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February 1, 2022

A new USGS study, in cooperation with the Pennsylvania Department of Environmental Protection, explains 2015-2019 results from the Pennsylvania Groundwater Quality Monitoring Network of 28 wells across the Commonwealth.


Pennsylvania leads the nation in the number of people who use private domestic wells for water supply, but water from those wells and ambient groundwater quality have historically not been routinely monitored. USGS and the Pennsylvania Department of Environmental Protection established a state-wide Groundwater Quality Monitoring Network in 2015. Water samples from each of the 28 monitoring wells were collected twice per year through 2019. 

A new USGS report explains these ambient groundwater monitoring results for 2015-2019. Key findings include: 

  • Results of sampling largely meet Environmental Protection Agency drinking water standards; exceedances were recorded for nitrate (3 percent of samples), iron (32 percent), manganese (36 percent), and aluminum (5 percent). 

  • Samples from 64 percent of wells exceeded the lower proposed drinking water standard for radon of 300 picocuries per liter (pCi/L), while 7 percent of wells exceeded the higher proposed standard of 4,000 pCi/L. 

  • There were no exceedances for volatile organic compounds (VOCs), but one well had a tribromomethane detection. 

  • Methane was detected in three wells, with one sample exceeding the Pennsylvania action level of 7 milligrams per liter (mg/L). 

  • pH and dissolved oxygen varied widely across the network; 42 percent of pH values were either above or below the drinking water standard range of 6.5 – 8.5 units. Dissolved oxygen ranged from 0 – 13.9 mg/L.  

  • Analysis of major ion concentrations from all samples indicate that calcium/bicarbonate water is the dominant water type. 

Selected recent results can be accessed via an interactive Web Tool.

Photograph showing a groundwater monitoring well in a green field with water sampling equipment including a pump and tubing.
Groundwater sampling equipment at monitoring well TI 470 in Tioga County, Pennsylvania. (Matthew Conlon, USGS)


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