Exploring the Impact of Septic Systems on a Coastal Community

Students at the University of North Carolina spend a semester investigating groundwater contamination risks in the Outer Banks, share their findings through wastewater podcasts.

Exploring the Impact of Septic Systems on a Coastal Community

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The Outer Banks region of coastal North Carolina has seen increased flooding and more intense storms in recent years. A related concern is that septic systems in unsewered areas are leaking pathogens and other pollutants into a rising groundwater table.

Students at The University of North Carolina at Chapel Hill spent last fall’s semester studying that issue at the UNC Institute for the Environment’s Outer Banks Field Site. They presented their findings in December 2019.

Their research covered an area of the town of Nags Head called the Gallery Row Sub-watershed. They found roughly half of the area is highly susceptible to groundwater pollution from septic systems because the depth from the surface to the groundwater is three feet or less. The research also probed a variety of stakeholders for their perceptions on the severity of the pollution risks and what to do to address them.


The Outer Banks is chain of barrier islands off the North Carolina coast. The Gallery Row Sub-watershed has low elevation and dish-shaped topography. Flooding is a growing problem there, largely because of climate change and extensive development with impervious surfaces that contribute to increased runoff.

As one response to the flooding, the town of Nags Head in 2018 launched a groundwater lowering initiative in the Gallery Row area, drilling wells and pumping water from underground to surface reservoirs. This increases the separation between the land surface and the water table, creating more space to store water in wet periods.

The town also created what is now the Todd D. Krafft Septic Health Initiative as a way to reduce septic system failures. The program provides financial incentives for residents to pump, inspect and repair their septic systems. Those include low-interest loans for major repairs.


The students’ presentation, “People, Water, and Septic: A Coastal Case Study,” highlighted the methods and findings in the second year of a three-year project. They focused on understanding what areas of sub-watershed are subject to mixing of wastewater and groundwater, and whether levels of wastewater components have decreased since the groundwater was lowered.

“It’s a complicated topic,” observes Andy Keeler, Ph.D., co-director of the Outer Banks Field Site and one of three advisors to the student team. “The students understand that it wasn’t their job to tell people what to do or to come up with a single right answer. Their job was to use the tools of research to learn new things about wastewater and stormwater and how the public and governments think about the options they have.”

To assess the risk of pollution from septic systems, the students took measurements of depth from the surface to the groundwater spanning more than a month and covering several locations. They used GIS technology to map areas of high, moderate and low susceptibility to interactions between septic system effluent and groundwater. 

They used a three-foot depth to groundwater as the marker for high susceptibility because that is the minimum separation specified in state law for adequate effluent treatment in the soil. Half of the sub-watershed mapped as highly susceptible included mostly low-lying and flat areas near roads, homes and businesses.


To check for the influence of septic system effluent on the groundwater, the students tested a series of samples from four groundwater wells and one surface drainage ditch for fecal bacteria and nutrients. They noted whether the samples were drawn on dry days or on days after rainfalls.  They then compared the results with testing from the 2018 phase of student research.

Nutrient levels could not be distinguished from natural background; only the surface water ditch showed meaningful concentrations of E. coli, at levels below the U.S. Environmental Protection Agency threshold for recreational waters. The 2019 levels were significantly lower than those of 2018; the students said that could be attributed to the groundwater lowering project and to less rainfall and drier soil conditions than in 2019.

Sampling for enterococcus bacteria showed levels in excess of the EPA threshold, an indicator of possible contamination from septic systems.


To assess perceptions of pollution risks and knowledge about the problems, the students conducted qualitative research, interviewing septic system professionals, public officials, researchers and property owners and then used software to analyze the transcripts for patterns of keywords and phrases.

Most of those interviewed said they had noticed the area’s flooding problem and attributed it to development with impervious surfaces, more severe storms and a higher water table. Septic professionals, public officials and researchers perceived a very high risk of septic-system-related pollution, while property owners were more concerned about pollution of the ocean. The interviews revealed that people had strong connections to local waters.

The students publicized their research by way of a three-part podcast, Flushed, available at www.outerbanks.web.unc.edu.


“The students did a really good job of providing evidence that Nags Head’s groundwater lowering has helped prevent the mixing of septic effluent and groundwater,” Keeler says. “The qualitative phase brought out that people care deeply about water quality. Many people hadn’t thought about their septic systems as one thing threatening that water quality. We hope the students’ podcast and written report will help the town to educate residents about that issue.”

Keeler notes that next year’s third phase of the research may include an assessment of onsite wastewater treatment technologies beyond traditional septic systems. Meanwhile, he sees the students benefitting greatly from their work.

“They come from university with a very good education in environmental science and policy, but it’s different when they see what it’s like in the real world, where people have to make difficult decisions and tradeoffs in the face of limited information and limited financial resources,” he says. “It’s valuable for them just to get out and listen to people’s complex and mixed views about the environment.

“It’s a really important part of their education to realize that there aren’t any simplistic solutions to these problems. We stress there are many ways to use science to influence public policy. We’re trying to show them that one thing they can do with their academic and research training is to participate in public debates in ways that can help people make better decisions.”

The research team members were Anna-Gray Anderson, Avery Morea, Emily Galvin, Claire Bradley, Sarah Henshaw, Emma Calhoun, Hayley Kaplan, Connor Badgett, Rachel O’Reilly, Bailey Williams, Peter Marcou and CriShaun Hardy. 


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