Groundwater in North Carolina

Over 3 million North Carolinians rely on groundwater as their primary drinking water source.

Despite the large number of private wells in North Carolina, fewer than 200,000 were tested for contaminants in the last decade (2000-2010).  The North Carolina Division of Public Health recommends testing every year for coliform bacteria, every two years for heavy metals, nitrates, nitrites, lead, copper, and volatile organic compounds, and every 5 years for pesticides.1

Since 2008, all newly constructed drinking water wells in North Carolina must be tested for bacterial and chemical contaminants within 30 days of the well completion; however, there are no other required tests for private wells in North Carolina.2  

What is groundwater?

Groundwater is water that is found under the earth’s surface “between rocks and soils”.3  Groundwater is typically composed of rain and snowmelt that seep through the soil and collect in hollow spaces and crevices of rocks.  Groundwater provides the majority of drinking water to private wells in North Carolina in addition to 1.9 million people on community water systems.4   

North Carolina groundwater

 
 

In North Carolina, groundwater

 

percolates through soil and flows between small fissures and fractures in rock.   Groundwater is recharged by rainfall and snowmelt that soak through the soil and eventually enter the water table. 

 
The water table is the level at which the ground below is completely saturated with water.  The depth of the water table can vary based upon the amount of precipitation that enters the ground and the amount of water that is withdrawn from the aquifer.   
Water follows the path of least resistance.  It can travel horizontally through open seams of rock or be pulled by gravity to deep supplies of groundwater.  Eventually all water flows back to the earth’s surface and is released to rivers, lakes, and streams.  Depending upon the depth of the groundwater, this process can take hundreds of years.3

Groundwater zones

Groundwater begins as precipitation that seeps through plant roots, soil, and rocks and eventually enters hollow spaces or porous spaces underground where it may stay for many years. 

 
Water that is still close to the surface is considered “soil water” and is available to plant roots.  As the water moves deeper it becomes “vadose water”, and eventually, when it reaches the saturated zone, it is groundwater. 

Underground water can be categorized into two zones: 1) unsaturated and 2) saturated

 
The unsaturated zone is the space beneath the surface through which the water flows before it reaches the water table.  Some water that is in the unsaturated zone is taken up by plant roots and is referred to as “soil water”.  The rest of the water in the unsaturated zone, called “vadose water” follows gravity downward until it eventually reaches the saturated zone which is completely filled with water. 

The saturated zone is the depth at which all spaces between soil, rocks, and sediments are filled with water.  The water in the saturated zone is what we finally consider groundwater and what is typically used for drinking water supplies.  Groundwater may occur at depths of hundreds to thousands, of feet below the surface. 

Groundwater contamination

 
Water in North Carolina flows between the soil, clay, and small cracks in underground rocks before it finally becomes groundwater.  Some contaminants can also follow this pathway and may influence the quality of your drinking water. 

Groundwater can be contaminated by:

  1. Surface run-off that carries pollutants through the soil and into underground water supplies (such as rainwater that washes off of parking lots and roadways),
  2. Leaking storage tanks and landfills,
  3. Industrial discharges into surface waterways, and
  4. Underground injection of waste products. 
Contaminants can also enter groundwater supplies from natural sources such as the erosion of mineral deposits, volcanic off-gassing and decomposing waste. 

Just as the groundwater flow is subject to change, the distribution and concentration of contaminants in an area may change.  Regular groundwater testing is important to identify contamination problems early

More groundwater resources

NC Department of Environment and Natural Resources (NC DENR): The Groundwater Cycle.

 
United States Geological Survey: What is Groundwater?
 
 
References
  1. North Carolina Division of Public Health.  (2011, April).  Private well water and your health.  North Carolina Department of Health and Human Services.  Retrieved from http://www.epi.state.nc.us/epi/oii/pdf/PrivateWellWaterFactST.pdf
  2. North Carolina Department of Environment and Natural Resources.  (2008, July).  Section.3800. Private Drinking Water Well Sampling.  Retrieved from http://www.deh.enr.state.nc.us/osww_new/new1/privwells.htm
  3. North Carolina Department of Environment and Natural Resources.  (n.d.).  Basic groundwater flow.  On-site Water Protection: Private Wells Branch.  Retrieved from http://www.deh.enr.state.nc.us/osww_new/new1/privwells.htm
  4. Kenny, J.F., Barber, N.L., Hutson, S.S., Linsey, K.S., Lovelace, J.K., & Maupin, M.A. (2009).  Estimated use of water in the United States in 2005.  U.S. Department of the Interior and U.S. Geological Survey.  Retrieved from http://pubs.usgs.gov/circ/1344/