1. Southeastern Section - 62nd Annual Meeting (20-21 March 2013)Hydrogeological
Investigations in the U.S. and the Caribbean (Posters) Wednesday, 20 March 2013:
8:00 AM-5:30 PMCaribe Hilton San Cristobal Ballroom Geological Society of America
Abstracts with Programs. Vol. 45, No. 2, p.12
SOUTHEASTERN UNITED STATES PIEDMONT HYDROGEOLOGY: IMPROVING
OUR UNDERSTANDING OF GROUNDWATER FLOW IN SAPROLITE AND IN
FRACTURES OF PARTLY WEATHERED AND UNWEATHERED CRYSTALLINE
METAMORPHIC AND IGNEOUS ROCKS: OCCURRENCE AND MIGRATION OF
GROUNDWATER IN CRYSTALLINE ROCKS, FRACTURES AND IN SAPROLITE
Paper No. 7-6 Presentation Time: 8:00 AM-5:30 PM
PRIVETT, Donald R., 1 Circle St, Great Falls, SC 29055, drprivett@gmail.com
''We shall never cease from exploration and the end of all our exploring will be to arrive
where we started and know the place for the first time.” T. S. Eliot critic, dramatist & poet
(1888–1965)
Complex processes of groundwater flow (GF) in Piedmont rocks is not entirely
understood even after 60 years of study by many prominent hydrogeologists and
geologists. GF is near chaotic because time and spatial interrelated and intra-related
ever changing, extremely complex, almost indecipherable and indeterminable variables.
Changes from surface soils to underlying clay-rich saprolite to partially weathered rock
to fractured unweathered rock yield a highly transitory complex system. Saprolite and
residual soils are present in over 95% of the surface area and to depths of 20 - 80 feet
in most areas.
The mineral composition of the parent rock, the degree of weathering and its thickness,
mineral grain orientation, presence of veins, joints, and shear zones, the orientation of
the foliation, differential flow, and other factors determine specifics of seepage and
water flow.
Surface and near-surface materials are divided into:
1.Regolith zone (alluvium, soil a and b horizons) is unconsolidated or semi consolidated
mixture of clay and fragmental material ranging in size from silt to cobble size. The
saturated regolith provides the water storage most groundwater system and supplies
water to any interconnected fractures.
2.Transition/saprolite zones serve as conduits for rapid movement of groundwater,
saprolite merges below with partly weathered rock and underlying unweathered
fractured crystalline bedrock. Crystalline rocks have principal openings along fractures,
that decrease with depth.
3.Saprolite/partially weathered rock. Saprolite deposits retain the texture from the parent
rock, the chemical composition, is altered to a clay-rich material derived from in-place
weathering of bedrock.
4. Bedrock may be unweathered, gradational and may be mixed partly weathered with
unweathered core stones. Clay filled bedrock joints and fractures, may serve as
channels for fluid flow and have a greater directional permeability than saprolite.
Piedmont bedrock has very few fractures at depths greater than 400 feet (LeGrand,
1967).
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