Septic Systems: The Underground Cost of North Carolina’s Growth

“Will it perc?” It’s the question every builder or homebuyer should know when evaluating land for a new build. Homeowners generally dream of functional or cosmetic construction upgrades like hardwood floors, larger garages, and fancy countertops or fixtures. 

But as North Carolina’s population boom continues, more builders and homeowners are encountering the high cost of an improvement they’ll hopefully never see — the septic system.

How Septic Systems Use Soil As A Filter

No matter what you pour, flush or dispose of down a drain, it all has to go somewhere. Over half of NC homes are outside the reach of municipal sewers and rely on septic systems for waste disposal. That figure is closer to 80% in NC’s dispersed coastal areas. With population projections for increased growth statewide, the number of septic systems are expected to rise. 

Conventional septic systems have been around and affordably functioning for decades. They consist of three main parts: a septic tank, a drain field, and the soil beneath the drain field. 


The tank is a watertight container, usually precast concrete, buried in the ground just outside the home. The tank’s purpose is to temporarily hold household wastes, separate solids from liquids, and allow some anaerobic digestion of solids.

After about two days, liquid sewage effluent flows out of the tank through perforated pipe, delivering still-hazardous liquid to gravel and the soil beneath the drain field where the real wastewater treatment occurs.

What Factors Affect Septic Requirements? 

Increasingly, new construction areas don’t qualify for conventional systems. Demand is forcing building into areas with more challenging soils to manage. Landowners are increasingly confronted with denied permits or requirements for complex waste systems.

“The problem is that we’re already using our most suitable soils,” said North Carolina State University extension specialist Erik Severson. “Across the state, we have enormously different soils, some of which are challenging to drain.”

Severson says that geology and/or population density can be the issue, especially in metropolitan areas. 

“In the Charlotte area, there are several limiting soil types. In Wake County, demand is concentrating bigger houses onto smaller lots, some of which have been previously denied conventional systems. These factors add up to costlier systems. The cost of pretreatment can add 30,000 to 70,000 or more over the cost of a conventional system, depending on the system and site.

North Carolina is home to over 400 soil types, some of which aren’t suitable for any septic system, even advanced types. Areas with slow drainage, fractures, or high water tables necessitate more complicated engineered or pretreated systems. All common in NC’s mountains and coast.

Coastal areas have quick-draining sandy soils that allow for rapid groundwater movement, which seems like a good thing, except when there’s too much.

Year-round, many coastal areas have perennially high water tables that would set conventional drain fields too close to natural groundwater, posing human and environmental health risks.

“Septic systems with advanced pretreatment may mitigate some of the risks of ground and surface water contamination in areas with high seasonal water tables,” Severson said. “ The pretreatment devices remove pathogens and nutrients before the wastewater is dispersed into the receiving soil.”

Severson says the paramount goal of all onsite waste systems is safety.

“We don’t want effluent to reach groundwater where it could have significant human health or environmental impacts.”

Education & Training Are Key to Safe Septic Function

All septic systems require periodic maintenance. Septic tank solids must be occasionally pumped out; otherwise, they can create a thick biomat or bacterial slime layer that clogs the soil. An improperly maintained system can fail, causing untreated sewage to back up into the home plumbing or rise above ground and potentially into surrounding groundwater.

Despite this fact, Severson says that soil is a reliable method of treating wastewater, and the vast majority of residential systems in NC are considered safe. One key reason is the state-required training and certification of septic system installers and inspectors. In this case, knowledge is power and protection.

NC State Onsite Wastewater Training 

Severson teaches onsite wastewater training and continuing education classes totaling over 300,00 credit hours at the university’s Lake Wheeler Road Field Laboratory and Mills River training sites. These classes are approved by the North Carolina Onsite Wastewater Contractor Inspector Certification Board and prepare attendees to take state-required board exams and for continuing education credits.

Each year, the Onsite Extension program serves over 1,100 installers, inspectors and operators with personalized, hands-on training. Severson says these skills, while state-required, also make businesses more stable and marketable in a rapidly growing industry. 

“These professionals know the liability landmines that exist in this business. Installing a system that the soil and site can’t accommodate can create a financial mess. They need and want the best possible training to hone their skills.”

Septic System Help for Homeowners

NC State Extension also provides educational materials for homeowners, including a handy Septic System Owner’s Guide that provides use guidelines, a recommended maintenance schedule and a record log that could potentially save homeowners untold costly, messy repairs.

Demonstration & Training Improvements

NC State’s onsite wastewater training is getting its own upgrade this year. New technical product displays and hands-on opportunities will provide the most current skills training.

Because of the significant industry demand for onsite professionals, Severson’s group also offers online classes for some sessions:

“Housing demands are driving the sustained growth of the onsite wastewater industry because you cannot have an occupied dwelling without a functioning septic system.  As a result, NC needs more installers and folks in the onsite wastewater industry, all of whom need training and yearly continuing education.  

Our programs are tailored to the specific needs of the clients (operators, installers, soil scientists, engineers, and point-of-sale inspectors), offering them skills and knowledge to create thriving small businesses.”  

Want More Pack Impact?

Crop and Soil Sciences impacts businesses, students, and NC citizens through specialized soil programs. Follow how our discoveries affect agriculture and environmental science by joining our weekly newsfeed.

If you are a student interested in soils or environmental science, investigate our undergraduate and graduate degree programs. Then join us for a guided email tour of our department and university.  

Improving NC’s landscape and economy through environmental quality is just part of how we are growing the future.

NC State's logo in a soil pit