Formatted Title:

Lake George Canal - Middle Section Sediment Remediation: Utilization of a Geogrid for Sediment Stabilization

Background/Objectives:

The Lake George Canal – Middle Section Sediment Remediation Project (LGC-M) involves highly complex, weak, non-aqueous phase liquid (NAPL) rich sediment. The USEPA’s Great Lakes National Program Office (GLNPO), along with the U.S. Army Corps of Engineers – Chicago District (CELRC), the Engineering Research and Development Center (ERDC), and J.F. Brennan (Contractor), completed a Great Lakes Legacy Act authorized remedial action project for the LGC-M in 2023. The LGC-M is located within the Indiana Harbor Canal waterway system of northwestern Indiana. Sediments in the project footprint contained elevated levels of total polyaromatic hydrocarbons (TPAHs, >400ppm), NAPL (>10%), and other contaminants from legacy operations at adjacent petroleum refinement and storage facilities.

This presentaiton or poster will highlight utilization of a dual-panel, slacking, biaxial geogrid as a corrective action measure for stabilization of weak, contaminated sediment.

Approach/Activities:

The original remedial design specified placement of a 1-foot-thick sand stabilization layer to be placed in thin lifts for surcharging the sediment and building strength over a 90-day “stabilization period”. Stabilization of the sediment was necessary to support constructibility of subsequent capping operations. During placement of the stabilization layer, the contractor observed that slopes were failing and at least one location of the site showed signs of sediment overturning. The design team was notified, and further investigation revealed that this geotechnical behavior was contrary to preliminary predictions of the slope stability model.

Working with the contractor, GLNPO, ERDC and CELRC moved forward with placement of two large, overlapping geogrid panels as an alternative stabilization strategy. The geogrids provided the necessary structural stability with sufficient permeability to prevent pressure buildup of ebullition due to methanogenesis of the oil-rich underlayer. Grid aperture size was based on anticipated soil-bridging span of the sediment. Geogrid panels were sewn into two contiguous mats to blanket the 12-acre project area. Panels were sewn together on a floating barge that worked with divers to place the geosynthetic at the canal bottom. Each panel was secured to respective bank area (i.e., north bank and south bank) and with sufficient overlap to anticipate future sediment consolidation.

Results/Lessons Learned:

The geogrid successfully stabilized the sediment and allowed for placement of the remaining active capping layer, and capping was successfully completed in late 2023. The presentation or poster will convey that early and frequent communication between the contractor, partners, and subject matter experts led to a successful adaptive management strategy for sediment stabilization. Ultimately, the strategy led to successful stabilization of very weak sediment while addressing risks related to future consolidation and potential gaseous ebullitions. The geogrid approach may be a novel stabilization that could be employed at other sites with weak sediment, stability concerns, and ebullition potential.

Zach Ostrum

Affiliation

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(Group 2, Poster Board #71) Lake George Canal - Middle Section Sediment Remediation: Utilization of a Geogrid for Sediment Stabilization