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The “burn scars” from forest fires threaten drinking water in the west

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Colorado had its worst fire season last year with the three largest fires in state history and more than 600,000 hectares burned. However, some of the effects did not appear until July this year, when heavy rain pushed sediments from damaged forests down the mountain slopes, causing mudslides that closes sections of Interstate 70 for almost two weeks.

Huge amounts of sediment choked the rivers that supply most of the state’s water. In Glenwood Springs, in western Colorado, the water became so cloudy that the city had to close the valves that pump water from nearby rivers twice to avoid overloading the filtration system. The city council sent warnings to the city’s 10,000 residents, urging them to minimize water use until the sediment moved downstream.

Forest fires and their permanent effects are becoming a way of life in the West as climate change and management practices cause the number, intensity and area of ​​fires to increase while increasing the length of the fire season. In “burn scars,” where fires decimated forest systems that held the soil in place, an increase in droughts followed by heavy rainfall poses another type of water threat that is essential to community health.

“You know about it; it’s in the back of your mind,” said Paula Stepp of Glenwood Springs. “But until you face this, you don’t know how it will affect your town.”

Dirty, cloudy water can contain viruses, parasites, bacteria and other pathogenic pollutants. However, experts say cloudy water from burn scars is unlikely to get into people’s faucets because water utilities would catch it first.

Still, the cost of municipal utilities – and the residents who pay for the water – is immense. Small rural towns in particular face the choice of spending millions of dollars trying to filter cloudy water or stopping their water intake and risking bottlenecks in areas where water may already be scarce.

And as fires get closer to communities, burning synthetic materials from homes and other buildings can create toxic compounds that end up in water supplies, as was the case in California after major fires in 2017 and 2018.

“If we [fires] off, we become less aware of them, ”said Hydrologist Kevin Bladon, Oregon State University. But from a water perspective, “then all the problems begin”.

The capital of Montana, Helena, gets its drinking water supply from the Upper Tenmile Creek watershed in a forest full of trees that have been killed by beetle infestations. City guides fear that a fire would quickly chew through this dry fuel and expose the catchment area to sediment contamination. Despite a logging project where many of these trees were cut down two years ago, The fire hazard remains and city guides fear that the resulting sediments will flood the water treatment plant and shut down the primary 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 put the Tenmile facility out for a season or two,” said Ryan Leland, director of public works at Helena.

To protect itself from this, the city is in the early stages of planning a basin that can catch sediment before the water reaches the facility, Leland said. The city also recently announced plans to drill three groundwater test wellsthat would give them another drinking water supply option if something happened to the Upper Tenmile watershed. 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 burn scars that later flooded and contaminated water sources.

Greeley had to shut off the inlet from the Cache la Poudre River for 39 days this year because the water was contaminated with sediments, ash and organic matter. “Normally we would never turn it off,” said Greeley Water and Wastewater Director Sean Chambers.

To deal with this, the city has traded water with a nearby agricultural company that owns reservoirs that are used for irrigation. The exchange gives the cloudy water to the farmers and diverts the reservoir water to Greeley. “If we didn’t have the trade, it would be the cost [of buying water] would be astronomical, “said Chambers.

However, Chambers acknowledged that this system is a luxury that smaller cities may not enjoy. Greeley is ten times the size of Glenwood Springs and has spent more than $ 40 million this year to recover from the Cameron Peak Fire – the largest fire in Colorado history that burned for four months in 2020. Those costs could rise with persistent rain, he said. Bigger cities also tend to have better filtration systems that can handle more sediment, clog filters, and require utilities to add chemicals to remove contaminants before the water is potable.

While arid states like Colorado anticipate fires every year, recent fires in wetter places like western Oregon have surprised researchers. Last September, Fires burned about 11% the state’s Cascade Mountain Range, leaving burn scars over the rivers and reservoirs that supply much of the state’s water.

“We have to be very proactive,” said Peter Robichaud, Research Engineer at the US Forest Service in Moscow, Idaho.

After a wildfire is extinguished, Robichaud’s agency and other specialist teams dispatch to assess the risks of erosion and ash for the water supply. Your data can help land managers decide whether to take action such as thinning forests over rivers, dredging contaminated reservoirs, covering the area with mulch or seeds to reduce erosion, or creating a plan for alternative water sources.

Even warning of a flood could help immensely, said Stepp, a resident of Glenwood Springs. She is the managing director of the non-profit Watershed Council in Middle Coloradowho recently worked with the US Geological Survey to Install rain gauge along the Glenwood Canyon. These monitor the weather upstream and notify water users downstream that a sediment-laden flood may be imminent.

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

Although debris flows can bring soil bacteria into the water supply, municipal utilities can disinfect them with chemicals like chlorine, said Ben Livne, Hydrologist at the University of Colorado-Boulder. But these disinfectants can themselves create a problem: organic matter from sediments can interact with these chemicals and create carcinogenic by-products that are difficult and expensive to remove.

Chemical by-products and heavy metals from burned structures represent a further hazard from water. “Treatment could be very problematic,” said Livneh.

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

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

California is relatively lucky when it comes to sediment flow. Years of drought in most states mean burn scars remain intact – although heavy rain could wash away years of debris.

It’s unclear how long burn scars will continue to pose a landslide risk, said Bladon, the Oregon hydrologist. But parts of Alberta in the Canadian Rockies, for example, saw extremely cloudy water for a decade after a fire in 2003.

“I’m afraid we may not have seen the worst,” said Solomon.

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