Project Spotlight


This page presents a Roth Hill project showcasing one or more of our fields of expertise. To find out how we can put our services to work for you, please contact Greg Hill at 425-869-9448 or ghill@rothhill.com.

Citywide Sewer System Project, City of Carnation


project_sl3.jpgAs City Engineer for the City of Carnation, Roth Hill has designed a vacuum sewer system to serve the entire City, the last unsewered City in King County. The vacuum system consists of about 11 miles of vacuum sewer pipe, five main vacuum sewer trunk lines, a single vacuum station, and about 280 vacuum valve pits. Total construction costs for the collection and conveyance system is estimated to be approximately $16 million; with the treatment plant included, total construction costs are approximately $25 million.. Roth Hill is coordinating closely with the King County Wastewater Treatment Division, which is designing, permitting, building, and operating the treatment facility. This project required numerous permits for both the City of Carnation’s collection and conveyance system and King County’s wastewater treatment plant.

Other elements of this project included:

  • We provided subconsultant coordination to collect the geotechnical, wildlife, wetlands and archaeological information necessary for construction, permitting, and project approvals at the local, State, and Federal levels.
  • We prepared the NEPA Environmental Assessment and coordinated agency reviews and approvals with the Washington Department of Ecology and the United States Environmental Protection Agency (USEPA). We also coordinated the Endangered Species Act (ESA) Section 7 approval process with the USEPA, National Marine Fisheries Service, and the United States Fish and Wildlife Service.
  • We prepared and acquired approximately 40 easements without condemnation.
  • Our funding team worked diligently with City staff to obtain several grants and low interest loans from various sources, including:
    • Washington State Legislature – two line item grant appropriations totaling $3.5 million
    • Public Works Trust Fund (PWTF) – three low-interest loans totaling $11.0 million
    • State and Tribal Assistance Grants (STAG) – two grants totaling $1.3 million
    • Department of Ecology Centennial Clean Water Fund (CCWF) - $3.25 million grant and $6.75 million 0% loan pending
    • Community Development Block Grant (CDBG) - $0.5 million grant
  • Our community involvement team presented information showing that over the long-term, the cost of the sewer system would be roughly the same as they were currently paying to maintain their septic systems. In addition, we provided residents with information that explained the benefits of the sewer system, including protecting of the environment, and public health and safety.