Private Well Data

Groundwater Quality Indicators from Private Drinking Water Well Testing

Drinking water quality is a critical issue for the North Carolina Department of Environmental Quality (NCDEQ). Drinkable groundwater is an essential resource that must be monitored and protected for its quality as a water supply for future use by North Carolina citizens. NCDEQ is using water quality sampling information to assess regional water quality in groundwater resources in North Carolina. To understand the regional distribution of North Carolina groundwater quality, NCDEQ is mapping commonly sampled chemical parameters that have been found in groundwater in some wells in the state. This effort to characterize state groundwater resource quality is expanding to include as much groundwater quality information as is available.

Subsurface aquifer conditions vary across the State, and groundwater quality differs as well. Since groundwater quality is affected by regional naturally occurring conditions, it is important that information be collected to determine whether an existing or potential well's groundwater may require treatment to ensure the healthful use of that water. Potential human groundwater quality impacts must also be addressed.  

Sampling of Private Drinking Water Wells in North Carolina

Under the statewide private well testing program administered by the Department of Health and Human Services (DHHS) and local health departments, all new private drinking water wells since 2008 are sampled by local health departments and analyzed for a standardized list of chemical constituents by the State Laboratory for Public Health in the Department. Sampling may also be performed for private wells at any time. 

When an individual well exceeds health based drinking water or DEQ groundwater standards for one or more contaminants, the local health department, along with DHHS, provides the well owner with information about the constituents that have been found and what steps are necessary to protect the well users’ health. Where appropriate, local health departments contact DEQ for assistance in identifying the source of contamination - often naturally occurring - and other affected well users.

Private Well Dataset

In addition to their value to individual well users, the tremendous dataset created by routine sampling of private wells is the most abundant source of data on the current status of groundwater quality across the state. DWR has used this information to help understand where groundwater quality problems occur and where more information is needed about groundwater quality, soils and rock types where private wells are installed, or human activities that affect groundwater quality.  

The following summary table is an effort to show individual chemical parameters from groundwater samples collected at private drinking water wells from July 2008 to April 2009, and from January 2018 to December 2019, by local health departments. The samples were analyzed by the State Laboratory for Public Health, which provided the data to DWR. This is not a comprehensive effort to assess state groundwater quality, but rather an initial and expanding effort to understand the state’s groundwater resources using information collected from all newly installed and other private wells during the two time periods.  

For these wells, samples were collected and analyzed for one or more of the parameters. In a few cases, a single well may have been sampled more than once. No attempt has been made to remove these duplicate or follow-up samples from the dataset. 

Statewide Comparison to DEQ Groundwater Standards

The following parameter table shows the number of samples collected and analyzed by the State Laboratory for Public Health during the 2008-2009 and 2018-2019 years, the number and percent exceeding NC groundwater standards, and a comparison of the two time periods. You can see interesting variations in groundwater quality that may be due to a number of factors including well construction, sampling methodology, differing locations of new wells due to population growth, additional well installations in areas with differing soil and rock types with differing levels of naturally occurring constituents (parameters), and other factors. 

    2008-2009     2018-2019      
Parameter NC Groundwater Standard Number of Samples Collected at Well Number of Samples Exceeding NC Groundwater Standard * Percent of Samples Exceeding NC Groundwater Standard * Number of Samples Collected at Well Number of Samples Exceeding NC Groundwater Standard * Percent of Samples Exceeding NC Groundwater Standard * Percent Difference (2018-19 - 2008-09)
Arsenic 10 ppb 3935 79 2.00% 10289 233 2.26% 0.26%
Barium 700 ppb 3197 0 0.00% 10280 11 0.11% 0.11%
Cadmium 2 ppb 3197 0 0.00% 10281 13 0.13% 0.13%
Chloride 250 ppm 2064 13 0.60% 10202 52 0.51% -0.09%
Chromium 10 ppb 3197 37 1.20% 10280 174 1.69% 0.49%
Copper 1000 ppb 3930 4 0.10% 10290 43 0.42% 0.32%
Fluoride 2 ppm 3933 69 1.80% 10686 124 1.16% -0.64%
Iron 300 ppb 3934 1383 35.20% 10291 1743 16.94% -18.26%
Lead 15 ppb 3944 131 3.30% 10391 129 1.24% -2.06%
Manganese 50 ppb 3933 989 25.10% 10288 2880 27.99% 2.89%
Mercury 1 ppb 3195 0 0.00% 10272 3 0.03% 0.03%
Nickel 100 ppb 3257 0 0.00% 45 0 0.00% 0.00%
Nitrate 10 ppm 3091 28 0.90% 8490 50 0.59% -0.31%
Nitrite 1 ppm 3092 2 0.10% 8490 4 0.05% -0.05%
pH 6.5-8.5 3931 923 23.50% 10203 1263 12.38% -11.12%
Selenium 20 ppb 3197 2 0.10% 10280 22 0.21% 0.11%
Silver 20 ppb 3197 0 0.00% 10238 0 0.00% 0.00%

* Number of Samples Exceeding NC Groundwater Standards likely due to naturally occurring conditions of soil and rock types at the well site. 

(ppb = parts per billion or micrograms per liter; ppm = parts per million or milligrams per liter)


For North Carolina water quality maps, follow this link:

USGS National Uranium Resource Evaluation (NURE) Program