Duke Energy has been ordered to take immediate steps to halt the spread of groundwater contamination originating from coal-ash storage basins at its L.V. Sutton Power Plant in Wilmington, N.C.

The North Carolina Dept. of Environment and Natural Resources (DENR) issued a notice of regulatory requirement to the Charlotte, N.C.-based utility after high levels of boron were found during routine tests at monitoring wells located at or beyond the facility's compliance boundary, as well as at three water-supply wells within a half mile of the facility.

DENR says boron levels in the water-supply wells were below state groundwater standards of 700 micrograms per liter but much higher than concentrations found in area background wells. Duke Energy faces a July 9 deadline for controlling the contamination and submitting a plan for monitoring its effectiveness.

DENR spokeswoman Sarah Young says the specifics of the strategy are up to the utility. "There is no time line for subsequent review and implementation because it depends on how extensive the plan is," Young says.

In March, DENR fined Duke Energy $25.1 million for violations of state groundwater standards at the plant, which was opened in 1954 as a 575-MW coal-fired facility and converted to natural gas in 2013. The utility has appealed the fine, taking issue with the methodology for calculating the amount. Duke has submitted plans to close the Sutton plant's storage basins, estimated to hold seven million tons of ash.

Beginning this fall, plans call for approximately two tons to be excavated from the basins for transport by truck and rail to a reclaimed Chatham County, N.C., brick mine, which also is receiving coal ash from other local Duke Energy powerplants. The remainder of the ash will be stored dry in a fully lined landfill, to be built on the Sutton plant property.

The landfill's design is under review by state regulators, with construction expected to begin early in 2016.