The Camp Lejeune Marine Corps Base occupies 164 square miles in the Coastal Plain of North Carolina, including 30 square miles of the New River estuary that bisects the Base. As much as 1,500 feet of unconsolidated or partly consolidated sand, limestone, silt, and clay beds that contain seven aquifers separated by six confining units underlie the Base. Freshwater is present in aquifers to a depth of about 300 feet in the area and is the principal water-supply source for the Base. Ground-water withdrawn for the military and civilian population of about 68,000 at the Base increased from about 4 million gallons per day in 1941 to more than 7 million gallons per day in 1986. In the last decade, water demand has not increased substantially; however, certain wells have been discontinued, and new wells have been drilled in different locations. Well-acceptance tests indicate an average specific capacity of 6.3 gallons per minute per foot of drawdown for 33 wells finished in the Castle Hayne aquifer. Estimates of transmissivity based on estimated specific capacities that were adjusted to represent full aquifer penetration, ranged from 4,300 to 24,500 feet squared per day and had an average of 10,200 feet squared per day; the average estimated hydraulic conductivity is 35 feet per day. Records for more than 160 wells indicate that the average water-supply well at the Base has a depth of 162 feet, a casing diameter of 8 inches, about 37 feet of well screen, and a yield of 174 gallons per minute. Ground-water level naturally fluctuates as much as 4 feet seasonally, but effects of pumping on water-level fluctuations are much greater, depending on the rate of pumping and proximity to production wells. Natural ground-water discharge from the Castle Hayne aquifer is to the New River and the Atlantic Ocean. The hydraulic gradient in the Castle Hayne aquifer is 5 to 15 feet per mile in areas unaffected by pumping and is as much as 200 feet per mile within major pumping centers. Estimated velocities of ground-water movement range from 0.06 to 16 feet per day. The specific conductance of water in wells ranged from 251 to 1,213 microsiemens per centimeter. Wells that contained water with specific conductance values greater than 800 microsiemens per centimeter are suspected of being affected by saltwater. Freshwater bearing deposits consist of two aquifers: the surficial aquifer and Castle Hayne aquifer. Clay beds within the Castle Hayne aquifer are less than 30 feet thick, are discontinuous, and comprise between 15 and 24 percent of the aquifer. Additional test holes are needed to fully describe the hydrogeologic framework in the central and southwestern parts of the study area. Observation wells are needed in the beach areas of the Base and near the Air Station.