Neuse River: Report Card for a Watershed
Micah Reyes never imagined he would have to go snorkeling in the Neuse River to earn his master’s degree. But the Department of Marine, Earth and Atmospheric Sciences (MEAS) graduate student’s plunges into the river southeast of Raleigh have helped solve a riddle that has stumped environmental officials in recent years.
“The Neuse River provides drinking water to communities downstream, so it’s critically important to protect it.”
Discharge from Raleigh’s Neuse River Wastewater Treatment Plant and other known sources of pollution couldn’t account for the high nitrate levels in the river below the plant, says Dr. Bill Showers, MEAS professor and RiverNet director. RiverNet uses underwater sensors to provide real-time monitoring of Neuse River water quality between Raleigh and New Bern, and Showers says not being able to track the source of the excess nitrates was troublesome. He identified three possible sources for the excess nitrate loading: nearby creeks, runoff from farm fields adjacent to the plant, and deep groundwater. Four main creeks drain the area near the plant, but tests show they were responsible for only some of the nitrates. Riparian buffers effectively trap and filter nitrogen in runoff from nearby fields, so they weren’t responsible. That left groundwater as the only explanation—and led to Reyes’ underwater adventures.
Reyes first canoed the area near the wastewater plant and found a “hot spot” upstream by using a pump he rigged up to take continual nitrate readings. Then, he and Showers conducted a magnetic survey of the area and found that underground formations of volcanic rock cut through bedrock in several spots near the plant, creating channels for groundwater to flow into the river. Finally, Reyes devised a pressure transducer that he placed in the riverbed to measure how much groundwater was bubbling up from beneath. Showers says the findings show that, depending on climate conditions, nitrates from groundwater equal about a quarter of the wastewater plant’s annual discharge into the river.
The groundwater near the plant is tainted by nutrients from the plant’s organic sludge, which was spread onto surrounding fields for years. State environmental regulators forced Raleigh to stop the practice in 2002, but the nutrients’ legacy remains underground. Tests of nearby monitoring wells have shown nitrate levels as much as 16 times the federal standard for surface water, and the Neuse River also shows elevated nitrate levels near the wastewater plant. “We have the technology to
deal with this,” Showers says, noting Raleigh is building two wetlands in the area to filter nutrients from nearby creeks. “The Neuse River provides drinking water to communities downstream, so it’s critically important to protect it.”