Arsenic in Rockingham County Water: What Government Sampling Reveals About Bedrock Aquifer Levels

What do 'detected', 'median', and 'range' mean in the government sampling records for arsenic?

In the U.S. Geological Survey’s sampling of Rockingham County bedrock aquifer wells, arsenic measurements are reported with terms that describe how often and at what levels arsenic was found. "Detected" means the measuring equipment found some arsenic concentration above its reporting limit, not that it is necessarily problematic. The "median" is the middle value of all detected results—in this case, 21.75 micrograms per liter (ug/L). The "range" shows the lowest and highest detected values, from 0.3 to 43.3 ug/L in this area. These figures summarize results from many wells, not any single home’s water.

How many samples and wells were tested, and what does this mean for my household?

The data come from 126 arsenic results across 29 separate wells sampled between 2011 and 2021, all located within the bedrock aquifer of Rockingham County. These wells were between 150 and 900 feet deep. The number of samples and wells is enough to characterize arsenic levels broadly in this geologic setting, but it cannot specify the condition of an individual household’s water. Your well’s arsenic concentration can differ from these area medians and ranges because local geology varies substantially. Only direct testing of your water can determine your actual arsenic level.

What are the potential health effects if arsenic in well water goes untreated over the years?

Arsenic is a naturally occurring element that can enter groundwater through rock and soil contact. Long-term exposure to elevated arsenic concentrations in drinking water is associated with health risks, including certain cancers and skin conditions. These risks depend on arsenic concentration and exposure duration. The federal government has set standards to limit arsenic in drinking water to reduce these risks. While no sample from this Rockingham County bedrock aquifer dataset exceeded federal thresholds, untreated arsenic at high levels can pose health concerns over many years.

How does water treated with a Pentair Arsenic Filter differ at the tap?

Water treated by the Pentair Arsenic Filter system is designed specifically to reduce arsenic concentrations to well below federal limits. The system uses filtration technology tested and documented to remove arsenic from household water. When used as intended, tap water after this filtration has significantly lower arsenic levels, which reduces potential health risks from exposure. The system ships ready to configure and can be added to household plumbing to provide continuous treatment.

How do public water system records compare to private well testing regarding arsenic?

Public water systems are regularly monitored and must comply with federal arsenic standards, so their water records reflect compliance and are publicly accessible. They do not represent private well water quality. Private wells, which many Rockingham County households rely on, can have very different arsenic levels that only test results from the specific well can reveal. Government sampling like the USGS data described here provides a regional context but is not a substitute for direct private well testing.

The U.S. Geological Survey's arsenic sampling in Rockingham County’s bedrock aquifer covers 126 results from 29 wells sampled over a decade. This regional information offers context but cannot define conditions in your well. You can consult the USGS site for more detail on these quantified measures.

Where this information comes from

Source: USGS groundwater sampling. Sampled 2021-12-30. These figures describe groundwater sampled in this area. They are not a test of any individual private well - only a test of that well can establish its own water.

On record: U.S. Geological Survey sampling of Arsenic in the BEDROCK aquifer (Rockingham County): 126 results from 29 wells, median 21.75 ug/L, range 0.3-43.3 ug/L; none above any federal threshold