Greywater Treatment & Infiltration at the Bullitt Center

Living Building Challenge Certified

Greywater from the building is screened and collected in a 500-gallon stainless steel tank in the basement. From that tank, greywater is pumped up to a subsurface flow recirculating gravel filter system (constructed wetland) located in a green roof area visible from the 3rd floor office space. A new dose of greywater is pumped up to the gravel filter every 2 hours when greywater is present. The greywater is recirculated within the gravel filter every 30 minutes. When the treated greywater reaches a certain elevation, it flows through a screened pipe inlet and flows by gravity down to a modified drainfield area within the planter strip in the 15th Ave. Right-of-Way (see related case study Private Water and Pedestrian Flow in the Public Right of Way, McGilvra Park Seattle, forthcoming).

The treated greywater is distributed throughout the planter strip through shallow drip irrigation piping where it is absorbed by native plants. Any excess treated greywater not absorbed by the plants filters through a compost amended soil section, and into a gravel section where it will infiltrate into the native soils below.  The right-of-way section along 15th Ave also infiltrates excess stormwater not captured by the rainwater harvesting system, to mimic the undeveloped (forested) hydrology of the site.  Any excess water not infiltrated in the 15th Street drainfield will discharge to the City’s separated stormwater main.

Greywater flows from the building’s sinks, showers, floor drains, and dishwashers was estimated to be 345 gallons per day, well within the threshold for local permitting through PHSKC (<3,500gpd).  However, they knew it would require multiple code waivers to meet the Living Building Challenge requirement to treat 100% of greywater and stormwater on such a small urban lot, given the prescriptive nature of the current regulations for on-site sewage systems. So the local jurisdiction environmental health officer asked his counterpart at the Washington State Department of Health (WSDOH) to review the greywater treatment components including the recirculating gravel filter system (green roof constructed wetland) and drainfield (irrigation/infiltration area).

In a unique agreement to share regulatory the WSDOH accepted responsibility to review, inspect and permit the system. All indoor plumbing components were permitted through PHSKC in accordance with the local plumbing code (2009 UPC). Although the Living Building Pilot Ordinance technically does not apply to the State health department, it was Seattle’s initiative under the ordinance which secured the agreement for WSDOH to review and approve multiple rule waivers to allow the greywater system as an Onsite Sewage System, including:

• Because the Bullitt Center had little space for a drainfield, compliance would require innovative use of extremely limited space.  Regulators could see that the building’s low flow fixtures, green roof and specific occupancy would result in lower-than expected volume, so they granted a reduction in amount infiltrative space required to treat the greywater.
• They reached a unique agreement with the City of Seattle to locate the drainfield area within the 15th Avenue Right-of-Way, not usually allowed.
• They were allowed fewer “test pits” closer together because the total area was only 375 square feet; additional infiltration tests were conducted immediately adjacent to the drainfield area.
• The area selected had unique challenges of its own, namely that the near-surface soils had poor infiltrative capacity, not enough to handle the expected volume within the 375 sf of space available.  Normally required to be no more than 3 feet below surface, they were granted an alternative solution by installing an underdrain and vertical infiltration trench down to a depth of 12 feet, where suitable infiltration soils could be found.
• Finally, the State regulations require sufficient reserve area to treat and dispose 100% of the design flow.  Bullitt Center was granted a waiver allowing for no drainfield reserve area because their basement greywater tank has an emergency-only backup connection to the City Sewer. If there are any problems with the designed primary drainfield, the greywater will be routed to the sanitary sewer system until the issues are resolved. In addition, redundant distribution piping was installed in case the primary distribution piping was to fail.

The following additional code innovations are combined with the greywater system to achieve the Living Building Challenge “net-zero” water imperative.

• Blackwater from the building’s toilets conveys directly to composting units in the basement of the building, which were permitted through PHSKC not the State DOH; this system is described in a separate case study “Composting Toilets at the Bullitt Center.”
• Rainwater is collected from the building’s rooftop solar array and stored in a large cistern in the basement for non-potable as well as potable (drinking water) use. This required the Bullitt Center to become a Group A public water utility.  This system will be described in a forthcoming case study in the Code Innovations Database.

Additional Resources

Backed by its mission to protect the Pacific Northwest’s natural environment and promote healthy and sustainable ecosystems, the Bullitt Foundation wanted their new headquarters to be built to the highest level of sustainability. They also wanted the building to be a demonstration project that would set a new standard for developers, architects, engineers and contractors. The rigorous performance standard set forth by the Living Building Challenge was the perfect tool to demonstrate not just “sustainable” but restorative urban development.

The Bullitt Center is a 52,000 square foot, six-story commercial office building in the Capitol Hill neighborhood of Seattle, WA. The Center is home to a number of commercial office tenants who are successfully operating their businesses, while working in a net-positive energy environment. The Bullitt Center aims to advance the awareness and adoption of high-performance building through ongoing educational efforts, and by demonstrating that performance-based design works in a market-rate commercial project.

The Center is powered by a 244 kW rooftop solar array, composed of 575 PV panels. All rainwater that falls on the site is collected in a cistern in the basement, treated to potable drinking standards, and supplies all water needs of the building. The building is a type-IV heavy timber structure, made of Forest Stewardship Council (FSC) certified glulam beams and dimensional lumber (see related case study on Bullitt’s Mass Timber structure). The building sits atop a ground-source heat exchange system made up of 26 wells, each reaching a depth 400 feet. All materials used in the building were screened for compliance with the Materials Red List to restrict toxic chemicals. The wide variety of performance-based attributes are shared with the public through an ongoing tour program, a public exhibition space, and a number of research projects all managed by the University of Washington’s Integrated Design Lab.

• Chapter 246-272A WAC
• Code of the King County Board of Health Title 13
• Code of the King County Board of Health Title 2
• 2009 UPC, as adopted and amended by the State of Washington

• Ord_124102-bullitt-greywater-permit-1.pdf
• Final-Letter_Project-Review-for-Cascadia-Center-1.pdf

• "Regulatory Pathways to Net-Zero Water: Guidance for Innovative Water Projects in Seattle." February 2011 by the International Living Future Institute.
• "Optimizing Urban Ecosystem Services: The Bullitt Center Case Study" by Stuart Cowan et al, Published June 1, 2014 by EcoTrust, Portland Oregon