Norfolk Sediment Remediation - Seattle, Wash.
The project removed approximately 5,000 cu yd of contaminated sediments adjacent to the Norfolk combined sewer overflow outfall on the Duwamish River. The location, trapped between two low level fixed bridges, required installation of a temporary trestle to mobilize a 125-ton crawler crane onto a special barge with containment cells and anchor winches. All materials were mechanically dredged according to a detailed contour plan requiring 2-4 ft cuts. Once on the work barge, spoils were transferred to the trestle, then stockpiled and stabilized for moisture content prior to shipment. Over water, the containment protocol was three layers of filter cloth and a straw bale. On land, a double-lined plastic membrane trapped all drainage. Water was stored and tested prior to disposal in the sewer system. After confirmatory testing, the site was backfilled with clean sand matching the general gradation of naturally occurring sediment.