Aspen deliberates updating plan that manages stormwater runoff, pollutants

Aspen City Council disagreed on proposed updated strategies to control the stormwater sediment and pollutant load flowing into the Roaring Fork River during development projects. 

Central to city council’s Nov. 17 disagreement regarding updates to the city’s Urban Runoff Management Plan was the threshold at which a development would call for adherence with various stormwater infrastructure requirements. The city estimated it would cost $25,000 to $30,000 for developers to hire a stormwater system engineer and $115,453 to install a stormwater system itself, though it did not say if these costs were mutually exclusive. 

In the proposed update to the code, developers must plan to manage runoff with a “major grading plan” if an interior remodel is greater than 50% of the total building footprint and if the site’s impervious area, or area that prevents water from absorbing into the ground, is greater than 50%. This would be a continuation of the existing code regulations. 

If the impervious area of the site is less than 50%, an interior remodel of greater than 75% would also require developers to install a system to manage runoff. 

“What I struggle with is that there are interior remodel thresholds that are triggering major exterior construction work that wouldn’t otherwise occur, necessarily,” Council Member Bill Guth said in the Nov. 17 City Council Work Session.

He said the impact on the community from doing additional exterior work for these types of updates would be greater than if the developer were to not install the stormwater system at all. 

What’s happening in Aspen, in one click.

Sign up for the Sunrise Rundown at AspenTimes.com/newsletter

“And I take issue with this. I think it’s an overreach,” he said. “I think that if you look at the full cycle of the impact, from an environmental standpoint, I don’t think that we’re getting a return on investment.”

Mayor Rachael Richards, alternatively, supported the requirement threshold, emphasizing the importance of protecting the natural environment from pollutants. 

“If they’re remodeling, and we’re going to say, you have to come up to the current electric code, the fire code — you can’t just put in old water fixtures if there’s new water fixtures required,” Richards said. “And so this is about coming up to code with what might be your land and your property around it.”

Stormwater management is also required if the development area addition, repair, or demolition, exceeds 1,000 square feet, among other thresholds. 

Richards said if the city just relies on demolitions, rather than remodels, to require developers to meet the stormwater code, “we’d be waiting a very long time.”

Apart from council members’ disagreements, city staff and consultant Wright Water Engineers suggested various ways the city can implement effective residential sediment removal and stormwater control measures to reduce flood risk and river pollution.

They suggested installing residential sediment removal drywells, belowground infiltration systems that collect and allow stormwater to slowly seep into the ground. Over 30 years, a drywell can remove 345 pounds of sediment from stormwater. 

“If every lot under 3,000 square feet in the city of Aspen treated stormwater, approximately 15,000 (pounds) of excess sediment and associated pollutants would be stopped from entering the river every year,” a city staff report states.

City staff and the consultant also suggested installing “receiving pervious areas,” vegetated areas that absorb runoff from areas where stormwater cannot infiltrate. 

“What happens when an impervious surface drains across a pervious area, (is) you have an opportunity for some of that runoff to infiltrate,” Andrew Earles, vice president of water resources for Wright Water Engineers, said. “The vegetation also filters the runoff and allows some of the sediments to drop out.”

He also suggested rain gardens and permeable pavements, which are vegetated and paved areas that allow for water infiltration into the ground. He noted that the city already has some of this stormwater technology in place. 

Additionally, city staff seeks to update the readability and usability of the Urban Runoff Management Plan, as well as the plan’s technical components like its rainfall and mudflow data.

Council did not immediately decide on whether to move forward with the updates but directed staff to revisit the discussion with the city sometime next year after further investigating how to implement various stormwater systems.

Skyler Stark-Ragsdale can be reached at 970-429-9152 or email him at sstark-ragsdale@aspentimes.com.