Structural and Lithologic Controls on Ground-Water Availability in a Granite and Biotite Gneiss in the Conyers, Georgia, Area
Author(s)
Khallouf, Donna D.
Williams, Lester J.
Advisor(s)
Editor(s)
Hatcher, Kathryn J.
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Abstract
Historically, the lack of primary permeability in crystalline rocks of the Piedmont physiographic province of Georgia was believed to result in
low ground-water yields. However, focused study of
lithology, foliations, and fractures in crystalline rocks in
the vicinity of the city of Conyers, Rockdale County,
Georgia, shows that geologic controls can contribute to
high well yields in these rocks. Although surface
geologic mapping indicates that the Conyers area
primarily is underlain by granite gneiss, borehole video
images show that subsurface lithology is an interlayered
granite gneiss and biotite gneiss. Preferential weathering
of the biotite gneiss is a significant factor controlling
well yield. Most of the yield in each of the two wells
studied is from openings along lithologic contacts
between the granite gneiss and biotite gneiss, or from
openings along compositional layering within the
biotite gneiss. The biotite gneiss is thin at land surface,
but distinctive enough to be mapped. This geologic unit
could be useful for identifying high-yielding areas
within the granite gneiss.
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Date
2003-04
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Resource Type
Text
Resource Subtype
Proceedings