HYDROGEOLOGIC FRAMEWORK AND GROUND WATER CONDITIONS IN THE NORTH CAROLINA CENTRAL COASTAL PLAIN

The population of the North Carolina Central Coastal plain historically has relied heavily on the Cretaceous Black Creek and upper Cape Fear aquifers for water supply. Estimated total pumping rates from these aquifers have increased from 120,000 gallons per day in 1910, to 116 million gallons per day at present. As indicated by water level measurements from ground water monitoring wells, the potentiometric surfaces of these aquifers have been declining since the year 1900. For the last 25 years, water levels have been dropping at a rate of 2 to 8 feet per year, forcing many well field operators to lower pump intakes in order to maintain water supply. Declining water levels have resulted in a loss of yield of the aquifers in many well fields, and over certain areas in the Central Coastal Plain have resulted in aquifer dewatering.

The system of eight regional aquifers and intervening confining units found in the Quaternary through Cretaceous age sedimentary wedge beneath the Central Coastal Plain were delineated in terms of their lateral distribution, thickness, hydraulic properties, and relationship to stratigraphic units. Moreover, aquifers were described in regard to ground water flow interactions, distribution of salt water and chloride concentrations, and natural or pump induced ground water movement. A regional network of cross sections was constructed across the study area in order to trace the lateral distribution and thickness of hydrogeologic units. Maps of the elevation of the tops of units were constructed, along with maps of the thickness of aquifers and confining beds, and the percentage of permeable material and net thickness of permeable material of each aquifer. Potentiometric surface maps were prepared for the Peedee, Black Creek and Upper Cape Fear aquifers using water level data collected by the NC Division of Water Resources.