Dr. Mike O’Driscoll has a long history with East Carolina University. He first started as a geology instructor in 2004 and has since climbed the faculty ranks to become a Professor in the ECU Department of Coastal Studies. Though his main office is in Greenville, his friendly face is always a welcome sight on our coastal campus.
Over the years, O’Driscoll has focused his research on water resources and policy. He is particularly interested in the factors that regulate groundwater and nutrient inputs to surface waters in coastal watersheds, and he considers Northeastern North Carolina a perfect place to conduct his work. In fact, a portion of his work lately has focused on implications sea level rise might have for onsite wastewater treatment systems. Sites along the Outer Banks provided key insights for a recently published study he led.
Sea level rise (SLR) is a hazard that coastal communities around the world will increasingly face in the coming years. And while many think about what’s above ground when it comes to SLR impacts, fewer tend think about the just-as-important, yet out-of-sight, underground infrastructure.
Many coastal communities, like those found on the Outer Banks, rely heavily upon onsite wastewater treatment systems- colloquially referred to as septic systems- to properly treat wastewater flowing from their homes and businesses. In the most simple terms, a traditional septic system is comprised of a tank and drain field. The tank receives wastewater directly from the dwelling on site and provides initial treatment. The drain field, as its name suggests, allows the wastewater to drain through the surrounding soil thereby allowing further filtration before it reaches the groundwater table below. The main treatment occurs in unsaturated soils beneath the drainfield, so if those soils are saturated due to shallow groundwater levels, systems may malfunction and not treat the wastewater. If wastewater treatment is inadequate, it could lead to bacteria and virus contamination of the groundwater.
This graphic illustrates the inundation that may occur when groundwater levels rise.
In an ideal set up, there should be ample space between drain field and the groundwater table to ensure the wastewater has been thoroughly treated before interacting with the groundwater itself. The satisfactory and/ or required amount of filtration space, formally known as vertical separation distance, or VSD for short, is typically based on the seasonal high-water table, and may vary depending on soil type, as well as state and local regulations.
For example, many states in the US require at least 60 cm VSD, but South Carolina only requires 15 cm. Even still, North Carolina VSD requirements are 30 cm for loam, clay, and silt soils and 45 cm for sandy soils such as those found on the Outer Banks. Pair these discrepancies with increasing coastal hazards such as sea level rise or large rain events, and even new, or currently high-functioning, septic systems have a bleak outlook.
The study previously mentioned, done in collaboration with Drs. Charlie Humphrey (ECU), Guy Iverson(ECU), Jared Bowden (North Carolina State Climate Office), and Jane Harrison (North Carolina Sea Grant), revealed that SLR does influence groundwater levels to some extent. The team compiled data from thirteen sites, mapped below, in Dare County. The amount of available information for the various sites spanned decades. Eight groundwater monitoring wells were installed by NC DEQ in the early 1980s, but the five remaining wells were not installed until 2019-2020 by the project team. The researchers focused on groundwater levels at the thirteen sites through 2022, and used additional data from the NOAA tidal gauge at Duck, NC to incorporate sea level rise trends.
The map shows the location of the different wells and sites used during the study.
Among their findings, O’Driscoll and his colleagues noted:
- SLR at Duck is occurring at a rate of 4.8-4.9 mm/ year.
- Average groundwater rise in Dare County was approximately 7.5-7.6mm/ year from 1984-2022.
- All sites but one (Stumpy Point) indicated that groundwater levels were rising with sea level.
- Sites also experienced temporary rises in groundwater levels for weeks to months after heavy precipitation events, as evidenced in July 2018 when the area received almost 30 cm of rain over five consecutive days.
It is expected that as sea level rise increases, it will impact the high-water table and thereby decrease the available vertical separation distance. This will likely result in higher numbers of already established septic systems that will become more frequently inundated and stay that way for longer periods of time and increase the failure rates of septic systems in low-lying areas. Areas of highest concern include South Nags Head; sound side, low-lying portions of Roanoke Island; and mainland Dare County. Septic systems that become stressed or inundated in turn pose contamination risks to groundwater, as well as surface water. They may also become a nuisance to property owners as highlighted last year in a story published by The Washington Post which featured O’Driscoll and various other experts in the field.
Though not on the coast perhaps as much as he’d like to be, Dr. Mike O’Driscoll conducts research that is both relevant and crucial to Outer Banks communities and finds as many opportunities to visit the coast as he can. He collaborates regularly with the Town of Nags Head and was just recently interviewed for the town’s One Water Concept video (below). His research in collaboration with Drs. Charlie Humphrey and Guy Iverson at ECU’s Environmental Health Sciences Program, has led to growing awareness of the wastewater management challenges that coastal communities face in an era of sea level rise and more intense storms. Recently, in collaboration with the NC Department of Environmental Quality, NC Department of Health and Human Services, the North Carolina Office of Recovery and Resiliency, and researchers across the UNC system, a Coastal Plain Sustainable Wastewater Management Workgroup was initiated to help raise awareness, enhance collaboration, and leverage research to support resilient wastewater management in the region.
O’Driscoll has dedicated years to researching surface water and groundwater interactions, among other things, in Eastern North Carolina and has proved to be a vital resource for our local, coastal communities.
Based at the Coastal Studies Institute (CSI), the North Carolina Renewable Ocean Energy Program (NCROEP) advances inter-disciplinary marine energy solutions across UNC System partner colleges of engineering at NC State University, UNC Charlotte, and NC A&T University. Click on the links below for more information.
ECU's Integrated Coastal Programs (ECU ICP) is a leader in coastal and marine research, education, and engagement. ECU ICP includes the Coastal Studies Institute, ECU's Department of Coastal Studies, and ECU Diving and Water Safety.
The ECU Outer Banks campus is home to the Coastal Studies Institute.
