Hydrogeologic framework of U.S. Marine Corps Base at Camp Lejeune, North Carolina

Abstract

The hydrogeologic framework at Camp Lejeune consists of the surficial, Castle Hayne, Beaufort, and Peedee aquifers and intervening confining units. The Castle Hayne aquifer furnishes about 7 million gallons of water per day to Camp Lejeune, but the surficial, Beaufort, and Peedee aquifers, which contain freshwater in places, are not used for supply. The Castle Hayne aquifer is composed of 60 to 90 percent sand and limestone with clay and silt beds, and ranges from 156 to 400 feet thick. Hydraulic conductivity of the aquifer ranges from 14 to 91 feet per day. The Castle Hayne confining unit, which overlies the Castle Hayne aquifer, is composed of silt and sandy clay and averages 9 feet thick where present. This confining unit is incised by the New River and its tributaries, as well as some paleochannels. The effects of pumping from the Castle Hayne aquifer have not significantly affected natural head gradients in the aquifer. However, the potential exists for lateral migration of saltwater where wells are located near streams or paleochannels that have incised the confining unit. Except for one measurement of 960 milligrams per liter chloride in a water sample from the bottom of the Castle Hayne aquifer, dissolved-chloride concentrations in water samples from the Castle Hayne aquifer were less than 120 milligrams per liter. It is not known whether this occurrence of saltwater in the Castle Hayne aquifer is widespread or localized, but its presence indicates a potential for upward movement of saltwater beneath pumped wells. From 1987 to 1989, geological, geophysical, and hydrologic data were collected and integrated with existing data from more than 180 wells. Nine test wells were constructed to obtain stratigraphic, lithologic, and hydrologic data. Borehole geophysical logs, driller's logs, and drill cuttings were examined, interpreted, and correlated to establish the lithology and stratigraphy of the freshwater-bearing aquifers and confining units. Hydrogeologic sections and maps of the thickness and altitude of the tops of the aquifers were constructed to provide the basis for correlation and interpretation of the data. These define the framework consisting of the surficial, Castle Hayne, Beaufort, and Peedee aquifers and intervening confining units.