Toward a Cybernetic Site
Sidwell Friends, a first for constructed wetlands
Philadelphia-based firm KieranTimberlake Associates is no stranger to site innovation, having developed the prefabricated Loblolly House for a sensitive coastal wetland site in Delaware [record, November 2006, page 185]. For the firm's recent expansion of the Sidwell Friends School in Washington, D.C., the architects incorporated a constructed wetland into a courtyard of the building in order to process its wastewater for reuse in flushing toilets, among other uses for nonpotable water. The district's health department hasn't approved the wetland's gray water for irrigation purposes, so a separate system collects storm-water runoff for irrigation.
The wetland, the first of its kind for D.C., occupies a series of terraces in the courtyard-premium space the architects argued should be used as much for teaching purposes as for lessening the building's water use. Opened in fall 2006, the expansion uses 90 percent less water than comparable buildings, which helped it earn a LEED Platinum rating from the U.S. Green Building Council. "Primarily, it had to pump sewage," says Stephen Kieran, FAIA, the project's architect. "But it also had to be beautiful, since it's right at the entrance to the building. It became an environmental aesthetic."
Unlike Indianapolis, the Sidwell project is located in a dense urban site, where architects must reconcile land use with significant economic pressure and a city government less inclined to approve unconventional technology for use at a school. The urban location further obscures the effects of the project's storm-water runoff, especially sensitive since Sidwell's location in Northwest Washington places the campus in the watershed of Rock Creek Park to the east.
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Sidwell's wetland was instigated by the project's environmental consultant, Bill Reed, but was designed with the guidance of Michael Ogden, a wetland expert and civil engineer with Natural Systems in Santa Fe, New Mexico. Ogden says Sidwell represents the first total reuse system-in that only negligible amounts of water leave the site via utility drainage systems-installed in an urban site in the country. "We don't normally think of wastewater-treatment systems as architectural elements," Ogden says, cognizant of the fact that generations of students passing through the school will now have first-hand experience with a process otherwise invisible in the urban landscape.
The six-and-a-half-day process, which treats nearly 8,000 gallons of water per day, begins with a primary treatment tank, where sewage from the 72,500-square-foot expansion/renovation project encounters anaerobic bacteria such as that found on the bottom of a pond. It is then pumped to a trickle filter, where it falls over rocks before moving on to the tiered wetland. Thus far, a typical gallon of water has been in the system roughly three days; the wetland itself requires another two days.