1. Environmental Dredging of Perfluorochemical-Impacted Sediment from a Sensitive Wetland Mark A. Gaetz (3M) Paul Lear (WRScompass)

2. Dredging 20122 Introduction Project Description Project Goals Project Execution Conclusions

3. Dredging 20123 Project Description Perfluorochemicals –Perfluorchemicals were utilized in manufacturing fire fighting foam, non- stick surface agents, and stain retarders –3M’s Cottage Grove, MN facility produced PFOA and PFOS

4. Dredging 20124 Project Description (cont.) Plant Wastewater Discharge –Process water from 3M’s Cottage Grove Facility was treated in the Wastewater Treatment Plant –The WWTP had a permitted discharge through a series of Ponds, drainage ditches and the East Cove –Perfluorochemicals released as part of the permitted discharge accumulated in the sediment in the Ponds, ditches and the East Cove

5. Dredging 20125 Project Description (cont.)

6. Dredging 20126 Project Description (cont.) On-going clean-up –3M has removed perfluorchemical-impacted sediment from the WWTP Ponds and the drainage ditches. –Removed sediment was transported to a nearby industrial landfill and placed in a monofill reserved for 3M solid wastes – Remediation of the East Cove is the final phase of the plant sediment clean-up

7. Dredging 20127 Project Description (cont.)

8. Dredging 20128 Project Goals for East Cove Remediation Removal of bulk of the contaminated sediment –Not going after every last molecule –Stream flow not disrupted by clean-up activities –Minimize spread of contamination during removal Off-site disposal in a 3M monofill cell Restoration of wetlands

9. Dredging 20129 Project Execution Site Preparation –Roadway improvements –Laydown area Erosion and Sediment Controls Sediment Curtain –Capture any suspended sediment before it reaches the Mississippi River

10. Dredging 201210 Project Execution (cont.) Laydown Area

11. Dredging 201211 Project Execution (cont.) Sediment Curtains

12. Dredging 201212 Project Execution (cont.) Sheetpile Installation –Isolation/flooding of dredge area –Divide dredge area/Allow stream flow to continue –Off-loading dock –Sandbar isolation

13. Dredging 201213 Project Execution (cont.) Installation of Sheetpiling

14. Dredging 201214 Project Execution (cont.) Installation of Off-loading Dock

15. Dredging 201215 Project Execution (cont.) Access to Sandbar Area

16. Dredging 201216 Project Execution (cont.) Isolation, Excavation, Backfilling, and Armoring of Sandbar

17. Dredging 201217 Project Execution (cont.) Weirs Controlled Water Depth and Maintained Stream Flow

18. Dredging 201218 Project Execution (cont.) Mechanical Dredging –Chosen because of Small area to be dredged Minimal potential for resuspension Direct load-out with minimal dewatering Minimal water treatment –Start on East side (water flow on west) –Change over to West side (water flow on east) –Bathymetric Survey to verify removal

19. Dredging 201219 Project Execution (cont.) Assembly of the Barges

20. Dredging 201220 Project Execution (cont.) Mechanical Dredging of Sediment using RTK DredgePak

21. Dredging 201221 Project Execution (cont.) Bathymetric Survey to Confirm Sediment Removal Elevations

22. Dredging 201222 Project Execution (cont.) Sediment Solidification - Initial –SAP added on barge (up to 0.5% by weight) Polymer retains several times its weight in water Removes free water from the dredged material so it will pass the Paint Filter Test

23. Dredging 201223 Project Execution (cont.) Solidification of Free Water in Sediment using SAP

24. Dredging 201224 Project Execution (cont.) Off-loading of Sediment Passing Paint Filter Test

25. Dredging 201225 Project Execution (cont.) Sediment Solidification - Final –Calciment™ added to the trucks while loading (up to 5% by weight) Improved structural integrity of the dredge material Allowed landfill equipment to track over it and compact it Landfill added more Calciment™ as necessary to support their operations

26. Dredging 201226 Project Execution (cont.) Solidification with Calciment™ to Improve Handleability at Landfill

27. Dredging 201227 Project Execution (cont.) Backfill with Local Soil Material –USACE-approval of material source –Placed in the wet (no compaction) –Restored pre-dredging sediment elevations

28. Dredging 201228 Project Execution (cont.) Removal of the Lined Off-loading Area and Start of Backfilling

29. Dredging 201229 Project Execution (cont.) Completion of Backfilling

30. Dredging 201230 Project Execution (cont.) Site Restoration –Removal of sheetpiling –Return of road to previous conditions –Seeding/Stabilization of disturbed slopes –Wetlands restoration

31. Dredging 201231 Project Execution (cont.) Removal of Sheetpiling

32. Dredging 201232 Project Execution (cont.) Restoration of the Roadway and Seeding of Slopes

33. Dredging 201233 Project Execution (cont.) Wetland Restoration

34. Dredging 201234 Conclusions Final sediment remedial activity at the facility successfully completed –Dredged and loaded-out 17,000 cy of contaminated sediment for off-site disposal –Added Calciment to improve structural integrity at the landfill –Backfilled East Cove to pre-dredging elevations –Restored the sensitive wetland

35. Dredging 201235 Conclusions Challenges Overcome –Regulatory delays –Railroad permitting delays –Landfill handling issues –Weather (delays pushed project back into late fall/early winter)

36. Dredging 201236 Conclusions Project team worked together to minimize the impact and cost of the challenges –3M –Minnesota Pollution Control Agency –Weston –WRScompass