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October 16, 2023

USGS, in cooperation with the Pennsylvania Department of Environmental Protection, compiled and evaluated data used to identify groundwater sources that are under the direct influence of surface water (GUDI) in Pennsylvania.

In the early 1990s, the Pennsylvania Department of Environmental Protection (PADEP) implemented the Surface Water Identification Protocol (SWIP) for the identification of GUDI sources (see New Groundwater Sources (PADEP)). Since then, more than 500 public-supply wells have been identified as GUDI. 

From review and comparison of PADEP records and datasets as of early 2022*, identified GUDI wells, compared to non-GUDI wells, had significantly

  • older median construction years,
  • shallower depths, and
  • static water levels closer to the land surface.

Carbonate aquifers had the highest percentages of wells designated as GUDI.

Public water-supply wells designated as GUDI largely occurred in unconfined aquifers and had high average yield and shallow static water levels.


Map of Pennsylvania with areas of pink, yellow, blue, and green, with open white and yellow circles, and black and red dots.
Graphical abstract (from fig. 4, USGS Open-File Report 2022–1023,


Data compiled for study analyses provided by PADEP included source data derived from public water-supply system case files, a source-information database for public water-supply systems, and Microscopic Particulate Analysis (MPA) results and associated water-quality data for public water-supply system groundwater sources. 

*MPA data reviewed was for samples collected in 1990–2014. 


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