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

Dredging Introduction Project Description Project Goals Project Execution Conclusions

Dredging 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

Dredging 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

Dredging Project Description (cont.)

Dredging 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

Dredging Project Description (cont.)

Dredging 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

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

Dredging Project Execution (cont.) Laydown Area

Dredging Project Execution (cont.) Sediment Curtains

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

Dredging Project Execution (cont.) Installation of Sheetpiling

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

Dredging Project Execution (cont.) Access to Sandbar Area

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

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

Dredging 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

Dredging Project Execution (cont.) Assembly of the Barges

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

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

Dredging 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

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

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

Dredging 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

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

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

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

Dredging Project Execution (cont.) Completion of Backfilling

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

Dredging Project Execution (cont.) Removal of Sheetpiling

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

Dredging Project Execution (cont.) Wetland Restoration

Dredging 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

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

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