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By Ronnie Wendt, Contributing Writer
November 2024
As Denver Water neared its 100th anniversary over a decade ago, it faced a challenging situation. Its buildings were aging and inefficient and did not do a great job of conserving water.
Today, the situation looks much better. The organization’s self-examination led to a $2.04 million overhaul of its 34.6-acre site in downtown Denver.
When the operations complex redevelopment project began, the average building age was 55 years, and the oldest building had been in service for 130 years. The redevelopment updated the water utility’s warehouse, trade shop and meter shop buildings and included a new six-story administrative building for over 600 workers, a wellness building and a parking garage.
Sustainability was a key focus for the entire project, resulting in LEED certification for every building and an advanced water source management strategy.
Leading the way
A goal of the redevelopment project was to apply leading-edge water resource management across the project, says Chance Coe, the utility's water quality lead on the ReUse For Us (RUFUS) system, an in-house blackwater recycling system that collects water from toilets, urinals, sinks and cafeterias.
“We wanted to put the right water source to the right use,” he says. “This is commonly known as a One Water strategy. As the largest water utility in the state, we had the resources and expertise to show what could be possible when managing our different water sources holistically.”
Denver Water enlisted the help of Stantec to determine water concept specifics. Tony Thornton, principal, Core Architecture Studio Leader for Stantec, says, “They were full of enthusiasm, and the commitment was there but needed some direction on what the final concept should look like.”
Stantec began assessing potential with Denver Water.
“We knew the project would be focused on sustainability and wellness, Thornton said. “But underneath it all, we understood that if we didn’t do something with water, we were missing an enormous opportunity for a major water utility.”
The partnership landed on a strategy that put smart water use, conservation and reuse at its center.
Initially, they instituted typical sustainability practices, such as installing WaterSense-labeled, low-flow fixtures in restrooms, break areas and the employee cafeteria.
“These are all straightforward things that a lot of projects do,” Thornton says. “But then we started looking at what else we could use water for.”
Eventually, a holistic water efficiency and reuse plan emerged. It integrated potable and non-potable water strategies, including low-water-use landscaping, bioswales and wetlands for water quality and control.
These strategies include rainwater capture for irrigation and a $1.83 million onsite wastewater treatment and recycling system for gray and black water recycling in the administration building.
“The design of these systems is a first in Colorado, neither had been attempted at this scale regionally,” Thornton says.
Stantec’s projections showed a 40 percent reduction in water use. But Thornton says Denver Water has yet to achieve this goal because of pandemic-related delays in system commissioning and full operation.
“Pointing to specific numbers for what we saved is still a work in progress, as we recalibrate to account for a sizable portion of our workforce being on a hybrid work schedule,” Coe says. “But we didn’t do this project just to point to specific savings. We did it to show Colorado how you can efficiently manage limited water resources to create a sustainable water supply.”
Overcoming regulatory challenges
There were a few challenges associated with the pairing of rainwater and recycled water. At that time, rainwater capture was only permitted on a very small scale in Denver, Thornton says.
“When the redevelopment work started, neither capturing and reusing rainwater nor flushing toilets with recycled water were legal,” Coe says. “A team of Denver Water attorneys and water rights experts spent two years getting a water right to use captured rainwater for irrigation at the complex as long as we replace water in the South Platte River.”
To use recycled water for toilet flushing, Denver Water worked with state legislators to introduce and enact HB 1069 in 2018. This act also directed the Colorado Department of Public Health and Environment to create regulations, which were enacted later in 2018, on ways to achieve that goal safely.
Coe says a variance with Metro Water Recovery also was needed to allow Denver Water to handle its wastewater without using Metro's treatment plants.
Construction, design obstacles
The next step of the redevelopment project involved tackling construction obstacles, including installing dual pipes and plumbing systems. The concept was new for plumbing contractors and inspectors but necessary for separating drinking water and recycled water, Thornton says.
“The plumbing trade didn’t understand it,” he says. “The State Department of Health didn’t understand it. We spent the better part of a year working with each jurisdiction, talking to the city and explaining it to them to get their buy in, talking to plumbers and getting their buy in, and getting building codes changed.”
Capturing larger amounts of water from a combined area of 82,000 square feet, including the administrative building and parking garage, was also a challenge, Thornton says.
Engineers addressed this issue with a strategy that gathers rainwater from the roof in 50,000-gallon underground cisterns. Another cluster of 25,000-gallon cisterns collects water from the on-site wastewater recycling system.
“Together, these cisterns feed the building’s irrigation system, providing 100 percent of the landscape needs for the administration building and its adjacent campus green,” he says, adding that the adjacent campus green covers nearly one-half of the complex’s 36 acres.
The onsite wastewater recycling system is also one-of-a-kind in Colorado, though similar systems have been built in California and other states.
“Locally, it is also the first to serve a single office building,” Thornton says.
The wastewater recycling system collects and purifies all the building's wastewater using mechanical and natural processes. This system was created and implemented through a collaboration among Stantec, Aqua Nova Engineering and Robiul Water.
The wastewater treatment system can handle 7,000 gallons of office wastewater per day. The raw wastewater flows from the administration building to a buried, multi-stage treatment unit. This unit aids in flow equalization and secondary treatment. Next, the clarified affluent is sent to a three-stage wetland process to further purify the water.
After this six-day clarification process, the clean non-drinking water is put to use for irrigation and filling toilet bowls in the administration building.
To the casual observer, the lobby wetlands “appear to be a very large indoor planted area filled with natural species,” Thornton says. “But this component is actually one of the later stages of the blackwater recycling system, as it cleans the building’s gray and black water for reuse in restrooms and for irrigation.”
Maintenance needs for the system are also straightforward, Coe says.
“We treat this system similarly to our other water treatment facilities at Denver Water,” he says. “The Colorado Department of Public Health and Environment requires that we maintain a certified water and wastewater operator to manage our reuse system. Our treatment operators routinely monitor and adjust various biological processes within our multi-stage treatment unit, our constructed wetlands and our control room, which comprises filtration, UV disinfection, and hypochlorite addition.”
Denver Water also employs asset management technicians to perform regular maintenance and maintain various equipment, including blowers, pumps, mixers and meters.
“While the system design and programming components intended to require far less from an operational perspective, we have found that it pays off for our systems to take a proactive approach to maintenance and operations,” he says.
Pandemic-related challenges
The pandemic presented a share of problems in getting the system up and running.
Denver Water started the redevelopment project in 2012 and completed construction in two phases over five years. In 2019, rainwater capture and passive stormwater management began, and the administrative buildings' wastewater treatment system was finished. The system started operating in 2024 after going through startup and commissioning phases, which were delayed due to the pandemic.
Coe says many employees worked remotely during the pandemic, limiting the population of the building for over 18 months. In fact, fewer than 50 people occupied the building during the pandemic.
“But the system requires input to run as intended,” he says. “If people are not using the restrooms on a regular basis, there isn’t enough wastewater generated to have the system work as originally intended.”
Many Denver Water workers still work a hybrid schedule, so the average occupation of the building has not approached the original 600-person figure.
“Our operators had to start up and commission the system under very different parameters than were originally designed,” he says.
Another unexpected issue related to COVID-19 arose out of the overuse of disinfecting wipes in the building. Coe says the operations team often found wipes in the treatment system.
“Considering the scale of the operation, these wipes had a large negative impact on the biological treatment process,” he says.
Ronnie Wendt is a freelance writer based in Minocqua, Wisconsin.