Aspen: Jenny Adair wetlands project doing its job

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From the Aspen Daily News (Will Grant):

The city of Aspen’s Jenny Adair Regional Stormwater Quality Project is an artificial wetlands area off N. Mill St. intended to reduce pollutants into the Roaring Fork River by channeling stormwater runoff through a series of filters. The city built the wetlands in 2007 and says the wetlands have saved the river 144 tons of trash, sediment and oil in two-plus years. “We’re so impressed with the project,” said city of Aspen stormwater manager April Barker. “It’s only been here two years, and already it’s doing exactly what we wanted.”

What the city wanted was someplace where the flushed pollutants could settle out before the stormwater runs into the river. The wetlands system acts as a filter by slowing down the water, which allows most things suspended in the water to settle out and, later, for microbes to do their part to improve the water quality. Sediment is the number one pollutant in stormwater runoff in Colorado, Barker said. Sediment can change the river morphology, increase the water temperature and often acts as a place for other pollutants to attach themselves.

The process starts when stormwater runoff from the city is diverted to one of several vaults buried in the ground between Aspen and the Roaring Fork River. The vaults are concrete boxes about 9 feet deep and 20 feet square. The water runs through a 3-foot-wide convoluted channel intended to slow the water through the vault. The water gradually drops its sediment load in the channel; heaviest sediments form at the front of the channel, finer sediments collect downstream. A metal grate catches anything floating on the surface. The vaults remove about 50 percent of the runoff’s initial sediment load, Barker said, and the wetlands remove 80 percent of the sediment that makes it through the vaults. Before the water leaves the vault, it runs through a small opening at the base of a division wall within the vault. By forcing the water through an opening at the bottom of the wall, any oil on the surface of the water will be left in the vault…

After the water leaves the vault it flows into the wetlands. Vegetation in the wetlands keeps the water moving at a slow pace and absorbs some nutrients in the water that are considered pollutants…

After slowly running through the vegetation, the water enters a settling pond, which is its last stop before running into the river. Although the pond allows further settling out of pollutants, it is also where the microbes do their part. Microbes in the water perform denitrification, meaning they convert nitrate in the water to nitrogen gas. Nitrate in high concentrations is harmful to nearly everything, including humans, but the microbes grow off it. The microbial treatment is a significant one, according to Dr. Diane McKnight, a professor of civil, environmental and architectural engineering at the University of Colorado. She has researched the dynamic interaction of chemical, biological and hydrologic processes in aquatic ecosystems and says the microbes do an important job. “What the wetland does is create areas where the water has retention time,” McKnight said, “as opposed to having that process happening more slowly in the stream or not happening until way down stream.” The microbial process affects a chemical change in the water, as opposed to the physical change when the pollutants settle out. After the microbes do their thing, “the metals have a changed chemistry so they’re no longer moving with the water,” McKnight said. “The water leaves the wetlands without the metals.”[…]

The Jenny Adair project has received two awards: The 2008 President’s Award from the Associated Landscape Contractors of Colorado, and an award from the American Society of Landscape Architects. The AALC President’s Award is not given every year and has been awarded only once in about 30 years, Ellsperman said. It recognizes the functionality and sustainability of the project. The ASLA award recognizes the project’s attractive, natural design.

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