GEOLOGY OF GROUND WATER RESOURCE DEVELOPMENT AND PROTECTION PLANNING ALONG THE WISCONSINAN GLACIAL BORDER, NORTHAMPTON COUNTY, PENNSYLVANIA, U.S.A

Structural elements in bedrock units and the thickness of sediment along the Wisconsinan glacial border in the Slateford Creek watershed Northampton County, Pennsylvania, U.S.A. were mapped for ground water resource development and protection planning. The Slateford Creek watershed (7.5 km²) is on the southeastern slope of Kittatinny Mountain. It is underlain by ridge-forming quartz sandstone and conglomerate units and slate, slaty-shale and graywacke which form the primary water-bearing bedrock units. Prominent joint orientations, bedding, and cleavage are NE striking. A less prominent, conjugate joint set strikes northwestward as does a fracture set (305/76N and 321/50S) apparently related to folding. Published fracture traces did not correspond to prominent structural orientations. Straight stream segments trend NE, suggesting exploitation of that structural fabric by geomorphic processes. The NE trending fractures are likely dominant pathways for ground water flow. End moraine and ground moraine till cover much of the area and are important contributors of water to underlying bedrock. A saturated lag gravel unit along the axis of a buried valley was identified as an aquifer. Understanding the geometry of the unconsolidated deposits is crucial for developing an accurate conceptual model for ground water flow, developing new ground water sources, and providing boundary conditions for wellhead protection area delineation. The geometry was ascertained by constructing a detailed isochore map from field observations, drilling logs and residual gravity anomaly data. Power spectra analysis of gravity data showed dominant source depths at 150 ft., 60 ft., and 10ft.; consistent with borehole data. Bedrock topography derived from DEM and isochore data suggested a buried bedrock divide within the watershed and that end-moraine deposits have diverted southward drainage from the western portion of the watershed. The suggested lack of coincidence of ground water and surface water divides has important implications for ground water flow patterns and water budgets.