Hydrogeologic Evaluation Of The North Branch Of The Neshaminy Creek Watershed Bucks County, Pennsylvania

Abstract

The North Branch of the Neshaminy Creek Watershed is located near Doylestown in Bucks County, Pennsylvania. As has happened in many other suburbs of Philadelphia, the development of the North Branch Watershed has increased the demand on its water resources. This hydrogeologic study evaluates the Lockatong Formation's geologic control upon the hydrology of this watershed. Hydrogeologic information for this study was collected from March 1986 to May 1987. Investigations conducted during this study include geologic field observations of bedrock, a fracture trace analysis, a morphometric analysis of the North Branch stream network, establishment of a stream gauging network, establishment of a monitoring well network, measurement of Lake stage, establishment of a rating curve for a weir measuring the surface water outflow from the watershed, a pump test, monitoring the well recoveries of newly drilled wells, logging well drilling, an analysis of surface and groundwater quality and the formulation of a water budget. Ninety (90) percent of the North Branch watershed is underlain by the Lockatong Formation. The Lockatong Formation produces the primary geologic control of North Branch hydrology. This study proposes that the Lockatong Formation in the North Branch watershed has produced leaky confined groundwater conditions. Within this leaky confined groundwater system it has been suggested that the tilted Lockatong shale beds act as semi-confined aquifers transmitting groundwater coplanar to the Lockatong Formation bedding. Vertical groundwater leakage within this semi-confined system is allowed by sets of vertical fractures observed to exist within the Lockatong. Within this model of groundwater flow vertical fractures and shales not only provide means of transmitting groundwater, but also provide conduits for accepting groundwater recharge and discharging baseflow into streams.