Carnation Wastewater Treatment Plant Planning and Design

King County Dept. of Natural Resources and Parks, 

Carnation Wastewater Treatment Plant Planning and Design

2008 WateReuse Small Project of the Year Award - WateReuse Association
Project Highlights: 
  • Treatment facility can treat up to Class A reclaimed water quality standards and has additional capacity to meet growing demands
  • Reclaimed water from the plant provides drought tolerant hydrology to a degraded natural wetland, resource to organic farms and blue-ribbon spawning habitat, helps with in-stream flow issues, and is an extra source for a nearby ecological preserve, Chinook Bend Natural Area
  • Treatment facility offers educational and recreational opportunities to the community
  • King County received its first LEED Certification for its Operations Building
Admin Building
The Operations Building, which screens the entire facility, integrated the agronomic theme facility into the community’s culture and incorporated sustainable LEED elements.

Lack of centralized sewage collection and treatment limited growth and prevented development plans within the City of Carnation. To enable the City to grow, it partnered with King County in Washington state to provide local wastewater treatment and selected Carollo to provide planning, design, and engineering for the Carnation Treatment Plant.

The City of Carnation is located in the Snoqualmie Valley near Snoqualmie River, which is home to spawning chinook and coho salmon (both listed as endangered species). Stakeholders are concerned about preservation of wildlife habitats, as well as maintaining property values, ensuring public health, and aesthetics. The project team proactively worked with stakeholders, including regulatory agencies, tribes, and environmental groups, to integrate the treatment system into the community culture. The project’s success resulted from the development of these strong interagency partnerships supporting the long-term holistic integrated water resource management approach consistent with policy goals made at local, state, and national levels.

One of King County’s treatment objectives was to provide the facility with the flexibility to treat up to Class A reclaimed water quality standards. This enables the effluent to be discharged or used in a variety of ways. Based on King County’s preference and desire to use advanced technology and Carollo’s engineering judgment and experience, Carollo recommended a membrane bioreactor (MBR) for secondary treatment at the facility. A life-cycle cost analysis showed the MBR was comparable to conventional secondary treatment plus tertiary filtration. The MBR design included five parallel membrane trains, each allowing space for additional membrane units to be installed when required. The space for additional membrane units provides flexibility for increasing the capacity of the plant without constructing additional tankage. In May 2008, King County began operation of the 0.4-mgd MBR wastewater treatment facility and discharges to a river outfall to meet the needs of Carnation’s designated Urban Growth Area.

The Carnation Wastewater Treatment Facility excels as a sustainable solution for the City of Carnation to treat their wastewater. It allows the city to grow and use reclaimed water for beneficial uses in this pristine rural environment known for organic farms and blue-ribbon spawning habitat. This facility offers ample public education opportunities to illustrate how reclaimed water is a valuable water resource that is not yet appreciated as a solution for water quality and quantity challenges in Washington state. The reclaimed water from the reclamation plant will be used as an extra source of hydrology at a nearby ecological preserve, Chinook Bend Natural Area. This demonstration project shows how reclaimed water can help with in-stream flow issues and can help restore the quality of wetlands that have been degraded over time. This project offers educational and recreational opportunities to nearby schools, youth camps and the many recreational users of the Snoqualmie Valley.

Consistent with King County’s initiative for sustainability, the team minimized the building impact for the facility on the environment. In October 2009, King County received its first LEED Certification for a building within their wastewater facilities. Key success metrics associated with the Operations Building include:

  • 62% reduction of water required for irrigation
  • 34% reduction of water use
  • 37% energy performance increase
  • 98% of construction waste diverted from landfills
  • 29% of materials recycled
  • 35% of materials manufactured locally/regionally
  • 98% of spaces daylighted
  • Use of green power