Let it rain: A holistic plan for water use and reuse in a sustainable building

July 15, 2019 Tony Thornton

Denver Water’s new complex pushes the boundaries of sustainability with its innovative water efficiency

 

“We forget that the water cycle and life cycle are one.”—Jacques Yves Cousteau. Where Mr. Cousteau was undoubtedly considering the world’s oceans, the quotation applies equally well to the cycle of fresh water supply that sustains our communities. As the oldest and largest supplier of potable water in Colorado, Denver Water delivers to 1.4 million people across the Denver metro area and doesn’t want our communities to forget the importance of this connection either. So, when it came to redeveloping its aging 36-acre central operations complex, the western water utility was intent on exemplifying, by design, its leadership in clean water efficiency, use, and reuse.

Serving as the front door to their redesigned complex is Denver Water’s new, six-story, 186,000-square-foot Administration Building. Planned to open later this year, the building will be a showpiece for sustainable design with its targets set on net zero energy use and LEED Platinum Certification. It also will incorporate numerous employee wellness concepts.

 

The new 186,000-square-foot Denver Water Administration Building, which is targeting net zero energy and LEED Platinum Certification.

 

Long and thin in its form, the building is shaped to maximize daylighting while reducing the need for artificial lights. The building is often playfully referred to as a skyscraper turned to lie on its side. The very determined shape of the building echoes the utility’s principles distinctively focused on being good stewards of the environment and its employees. Yet, it’s in water efficiency where Denver Water really wants to make its mark with this facility.

Our team was brought in to help crystallize Denver Water’s vision and bring it to life. Beginning in 2011, we initiated a collaborative design process that involved master-planning the existing complex to remain in active use as nine new and renovated buildings were phased into the complex’s construction. The redevelopment then culminates in its innovative administration building and a host of water efficiency initiatives that will set it apart.

 

It’s all about “One Water”

Under Colorado laws, the use and reuse of water is complex and restrictive, but we knew Denver Water was committed to making a difference for the future. Denver Water wanted to expand the legal barriers of what was permissible, while providing safe and replicable water-efficiency solutions to a development community of all scales.

Dubbed as “One Water,” the team envisioned these solutions as components of a holistic plan for smart water use and reuse in design and practice. Thus, One Water promotes the right water source for the right use. 

_q_tweetable:The pairing of rainwater and recycled water had never been done like this before anywhere._q_Integrated within the building’s core design, this philosophy brings together a number of effective potable and non-potable strategies such as low-water use landscaping, bioswales, and wetlands for water quality and control; low-flow and WaterSense-labeled fixtures for restroom, break areas, and cafeteria water use; and a highly efficient radiant-hydronic system. The latter is an interior conditioning system supercharged by an on-complex plant designed to use the variable temperatures of one of Denver Water’s own high volume, city water supply mains as a heat sink. Still, as impressive as this lineup is, the facility’s two most innovative strategies are the combined systems of large-volume rain capture and office scaled, on-site wastewater recycling for toilet flushing and irrigation purposes.

Being innovate comes with challenges, however.

Denver Water’s experts conduct ongoing analysis, and they knew what the future of water supply versus demand looks like in Colorado and the surrounding regions. They also recognized that as a prominent water resource manager in Colorado, Denver Water had a responsibility to find a pathway to change.

We’ll start with rainwater capture. The concept isn’t new, and at very small scales it is allowed within the City of Denver. But capturing the much larger volumes of rainwater off the total combined 82,000-square-foot area of roof structures from the Administration Building and adjacent parking garage is an additional challenge that Denver Water is still working through.

It’s part of a pilot concept. By partnering with other sizable developments, Denver Water is considering similar exchanges to encourage more large-volume, on-site capture scenarios within the region.

The collected rainwater from the roof structures is stored in a 50,000-gallon cluster of exterior, below-grade cisterns. These cisterns are in turn adjacent to another 25,000-gallon cistern cluster that collects water from the onsite wastewater recycling system. Together they feed the building’s irrigation system, providing 100% of the landscape needs for the Administration Building and its adjacent campus green—a total coverage area of nearly 1/2 of the complex’s 36-acre site. Denver Water provided water-modeling studies, allowing the team to set the irrigation boundary, determine the most appropriate drought-tolerant plant material, and to size the total volume of cistern storage required.  

 

The Denver Water Administration Building, part of a 36-acre central operations complex. 

 

The onsite wastewater recycling system (WRS) is truly unique to Colorado. Locally, the system is the first of its kind to serve a single office building. The WRS functions by collecting all the building’s wastewater and cleaning it through a series of mechanical and natural processes. Stantec partnered with the team of Aqua Nova Engineering and Robial Water, to design and commission the WRS. Jay Thrasher from the Aqua Nova and Robial Water team further describes the system as follows:

“The WRS is designed to treat up to 7,000 gallons a day of office wastewater. Raw wastewater flows from the Administration Building to a buried Multi-Stage Treatment Unit (MSTU), which provides flow equalization and secondary treatment. Clarified effluent is pumped from the MSTU to a three-stage wetland process. The Stage 1 Wetland, located in the Administration Building lobby, consists of a two fill-and-drain wetlands that mimic coastal wetlands where tidal patterns create both anoxic and aerobic environments for nutrient removal. The Stage 2 Wetland consists of two vertical flow, gravel bed wetlands, also located in the Administration Building lobby. This stage provides supplemental nitrogen removal (nitrification and denitrification). The Stage 3 Wetland is a horizontal flow subsurface wetland located just outside of the lobby, which provides final polishing of the effluent to very high-quality levels. Wetland effluent is filtered and disinfected with chlorine and UV systems prior to reuse for toilet flushing and or as additional irrigation supplement.”

The local city and state agencies have never reviewed a WRS in an application like this. A safe design has been paramount for everyone. It’s been and still is an enormous collaboration effort with the City of Denver and State of Colorado to get us to the point where everyone is comfortable with this new type of design. And now, they’re all watching and rooting for us to bring it to a successful completion.

It’s no exaggeration to describe the challenge as substantial. Getting the WRS approved to function as Denver Water desired, meant better defining how the local plumbing code was to be interpreted by the regional field inspectors, and it also meant amending the state’s Regulation 84 to allow WRS water to be used in toilet-flush applications.

The pairing of rainwater and recycled water had never been done like this before anywhere. Taken as a whole, the One Water strategies built into Denver Water’s new Administration Building are expected to reduce potable water consumption by an amazing 75%. It will be spectacular when it’s up and running—a real learning curve for the whole community.

 

One Water education

Educating the public on how the system works is part of the project.

Portions of the WRS will be on display to the public as they enter the building’s lobby. After the heavy cleaning of the wastewater has taken place in the earlier MSTU stage, planted areas atop and fed by the later stage wetland tanks are located within the building’s entrance lobby. At first, new visitors may feel they are looking at an unusually large planter highlighting some of our native flora and providing a visual connection that blurs the line between indoor and outdoor spaces. But as they are drawn to it there will be educational information about the WRS.

Education about the WRS and the building’s other water-efficiency systems and sustainability features will be included in an array of informational signage and graphics along with information about the journey of water from source to tap.

Through this facility, Denver Water has an important story it’s telling. They want the public to know about how we get our clean drinking water, where we are with our consumption rates, and about how critical it is that we employ every water-efficiency strategy at our disposal if we hope to keep up with the growing demand over the next 20 years.

With all its smart, efficient design, Denver Water’s new operations complex and Administration Building hope to provide a positive example of efficient water resource management for the community.

A version of this story was first published Water Quality Products.

About the Author

Tony Thornton

Tony Thornton is a senior associate based in Denver, Colorado. He has nearly 25 years of commercial, residential, mixed use, and institutional design project experience, with an artistic and design background.

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