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Overview of Steps to Complete CSI Program Update

The 2017 CSI program update is based on data collected during WTD's Decennial Flow Monitoring project in the 2009-2010 and 2010-2011 wet seasons.

The update will verify, make adjustments to, and identify new conveyance system needs.

Stage Expected completion date

Update planning assumptions

Dec 2013
Complete a regional needs assessment Dec 2015
Develop conceptual projects and planning level cost estimates Dec 2015–2016
Prioritize conceptual projects Dec 2016
Complete Program Update 2017

Update process

Planning assumptions are necessary to forecast future peak flows in the sewer system. The CSI program uses planning assumptions to forecast future 20-year peak flow rates and determine where capacity improvement are needed to meet projected demands.

WTD works with the Engineering and Planning subcommittee of the Metropolitan Water Pollution Abatement and Advisory Committee (MWPAAC) and utilizes the Puget Sound Regional Council’s (PSRC) population and employment forecasts  in the planning assumptions. The forecast data is reviewed with local agencies for input during the regional needs assessment discussions.      

Updated Planning Assumptions for Wastewater Flow Forecasting  Jul 2014 (1.73MB)

PSRC Population and Employment Forecast Summary Aug 2014 (4.66MB)

The regional needs assessment, or RNA, assesses the separated conveyance system to identify portions that need to be expanded to allow for 20-year peak flow in 2060. It provides the basis for identifying and evaluating alternative approaches to making capital investments to address capacity needs.

The regional needs assessment is complete and the results are in the report at the link below. As is the case with other CSI Program Update activities, the RNA includes review and input from the MWPAAC Engineering and Planning Subcommittee  and the local agencies that contract with WTD for wastewater treatment services.

Regional Needs Assessment  May 2015 (4.5 MB)

The Conceptual Projects to Meet Identified Capacity Needs report is compete and available at the link below.

Conceptual Projects to Meet Identified Capacity Needs , May 2017 (15.2 MB)

Recognizing that it is not practical to simultaneously carry out all projects needed, a prioritized list of projects will be established to guide improvements in the separated portion of the conveyance system.
Conveyance System Improvement

For more information, please contact:

Steve Tolzman

Steve Tolzman
Capital Project Manager