Wildfire ‘burn scars’ threaten West’s drinking water

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Colorado experienced its worst fire season last year, with the three largest fires in state history and more than 600,000 acres burned. But some of the effects did not appear until July, when heavy rains pushed sediment from damaged forests down the mountains, causing mudslides that closed sections of Interstate 70 for nearly two weeks.

Huge amounts of sediment choked the rivers that provide most of the state’s water. In Glenwood Springs, western Colorado, the water became so cloudy that the city had to twice shut off the valves that pump water from nearby rivers to avoid overloading its filtration system. City administrators have sent alerts to the city’s 10,000 residents, telling them to minimize water use until the sediment moves downstream.

Forest fires and their lasting effects are becoming a way of life in the West, as climate change and management practices lead to an increase in the number, intensity and area burned of fires, while prolonging the duration. of the fire season. In ‘burn scars’, where fires have decimated the forest systems that held the soil in place, an increase in droughts followed by heavy rainfall poses another threat to water supplies that are essential to healthy communities. .

” You know it ; it’s on the back of your head, ”said Paula Stepp, Glenwood Springs resident. “But until you face it, you don’t know how it’s going to impact your city.”

Dirty and cloudy water may contain viruses, parasites, bacteria and other contaminants that cause disease. But experts say cloudy water from burn scars is unlikely to reach people’s taps because water utilities would catch it first.

Yet the cost to municipal utility systems – and the residents who pay for water – is immense. Small rural towns in particular face the choice of spending millions of dollars trying to filter cloudy water or shutting off their intake and risking shortages in areas where water may already be scarce.

And as fires get closer to communities, burning man-made materials in homes and other buildings can create toxic compounds that leach into water supplies, which has happened in California. after major fires in 2017 and 2018.

“When we put [fires] outside we become less aware of it, ”said hydrologist Kevin Bladon, Oregon State University. But from a water point of view, “that’s when all the problems start”.

Montana’s capital, Helena, gets its clean water supply from the Upper Tenmile Creek watershed, a dense forest of trees killed by beetle infestations. City officials fear a fire could quickly chew this dry fuel and leave the watershed exposed to sediment contamination. Despite a logging project that destroyed many of these trees two years ago, the threat of fire remains and city officials fear the resulting sediment would submerge the water treatment plant and shut off the main water source for 40,000 people.

“If we had a fire up there, depending on where it is and how big it is, it could shut down the Tenmile plant for a season or two,” said Ryan Leland, Helena’s public works manager.

To protect against this, the city is in the early stages of designing a basin that can trap sediment before water reaches the plant, Leland said. The city also recently announced plans to drill three groundwater test wells., which would give them another option of supplying drinking water if anything happened to the Upper Tenmile watershed. The treated water from the Missouri River is the city’s current emergency supply.

The Rocky Mountains and about 200 miles separate Glenwood Springs from Greeley in northeast Colorado. But the 2020 fire season caused similar problems in both cities, creating scars from burns that then flooded, contaminating water sources.

So far this year, Greeley has had to close its catch of the Cache la Poudre River for 39 days because the water was contaminated with sediment, ash and organic matter. “Normally we would never turn it off,” said Sean Chambers, Greeley Water and Sewer Director.

To cope, the city has traded water with a nearby farming business that has reservoirs used for irrigation. The exchange gives the murky water to the farmers and redirects the water from the reservoir to Greeley. “If we didn’t have the trade in place, the cost [of buying water] would be astronomical, ”Chambers said.

But Chambers admitted that this system is a luxury that small towns may not enjoy. Greeley is 10 times the size of Glenwood Springs and spent over $ 40 million this year recovering from the Cameron Peak fire – the largest blaze in Colorado history, which burned for four months in 2020 These costs could increase as the rain continues, he said. . Big cities also tend to have better filtration systems that can handle more sediment, which clogs filters and forces utilities to add chemicals to remove contaminants before the water is safe to drink.

While dry states like Colorado expect fires every year, recent fires in wetter places like western Oregon have caught researchers off guard. Last September, fires burned about 11% of the state’s Cascade mountain range, leaving scars from burns over the rivers and reservoirs that supply much of the state’s water.

“We have to be very proactive,” said Pierre Robichaud, research engineer at the US Forest Service in Moscow, Idaho.

After a forest fire is extinguished, Robichaud’s agency and others send teams of specialists to assess the risks that erosion and ash pose to the water supply. Their data can help land managers decide whether to take measures such as thinning out forests above rivers, dredging contaminated reservoirs, covering the area with mulch or seeds to reduce l erosion, or developing a plan for alternative water sources.

Even a flood warning could help immensely, said Stepp, the Glenwood Springs resident. She is the general manager of the association Middle Colorado Watershed Council, who recently collaborated with the US Geological Survey to install rain gauges along Glenwood Canyon. These monitor weather conditions upstream and notify water users downstream that a sediment-laden flood could occur.

She said it is crucial for small communities in particular to partner with state and federal agencies. “Basically we work with everyone,” she said.

Although debris flows can bring bacteria from the soil into water supplies, city utilities can disinfect them with chemicals like chlorine, said Ben Livneh, hydrologist at the University of Colorado-Boulder. But these disinfectants themselves can be problematic: organic matter in sediments can interact with these chemicals and create carcinogenic byproducts that are difficult and expensive to remove.

Another water-borne hazard comes from chemical byproducts and heavy metals from burnt structures. “These would be potentially very problematic to deal with,” Livneh said.

After the Tubbs fires in 2017 and 2018 Camp that devastated communities of Santa Rosa and Paradise in northern California, researchers examining tap water from nearby homes found benzene and other carcinogens. Public health researcher Gina Solomon at the Public Health Institute in Oakland, Calif., said the contamination likely came from plastic pipes that were melting and leaking chemicals into the water.

Smoke and ash from burnt structures can also add toxic chemicals to water supplies. “The smoke from the fires is a really nasty brew,” Solomon said.

California has been relatively lucky when it comes to sediment runoff. Drought that has lasted for years in most states means burn scars remain intact, although heavy rain can wash away years of debris.

It is not known how long scars from burns continue to pose a landslide risk, said Bladon, the Oregon hydrologist. But parts of Alberta in the Canadian Rockies, for example, continued to see extremely murky water for a decade after a fire in 2003.

“My fear is that we haven’t seen the worst yet,” Solomon said.


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