North Mercer Interceptor & Enatai Interceptor Upgrade

VMS facilitated a Value Engineering study with a focus on constructability aspects of King County WTD’s North Mercer Enatai Interceptor Upgrade project. The project addresses the need for additional capacity in the North Mercer Island and Enatai Interceptors, as part of King County’s Regional Wastewater Services Plan, which is implementing major improvements to ensure that the regional sewer system keeps pace with growth and continues to meet all regulatory requirements. The project is being designed around challenging hydraulics, constrained staging, the potential for significant and undesired community impacts and permitting struggles. 

Study Objectives

  • Analyze the current project design, estimate, and schedule
  • Provide possible cost and/or schedule saving recommendations
  • Provide performance improvement recommendations

Study Outcomes

  • Five of the 12 alternatives developed by the VE team for project improvement were accepted for implementation, and two are being studied further for potential acceptance.
  • Accepted VE alternatives will save the project $2,300,000 while enhancing performance by 9%, resulting in an overall value improvement of 13%.
  • The accepted alternatives will improve maintainability based on changes to the NMPS site and generator building and due to the use of above-grade discharge valving.
  • Constructability will be improved based on reduced excavation depth along portions of the proposed alignment, and various aspects of other alternatives as well.

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