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'All of the above' may include underneath our feet

As Denver Water looks to increase water security, a slice of its supply could be stored deep below the city.

Denver Water is drilling deep into an important question: Can it store small portions of its water underground to augment its supplies in mountain reservoirs?

The utility is taking another step toward finding an answer with a test project this fall in the heart of Denver.

Denver Water plans to drill an exploratory well several hundred feet deep in the Congress Park area, a round-the-clock project that will take several weeks. The site will be the southeast corner of Denver Water’s Capitol Hill facility at 1000 Elizabeth Street, not far from the Denver Botanic Gardens.

Bob Peters, a water resource engineer, is pictured here in 2015 near an earlier ASR drilling test site. Photo credit: Denver Water.

The project is part of Denver Water’s “all of the above” strategy to ensure it can meet future demands in its service area. Combined with conservation and efficiency, new reservoir storage and water recycling — among other approaches — storing some water underground would increase the utility’s options as the region grows and climate change stresses water supplies.

“Storing excess water underground in wet years would provide a savings account of sorts to help the community endure dry periods,” explained Bob Peters, water resource engineer for Denver Water. “It gives us another place to turn when supplies get tight.”

This project comes after an earlier study, in 2015 and 2016, when Denver Water drilled boreholes at eight locations to better understand the rock composition underneath the region.

Those findings were promising enough to lead Denver Water to this next step, the construction of a pilot well facility. Depending on what engineers discover from the exploratory well, operational wells could eventually be constructed and used to test injection and removal of waters, the challenges associated with that and the effects on water quality throughout the process.

The concept, known as Aquifer Storage and Recovery (ASR), is a more sophisticated version of what people have been doing for centuries around the world. Similar projects are in use or under study in several communities along the Front Range, including Greeley, Highlands Ranch and Castle Rock. 

“This method has been successful for other utilities on the Front Range, but more study is needed to learn about the aquifers under our feet in Denver,” Peters said. “This program will help us determine if pursuing ASR is a smart long-term investment for Denver Water. More study will likely be needed after this project is complete, but it is an important step.”

Drills like this one used at previous test sites will probe hundreds of feet underground as part of Denver Water efforts to determine suitable below-ground storage areas for small volumes of water. Photo credit: Denver Water.

Storing water underground isn’t a substitute for reservoir storage; for starters Denver Water relies on its mountain reservoirs to capture the water from melting snow before it can move it onward to treatment plants and other storage sites, including any future underground locations.

And the volumes to be stored underground would be relatively small, in the 400-to-500 acre-feet range for each site that might be built. Compare that to Denver Water’s big mountain reservoirs that store volumes from nearly 50,000 to more than 250,000 acre-feet.

Even so, it could be an important way to set aside water that could then supplement supplies in dry years. Keeping water underground also has the benefit of preventing evaporation. That said, there are also drawbacks: water would need to be treated both before injection and after recovery, adding cost and complexity to water management.

“Our long-term planning relies on an array of options; ASR has the potential to be one more part of a mosaic of solutions that ensures our customers have the water they need down the road,” Peters said.

Read more about Denver Water’s long-term water planning strategies.

Denver Water engineers are aware of another challenge facing the upcoming pilot project. People seeing a big drilling rig with sound walls in the Congress Park area could initially mistake it for oil and gas drilling, often short-handed as “fracking.” It is not that. The project is entirely about finding potential underground locations to store excess water the utility might have in future wet years.

The project won’t be without disruption: the drilling will occur 24 hours a day, seven days a week, in the interest of rapidly completing the work over a four-to-six-week period. 

Denver Water is working through Denver’s Department of Public Health and Environment on noise issues related to the project and will install a sound monitoring system and sound walls to reduce the impacts of noise and light to nearby residents. 

“We understand this project will create a short-term disturbance to the neighborhood, and we are going to do everything we can to minimize that,” Peters said. “At the same time, this is a critical part of our work to look forward and ensure a reliable and safe drinking water supply decades into the future.”