Tony Thornton is lead architectural manager for Stantec. Thornton can be reached at [email protected].
As the oldest and largest supplier of potable water in Colorado, Denver Water delivers water to 1.4 million people across the Denver metro area. When it came to redeveloping its aging 36-acre central operations complex, the western water utility wanted to exemplify 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-sq ft administration building. Planned to open later this year, the building showcases sustainable design with its targets set on Net Zero Energy use and LEED Platinum Certification, as well as incorporating numerous employee wellness concepts. Long and thin in its form, the building is shaped to maximize daylighting while reducing the need for artificial lights. The building often is playfully referred to as a skyscraper turned to lay on its side. The shape of the building echoes the utility’s principles focused on being good stewards of the environment and its employees. Denver Water wants to make its mark for water efficiency with this facility.
To help bring to life Denver Water’s vision, the global architecture and engineering firm Stantec was chosen. Beginning in 2011, Stantec 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 culminates in the administration building and a host of water efficiency initiatives.
“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,” said Tony Thornton, Stantec’s lead architectural manager for the project. “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 “one water,” the team envisioned these solutions as components of a holistic plan for smart water use and reuse in design and practice. One water promotes the right water source for the right use. 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 an 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. The facility’s two most innovative strategies are the combined systems of large-volume rain capture and office scaled, onsite wastewater recycling for toilet flushing and irrigation purposes.
However, innovation comes with challenges.
“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,” Thornton said. “They also recognized that as a prominent water resource manager in Colorado, Denver Water had a responsibility to find a pathway to change.”
Denver Water started with rainwater capture. It is allowed within the city of Denver at small scales. Capturing the much larger volumes of rainwater off the total combined 82,000 sq ft area of roof structures from the administration building and adjacent parking garage is an additional challenge that Denver Water still is navigating.
“It’s part of a pilot concept,” Thornton said. “By partnering with other sizable developments, Denver Water is considering similar exchanges to encourage more large-volume, onsite capture scenarios within the region.”
The rainwater collected from the roof structures then is stored in a 50,000-gal cluster of exterior, below-grade cisterns. These cisterns are in turn adjacent to another 25,000-gal 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 half of the complex’s 36-acre site.
Stantec’s team included the engineering firm IMEG to help develop the rain catch system in collaboration with water modeling studies provided by Denver Water. The model data allowed 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.
Locally, the onsite wastewater recycling system (WRS) is the first of its kind to serve a single office building. The WRS functions by collecting all of the building’s wastewater and cleaning it through a series of mechanical and natural processes. Stantec partnered with Aqua Nova Eng. and Robial Water to design and commission the WRS.
“The WRS is designed to treat up to 7,000 gal 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,” said Jay Thrasher, a member of the Aqua Nova and Robial Water team. “Clarified effluent is pumped from the MSTU to a three-stage wetland process. The Stage I wetland, located in the administration building lobby, consists of two fill-and-drain wetlands that mimic coastal wetlands where tidal patterns create both anoxic and aerobic environments for nutrient removal.
The Stage II 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 III 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 [ultraviolet] systems prior to reuse for toilet flushing and or as additional irrigation supplement.”
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,” Thornton said. “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%.”
The updated building provides educational opportunities for visitors.
“Portions of the WRS will be on display to the public as they enter the building’s lobby,” Thornton said. “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 only at an unusually large planter, which highlights some of our native flora and provides 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 for them to digest.”
Education about the WRS and the building’s other water efficiency systems and sustainability features will be included on 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 its telling” Thornton said. “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 alone.”