Hydrogeologic unit map of the Piedmont and Blue Ridge Provinces of North Carolina
Water-Resources Investigations Report 90-4035
By C.C. Daniel, III and R.A. Payne, R.A.
Abstract
The numerous geologic formations and rock types in the Piedmont
and Blue Ridge provinces of North Carolina have been grouped
into 21 hydrogeologic units on the basis of their water-bearing
potential as determined from rock origin, composition, and
texture. All major classes of rocks--metamorphic, igneous, and
sedimentary--are present, although metamorphic rocks are the
most abundant. The origin of the hydrogeologic units is
indicated by the rock class or subclass (metaigneous,
metavolanic, or metasedimentary). The composition of the igneous,
metaigneous, and metavolcanic rocks is designated as felsic,
intermediate, or mafic except for the addition in the
metavolcanic group of epiclastic rocks and compositionally
undifferentiated rocks. Composition is the controlling attribute
in the classification of the metasedimentary units of gneiss
(mafic or felsic), marble, quartzite. The other metasediments
are designated primarily on the basis of texture (grain size,
degree of metamorphism, and development of foliation).
Sedimentary rocks occur in the Piedmont in several downfaulted
basins. A computerized data file containing records from more
than 6,200 wells was analyzed to determine average well yields
in each of the 21 units. The well yields were adjusted to an
average well depth of 154 feet and an average diameter of 6 inches,
the average of all wells in the data set, to remove the
variation in well yield attributed to differences in depth and
diameter. Average yields range from a high of 23.6 gallons per
minute for schist to a low 11.6 gallons per minute for
sedimentary rocks of Triassic age.
Citation:
Daniel, C.C., III, and Payne, R.A., 1990, Hydrogeologic unit map of the Piedmont and Blue Ridge Provinces of North Carolina: U.S. Geological Survey Water-Resources Investigations Report 90-4035, 1 sheet, scale 1:500,000.
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North Carolina Water Science Center
U.S. Geological Survey
3916 Sunset Ridge Road
Raleigh, North Carolina 27607
(919) 571-4037
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