This web map summarizes PFAS monitoring data from both public supply wells and private wells across Pennsylvania.

The dataset includes 167 private wells monitored by Penn State researchers in 2023 and 2024 and 406 public supply wells studied by the Pennsylvania Department of Environmental Protection (PADEP) in 2021-2022. Explore the county-based summaries on PFAS detection frequencies, average concentrations, and exceedance of US EPA maximum contaminant levels (MCLs).

Guide to Using the Tool

This web map summarizes data from both public supply wells and private wells across Pennsylvania. In total, there were 167 private wells monitored by Penn State researchers in 2023 and 2024. Private well study participants were recruited from the Master Well Owner Network (MWON). Monitoring data from 406 public supply wells studied by the Pennsylvania Department of Environmental Protection (PADEP) from 2021-2022 were also included. Results shown on the map reflect summaries from both data sets and is not being updated with any new monitoring data.

When the tool opens, the 'Legend' tab will show you the meanings of the colors used in the maps. The 'Layers' tab will allow you to view or hide different data layers by clicking on them. For each layer, refer back to the legend to view data ranges and interpret the color coding.

A brief description of the data layers and how to interpret them is given below:

Number of Data Points per County

The number of data points per county layer displays the number of samples that were taken in each county. This layer is important for understanding all of the other layers. It helps us to interpret the amount of data used in calculating various aspects such as detection frequency, average concentration, and exceedance of drinking water standards.

Detection Frequency

Detection frequencies show us how often different PFAS compounds were found in collected samples for each county. It is calculated by dividing the total number of samples in which PFAS compounds were detected by the total number of samples tested in each county, then multiplying by 100 to get a percentage.

Average Concentration

The average concentration layer is given in the units of nanograms per liter (ng/L) and represents the mean concentration from each county. It is calculated only using samples that have concentrations above the method reporting limit (MRL). The MRL is defined as the lowest concentration the laboratory method is able to reliably quantify.

PFOS Exceedance

The perfluorooctanesulfonic acid (PFOS) exceedance layer shows the percentage of samples from each county that are over the federal limit set by the US Environmental Protection Agency (USEPA). For PFOS, this limit is set at 4 ng/L.

PFOA Exceedance

The perfluorooctanoic acid (PFOA) exceedance layer shows the percentage of samples from each county that are over the federal limit set by the US Environmental Protection Agency (USEPA). For PFOA, this limit is set at 4 ng/L.

PFHxS Exceedance

The perfluorohexanesulfonic acid (PFHxS) exceedance layer shows the percentage of samples from each county that are over the federal limit set by the US Environmental Protection Agency (USEPA). For PFHxS, this limit is set at 10 ng/L.

PFNA Exceedance

The perfluorononanoic acid (PFNA) exceedance layer shows the percentage of samples from each county that are over the federal limit set by the US Environmental Protection Agency (USEPA). For PFNA, this limit is set at 10 ng/L.

Hazard Index Exceedance

The hazard index (HI) is a method of estimating the combined potential health risks of multiple PFAS chemicals in drinking water. The US EPA set the HI limit of 1 (unitless) for a mixture of two or more compounds: PFHxS, PFNA, hexafluoropropylene oxide dimer acid (HFPO-DA), and perfluorobutanesulfonic acid (PFBS). The HI is calculated by dividing the measured concentration of each of the PFAS chemicals by a reference safe concentration limit in drinking water. The calculated ratios are them summed. If the total is greater than 1, then the drinking water MCL is not met but if the sum is less than 1 then the MCL is met.