A series of hearings over the last year has allowed the public to weigh in on the construction of a limestone quarry in southern Beaufort County. The next one is slated for July 30 and it’s all about water, specifically, concerns the public may have about proposed use of 12 million gallons per day, pumped from the Castle Hayne Aquifer by Martin Marietta Aggregates, Inc. for the purpose of mine dewatering.
At stake is a Central Coastal Plain Capacity Use Area Water Withdrawal Permit that will give another state sanctioned go-ahead for the pit mine.
The hearing will take place at 6 p.m. in the Building 8 auditorium of Beaufort County Community College. Doors open at 5 p.m. for speaker registration and sign in.
Just as many Beaufort County residents have expressed objections to the mine operation’s need to dump 12 million gallons of fresh water per day into the headwaters of Blounts Creek, many are questioning the wisdom of taking as much water out of the aquifer that supplies water to public water supplies and privately owned wells.
How it will affect groundwater levels in the area is, at this point, unknown. But well-owners within the “drawdown zone,” an oval extending 6 miles West and 7 miles East of the center of the proposed 649-acre pit area, could possibly see lower water levels once the mine is in operation, due to the regional nature of the Castle Hayne.
The Castle Hayne is the most productive aquifer in North Carolina: wells typically yield 200 to 500 gallons per minute, but can exceed 2,000 gallons per minute, according to the North Carolina Department of Environment and Natural Resources. But large portions the limestone, sandy limestone and sand materials composing it are well connected — so connected that major withdrawals cause pressure reductions many miles from the pumping center. While the wells are high yielding, it remains that pumping at one well affects water levels in wells for miles around.
As part of the permitting process with the North Carolina Department of Environment and Natural Resources’ Division of Water Resources, MMA contracted independent consultants Groundwater Management Services, Inc. to determine the amount of groundwater to be withdrawn and define the size and magnitude of drawdown needed to operate the pit mine.
GMA produced a map of residences relying on well water for which drawdown from mine operations is expected to be more than five feet. According to the 2010 report, 195 properties, from N.C. Highway 33 to the northeast and N.C. Highway 17 to the west of the pit mine, could be affected.
But for those well owners within the mine’s “zone of influence,” NCDENR DWR requires a response plan from MMA, should water supplies be affected. On April 8, MMA submitted a plan that includes providing temporary water supply until a permanent supply can be realized for those whose “declining ground water level is a direct result of pit dewatering or mine activities.”
The document states that MMA, at its own expense, will fix the water issue “either by rehabilitation or repair of the existing water supply well, drilling of a new water supply well of the same diameter, or by connecting the residence to a public water supply.”
The report also mapped out geographical areas where mine activities could have an entirely different effect: sinkholes. Though none appear to be active sinkholes, GMA cited 12 closed depressions that have the potential to become sinkholes, most of which occur on private farmland, according to the report.
While MMA has provided a response plan for the loss of private water supplies, another issue looms: the potential for the intrusion of salt water into the Castle Hayne.
Under normal conditions, the seaward movement of freshwater prevents saltwater from taking over coastal aquifers. The place where the two types of water come together usually happens far beneath the land surface, but enough groundwater pumping can reduce freshwater flow toward the coast. If that happens, saltwater will be drawn toward the freshwater zones of the aquifer, sometimes in a vertical “up-coning” near discharging wells. One of the possible effects is costly water treatment to turn salt water drinkable.
Mine dewatering is the single largest use of the Central Coastal Plain Capacity Use Area groundwater of which the Castle Hayne Aquifer is a part, according to NC DWR. In 2012, 88.35 million gallons per day were used for mine dewatering, as compared to 52.5 mgd used by public water supplies in 14 eastern North Carolina counties.
DWR staff requests that those interested in commenting at the public hearing also submit written copies of oral comments. Based on the number of people who wish to speak, the length of oral presentations may be limited, according to a DWR press release.
Written comments may be submitted to Gabrielle Chianese, Division of Water Resources, 1611 Mail Service Center, Raleigh, NC 27699-1611. Comments may also be submitted electronically to CCPCUA@lists.ncmail.net. All comments must be postmarked or emailed by Aug. 31, 2013.