1. Slip 4 Early Action Cleanup, Seattle, WA Dredging 2012 Conference PIANC USA/COPRI ASCE San Diego, CA October 23, 2012 David Schuchardt, P.E. (Seattle Public Utilities) Eric Pilcher, P.E. Reid Carscadden, P.E. (Integral Consulting Inc.)

2. Project Overview • Early Action within Lower Duwamish Superfund Site • 3.5 Acres; PCBs • Design completed 2007 • Source Control Actions • Construction completed 2012 • 5 other Removal Actions - 50% risk reduction Lower Duwamish Waterway

3. Cleanup Goals: • Clean sediment surface (below SQS) • Ensure the surface remains clean • Eliminate unacceptable risks Remedy Selection

4. Making the Slip 4 Cleanup Decision: Integrating Objectives

5. Project Overview - Setting

6. Selected Remedy - Primary Design Elements • 10,000 cy dredging & shoreline excavation • 30,700 cy capping • 0.5 acre pier demolition • 1 acre new intertidal area • Institutional Controls

7. Cap Design • 12-in Sand & Gravel Chemical Isolation Layer • 0.5% GAC Amendment • Variable Thickness Protective Armor Layer Chemical Isolation Layer

8. GAC Cap Amendment Benefits • High sorptive capacity • Demonstrated success • Easy to specify • Consistent QC protocols • Compatible particle size – reduces floatation • Conventional placement methods • Uniform coverage • Small (~20%) cost increment

9. Pier Demolition

10. Dredging and Bank Excavation

11. Barge Dewatering BMPs • Main Barge = 92.4 NTU • Holding Cell = 87.4 NTU • Filter Bag = 39.0 NTU • GAC = 28.5 NTU

12. Transloading – Re-Purposing Existing Infrastructure

13. Cap Placement & Armoring

14. Habitat Enhancement • Beach Sand • Anchored Woody Debris • Expanded Intertidal

15. Conversion of Deeper Berthing Area to Habitat

16. Pre- and Post- Cleanup Conditions

17. Questions? Acknowledgments: City Team EPA Integral Consulting Inc. Lally Consulting Kiewit/General Construction Company Dave Schuchardt, City of Seattle Dave.Schuchardt@seattle.gov