Aspen Journalism is compiling a data dashboard highlighting metrics of local public interest, updated at least every Friday. Check back for updates as we add more features.

What local wastewater data tells us about the number of people in town

Wastewater flow rates reported by the Aspen Consolidated Sanitation District, located near the Aspen-Pitkin County Airport, provide a benchmark that correlates with the volume of people in town at a certain point in time.

According to ACSD data, the volume of wastewater coming through the treatment plant dropped by 35% within seven days mid-March 2020 — that’s when the ski lifts shut down due to COVID-19. The 2020 flow rates remained lower than 2019 levels for most of the summer season until mid-August when the numbers started to catch up. During the fall season, the flow rates exceeded the 2019 numbers, up to a 3.5% increase for October 2020.

The volume of wastewater totaled 97.73 million gallons from September through November 2011. In fall 2020, that volume went up to 102.939 million gallons. It’s the highest volume for those fall months over the last decade, while the total volume for 2020 was the lowest, at 439 million gallons.

This spike last fall could reflect the influx of newcomers and part-time residents in Aspen who decided to spend more time in the valley than usual with the rise of remote work and online learning that came with the COVID-19 pandemic.

As the winter season was approaching and COVID cases spiked again, the volume of wastewater passing through the facility was reduced compared to the previous year, down to a 15.8% decrease in January 2021 compared to January 2020.

With the recent reopening of the county and the town as the number of cases in Pitkin County has dropped, the flow rates have started increasing and met the 2019 levels on June 1, 2021.

Local stream flows remain low

The gauge operated by the Aspen Center for Environmental Studies near the Mill Street bridge is the only gauge indicating Roaring Fork steam flow as the river runs through central Aspen. This is an important reading, distinct from the U.S. Geological Survey gauge upstream at Stillwater, since the ACES gauge measures the river below the Salvation and Wheeler ditch diversions. It therefore shows the Roaring Fork at its most endangered, reduced by both transbasin diversions to the Front Range from the headwaters near Independence Pass and by local water users — and before the channel is replenished by flows from Hunter, Castle and Maroon creeks.

The ACES gauge shows that on June 28, the river was flowing at 84 cfs on average, compared to 426 cfs on the same day in 2019 and 101 cfs on June 28, 2020.

Data from the in-town ACES gauge shows that the daily average for the Roaring Fork River in 2020 was 53.9 cfs, down from 142.2 cfs in 2019. 2018 was another low-flow year for the river, with an average of 38.8 cfs. With a longer-lingering snowpack in 2019, less than 1% of the state was abnormally dry, while in June 2020, 72% of Colorado was abnormally dry, according to the U.S. Drought Monitor. The U.S. Drought Monitor’s weekly report published on July 1, 2021 showed that about 45% of the state was abnormally dry this past week.

On June 28, the USGS gauge located at Stillwater, just outside of town, recorded the Roaring Fork River flowing at 110 cfs, which is 26 cfs more than the ACES gauge. On June 30, this flow was at 112 cfs, 33% of average. Last year, on that same day, the river was flowing at 126 cfs.

After a slight spike for the local watersheds thanks to rainfall around June 25-27, flows have since been dropping. The Colorado River below Glenwood Springs spiked on June 25 at 3,090 cfs. On June 30, it was flowing at 2,490 cfs or about 29% of average.

Low water levels for Lake Powell in June

Lake Powell’s water elevation has been particularly low this June, ending the month with an elevation of 3,560 feet, or about 140 feet from full pool. On June 30, the reservoir was 34.2% full.

Last year, on that same day, the reservoir was 52% full and 53% full in 2019, while the water elevation was about 89 feet from full pool in 2020 and 88 feet in 2019.

If the surface elevation of the reservoir on the Utah-Arizona state line, which stores Colorado River water, drops below 3.525.5 feet, it would trigger a host of consequences, including changes to operations of Glen Canyon Dam affecting hydropower production, releases from upstream reservoirs to prop up Lake Powell, and potential litigation between the seven states that share water under the 1922 Colorado River Compact.

Air temperature dropping

After a heat wave that saw temperatures approach all-time record highs in Aspen, air temperatures recorded at the Aspen-Pitkin County Airport started to drop between June 22 and June 23, from 87°F on June 22 to 77°F on the next day for the maximum temperature. The maximum air temperature went down to 65°F on June 26, which is 12.7°F below normal. Minimum temperatures reached their lowest on June 27 with 39°F, nearly 5°F below normal.

Editor’s note: The wastewater chart has been updated and corrected. The chart showed a spike in flow rates on Feb. 23 that didn’t occur.

Laurine Lassalle is Aspen Journalism’s data desk editor, where she works to catalogue and analyze local public data. She also heads our our “Tracking the Curve” project, documenting COVID-19 in Pitkin,...