Precise Positioning Aids White Lake
Working for environmental engineering group Earth Tech, Faust and Cable Arm personnel set up the project in a two-acre area that had been contaminated with polychlorinated biphenyls (PCB's) and hexachlorobenzene (C-66) by an outfall from Hooker Chemical Company in the 1970's.
Hooker was purchased by Occidental Petroleum Corporation and renamed Occidental Chemical Corporation. Occidental Petroleum is complying with a 1993 administrative order from the Environmental Protection Agency to remove the pollutants. Miller Springs Remediation Management, Inc., a subsidiary of Occidental Petroleum, is managing the remediation, with Earth Tech as prime contractor.
Faust used their Link Belt clamshell dredge Comanche, on the project. The clamshell system, managed by Ray Bergeron, John Lajeunesse and Sam Harrell, consisted of a four cubic yard Cable Arm Environmental clamshell bucket equipped with sensors that communicated with Clamvision bucket positioning software. A monitor at the operator's station displayed real-time position of the bucket and the progress of the dredging.
The spuds were removed from the barge, and a five-point anchor mooring system was added. The anchors were placed outside the dredging area, to avoid disturbing contaminated bottom material.
Faust used a "down rigger" built by Cable Arm, which passed the winch wires down through the spud wells so the cable was 12 feet below the water's surface, allowing boats and barges to pass over it. Two anchors were set in front and one aft of the barge for moving, and two were set to the sides for stabilizing.
Sensors on the bucket provided depth, orientation, and closing information to the computer running Clamvision. Coordinates were provided by a real time kinematic (RTK) global positioning system from NovAtel, which has a 20-centimeter accuracy. A tide gauge developed by Cable Arm provided water level information, and hydrographic surveys run on two-foot centers provided up-to-date bottom information. Surveys were performed by Faust and Cable Arm, using a Ross 825 dual frequency echo sounder.
Raw echo sounder data were processed using Hypack Max software, and then exported to Rockware and Canvas software packages for volume calculations and data presentation, and to ClamVision for surface model creation and target depth calculations. For dredging, operator David Brown could see the real time position of the dredge and clamshell as well as the dredging site pattern. (See cover.) The bite patterns are colored, with the color tied to the amount left to remove, said Harrell. Red means that everything (target material) is gone. The sensors allowed accurate one-foot cuts on the uneven bottom surface.
Two numbers on the bottom left hand side of the screen indicate the bucket depth and target depth. Target depth is calculated from a three-dimensional model of the bottom created in ClamVision, the clamshell's capacity (to prevent overfilling), and amount of material to be removed at a given location. The operator lines the bucket up with the target position before lowering it. When it reaches target depth, a red light signals him to stop. An indicator signals that the bucket is completely closed and sealed, at which time it can be raised and the load placed in the adjacent barge. The bucket was rinsed in a wash tank after every cycle, and cycles were two to three minutes long, in 35 to 60 feet of water.
Rinsing the bucket allowed Faust to forego the use of silt curtains, said Bergeron. For every 50 yards of material dredged, a yard of sediment was left in the wash tank. This is contaminated sediment that would otherwise have entered the water column, he said.
Earth Tech monitored for turbidity 24-hours a day, using six stations, each equipped with two OBS-3 sensors, one at 10 feet and one at 45 feet deep, and strategically placed around the dredging zone. In addition to the fixed sensors, Earth Tech and Cable Arm monitored turbidity around the barge and dredge cell. If the readings increased in an area, they were able to stop immediately and correct the action causing the rise in turbidity.
Other factors contributing to the low turbidity levels were the overlapping side plates on the bucket, the side seals and close switch indicators on the bucket, minimum incidents of overfilling the bucket, consistent operation of the crane, and the fact that all the crew members were aware of the turbidity criteria, said Lajuenesse, who, along with Sam Harrell, was present throughout the project.
Faust contracted Resource Engineering & Testing to provide health, safety and quality control services. Quality control officer Darrell Nicholas praised the quality of the project and the personnel.
"This is the most detailed survey I've ever been on," he said. "The cooperation between Earth Tech, Faust, their subcontractors and vendors was exceptional," he said.
Marcus Faust praised his employees who ran the project, headed by project manager Steve Absher. The regulatory agencies and local residents, who had been lobbying for the cleanup for decades, are happy, said Faust. The company had 13 crew members on the dredging shore-based material handling portion.
"Safety professional Les Powell called me to say that I have some wonderful employees," said Faust, and claimed that these were some of the best people he had ever worked with, because of their sincere desire to do the job in a professional manner.
Earth Tech designed and operated the material handling and treatment operation under the management of Devon Draper.
Barges were unloaded into trucks using a CAT 350 material handler. The material was trucked to a mixing tank, and then pumped into 11 Envirotubes provided by Wickoren & Associates. These were 45 feet in diameter and 200 feet long. Purified water was returned to the lake, and the dewatered material will be handled according to the amount of contamination it contains.
The pumping system was designed and operated by Don Searles of Dredging Specialists.
The dredging design statement for this project states that there were 8500 cubic yards of contaminated sediment approximately 200 to 450 feet off Dowies Point in White Lake in 35 to 60 feet of water. The contaminants covered approximately 1.6 acres, or 70,000 square feet. There was an estimated 1292 cubic yards of material containing more than 50 mg/kg of PCB's, concentrated in one to two feet of bottom sediments. Other areas had contaminants in lesser amounts, and all the material was intricately categorized to minimize handling costs.
The most highly contaminated material cost hundreds of dollars per cubic yard to treat, said Faust, while material with less contamination cost $20 to $30 a yard to treat. By "surgically" removing the material to a three-inch tolerance, they were able to save the owners millions of dollars in treatment costs, he said. Ray (Bergeron) was able to do this because of the quality of his electronics, said Faust.
White Lake is north of Muskegon, Michigan, and is connected to Lake Michigan by a channel. Sediment removal ended on Friday, August 29, and Earth Tech and EPA officials spent the Labor Day weekend testing the area. Any remaining contaminated material will be removed in the following weeks if any is found.
Please see our next issue for a final report on this project.