Private Well Water Quality

Private Well Water Quality

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 DHHS and local health departments, all new private drinking water wells are sampled by local health departments and analyzed for a standardized list of chemical constituents by the State Laboratory of Public Health in the Department of Health and Human Services.

When an individual well exceeds drinking water or groundwater standards for one or more contaminants, the local health department, along with DHHS, provides the well owner with information about the contaminants 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 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 or human activities that affect groundwater quality.  

The following maps and summary table are an effort to plot individual chemical parameters from groundwater samples collected at the wellhead of private drinking water wells from July 1, 2008 to April 30, 2009 by local health departments. The samples were analyzed by the Department of Health and Human Services 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 private wells since July 2008.  

For these wells, samples were collected and analyzed for one or more of the parameters: arsenic, barium, cadmium, chloride, chromium, copper, fluoride, iron, lead, manganese, mercury, nickel, nitrate, nitrite, ph, selenium, silver, sulfate, and zinc. Well water flowing through a home distribution system may have a different quality than water in the well itself, so samples taken from kitchen faucets and other indoor sources were not used to create these maps. 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. 

Mapping the Samples

To find locations for well information so that useful maps can be created, the process of geocoding must be performed on well sample address information. This process uses online services to match addresses with map location information (latitude and longitude). The purpose of geocoding well sample information is not to precisely locate individual wells, but to place a well's groundwater quality information at a location useful for showing water quality near the well's location.

Address information is often inaccurate or unavailable, so water quality information for wells that cannot be properly located was not used in the maps, though it was used to generate statistics regarding the number  and percentage of samples exceeding the state groundwater standard.

With the exception of pH, the lowest value shown for each parameter on the maps is the North Carolina groundwater standard for that parameter. (The groundwater standard for pH is a range, 6.5 to 8.5; it is possible for a sample to test lower than the standard or higher than the standard.)

Statewide Comparison to Groundwater Standards

The following paramter table shows the number of samples collected, the number exceeding state groundwater samples, and the number mapped for each parameter. Select a parameter to see mapped sample locations.

 

Parameter

Groundwater Standard

Number of Samples Collected at well

Number Exceeding State Groundwater Standard

Percent of Samples Exceeding State Groundwater Standard

Number of Samples Mapped

Arsenic

10 ppb

3935

79

2.0%

1110

Barium

700 ppb

3197

0

0.0%

412

Cadmium

2 ppb

3197

0

0.0%

412

Chloride

250 ppm

2064

13

0.6%

1104

Chromium

10 ppb

3197

37

1.2%

412

Copper

1000 ppb

3930

4

0.1%

1105

Fluoride

2 ppm

3933

69

1.8%

1105

Iron

300 ppb

3934

1383

35.2%

1109

Lead

15 ppb

3944

131

3.3%

1119

Manganese

50 ppb

3933

989

25.1%

1108

Mercury

1 ppb

3195

0

0.0%

411

Nickel

100 ppb

3257

0

0.0%

0

Nitrate

10 ppm

3091

28

0.9%

311

Nitrite

1 ppm

3092

2

0.1%

311

pH

6.5-8.5

3931

923

23.5%

1106

Selenium

20 ppb

3197

2

0.1%

412

Silver

20 ppb

3197

0

0.0%

412

Sulfate

250 ppm

1010

17

1.7%

85

Zinc

1000 ppb

3930

276

7.0%

1105

 

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

 

For more North Carolina water quality maps, follow this link:

USGS National Uranium Resource Evaluation (NURE) Program