The historic flooding from Hurricane Florence has unleashed massive amounts of contaminants causing widespread pollution of streams, rivers, and lakes. Less obvious, but of considerable concern, are the effects on groundwater. Attention to groundwater quality is needed, both immediately and longer-term.
The sources of contamination are many in the region impacted by the storm: compromised hog-waste lagoons, dead animal carcasses, runoff from fields where billions of gallons of manure are sprayed annually, partially or wholly untreated sewage from municipal treatment plants suffering from power outages, breached coal ash storage ponds, and flooded hazardous waste sites, among others.
Much of the contaminant load in surface water will find its way into groundwater.
Of most immediate concern are the effects on homeowners’ wells, along with wells in trailer parks, campgrounds, and elsewhere that are used without treatment. Most of these wells are shallow, making them especially vulnerable to contamination.
Of particular concern are wells inundated by flooding. Mud and debris may have to be physically removed. But that’s just a start. No well is completely safe from flooding, but those with a cracked or improper cap are particularly vulnerable. Contaminated water also can fast-track into well water by flowing downward along the annulus between a well casing and the side of the borehole—again, older wells or those improperly constructed are most vulnerable. Wastewater from homeowners’ overloaded septic systems is yet another concern.
Most rural residents depend on a domestic well for their sole water supply. People whose wells have been flooded will need another source of water while their well is tested and disinfected. Disinfection is best done by a certified well contractor, which takes several days under normal circumstances when a contractor is available and may need to be repeated multiple times. Some wells may not be a safe source of water for months after the flood.
Bacteria and chemicals slowly seeping into the ground can contaminate groundwater even after the water is tested and found to be safe. Streams, rivers, and lakes are typically hydrologically connected to groundwater, resulting in the potential for widescale groundwater contamination throughout the region. It will be necessary to take long-range precautions, including repeated testing, to protect the safety of drinking water and to monitor the longer-term groundwater impacts.
As the region recovers from Florence, groundwater may be out-of-sight, but it should not be out-of-mind.
Dr. Bill Alley is the National Ground Water Association’s Science and Technology Director. Previously, he served as chief of the Office of Groundwater at the U.S. Geological Survey for nearly 20 years. Alley and his wife, Rosemarie, wrote the book High and Dry: Meeting the Challenges of the World’s Growing Dependence on Groundwater, which was released in early 2017.