International Dredging Review

International Dredging Review

Last December Cashman’s dredge Wood I temporarily left a maintenance dredging job to participate in a five-day demonstration project removing highly contaminated sediment from New Jersey’s Passaic River.

The New Jersey Department of Transportation (NJDOT) Office of Maritime Resources along with the U.S. Environmental Protection agency and the Corps of Engineers staged the test between November 30th and December 13th to characterize the sediment and to understand the hydrodyamics of the river. During dredging a fleet of boats zig-zagged across the river upstream and downstream of the dredge surveying and taking water samples at various depths.

The dredge was equipped with an eight-cubic-yard environmental Cable Arm Clamshell bucket charged with dredging 5000 yards of material in a 1 ½-acre area during the demonstration. The material is silt clay and sand. Core samples showed mixed contaminants in the area including dioxins PCBs metals and DDT among others.

A key component of the project was Cable Arm’s Clamvision bucket positioning system which allowed the operator to see the exact x y z position of the bucket at all times. Ray Bergeron along with colleagues John LaJeunesse Connie Boris Darrell Nicholas Sam Harrell Gerald Swain and Harry Steves were on hand to monitor and manage the positioning system and the dredging function.

Dredge operator Mike Lewis was instructed in the environmental dredging technique which included slow movement of the bucket through the water column lag time to allow water to drain and dipping in a wash tank before re-entering the water.

The sediment in the lower six miles of the Passaic River is contaminated in some areas with dioxins to 17 feet deep with heavy metals below that. One of the primary sources of dioxins was the former Diamond Alkali Company manufacturer of the defoliant Agent Orange between 1951 and 1969. The company discharged the dioxin 2378 TCDD into the river. The factory site adjacent to the river is now a Superfund site where groundwater is being systematically filtered and decontaminated by Diamond Alakali’s corporate successor Tierra Solutions Inc.

The authorized depth of the river is between 30 feet and 14 feet though it has not been dredged in the lower stretches since 1983 and there is no commercial traffic on it.

On December 8 about 40 people from different interest groups bundled against the cold assembled on an observation platform on the Diamond Alkali property upstream of the dredge. Project Manager Lisa Baron of NJDOT explained the project.

Among the visitors were scientists from the Louis Berger Group who will design a dioxin hot spot dredging project this year for New Jersey Department of Evironmental Protection (NJDEP) as an interim fix for a situation that will require a massive amount of dredging to remove all the contaminants. This activity is independent of the Lower Passaic River Restoration Project and this Environmental Dredging Pilot undertaken by the partner agencies.

The purpose of this dredging demonstration is to obtain site specific data for a feasibility study Baron said. The objectives are to test the environmental impact of the dredging to evaluate the performance of the Cable Arm bucket and sensors to monitor the re-suspension of sediment as a result of dredging vessel and scow movements and to test two treatment methods for the material: a sediment washing technique and a thermal destruction technology.

As the dredge worked boats from Rutgers University and the U.S. Fish and Wildlife Service crisscrossed the river above and below it sampling the water at various depths with a variety of testing equipment. In addition re-suspension was monitored from six moorings each taking samples one meter below the water surface and one meter above the sediment surface 24 hours a day.

The dredge is removing up to 5000 cubic yards of sediment from the top three feet of the sediment layer Baron explained. The material is loaded onto scows and taken to Bayshore Recycling Inc. on the Raritan River where it is loaded onto a 730-foot Great Lakes bulk carrier to await testing of the two treatment techniques this winter.
This is one of the most detailed pilot studies this early in the study process said Baron.

On the dredge screens depicting the bucket operation in real time were mounted in the crane cab on the bridge and in Bergeron’s equipment shed. Real time tide data allows the bucket to dig a precise depth no matter what the tide stage. Sensors on the bucket will read the sediment depth subtract the tide depth and dig an exact cut of sediment. The target depth is designed to avoid overfilling the bucket reducing the possibility of re-suspension of sediment in the water column.

Because of the nature of the sediment Stewart Chandler Cashman’s Safety Officer was on hand to set up a safety routine for the project.

“This isn’t the worst material to deal with but you have to treat it with respect” he said.

He established “dirty” and “clean” zones on the dredge as well as a contaminant reduction zone (CRZ) containing barrels for discarding and storing clothing used while working in “dirty” areas – primarily the deck of the scow where contaminated sediment may have splashed.
Anthony Carbone’s job was to sound the sediment level in the scow using a sounding line – a metallic plate on a line with markings every five feet. In order to do this he wore disposable boots gloves poly-coated suit and safety glasses. His work vest was worn only for this function and stored in the CRZ. The protective clothing was discarded in a special barrel and taken to a hazardous waste site.

On the evening of December 8 the Consultant Team (Malcolm Pirnie and TAMS/EarthTech) hosted a reception for the people involved in the project. Executives and dredge crew members from Cashman representatives from NJDOT the Corps of Engineers EPA and other involved groups gathered for drinks snacks and a special cake. The dredging was to be completed on December 9 but a blizzard virtually stopped traffic. Due to health and safety issues sampling was not executed and the final dredging was re-scheduled for December 10.

After the job was completed the dredge and scows were decontaminated and the Wood I returned to its ongoing maintenance job.

Information derived from this pilot project is being analyzed and the report is expected sometime this summer.