Staff photo by Allison Potter
Wrightsville Beach Public Works Director Mike Vukelich said this well near Salisbury Street has experienced saltwater intrusion during peak water demand, at times forcing officials to reduce the volume of water withdrawn.
Wrightsville Beach irrigation accounts for up to half of the town’s water withdrawal from a groundwater supply that has for years shown signs of deterioration.
Town public works director Mike Vukelich said in a Jan. 17 interview that residents who use large amounts of water to keep their lawns green through the summer are taxing an aquifer that already experiences isolated cases of saltwater intrusion.
“We have one well here. During high withdrawal periods we have to throttle it back from its maximum capacity because we were exceeding the state limit for salt,” Vukelich said. “Several years ago I sent a letter to the 20 highest users in town … it didn’t appear to make a lot of difference.”
Dr. Roger Shew, a geology professor at the University of North Carolina Wilmington, described saltwater intrusion by comparing the well to a straw sucking water from the aquifer.
“Freshwater withdrawals create a cone of depression, where the water table will drop around the well bore,” Shew said. “If you’re also pulling water at a really rapid rate … you can also pull in saltwater, which is below the freshwater because it is denser. So if you pull in too much you can also start sucking in the saltwater in from the bottom.”
During its annual retreat Jan. 11, the Wrightsville Beach Board of Aldermen discussed three potential contingency plans, should Wrightsville Beach’s wells be rendered unusable.
Officials discussed a possible agreement between the Cape Fear Public Utility Authority and Wrightsville Beach to purchase water directly from the authority. The two agencies already have an agreement to supply water during an emergency situation.
Another option is to build a nano-filtration plant similar to the one used by the CFPUA in Ogden, which would provide freshwater by pushing saltwater through a series of specialized filters. However, Vukelich said that option could be considerably more expensive.
The third option is aquifer storage and recovery (ASR). Treated freshwater would be pumped into the aquifer during the colder months, when demand is lower. It would allow the town to offset unsustainable water withdrawals that are causing ocean water to advance toward the wells during the summer months.
But Shew warned that ASR can come with its own risks to the aquifer.
“One of the major concerns is that you don’t want to inject anything that could damage the aquifer,” Shew said. “What you don’t want to do is inject anything that would lead to the reduction of the storage volume and the permeability, which is the ability to draw the water back out.”
He added the injected water would also need to be treated for bacteria to avoid contamination.
However, Wrightsville Beach Town Manager Tim Owens suggested in a Jan. 21 interview that ASR is currently the most likely scenario, although all options are still on the table.
“We’re really just in the early phase of looking at the different options to see which one is the best,” Owens said. “We’re bumping up against our maximum capacity right now, so we really need to look at it. … We don’t have to rush, but we want to be prepared for the future.”