Title: Paleochannel Definition at Cherry Point Marine Corps Air Station North Carolina by Beth Wrege, U.S. Geological Survey, Raleigh, NC
1Paleochannel Definition at Cherry Point Marine
Corps Air StationNorth Carolina by Beth Wrege,
U.S. Geological Survey, Raleigh, NC
Well stratigraphic data, and seismic data, which
were located using GPS technology were added to
the GIS database. These data are being analyzed
to locate probable paleochannels under the Cherry
Point Marine Corps Air Station.
Paleochannel Definition at Cherry Point MCAS The
U.S.Marine Corps Air Station, Cherry Point, North
Carolina, is located in south-eastern Craven
County in the Coastal Plain physiographic
province. The USGS-WRD and the USGS-GD
drilled stratigraphic test wells to determine
the loca- tion of paleochannels underlying the
MCAS. Borehole-geophysical surveys and
vertical-seismic profiles were run in the
stratigraphic wells. Seismic-reflection and
ground-penetrating radar (GPR) data were
collected along seismic lines transecting the Air
Station. Global Positioning System (GPS)
equipment was used to locate the wells and the
seismic lines. The GPS equipment and software
allowed for direct download of the location data
into the database. The data collected during this
project will be spatially analyzed using
geographical information system (GIS) methods.
Velocity calibration of the seismic-reflection
data and the GPR was assessed for both
hydrogeologic unit definition and energy
signature based on vertical seismic profiling
(VSP) run in the stratigraphic core holes.
Borehole geophysical surveys including gamma,
em-induction, resistivity, and gamma-gamma were
run in select boreholes. These geophysical data
will be combined to develop cross sections that
will transect the base from west-to-east. The
cross sections will be used to define portions of
the paleochannels. The Air Station is underlain
by four freshwater-bearing aquifers - the
surficial, Yorktown, and upper and lower Castle
Hayne to a depth of about 500 feet. The sediments
are saturated with saline water below this
depth. The aquifers are separated by clay
confining units except where these units are
absent or discontinuous. Ground-water
contamination has been found in the southern part
of the Air Station. In this area, pumping from
supply wells has created a potential for downward
movement of ground water from the surficial and
Yorktown aquifers into the Castle Hayne aquifer.
The potential for movement of water from the
upper aquifers to the primary regional
water-supply aquifer is greatest in areas where
clay confining units are missing. The occurrence
of paleochannels in this area creates the
potential for absence of confining units between
aquifers. Therefore, the mapping of the
paleochannels will identify zones most likely to
allow for movement of water between aquifers.
Some of the results of this study are published
in WRIR 95-252, Daniel III, C.C., R.D.Miller, and
B.M.Wrege, 1996, Application of geophysical
methods to the delineation of paleochannels and
missing confining units above the Castle Hayne
Aquifer at U.S. Marine Corps Air Station, Cherry
Point, North Carolina U.S. Government Printing
Office, U.S. Geological Survey Water Resources
Investigations Report 95-4252, 106pp.
Core Drilling
Stratigraphic determinations of the hydrogeologic
framework under the MCAS are being developed
Geologists analyzed the core data on site and
designed the monitoring wells
Continuous Core was collected using a wireline
mud-rotary system
Core recovery averaged over 90 including
unconsolidated sand.
Seismic Reflection
Collection and analysis of the seismic reflection
data is a joint effort by USGS-WRD and Kansas
Geological Survey
Seismic Sources were a 30.06 source or a 20
pound hammer
Utilities including fiber optics, communication,
high-voltage power lines, steam lines, and
pressurized fuel-lines were mapped and located,
data line placement is then determined
A 240-channel array was used to collect seismic
data
Geophones were placed at four foot intervals, and
cables were run to connect the geophones with the
seisomograph.
GPS of Seismic and Drilling
A First-Order Benchmark was used as the Base
Station
Survey-Grade GPS equipment was loaded with a data
dictionary. The data were down-loaded directly
into the GIS without a re-key process.
GIS Analysis and Synthesis
Vertical Seismic Profiling for calibration