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Coastal Water Supplies

by Art Langrish [based on article by Roger Rulifson] |
Feb 8, 2007

Coastal Water Supplies: Water, Water Everywhere and Not Enough to Drink

Coastal North Carolina is experiencing a human population growth that is putting increasing strains on fresh water supplies. In order to keep the fresh water flowing as fast as demand, may municipalities are turning to the use of Reverse Osmosis (RO) technology to treat groundwater supplies. This is fast becoming the preferred method of processing drinking water in coastal counties. In coastal North Carolina there are 12 RO water treatment plants (WTP's) in operation. The areas of need for RO plants are too far from the barrier islands and ocean coastline to use distillation (desalination) of ocean waters as the primary method of drinking water processing.

The RO process removes dissolved impurities from water through the use of a semipermeable membrane. As part of this process, the briny concentrate waste is discharged to local waters. In fresher waters the concentrate will act as a briny discharge, and in saltier waters the briny concentrate will actually be fresher than ambient waters.

At the present time there are no State or Federal criteria for assessing the environmental impacts of discharge waters on ambient water quality. Various State agencies have expressed concerns about the toxicity of this concentrate stream to estuarine organisms including fish and shellfish at early and adult life stages, to the benthic and pelagic fauna at the base of the food chain, and to submerged aquatic vegetation. Additionally, these agencies have expressed concern about prevailing water currents at the proposed site of discharge under various environmental conditions, especially wind and storm events.

East Carolina University's Institute for Coastal and Marine Resources (ICMR) is currently researching two proposed sites in northeastern North Carolina: A five million gallon per day RO-WTP plant for Pasquotank County, and a similar plant for Currituck County. Both counties cannot accommodate any more growth because water supplies are inadequate for current and future needs. The RO-WTP facility in Camden, NC, is being used as a model to determine concentrate effects. The facility discharges up to 200,000 gallons per day into Chantilly Bay, part of the lower Pasquotank River. A one-year study by the teams at ECU has concluded that the discharge plume is not detectable at 25 meters from the diffuser pipe, and the food-web does not appear to be affected by the concentrate discharge.

Continued environmental impact monitoring will be required, but it appears that well managed reverse osmosis water treatment plants are becoming a valuable asset to Eastern North Carolinas.

For the full excerpt of this summary or for more information, contact Roger Rulifson at Rulifson@ecu.edu or Terri Woods at Woodst@ecu.ecu