According to the National Academy of Sciences, “Some of the nation’s estuaries, lakes and other water bodies contain contaminated sediments that adversely affect fish and wildlife, which may then find their way into people’s diets and carry negative health impacts.” To answer these concerns, the EPA, by congressional order, commissioned the Academy to determine if dredging could be used as an effective cleanup method to remove highly contaminated sediments from waterways. The Academy discovered that while effective in removing sediment and harmful toxins such as PCB’s or dioxins, dredging techniques such as Mechanical, Hydraulic Cutter head, or Auger increased turbidity levels resulting in re-suspension of contaminated sediment. These contaminants can be fatal to the ecology, as well as humans.
Mechanical dredging causes the greatest contaminant disturbance due to the continual motion of the clamshell or excavator bucket in and out of the water. The other methods produce turbidity because of the cutter head or auger’s breaking down the material before it is pumped. The EPA has shutdown numerous environmental dredging projects because of their inability to keep turbidity levels low. Contaminant removal using dredging has proven to be difficult, costly, and time consuming. In addition to creating high turbidity levels, problems include:
- Low production rates and high water generation
- Production rates under 10 percent of in situ solids when using Hydraulic and Auger dredges
- Downtime from clogging
- The need to reposition anchors and cables required to advance and or swing the dredge
- Over-dredging as a result of varying terrain
Eddy Pump Corporation(EPC) has taken on the challenge of finding a solution. Their patented EDDY Pump technology addresses many of the concerns facing environmental dredging.
EPC is dedicated to reducing the harmful impacts that dredging has on the environment, while still making it a viable solution to reducing contaminants in our waterways. The company has implemented many technological advancements to achieve these goals, including:
- A high suction 8’’ Eddy Pump with production capabilities of 300-350 cubic yards per hour and capabilities of moving high viscous materials, such as drilling mud that centrifugal pumps are not capable of doing (see figure B).
- An intake closer to the target material and a suction opening which can be turned into the material face. These innovations reduces all detectable turbidity, rendering the cutter head obsolete. Furthermore a higher percent of solids are removed while eliminating much of the water intake.
- Slope following technology and a rotating self cleaning guard which eliminate the downtime associated with over-dredging and clogging.
- A turbidity shroud surrounding the rotating guard which limits any chance of stray contaminants being released into the water column.
- A training program for dredge operators using recorded data, and video which demonstrates how to achieve higher production and lower turbidity rates.
- A conical shaped head that has a wide flat contact patch with the ground. This was developed to eliminate windrowing and the residual contaminants that are left behind. This head design greatly reduces re-dredging and over-dredging that is typically responsible for a considerable amount of unwanted water pumped. (see figure below)
Eddy Pump technology has proven successful in such environmentally sensitive hot spots as the St. Clair River in the Great Lakes Region. Toxins, including PCBs, plagued an area of approximately 375,000 ft2 , causing numerous dredging problems. Eddy Pump removed 98-100% of the contaminated material maintaining non-detectable turbidity levels and production rates between 30-80% in situ.
The Ontario Ministry of the Environment monitored on a daily basis all contaminant levels of re-suspension. Results showed that the water quality remained, for the majority of the time, at or under the Ontario Ministry of the Environment’s (C of A) maximum allowable concentration level . Drinking water quality was also tested at 12 municipal water plants downstream from the dredging area. Bryce Feighner, the supervising district engineer with the Michigan Department of Environmental Quality reported that “all of the results were within drinking water standards.” Furthermore, independent tests conducted by Linda Schweitzer, an Oakland University professor, and Doug Martz, the chairman of the Macomb Water Quality Board stated that “preliminary test results of water in the St. Clair River show that no contaminants were released during the dredging.” Linda Schweitzer went on to say “The project gets a gold star. We got as close as 200 feet of the dredge site and there were no suspended sediments in the water. If we didn’t find anything within 200 feet, they won’t find it 20 miles downstream in drinking water intakes.” Since this effort, Eddy Pump Corporation has taken even steps to further reduce turbidity and increase production rates to 50-80% solids in situ.
With environmental consciousness leading the forefront of many dredging projects, new dredging technology is required for contaminant removal. Many out-dated dredging technologies are too harmful to both the environment and humans. The need for dredging technology that can create little or no contaminant re-suspension, while still having high production rates is the only viable answer to our contaminated waterways. Eddy Pump Corporation has proven to be a leader in developing a dredging technology to meet these needs.