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Dredge Material Reuse to Restore Industrially Influenced Benthic Communities

Dredge Material Reuse to Restore Industrially Influenced Benthic Communities. Eric Dott (presenting), Guy Partch , Michael Costello (deceased), Barr Engineering Company Jim Sharrow , Duluth Seaway Port Authority Walther van Kesteren , Luca Sittoni, Deltares. Overview.

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Dredge Material Reuse to Restore Industrially Influenced Benthic Communities

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  1. Dredge Material Reuse to Restore Industrially Influenced Benthic Communities Eric Dott (presenting), Guy Partch, Michael Costello (deceased), Barr Engineering Company Jim Sharrow, Duluth Seaway Port Authority Walther van Kesteren, Luca Sittoni, Deltares

  2. Overview • Industrially-influenced bays - degraded habitats • Concept - reuse dredged materials for habitat enhancement projects • Sediment Placement Challenges • Tremie-diffuser method for placement • Conclusions

  3. Problem- Industrially Influenced Estuary or Harbor Areas • Many backwater areas of estuaries and harbors are lightly or moderately contaminated from ubiquitous sources • No specific party holds responsibility for addressing contamination • Large areas of impact can cause significant degradation to the waterway ecology

  4. Industrially-Influenced Bays- Duluth/Superior Harbor and Lower St Louis River Estuary Source: Lower St. Louis River Habitat Plan, 2002. St. Louis River Citizens Action Committee and Resource Management Agencies.

  5. Industrially-influenced bays- lower St. Louis River Habitat Plan Source: Lower St. Louis River Habitat Plan, 2002. St. Louis River Citizens Action Committee and Resource Management Agencies

  6. Application of thin cover layer • Monitored natural recovery (MNR) is a remedy that typically uses ongoing, naturally occurring processes to contain, destroy, or reduce the bioavailability or toxicity of contaminants in sediment. • MNR is likely to be effective most quickly in depositional environments after source control actions and remediation of high risk sediment areas have been completed. • Enhanced MNR (eMNR) is the addition of a thin layer of clean sediment to accelerate the recovery process by engineering means. • Reference- Merritt, et al., 2009. Enhanced Monitored Natural Recovery (EMNR) Case Studies Review. SPAWAR Tech Rpt 1983, US Navy.

  7. Examples- MNR Applied • Costs vary, depending on size and time frame for recovery • Most projected costs < $2M

  8. eMNR Ecological Improvement Concept • Enhance natural deposition of clean, fine-grained sediment in stable backwater depositional environments • Achieve major habitat improvements by improving large areas by a little bit • Place on/in lightly contaminated material • Benthic community will mix/blend • No great change in depth

  9. Dredged Material Reuse Potential • Clean fine-grained or graded sediment from dredging projects or stored in a CDF • Habitat enhancement of industrially influenced estuary/harbor habitat. • Beneficial reuse to improve aquatic benthic communities

  10. More than 700 acres of industrially-influenced bays The Ideal Borrow Source Erie Pier • Nearby • Same material, clean • 2,000,000 cy available • Beneficial reuse of dredged fines • Extend life of facility

  11. Sediment Placement Challenges • Pumping discharge of organic fine slurry: • Turbidity at discharge • Spread of material to unintended areas • Separation of coarse fraction – irregular distribution • Transport back to dredged areas • Control of placement • Control of suspension and deposition • Significant shallowing of backwaters

  12. Tremie-Diffuser Method • Designed to deliver mud gently • Results in near laminar flow of dense high solids slurry- follows bed • Migrates radially from diffuser head • Thin uniform layers • Large areas can be covered economically

  13. Tremie-Diffuser

  14. Developed in the Netherlands Lake Zevenhuizerplas- Suspended Solids Standard Bell Diffuser Turbidity high using Bell diffuser- Max = 170 mg/L Tremie-Diffuser Turbidity low using Tremie-Diffuser at bed - Max = 35 mg/L Refs. Costello, et al. (2007), Mastbergen et al. (2004)

  15. Applied Large Scale • Inclined Large Scale Tremie-Diffuser • Pilot tested for industrial high volume, high solids material placement below water • Minimize coarse fraction segregation • 90 feet of water • 61% solids • 14,000 gpm • 8 ft/sec • 3,000 dry tons per hour • Equal to 58,000 gpm @ 20% solids • 28 inch line

  16. Shallow Water Delivery Proposedfor Duluth-Superior Harbor

  17. Example Platform Configuration

  18. Cost Comparison for Shallow Sheltered Bay Remediation example: 15,000 to 100,000 cy Project Scale Versus Sediment Habitat Enhancement - $15-60/cy

  19. The Tremie-Diffuser Concept- • a means for applying habitat enhancement layer (eMNR) to industrially-influenced bays/estuaries • Mud delivered gently and economically • Large areas treated at low cost • Beneficially uses dredged fines that otherwise occupy valuable storage in dredge facilities • Pilot concept has been proposed for habitat restoration in Duluth/Superior Harbor

  20. Discussion/Questions Eric Dott Barr Engineering Company Duluth, Minnesota, USA 218.529.8234 edott@barr.com Jim Sharrow Duluth Seaway Port Authority Duluth, Minnesota, USA 218.727.8525 jsharrow@duluthport.con Lucca Sittoni Deltares Delft, The Netherlands +31(0)88 335 79 34 Luca.Sittoni@deltares.nl

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