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The Silver Queen Gondola on Aspen Mountain in March 2019. (Jesse Paul, The Colorado Sun)

On March 15, the day after ski resorts in Colorado were ordered to close, water treatment workers in Vail and Aspen scrambled to deal with a drastic drop in wastewater flowing into plants. 


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“In Vail, our staff had to basically turn off two-thirds of the plant in only four days,” said Diane Johnson with the Eagle River Water & Sanitation District. 

Turning off a wastewater treatment plant is no pull-a-plug-and-walk-away affair. They are basically ecosystems, where armies of microscopic organisms clean wastewater coming into the plant — influent — so it can be discharged into the local watershed as effluent. So staff at the plants in Aspen and Vail had to adjust biological processes that involve billions of microorganisms — bacteria, protozoa, metazoa and others — that do all the dirty work removing the organic stuff in wastewater. 

It’s a complicated process that can be a challenge to shift, especially unexpectedly. But the biologists and water engineers at two of the busiest resort-area treatment plants in Colorado did just that. The teams at the Vail and Aspen plants are accustomed to sudden shifts. It happens every year in April, when the lifts stop turning for the season and the resort communities transition into the off-season. 

But when the shift is unplanned, crews have to hustle. At the Aspen Consolidated Sanitation District’s treatment plant, biologists and engineers saw a 40% reduction of inflow on March 15 as hotels emptied and second-homeowners decamped. 

By March 19, two days after Vail Resorts and Aspen Skiing Co. announced the temporary closure of their resorts would last through the rest of the season, flows into Aspen’s wastewater treatment plant were 935,000 gallons a day, down from 1.4 million gallons a day the week before and from 1.5 million gallons a day on the same day in 2019. In a matter of days, the 1.5 million gallon daily influent volume at the Vail plant dropped by half. 

Eagle River Water and Sanitation District was treating close to 1.5 million gallons of wastewater a day on March 13, the day before the Vail ski area was ordered to close. Within days the treatment plant saw the water flowing into the plant from Vail’s homes, hotels and businesses drop by half.

“A reduction in flow is always much easier to deal with than a sudden increase in flow,” said Nathan Nelson, the wastewater treatment manager for the Aspen district. 

Nelson’s team relies on sensors and daily lab tests that determine the right mix of nutrients and microbes to help clean the incoming water. 

“Operators plug all that data into a spreadsheet then take whatever corrective actions are needed to ensure the microbes have an environment conducive to the treatment goals,” Nelson said. 

The sudden need for protective equipment for workers who remained on the job during the pandemic was nothing new for wastewater treatment teams. They are surrounded by pathogens and dangerous viruses in wastewater every day. 

“PPE is part of their daily jobs,” said Johnson, describing how the Eagle River district’s workers  were embracing new protocols to stay apart from each other while protecting the valley’s water supply. “This is certainly something we’ve never seen.” 

The Colorado Sun — Email: Twitter: @jasonblevins