BEDROCK ELEVATION AND SHALLOW HYDROLOGIC SYSTEMS IN A GLACIATED REGION, NORTHWESTERN PENNSYLVANIA

A bedrock elevation map within northwestern Pennsylvania was created using data from 1,563 oil and gas well records and 170 water well records. Borehole data and limited surface outcrops used to construct this map identify shallow groundwater aquifers and surface mining deposits within the unconsolidated glacial sediments. Bedrock elevation across the county ranges from 857 to 1,635 ft above sea level, and delineates three main areas of low elevation that do not mimic modern surface topography. A ridge of high bedrock elevation correlates with the maximum advance of the ice sheet during the Wisconsinan. Higher bedrock elevation areas also appear to control surface water divides (at a variety of scales) within the four surface water basins in the study area, including enigmatic subtle surface water divides in low relief swampy areas. Regional patterns of remarkably consistent surface and groundwater chemistry within the study area may be the result of bedrock control on glacial sediment deposition. Our results modify the existing paradigm from previous sediment mapping efforts (Shiner and Gallaher, 1979) that suggest the thickest glacial deposits and major aquifer systems occur only within the modern river valleys.

Reference

Schiner, G.R. and J.T. Gallaher. “Map Showing Thickness of Glacial Deposits and Locations of Wells in Western Crawford County, Pennsylvania” [map]. 1:50,000. Commonwealth of Pennsylvania: Department of Environmental Resources, 1979.