The Riverbend power plant west of Charlotte will become the first in North Carolina to start draining its coal ash ponds under a permit granted Friday.
Draining water from the settling basins that hold more than 100 million tons of potentially toxic ash statewide is a key step in reducing their threat to water supplies.
Duke is under legislative orders to dig up the ash at Riverbend in Gaston County and three other power plants by 2019. Dry ash from the plant recently began being shipped by rail to a former clay mine in Chatham County.
The permit granted Friday, which got federal approval after a yearlong delay, will be a model for all 14 of Duke’s coal-fired power plants across the state. Environment secretary Donald van der Vaart called it the most stringent in the nation.
Similar permits for the other power plants are being processed, the Department of Environmental Quality said.
The permit lets Duke drain up to 1.4 million gallons a day of the most contaminated water in Riverbend’s two ash ponds – from the bottom, where ash has settled. The water will drain into Mountain Island Lake, Charlotte’s major water supply.
Mecklenburg County began preparing eight months ago, when it added three monthly water-testing sites on the lake to the three already in place.
“We knew they were going to be discharging this water and wanted to get some background data,” said county water quality chief Rusty Rozzelle. The extra data will be collected as long as the ash ponds drain into the lake.
Among the upgrades are two automated contaminant sensors, mounted on buoys upstream and downstream of Riverbend’s discharge pipe. The county split the $10,000 cost of each sensor, and the extra water analyses, with Charlotte Water.
Limits on the potentially harmful metals allowed in the discharged water, such as arsenic, selenium and mercury, were strengthened from a draft permit released last year. More frequent tests of the lake and of fish that could become contaminated were also required.
Duke began draining surface water from the Riverbend ponds in January. It will build a treatment system to clean water from the bottom of the ash ponds before it is discharged.
“Through both steps in the process, we are taking several steps to ensure that rivers and lakes remain protected and we remain within permit limits,” said company spokeswoman Catherine Butler.
Catawba Riverkeeper Sam Perkins, a watchdog of the lake, said he likes the new permit.
“This is actually a significant improvement and something we can say will work,” he said. “We’re happy that Riverbend’s cleanup can move forward.”
The permit regulates, for the first time, a dozen seeps from the Riverbend ash pond dams into the lake. Duke will have to test the seepage to learn whether it breaks water quality standards.
Perkins said the seeps aren’t a big issue at Riverbend, since the ash will be excavated, removing a source of contamination. But he said that’s not true at other Duke power plants, such as Allen on Lake Wylie, where Duke might be allowed to leave ash in place.