Sediment Capping – Lessons Learned from a Dynamic Sand-bed River

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Poster:

Sediment Capping – Lessons Learned from a Dynamic Sand-bed River

Presenter:  Russell Johnson (Amec Foster Wheeler Environment & Infrastructure, Inc.)
Authors:  Russell Johnson (Amec Foster Wheeler Environment & Infrastructure, Inc.), Randy Brown (Anchor QEA),
Robert Cleary and Peter LaGoy (Columbia Gas of Massachusetts), Andrew Timmis (J. F. Brennan Company, Inc.)

Abstract:

Tars from a former manufactured gas plant located in Springfield, Massachusetts impacted sediment over a 2-mile stretch of the Connecticut River. Tar residuals were discharged via pipes and flowed parallel to the shore, soaking into the sediment. The river has a dynamic sand-bed characterized by sand ripples and waves. The bottom continually changes and shifts, exposing then covering areas of tar-affected sediment with fine to medium sand. The selected capping remedy has been designed to maintain a cover over the impacted sediments.

A pilot-scale capping project is ongoing in multiple areas to cap tar-affected sediments with 12 inches of armor stone (i.e., gravel, cobbles). Three engineered cap types were designed to resist both natural and anthropogenic erosive forces in the river. Caps consisting of gravel and cobble material, with and without a fine gravel filter layer, were placed at eight different locations. Two of these caps were placed in a cellular configuration to evaluate enhanced, natural deposition of sand.

Project challenges during cap placement included federal- and state-listed endangered species, river access, weather, variable flow and permitting constraints. The lessons learned from these challenges (anticipated and unforeseen) included:

·       Flexibility of equipment needed to address changing weather conditions.

·       Site conditions prevented efficient and effective use of a fish exclusion barrier.

·       Site access conditions (equipment loading and transporting of material) limited production rates.

A monitoring phase will evaluate the effectiveness of these cap configurations to maintain a 12-inch physical barrier even during storm events. The lessons learned during both the construction and monitoring phases will be used to develop the full-scale design.

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http://mgpsymposium.com/poster-presentations/

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