Sustainability shaken, not stirred

February 2014 » Web Exclusive » PROJECT CASE STUDY
‘Cocktail tank’ blends water from three sources to meet irrigation needs.
Colin Nemeroff

Project: Conrad N. Hilton Foundation headquarters, Agoura Hills, Calif.
Project team:
Contractor: MATT Construction
Owner: Conrad N. Hilton Foundation
Lead design: ZGF Architects LLP
Structural engineer: KPFF Consulting Engineers
Civil engineer: Stantec Consulting Services Inc.
MEP engineers: WSP/Built Ecology
Construction management: Bigelow Development Associates
Landscape architect: Van Atta Associates

Filtered water is routed to an underground, 20,000-gallon cistern (i.e. the “cocktail tank”) where rainfall can accumulate and be used for irrigation. Photo: Stantec Consulting Ltd.

Project summary

Automated, self-blending cistern provides irrigation water with low salinity levels to support native plants.

Many non-profits broadcast their mission through a brochure or website, but one global organization asked a team of designers to deliver that objective using a very different medium. The Conrad N. Hilton Foundation was planning for a new facility to better accommodate the organization’s growing operational needs. Turning a challenge into an opportunity, the foundation set a goal to reflect its values and mission within the physical design of its new international headquarters.

An automated, self-blending cistern independently monitors and adjusts the salt content in the water supply using various source waters. Image: ZGF Architects LLP

Designing tradition, vision

Founded more than 70 years ago by namesake and acclaimed hotel industry icon Conrad N. Hilton, the Foundation is dedicated to its mission of “working to improve the lives of disadvantaged and vulnerable people throughout the world.” Among the Foundation’s current priority initiatives is the preservation and sustainable distribution of water to underserved global populations. When the decision was made to establish its new Southern California headquarters 30-miles outside downtown Los Angeles in Agoura Hills, the Foundation’s leadership sought to design a sustainable campus with minimal impact to the surrounding landscape.

“One of our hopes in creating this very special building was that it’s not only just for our use, but that it could be a model for others who have an interest in trying to make a difference on this planet by building in a more environmentally sensitive way,” said Steven M. Hilton, Foundation chairman, president, and CEO.

The Hilton Foundation tapped a collaborative design/construction team led by the Los Angeles office of ZGF Architects LLP to develop the 22,240-square-foot headquarters building on the 70-acre site. The first of an eventual four-phase project, the building was envisioned to target Leadership in Energy & Environmental Design (LEED) Platinum certification, using technology and design to reduce energy and water use significantly.

To meet sustainable goals, designers, contractors, and project owners used a “big room” approach — with all project partners collaboratively planning — to leverage building resources. The team also reviewed ways to reflect the building’s responsible design in the surrounding landscape. Project landscape architect Van Atta & Associates employed a mix of California native plants that blended with the surrounding natural environment while minimizing irrigation demand. While a simple concept, the delivery and sustainable maintenance of California natives on this project required a thorough plan.

The natives will get restless

Coastal sage, woodland, chaparral, volcanic breccia, and riparian woodlands were among the California native plant communities designated for the Hilton Foundation’s property. In addition to visually blending into the surrounding grasslands, these plant types would reduce the need for offsite water sources. To assist in irrigating the plants, the project team employed a variety of infiltration gardens and bioswales to encourage natural irrigation of the site. Collection methods also included a green roof system, which collects and filters rainwater. Filtered water is then routed to an underground, 20,000-gallon cistern where rainfall can accumulate and be used for irrigation. Upon researching the proposed cistern method, potential challenges were discovered:

  • Limited rainfall — Southern California receives a limited number of fall and winter storms, which reduces the effectiveness of a rainwater capture system.
  • Bigger isn’t always better — Total annual rainfall could provide substantial water to irrigate the site, but fresh water would only arrive in surges, creating the potential for stagnation when large, unused volumes accrue.
  • Seasonality — During the dry months of the year, the cistern would remain empty and offline from the site’s irrigation system. To address year-long water supply needs, the cistern could also be connected to three other water supply sources, including reclaimed, potable, and a future onsite groundwater well.
  • Hold the salt — California native plants require water with low salinity levels. With the reclaimed water as the most sustainable source, its saline levels were far too high to support healthy growth of California native plants. 

To make the system work, the water feeding the cistern would have to have the low salinity levels required for irrigation. Designers and planners from Stantec worked with the project team to devise a system where the various source waters could be blended to create a “cocktail mix,” which eliminates harm to the plants.

Creative cocktail discussions and solutions

With the knowledge that a blended water approach would be needed to irrigate the site’s plants, designers developed plans for an automated, self-blending cistern that can independently monitor and adjust the salt content in the water supply. The blending tank approach incorporated a sensor that measures the ability of the blended water to conduct electricity, which is directly related to the salt content of the water. If the sensor finds that saline levels are too high, it directs the system to allocate and adjust water from the different sources to dilute the mix. Because of the “mixology” involved in creating a balanced water supply, Stantec designers informally referred to the system as the site “cocktail tank.”

“The beauty of the cocktail tank is that we didn’t need to completely reinvent the wheel,” said Fred Cunningham, Stantec project principal. “The technologies and components that comprise the system are each fairly common, but we simply combined and purposed them in a new and innovative way that we’ve never tried before.”

Filtered water is routed to an underground, 20,000-gallon cistern (i.e. the “cocktail tank”) where rainfall can accumulate and be used for irrigation. Photo: Stantec Consulting Ltd.

During winter months, the cistern operates with a tank that is roughly half full to allow collection space for upcoming storms. When a storm is forecast for the area, the facilities operator can irrigate and empty the tank, creating space to refill with fresh rainwater. At the end of the rainy season, the operator can adjust the level in the tank, switching to reclaimed, potable, and well water sources to meet irrigation needs.

A LEEDing solution

The Hilton Foundation headquarters was opened and dedicated in October 2012 and, after 12 months in operation, data collected by the Foundation’s facility operators demonstrated success of the system. The cistern has provided for a highly efficient use of water, including considerable savings of potable water use. 

The cistern was part of a larger sustainable project design, which successfully earned LEED Platinum certification in 2013, with accreditors noting the use of innovations throughout the campus by the overall project team. Additionally, the cocktail system remains the first of its kind in the industry.

“My vision was a campus that integrates with the landscape, uses resources thoughtfully, and serves as a model to others committed to environmental stewardship,” Hilton said. We challenged teams to dream big … they rose to the occasion and surpassed our expectations.”

Colin Nemeroff is a community development project manager in the Sherman Oaks, Calif., office of Stantec. With more than 10 years of experience, he has managed planning and civil engineering services for commercial, residential, and municipal projects throughout California.

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