2014/03/12 Council Agenda Packet

2 CITY OF EVERETT WATER POLLUTION CONTROL FACILITY OUTFALL 025 PRE-DESIGN STUDY SCOPE OF WORK In follow up to the 2011 Pre-Design Evaluation prepared by URS Corporation(URS)in December 2011, additional pre-design evaluation work related to the emergency outfall at the Water Pollution Control Facility(WPCF)is needed to determine the most suitable design alternative to advance forward into design. The outfall is needed for emergency operation should the South Effluent Pumping Station become inoperable or there is damage to the cross-town pipeline. Presently the emergency outfall is covered in silt and is inoperable. The City has performed a dive inspection of this outfall and has observed the outfall and diffuser assembly to be embedded in silt. Historically,the City has flushed the outfall once every two weeks to keep it clear;however,the Corps has decreased the frequency and amount of dredging within the Snohomish River,and the periodic flushing is no longer working because the diffusers have been covered with too much silt. The scope of work for the 2011 work included the following tasks: • Data review and compilation. • Site investigations and meetings with the City. • Alternatives development including: o Alternative 1: Modify the Diffuser in Place. o Alternative 2a: Relocate Diffuser near the Shoreline,along original alignment. o Alternative 2b: Relocate Diffuser Downstream,along new alignment downstream of the I-5 Bridge. o Alternative 3: Additional O&M(including dredging). o Alternative 4: In-channel work to Improve Hydraulic Conditions at the Existing Outfall. • Planning level costs over the lifecycle of each alternative. • Technical memorandum. Based on the findings of the 2011 study,Alternatives 1,3 and 4 were not considered for further evaluation. Alternatives 2a and 2b were selected for further evaluation. Both Alternative 2a and 2b were found to have similar timelines for permitting and construction. Based on the mixing study results completed in 2011,Alternative 2b was found to have the best mixing dilution factors and the conditions appear most similar to the existing mixing zone study(Brown&Caldwell 1996). Alternative 2a was found to have a lower lifecycle cost(approximately$3.1M for Alternative 2a compared to$4.6M for Alternative 2b). Operation and maintenance needs,including anticipated dredging based on model output,will be considered for each alternative. In order to select the preferred alternative,additional evaluation is needed. The proposed work will be done to fill known data gaps and support the City in selecting a preferred option that can be permitted, installed,and will be operational over time. The following work tasks are included: • Task 1—Project Management • Task 2—Bathymetric Survey • Task 3—Geomorphology and River Hydraulics(Modeling&Sediment Transport) J:\Projects\E\Everett,City of\WPCF Outfall 025\00-Project Management\Scope&Budget\2013 Pre-Design Update and Design Phase\Scope of \work-Update Study Everett Outfall 025-02-03-14.doc Page 1 of 5 19