Formatted Title:

Remedial Dredging of Sediments at a Former Creosote Log-Dipping Site in Northern Idaho

Background/Objectives:

Environmental investigations and remediation were performed at a former creosote log-dipping operation on the bank of the St. Joe River in northern Idaho. The work, performed with oversight from the EPA and Coeur d’Alene Tribe, addressed contaminated river sediment and upland media. The site was remediated under a muti-phased approach with stringent tribal and federal requirements. Later phases included sediment dredging coupled with on-site beneficial re-use of sediments. Rather than off-site disposal, an assessment of sustainability, restoration requirements, and cost resulted in selection of on-site thermal treatment followed by sediment placement within the final restoration area of the upland remediation component. The presentation will review the approaches to sediment delineation, surface water and air quality monitoring as well as review lessons learned from contracting processes, dredging, turbidity management, on-site thermal treatment technologies implemented, and the approach to dredged sediment management.

Approach/Activities:

Five phases of remedial construction were completed over 10 years, resulting in numerous investigations and ultimately the dredging of approximately 30,000 cubic yards of sediment from the river followed by dewatering, thermal treatment, and final on-site placement of the dredged material. The most recent phase of remediation also included removal of large quantities of log debris, dredging, dewatering, and backfilling the riverbed to original grade. Surface water quality was monitored using monitoring equipment with remote telemetry, exceedance notifications, and real-time data display capabilities.

The final phase dredged sediment was successfully treated on site using an in-pile enhanced thermal conduction technology, mitigating the need for off-site transport and disposal. Earlier dredging activities on site relied upon on-site thermal treatment with rotary kiln technology. Rarely are two thermal approaches utilized on the same site with identical sediment and contamination profiles.

Results/Lessons Learned:

Lessons learned from multiple phases of dredging and thermal treatment include:

Construction cost savings were achieved by teaming with a dredge contractor early in the process, who was familiar with site conditions and had existing relationships in the local community.
Use of best management practices and turbidity control during dredging helped complete dredging of significant creosote-impacted sediments without releases to the surrounding environs. Lessons learned from the various types of turbidity control methods will be discussed.
Deploying a remote telemetry surface water quality monitoring system provided significant value over manual methods, reducing demand on construction staff and related health and safety concerns. Exceedance alerts supported immediate response action to protect water quality, and real-time data display and dashboard access aided in meeting regulatory expectations.
Thermal treatment was an effective method for achieving cleanup objectives for organic-rich dewatered sediments that helped reduce disposal costs. Lessons learned from both methods of thermal treatment will be discussed.

Remedial action is complete, and the project has been accepted and approved for transition to long-term monitoring.

Megan Schettler

Affiliation

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Remedial Dredging of Sediments at a Former Creosote Log-Dipping Site in Northern Idaho