Map of study area and data collection sites

Onslow County Region Ground-Water Flow

Monitoring well, Onslow County

Background

For the past three decades, ground-water levels in the central Coastal Plain of North Carolina have declined as much as 200 feet (ft) from overpumping and depletion of storage in the Black Creek and Upper Cape Fear aquifers of Cretaceous age. Because of these declines and the resulting increased potential for lateral saltwater migration along the coast and upward leakage of brackish water from deeper aquifers, the North Carolina Division of Water Resources instituted the Central Coastal Plain Capacity Use Area (CCPCUA) rules for 15 counties, effective August 1, 2002. Under the CCPCUA rules, ground-water withdrawal of more than 100,000 gallons per day from any of the Cretaceous aquifer systems is subject to a water-use reduction of as much as 75 percent over a 16-year period. Ground-water users in Onslow County that withdraw from the Cretaceous aquifers are subject to the CCPCUA rules.

The effects of the increased development of the Castle Hayne aquifer and the decreased use of the Black Creek aquifer are unknown. In 2007, the U.S. Geological Survey, in cooperation with the City of Jacksonville, Onslow Water and Sewer Authority, and the Marine Corps Base Camp Lejeune, began an investigation to delineate and describe the ground-water flow system in the Onslow County area. A computer base groundwater model will be created for all aquifers which underlie Onslow County Region.

Objectives

The objective of the proposed study is to develop and apply a ground-water flow and salt-transport model that can be used to analyze the effects of various scenarios that will enable water-resource managers to effectively manage ground-water withdrawals in Onslow County to ensure that the ground-water resource is sustainable and saltwater intrusion is minimized. A variable-density ground-water flow model will be developed for the surficial, Castle Hayne, Beaufort, and Cretaceous aquifer systems in Onslow County.

Approach

The objectives of the project will be completed in 3 phases:

• Phase 1: Assemble pertinent hydrogeologic data.
• Phase 2: MODFLOW Model Development and Calibration.
• Phase 3: Simulate Management Scenarios, Develop Dual Density Model, and publish model documentation and findings.