Salt levels on the decline

Published 9:18 am Friday, February 29, 2008

By Staff
Drought conditionsstill impact water flow
Staff Writer
Recent rains have driven salty water in the Tar River back downstream to where the river becomes the Pamlico.
While salinity levels at the U.S. Highway 17 bridge in Washington have decreased as a result of increased fresh water flow, the river is still relatively salty, according to Jill Paxson, an environmental specialist with the N.C. Department of Environment and Natural Resources’ Washington regional office.
DENR’s Division of Water Quality performs twice-monthly tests of the condition of the water at various points in the river. A test conducted Feb. 19 found a salinity of 2 parts-per-thousand at the U.S. 17 bridge. Salinity is measured as one gram of salt per 1,000 grams of water. That is the same salinity reading DWQ registered at the bridge in January 2007.
Last month, DWQ measured salinity near the riverbed at the bridge at levels between 16 and 20 parts per thousand. Salinity levels were not measured over 10 parts per thousand about 30 miles downstream at the mouth of the Pungo River in tests conducted a year ago.
While the water at the bridge is nearly fresh, according to DWQ tests, salinity was measured at 10 parts per thousand six miles downstream on Feb. 19. Water at the mouth of the Pungo River was found to have a salinity of 20 parts per thousand the same day.
Fresh water has a salinity of about 5 parts per thousand or less. Water in the Pamlico River was found to exceed that level less than five miles downstream from Washington in tests conducted last week. Seawater typically has a salinity of 35 parts per thousand.
In December, the river’s salt wedge — the area where salinity varies between zero and 10 parts per thousand — has been pushed past Washington to near Grimesland by backflow of saltier water from the Pamlico Sound. Public works officials in Greenville at that time feared the wedge might approach the city’s water treatment plant, which would require them to desalinate the city’s drinking water. There were also concerns that wastewater, which Greenville treats and releases downstream from its drinking water facility, might backflow upstream to where drinking water is pumped out of the river.
Recent rains and higher levels of flow from upstream have pushed the wedge back to Washington for now.
Pamlico-Tar Riverkeeper Heather Jacobs said the river and its watershed have rebounded, but that drought conditions are “still very much present and alive.” Recent rains have partially refilled the Tar River Reservoir near Rocky Mount, allowing regular release of fresh water from upstream, she said.
Despite rains and the release of water upstream, Jacobs said the river is still well below average flow for this time of year. She predicts that with the present outlook on future rains, the river will not be long in returning to “critical levels.”