Dredging success will need a chemical reaction

A new contractor hired to take over the troubled canal dredging project in Southern Shores is counting on good chemistry to get the job done.

The project was brought to a halt earlier this year after the previous company hired to do the work was unable to extract fine particles from the water before putting it back into the canals.

In a presentation to the Town Council Tuesday, Bob Wilson, president of Rowboat Dock and Dredge in Mooresville, explained how he will do it.

Rowboat Dock and Dredge was hired to take on the job by Byrd Brothers Emergency Services, which is responsible for guaranteeing that the work is done correctly. The previous dredging company was found in default after it was unable to bring the water to acceptable state quality standards before returning it to the canals.

The problem was not in getting the dredge spoil from the bottoms of the canals but in the technique used to separate it from the water after it was pumped out.

When the dredge material is pumped into a containment pond, large particles such as sand settle to the bottom fairly easily.

“The concern is in the other stuff,” Wilson said, which is mainly much finer silt and decaying organic material.

Wilson said he will use a technique called “polishing water.”

But first, a hydraulic cutterhead dredge in front of a vessel will essentially grind the material from the canal floors and send the slurry through a pipeline onshore and into a 2- to 3-acre containment pond in the Hillcrest neighborhood.

Large particles will settle out there.

The next step is where the chemistry comes into play. Polymers are commonly used to create a reaction causing the particles to bind together into larger ones so that they become heavier and settle to the bottom of a containment pond.

In the first dredging attempt, only one polymer was used and the bond was weak, Wilson said. The polymer method was attempted after a piece of equipment called a hydrocyclone could not get the water to meet state quality standards.

Wilson’s method will use dual polymers, with one of them enhancing a negative charge that occurs naturally in the particles and creating a stronger bond.

The polymers will be injected into the water as it leaves the first settling pond and moves into a second smaller one. Discharge from the second pond will be monitored to make sure it meets state standards before it is put back into the canals.

Wilson said the polymers he plans to use are organic and have been tested for safe use. He said samples have been taken from several areas of the canals and sent to companies to find the correct polymers.

His crews will first work on the interior canals, where the finer material makes up a higher percentage of the dredge spoil, Wilson said.

Rowboat Dock and Dredge has done work in Holden Beach, Atlantic Beach, Washington, N.C., Oriental and Asheboro, Wilson said. The company learned the technique to meet tougher environmental standards after years of work in sediment removal for chemical, paper and textile companies, he said.

“It’s tried and proven technology,” he said.

The Southern Shores project, he said, will take several months depending on the weather. The cut will be 4 to 6 feet deep.

Plans are to start in October. In the budget it passed Tuesday, the Town Council has allocated $1.4 million for the $1.7 million project.

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