Project Overview

Full Title
Cherry Point paleochannel delineation

Location
The MCAS at Cherry Point in Craven County

Cooperating Agencies
MCAS Cherry Point, NC

Project Chief
Beth Wrege

Period of Project
2004-2007

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Cherry Point Paleochannel Delineation

Project Summary

Drilling rig at Cherry Point, operated by Eugene Cobbs II and Eugene Cobbs III

Background

The U.S. Marine Corps Air Station (MCAS), Cherry Point, North Carolina, in southeastern Craven County, is in the Coastal Plain Physiographic Province. The MCAS is underlain by four freshwater aquifers -- the surficial, Yorktown, and the upper and lower Castle Hayne aquifers. Deeper aquifers in this area contain saline water. The upper and lower Castle Hayne aquifers are the principal water supply sources for the MCAS and surrounding communities. Beneath the MCAS, the upper Castle Hayne aquifer is composed of sands and sandy shell beds of the Pungo River Formation and limestone of the River Bend Formation. The lower Castle Hayne aquifer is composed of interbedded limestones, sandy limestones, and calcareous sands of the Castle Hayne Formation. The aquifers are separated by clay confining units that are locally discontinuous because of depositional and erosional truncations, including some that are associated with paleochannels. Where present, a confining unit above the Castle Hayne aquifer impedes the downward movement of potential contaminants to the water supply. If the confining unit overlying the Castle Hayne aquifer is absent or portions of it are missing, the lack of confinement could provide a conduit for movement of contaminants from the surficial aquifer to the water-supply aquifer.

Mike Stroble and Beth Wrege examining core from the Cherry Point drill site

Objectives

1. Using land seismic and borehole geophysical techniques, identify and map the occurrence of paleochannels in the subsurface to determine where vertical leakage can occur between surface deposits and the primary water supply aquifer beneath the Cherry Point MCAS.

2. Compile paleochannel and hydrogeologic information to establish a reliable hydrogeologic framework adequate to refine and revise an existing flow model constructed for the Cherry Point MCAS and surrounding area.

Approach

Lithologic descriptions were made from the cores, which also provided information on formation contacts, ages, and relative hydrologic properties. Borehole geophysical logs, particularly natural gamma logs, were used to correlate stratigraphic relations relative to other test holes. High-resolution seismic-reflection profiles were used to correlate stratigraphic units between test holes and to identify discontinuities in the confining units. In combination, the core descriptions, borehole geophysical logs, and seismic-reflection data were used to create hydrogeologic sections representing the subsurface at the MCAS.