Pennsylvania Water Science Center

Installing groundwater monitoring equipment


Joe Duris


Pennsylvania's Statewide Fixed Station Groundwater Quality Monitoring Network (GWMN)

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Pennsylvania’s Statewide Fixed Station Groundwater Quality Monitoring Network (GWMN) currently consists of a set of 22 groundwater wells located in 21 counties that are sampled twice a year for a host of chemical constituents. The GWMN was established to characterize the ambient groundwater quality of Pennsylvania aquifers and to provide a temporal dataset to address seasonal variability and long-term trends in concentrations of analyzed constituents.



Since 1985, the Pennsylvania Department of Environmental Protection (PaDEP) has collected groundwater-quality data in an ambient groundwater monitoring program from fixed stations. PaDEP’s program continued into the late 1990s, except in southwestern part of the state where monitoring was discontinued in 1989 because of resource constraints (PaDEP, 1997). Groundwater quality monitoring has been declining since the late 1990s except for a continuation of activities in the southeastern part of the state. When large-scale development of natural gas from the Marcellus Shale began in 2008, the need for information about the chemical quality of groundwater in shallow aquifers increased, especially in rural areas not served by public supply. As a result of the Marcellus Shale development, a significant number of groundwater wells have been sampled for pre-drilling reconnaissance by the gas extraction industry and concerned homeowners. However, these data represent single sample events while long- term temporal monitoring of groundwater in Pennsylvania aquifers is lacking or non-existent. PaDEP’s recognition of the need for a long-term groundwater quality network led to a cooperative project with USGS in 2014 to establish a long-term fixed station network initially focusing on the northeastern, north central, and western parts of the state. Subsequent development of the network for the entire state is planned upon availability of additional resources.

Why monitor long-term groundwater quality

Results from GWMN sampling can contribute to an understanding of long-term water-quality trends and can be used to gather information on the impact of land management practices on groundwater quality. Groundwater-quality changes through time could be the result of natural variability but they can also indicate effects of human activities, including (but not limited to) coal mining, oil and gas exploration, agriculture, on-lot septic systems, and commercial development.

Data collected are used to:

  1. determine the general background quality of the groundwater resources;
  2. monitor for changes in groundwater quality; and
  3. generate statistical reports and assessments of sample results and trends (Reese and Lee, 1998)

GWMP sampling can contribute to an understanding of long-term water quality trends, and can be used to gather information on the impact of land management practices on groundwater quality.

Where are we monitoring


Groundwater wells are selected that represent natural conditions, meaning there is no known contamination near the wells. Currently there are 22 wells in the network located in 21 different counties in Pennsylvania. The plan is to locate one monitor well in each county, similar to the drought monitoring network.

What we monitor

The network wells are sampled twice a year, once in the fall between the middle of October and the middle of November and again in the spring between the middle of April and the middle of May. These times coincide with the times of the year when water levels are lowest (Oct.-Nov.) and highest (April- May). This temporal design will tell us if any changes in water quality are due to water level depths within the aquifers.

Once a well is introduced into the network for the first time, samples are taken analyzed for a large list of constituents, to include: major ions, metals, nutrients, dissolved hydrocarbon gases, radiological elements, and volatile organic chemicals. If there are no water quality issues, subsequent samples are only analyzed for major ions, metals, and nutrients.

Data Access

Download all available data from the National Water Quality Monitoring Council. Please note data will be downloaded as a .csv file, and the process may take serval minutes. These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data.

Contact information

Joseph Duris
Water-Quality Specialist
USGS Pennsylvania Water Science Center
(717) 730-6930 

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