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New technologies under review as part of Gross Reservoir Expansion Project

The trees removed from the expanded reservoir may have a new life as “biochar,” improving soil for plants.
The Gross Reservoir Expansion Project will increase water storage on the north side of Denver Water’s collection system. Photo credit: Denver Water.

Expanding a reservoir has a lot of challenges, among them dealing with the trees and bushes that must be removed.

Leaving this biomass in place to decay under the surface of the water creates safety issues for recreators and water quality issues for treatment plant operators.

Denver Water, always on the lookout for new technologies, is considering a range of options to dispose of trees at Gross Reservoir that must be removed as part of the expansion project, including creating “biochar,” a type of fine-grained charcoal that helps the soil retain nutrients.

“Ultimately, it’s going to require a mix of approaches to perform this work as safely as possible while minimizing impacts to the community and environment,” said Travis Bray, an environmental scientist for Denver Water.

“It’ll be interesting to see whether and to what degree biochar will be part of the mix.”

In 2008, Denver Water hired a consultant to study and recommend the best way to clear approximately 430 acres of trees and vegetation along 12.5 miles of shoreline at Gross Reservoir.

Federal scientists improved sugarcane yields by improving the soil with a biochar amendment made from biomass. Photo credit,  Sophia Wojkowski, U.S. Department of Agriculture, Agricultural Research Service.

The 2008 study recommended a combination of techniques and approaches because of the steep topography in the area.

Denver Water is now developing an update to its 2008 tree removal and disposal plan to be shared with stakeholders before finalizing it. The updated plan still must consider the steep topography, but also with new methods and technologies now available, the preferences of the local community and ideas on how to reduce the impacts of tree clearing that were analyzed in the permitting process.

“Concerns about the environment and how we plan to transport materials were the top two items listed in responses to our 2017 community survey of Coal Creek Canyon residents and Gross Reservoir neighbors,” said Bray.

“These two issues relate not only to the construction but also to the tree removal methods. The material must be removed and disposed of in a way that minimizes the impact to local residents and the environment.”

Having read news accounts of the need to remove trees before filling an expanded Gross Reservoir, Denver Water was contacted by a Boulder County resident who mentioned that producing biochar might be a part of the solution. Denver Water gathered experts and stakeholders earlier this summer to learn more about it during an information session with various experts.

Lettuce growing in Minnesota field plots amended with 20,000 pounds per acre of biochar that was made from macadamia nut shells.  Photo credit, Amanda Bidwell, U.S. Department of Agriculture, Agricultural Research Service.

Biochar is made from biomass that’s burned at extremely high temperatures in a low-oxygen environment, a process that’s known as pyrolysis. The resulting biochar, when added to soil, can reduce the amount of fertilizer and water plants need to thrive.

The information session included a presentation by Dr. Francesca Cotrufo, a soil ecology professor at Colorado State University who is a lead researcher in the field of biochar, along with James Gaspard, CEO of Biochar Now, a leader in large-scale biochar production with a facility near Berthoud, Colorado.

Both speakers discussed how biochar is produced and provided insights into whether it should be considered as one of what will likely be many techniques employed to solve Denver Water’s challenge.

Other disposal methods under consideration include, creating a pre-cut community fuel wood depot, logging and hauling away on trucks, chipping and mulching and using an air-curtain incinerator.

Session participants included representatives from Denver Water, Northern Water, the U.S. Forest Service, the Colorado State Forest Service, private citizens and others who have a shared interest in forest health.

Denver Water is committed to consulting with experts from Jefferson County, Boulder County, wildland fire prevention professionals, local first responders and the Forest Service as well as finding opportunities to solicit public input and feedback as the tree removal plan is updated and finalized.