Browse by county
Click on a county on the map below
Or select a county from the list to view a chart of the average well-testing results for that county. Read more about the scope of the data and limitations.
North Carolina counties:
Scope of the data
County-level averages reported for each contaminant are based solely on private well tests from the North Carolina State Laboratory of Public Health from 1998-2010. County averages provide a useful way to observe an overall trend in a county, but are not detailed enough to predict the specific groundwater concentrations of contaminants in smaller regions and may not reflect the quality of groundwater in a single well. Private well data does not include monitoring wells or surface water samples collected by other state agencies.
County-level averages are intended to provide private well-owners, local health departments, and government decision-makers with a visual tool for understanding groundwater contamination across the state and potential public health concerns in individual counties. Because county-level maps are not specific to smaller geographic areas and cannot be assumed to represent uniform concentration levels across a county, testing private wells is the only way to know whether an individual well is contaminated.
County averages are calculated as the sum of all values recorded in a single county divided by the number of wells tested. Averages may be inflated because of a very high result at a single location, or may be artificially low because of a series of very low results. Data may also be skewed by the number of samples and the location in which the samples were taken. If only a few samples were recorded in an entire county, it is less likely that the reported average is reflective of a majority of wells in that county.
This project was funded by an ARRA supplement from the National Institute of Environmental Health Sciences (#P42ES005948) 2009-2011.