DGS Well Ec32-07
This report presents a new time-stratigraphic framework for the subsurface Potomac Formation of New Castle County, Delaware, part of adjacent Cecil County, Maryland, and nearby tie-in boreholes in New Jersey. The framework is based on a geophysical well-log correlation datum that approximates the contact between Upper and Lower Cretaceous sediments. This datum is constrained by age determinations based on published and unpublished results of studies of fossil pollen and spores in samples of sediment cores from boreholes in the study area.
In recent years there has been a renewed interest by both amateur and professional paleontologists in the rich upper Cretaceous exposures along the Chesapeake and Delaware Canal, Delaware (Fig. 1). Large quantities of fossil material, mostly clams, oysters, and snails have been collected as a result of this activity. Recent dredging (1978, 1981) by the United States Army Corps of Engineers has helped expose a rich vertebrate fossil assemblage. It includes representatives from the classes Reptilia, Osteichthyes, and Chondrichthyes.
Fluvial sands of the subsurface Cretaceous Potomac Formation form a major aquifer system used by a growing population in the northern Coastal Plain of Delaware. The aquifer is extremely heterogeneous on the megascopic scale and connectivity of permeable fluvial units is poorly constrained. The formation is characterized by alluvial plain facies in the updip section where it contains potable water. While over 50 aquifer tests indicate high permeability, the formation is primarily composed of fine-grained silt and clay in overbank and interfluvial facies.
To understand the effects of projected increased demands on ground water to supply water, a finite-difference, steady-state, nine-layer, groundwater flow model was used to simulate groundwater flow in the Coastal Plain sediments of southern New Castle County, Delaware. Results are published in DGS RI77