Item 7c Supp
Item No. 7c Supp Date of Meeting November 30, 2009 Port of Seattle T-5 Maintenance Dredging Update Port of Seattle Commission Briefing November 30, 2009 T-5 Maintenance Dredging Background: In September 08 Commission authorized $680K (expense project) for design and permitting Proposal included all berths in one dredging event to be completed by February 15, 2010 2 T-5 Maintenance Dredging Project Area 3 T-5 Maintenance Dredging Recent events: Current operating budget constraints Delays and phased construction approach to defer spending More time to pursue a long-term strategic maintenance permit Met with permit agencies regarding long-term maintenance permit 4 T-5 Maintenance Dredging Proposed long-term strategy addresses: Issues such as equipment tolerances Frequent sloughing/shoaling at T5 Minimum safety for newer deep draft vessels Future changes to sediment standards- upland vs. open water disposal Phasing: Berth 2 in early 2011, Berths 1 & 3 later 5 T-5 Maintenance Dredging Equipment tolerances (previous experience): Sheltered, harbor conditions Mechanical dredge Tight dredging standards (1' OD) 14 Vertical Elevation (Feet) 12 10 8 6 4 50% Available Material (0-2 ft) 2 5% Available Material (2-4 ft) 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 Horizontal Cross-Section Distance (Feet) Pre-Dredge Elevations Post-Dredge Elevations 2 ft below Required Dredge Depth Required Dredging4 ft below Required Dredge DepthDredging 0 2 ft below Required DepthRequired Dredge Depth Dredging 2 4 ft below Required Depth 6 T-5 Maintenance Dredging Intent of Overdepth Reflective of project conditions Reflective of dredge capabilities Avoid permit non-compliance for incidental depth excursions Not intended to obtain deeper than permitted project depths 7 T-5 Maintenance Dredging Dredge Prism Pre-Dredge Bottom Project Depth ( -45 MLLW or Required Dredging -50 MLLW ) Depth (Project Depth + 1' Advance Maintenance) Advance Maintenance Dredging (1ft) Sediment Undredged Material 1 ft Post Dredge Characterization Depth 2 ft Surface ( Z-Layer ) Limited Incidental Dredging Anticipated <10% Removal Overdepth Dredging (2ft) 50%-75% Removal 8 T-5 Maintenance Dredging Proposed New Strategy 10 Year Programmatic Permit Phased dredging over 10 years Streamlines regulatory process Eliminates perception of 'piecemeal' approach One foot (1') advance maintenance to extend interval between events, increase safety, lower cost, lower emissions (EX-15) Two feet (2') overdepth for equipment tolerances, vessel safety, compliance & contracting 50-75% sediments removed from 0'- 2' below required depth Zone of incidental excursions 5-15% sediments removed from 2'- 4' below required depth 9 T-5 Maintenance Dredging Phase I Dredge 1000' l.f. (Berth 2) Scheduled 2010/2011 dredging season Dredging to include 1' advance maintenance and 2' overdepth Provisions for incidental excursions below overdepth limits +/- 3,000 cubic yards Phase I construction costs depend on DMMO determination 10 T-5 Maintenance Dredging Phase II Berth 1 and Berth 3 Dredging to include 1' advance maintenance and 2' overdepth Provisions for incidental excursions below overdepth limits Dredge during 2011/2012 or 2012/2013 dredging season (if budget permits) +/- 11,300 cubic yards Requires new Suitability Determination from DMMO subject to future standards Berth 3 requires further study of slope stability (slope stabilization work is not included in the programmatic permit) 11 T-5 Maintenance Dredging Phase III: Subsequent Maintenance 10-year period Estimated 1-3 year frequency Not to exceed 40,000 cubic yards over ten year period Each event requires notification/coordination: U.S. Army Corps of Engineers Dredged Materials Management Office Muckleshoot & Suquamish Tribes Environmental Protection Agency Washington State Dept. of Ecology Washington State Dept. of Fish & Wildlife City of Seattle NOAA Fisheries/US Fish & Wildlife Service 12 T-5 Maintenance Dredging Next steps: For 2009 1. Submit JARPA for Programmatic Maintenance Permit 2. Undertake required agency consultation/coordination For 2010: 1. Receive regulatory approvals 2. Final design, bid, and construct Phase 1/Berth 2 3. Commission authorization for bid/award/construction for Phase I (anticipated summer 2010) 13
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