The Ground Water Characterization Program

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The Ground Water Characterization Program Helping
Secure Virginias Ground Water Resources For The
Future
The DEQ Office of Ground Water Characterization
is tasked with improving the understanding of
Virginias ground water systems. One component
critical to that effort is obtaining bore hole
geophysical logs. Bore hole geophysical logging
involves lowering electronic tools into wells and
boreholes to measure different properties. The
data collected is displayed graphically in
vertical strip charts as shown at the right.
DEQ stores, transports and operates their state
of the art computer controlled bore hole
geophysical logging equipment in a specially
modified vehicle. The truck is climate
controlled so it can be used in all weather,
except lightning, and it is equipped with four
wheel drive so it can reach almost any site a
drill rig can access. The cable and draw works
are capable of logging holes in excess of 2,500
feet deep.
Once a sufficient number of bore hole geophysical
logs have been collected in a given area,
hydrogeologic cross sections are created that
illustrate the underlying geology as shown below.
The geologic conditions control the movement
and occurrence of ground water and form the
framework for computer models utilized to predict
future ground water availability.
These charts are then interpreted by DEQ Ground
Water Geologists who identify and delineate the
specific water bearing zones, called aquifers,
from the non water bearing zones, called
confining units, as shown above. This
information also identifies the most productive
areas within the aquifer allowing well screens to
be placed in the best possible locations for
obtaining water.
Continuing growth in historically rural areas of
Virginias Coastal Plain is causing concern over
future ground water availability and expansion of
the Ground Water Management Area is a
possibility. Bore hole geophysical logs are
required for ground water withdrawal permits
issued in Virginias ground water management area
and obtaining them at the time of drilling is
easily done.
For more information contact Scott Bruce DEQ
Groundwater Characterization Program Phone
[phone] Email taylor.bruce_at_deq.virginia.g
ov
GWCP Fact Sheet 001-2010
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Using geophysical logs to place well screens
Case study Five public water supply wells in
Virginias Coastal Plain were drilled on a 75
foot by 100 foot parcel between 1960 and 2007.
All 5 wells were logged by their respective
drillers but only the most recent, well 5, was
also logged with down hole geophysical logging
equipment. The partial printout at the right
illustrates how DEQ Ground Water Geologists
utilized the data to identify the aquifers and
confining zones underlying the site and selected
the most productive water bearing zones within
the aquifer (blue cross hatching) for well screen
placements. You can see how the previous well
screens missed the best positions in the aquifer
with part of one screen even being placed in the
overlying confining unit (red cross hatching).
Nanjemoy/Marlboro Confining Zone
Aquia Aquifer
Well 4 Screens
Upper Potomac Confining Zone
Well 5 Screens
Well 3 Screen
Well 2 Screen
Well 1 Screen
Well 1 Specific Capacity 0.97
Upper Potomac Aquifer
Well 2 Specific Capacity 2.75
Well 3 Specific Capacity 2.75
Well 4 Specific Capacity 3.53
Well 5 Specific Capacity TBD