Marine Seismic-Reflection Profiling To Define Hydrogeologic Continuity At Camp Lejeune, North Carolina

Continuous marine seismic-reflection-profiling data were correlated with<br>land-based borehole geophysical and lithologic data to define the hydrogeologic<br>framework of Camp Lejeune Marine Corps Base in part of the Coastal Plain<br>Province of southeastern North Carolina. Marine seismic profiling was<br>particularly useful at Camp Lejeune because 25 percent of the study area is<br>covered by the New River estuary system.<br>A medium-power, wide-frequency seismic system was used to collect<br>continuous single-channel, shallow-marine seismic-reflection-profiling data for<br>more than 100 miles of transects across the estuary. Positioning of the boat<br>equipped with seismic instruments was controlled by an onboard integrated<br>navigation system; LORAN C and Global Positioning Systems' were integrated to<br>continuously plot boat position.<br>Onshore borehole geophysical and lithologic data were compared with<br>seismic data. A borehole acoustic-velocity log was used to generate an average<br>acoustic-velocity curve for the sediment, which was then used to convert the<br>seismic travel time to depth. The acoustic-velocity, single-point resistance,<br>and gamma-ray log data were adjusted for altitude and dip and correlated with<br>the seismic data.<br>Hydrogeologic sections constructed using these correlations show that the<br>combined thickness of the surficial, Castle Hayne, and Beaufort aquifers ranges<br>from approximately 200 feet at the western edge of the study area to approximately<br>490 feet at the eastern edge. Three sections of buried river channel<br>have been identified within the Castle Hayne aquifer underlying the New River<br>by seismic-reflection-profiling data. One of these channels has been correlated<br>with well-log data. Buried channels, if filled with permeable material,<br>can function as conduits for ground-water flow, thereby facilitating movement<br>of contaminants from land surface, or saltwater migration from the estuary to<br>supply wells.