C
hris Taylor, Public Works Director with
the Town of Liberty, contacted me to ask
whether the location for their new well was
in a good spot to obtain water. Liberty is
in the Piedmont of North Carolina in the
northeast corner of Randolph County. I told
Chris that sometimes prime locations for
high yielding wells can be located on aerial
photographs, topographic maps, or geologic
maps. Geologists look for dark areas or
vegetation on aerial photos that occurs in
lines, or “lineaments.” These lineaments
can indicate faults, joints, or cracks that can
mean high-yield wells. On topographic maps,
the structure of the underlying bedrock can
sometimes be revealed in the flow patterns of
the local rivers and streams, or the orientation
of hilltops and ridgelines. Geologic maps also
show the rock types and any faults or other
structures that can be exploited for water.
I readily agreed to take a look, on the provision
that you get what you pay for, and I wasn’t
charging anything. Also, I told Chris that he
needed to update his wellhead protection plan,
and I offered to help renew his plan if I looked
at his situation.
As always, I cautioned Chris that productive
wells have boreholes that intersect large or
numerous cracks in the bedrock that provide
water to the well, and that intersecting these
zones is a matter of some luck. But there are
some locations that statistically will provide
a better chance of a high yield. Avoiding
hilltops and ridges for well locations is a
good thing to do in the Piedmont, as the hills
and ridges are there because they resisted
erosion due to structural integrity (they
didn’t have many cracks for erosion to make
headway). Few cracks in the bedrock means
less chance of high yield.
Fortunately, Rural Water is equipped
with the Geographic Information System
program ArcMap
©
, and we have access to
high resolution aerial photos, topo maps,
and the Geologic Map of North Carolina
as layers. Public Water Supply Section
provided a layer showing the location, depth,
and yield of public water supply wells, and
online resources (NC OneMap) gave a layer
showing the surface water features across
the state.
Aerial photography showed the Town of
Liberty, the drainage in the area, and the road
network, but little else. No lineaments were
revealed and nothing was readily apparent
from the air, except the numerous man-made
ponds and impoundments. There is plenty of
surface water in the vicinity of Liberty and
this bodes well in the search for groundwater.
A first look at surface water flow patterns
showed a tree-like set of branching streams
(called a dendritic drainage pattern) that drain
water away from the center of Liberty, which
is located on high ground. Dendritic drainage
patterns indicate that the underlying bedrock
is relatively homogenous and has been
evenly eroded, except for the high ground
centered on Liberty. Surface drainage patterns
and topo maps revealed little in Liberty’s
quest for water, so next I took a look at the
geology. I told Chris that he would probably
want to avoid the middle of Town for a well
location because of the increased chance of
leaks or spills that could contaminate the water
table, and the gentle hilltop centered on the
Town limits.
Liberty is located squarely in the Carolina
Slate Belt of North Carolina. These rocks were
mostly deposited on or near the earth’s surface
by volcanic eruption and sedimentation
during the Cambrian period, more than 500
million years ago. Because the rocks are very
old, they have been changed by temperature
and pressure into low-grade metamorphic
rocks. Sometime during the Triassic-Jurassic
period, (about 200 million years ago) the slate
belt rocks were cut into by molten, iron-rich
basalts (diabase) in the form of nearly vertical
tablets, or dikes.
By Keith Starner, P.G.
S
earching
for
W
ater
in
L
iberty
12
|
Winter 2014
feature
