Hydrogeological Characteristics And The Effect Of Industrial Water Usage On The Regional Hydrology Of The Coastal Plain Of Northern New Castle County, Delaware

Abstract

Hydrogeological characteristics, including the elevation of the potentiometric surfaces of the major aquifers and their fluctuations over a 5-year period (1990-1994) in the coastal plain of New Castle County, Delaware, are discussed in detail in this study. Fluctuations in water levels and well production rates from data collected over a 15-year period (1980 to 1994) from more than 30 production - and 20 monitoring wells in the study area reveal that pumping in the tens of thousands of cubic meters (millions of gallons per day) has lowered potentiometric surfaces near major industrial wellfields by 20 meters or more. Since around the mid-l 970s equilibrium has been established between recharge to the aquifer system via annual rainfall and discharge from the aquifers through seepage into surface water bodies and industrial water usage. However, industrial, municipal, and agricultural users continue to place great demand on the aquifer system, and the centers of several cones-of-depression near industrial-use wellfields are now well below sea level. A steady-state simulation of regional flow aids in conceptualization of the interaction between the stresses which affect the regional aquifer system. The lowering of water levels by withdrawal of large amounts of water for industrial use opens the possibility of subsidence near the larger wellfields. Additionally, large cones-of-depression cause reversal of flow gradients, thereby complicating remediation efforts (such as those proposed for CERCLA sites, e.g. the Delaware City Industrial Zone) and potentially creating a water quality problem of salt-water intrusion from the nearby Delaware River estuary.