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King County WTD – South Magnolia Combined Sewer Overflow (CSO) Control Project


The existing South Magnolia Trunk Sewer (SMTS) conveys combined sewage flow from the South Magnolia drainage basin to the Interbay Pump Station for further conveyance to the West Point Treatment Plant. The SMTS has a capacity of 4.3 million gallons per day (mgd) and flows in excess of 4.3 mgd overflow into a weir in the County’s Magnolia CSO structure. The preferred alternative for controlling CSOs in the South Magnolia basin is to construct a horizontally directionally drilled (HDD) pipeline from the CSO Diversion structure in 32nd Avenue West, to a 1.8 million gallon storage tank in the general vicinity of 23rd Avenue West between West Garfield Street and West Marina Place. Project goal is to develop preliminary and final design documents for the preferred alternative and to provide engineering services during construction.



Since September 2011, P&M as a sub-consultant to TetraTech provided proactive cost estimating and critical path scheduling for the preliminary design and final design of South Magnolia Combined Sewer Overflow project. Microsoft Project was the scheduling tool used to communicate, plan and monitor the project’s WBS and CPM schedule. P&M also provided construction cost estimates using WinEst estimating software with detailed quantity takeoffs and pricing for the project’s pre-design phase and during final design phase. P&M developed and implemented earned value management practices, which included monitoring of schedule progress and performance to identify whether the project was behind/ahead of schedule and under/over budget.

Project Duration

2011 to 2013