282 Southern Shores Settling & Water Clarification Project

OVERVIEW – Dredging Town’s Canal System of Sediment

The canal system at the town of Southern Shores was in need of dredging. Built in the 1960’s, it was becoming too shallow for the homeowners to navigate their boats to the larger bodies of water. The dredge spoils were to be collected and treated in a two-stage lagoon system. The objective presented to WaterSolve was to treat the material entering the lagoon system from the dredge and get the solids to settle so the water could be returned to the canal system and meet the regulations set by the State of North Carolina. The requirements included extensive water toxicology studies, NTU (Nephelometric Turbidity Unit) monitoring to test for clarity, and pH monitoring of the discharge water.

CHEMICAL CONDITIONING

Samples of the material to be dredged from the canal system were sent to the WaterSolve lab for testing. Extensive testing revealed that a dual chemistry of a coagulant, followed by a flocculant, would be needed to settle this canal sediment. WaterSolve specifically formulated the chemistry for this project to settle the solids and make the water clean enough to return to the canal under the North Carolina guidelines. Pails of the sediment were treated with various doses of formulated chemistry and the supernatant water was sent to a lab for water toxicology studies. During these studies various aquatic critters were weighed and placed in the water. The trial tested the survival and weight gain of the critters. The test results of this trial were approved by the regulators for the project. WaterSolve then provided the proper documentation and information about the chemistry required to get the permit approved by the state.

THE RESULT

WaterSolve LLC was contracted by the dredging contractor to treat the dredge water entering the lagoon settling ponds. We supplied the chemistry, the chemical feed system, and the labor to operate the equipment throughout the project. WaterSolve’s mission was to inject the proper dose of chemistry to match the solids in the dredge water from the canal so the solids would settle to the bottom of the lagoon and the clean water could return to the canal within the guidelines set by the state of North Carolina. Periodic testing of the water was required and recorded by the WaterSolve personnel throughout the project. The chemical feed systems were assembled in a containment pad so that any spill or leak of the chemistry would be contained and readily cleaned up during the project. The anticipated flow from the dredge was 1700-GPM. However, the new 10” pipeline reduced the friction loss to the extent they were pumping 2200 to 3000-GPM throughout the project. We quickly ordered additional chemical pumps to meet the higher flow rates. A previous attempt to operate this project a year earlier resulted in the contractor’s inability to get the turbidity below 100 NTU’s when the requirement was 25 or below. There was some worry about meeting this requirement. When Tom Bennett (the Project Manager overseeing the project for Southern Shore) saw the chemical feed system in place and the NTU’s were 22 (below the 25 required) he remarked “We were working with Jiffy Lube and now we are working with NASA. This project was 8 years in the making and now it has a real chance for success”. The make-up of the dredge material varied a lot as the dredge proceeded through the canals. There were spots of heavy organics that caused high chemical demand and sand bars that were low in chemical feed rates. One portion of the project was dredging at the marina and between the markers going out into the sound. This passageway had a variety of materials ranging from high organics to high clays to high sand residual coming to the lagoons to be treated. The dual chemistry formulated by WaterSolve worked great throughout these changes in material and no changes were needed in the chemistry. There were a few times during operations that the NTU’s were above discharge limits, and the water was circulated and chemically treated to drop the NTU’s to meet the requirements. As the solids collected in the first lagoon a long reach excavator was used to remove some of the sand and mud to maintain the space so retention time of the water could remain at 15 to 30 hours before crossing over to the 2nd lagoon. The 2nd lagoon (or polishing pond) allowed more settling time and could be retreated if NTU’s were too high to discharge. Turbidity curtains in each lagoon helped deflect the water side to side so the water had better settling time before it was discharged. The dredging portion of the project started at the end of November 2010 and was successfully completed at the end of February 2011.