for gold, silver and lead.
A workgroup dedicated to Lincoln Creek and composed of officials from state, local and federal agencies, nonprofit environmental groups and others has been meeting often since the EPA report was released. Since the EPA is authorized to address elevated metal concentrations only from human-caused activities like mining, it’s unclear how the contamination would be cleaned up or what agency is responsible for it.
But the workgroup is making headway on the issue, said member Karin Teague, executive director of the nonprofit environmental group Independence Pass Foundation.
“It could be a model for how a community might respond to contamination in its watershed,” Teague said. “We are really getting our arms around the problem, the extent of it, the nature of it, and then, of course, the million-dollar question being: What, if anything, can be done about it?”
Pitkin County Environmental Health Manager Kurt Dahl and Pitkin County Healthy Rivers Administrator Lisa Tasker gave an update on the group’s progress to county commissioners at a work session Tuesday. There are plans for four different water quality projects this summer: the U.S. Forest Service plans to collect water quantity and flow data; Colorado Parks and Wildlife will monitor metals concentrations in Lincoln Creek and the Roaring Fork River; the Roaring Fork Conservancy will take samples below Grizzly Reservoir to look for impacts related to a Grizzly Dam rehabilitation project; and scientists and students from CU’s INSTAAR program will look for rare earth metals in the water, sediment and bugs of Lincoln Creek. Pitkin County has approved grants for three of the four projects so far.
Lincoln Creek is one of seven streams in the Roaring Fork basin’s headwaters that feed the Twin Lakes Reservoir and Canal Co.’s Independence Pass transmountain diversion system, which provides drinking water sources for Front Ranges cities, including Colorado Springs, which owns a majority of the system’s water. Grizzly Reservoir, on Lincoln Creek below the contamination source, is used as a collection pool for water collected from the creeks, which is sent through the Twin Lakes Tunnel to the Arkansas River basin and eventually to the Front Range. The Snake River system where McKnight has conducted research flows into Dillon Reservoir, Denver Water’s biggest storage bucket.
The EPA report said that in the case of Lincoln Creek, the dilution, the distance the water travels and the water-treatment process limit the impacts to drinking water. But since the issue is widespread across Colorado’s mountains, communities that get their drinking water from high-elevation streams could be impacted.
“These metal concentrations tend to be diluted when the small tributaries confluence with larger, cleaner streams, so we don’t tend to think of these as being a huge problem for large municipal water supplies,” Petach said. “But the place where it does really impact the drinking water supply is in high-elevation mountain communities that are receiving waters from smaller tributaries.”
The city of Aspen gets the majority of its drinking water from Castle Creek, a mountainous tributary of the Roaring Fork River. Aspen’s Utilities Resource Manager Steve Hunter said that source water protection is a key concern for the city.
“After talking with our water treatment staff, they are not seeing a rise in these metals at the treatment plant and all treated water meets or exceeds CDPHE/EPA requirements,” Hunter said in a prepared statement. He added that the city has not done source water sampling for these compounds in either Castle or Maroon Creek watersheds as CDPHE/EPA does not require testing Aspen’s source water for these compounds.
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