Piedmont and Blue Ridge aquifers consist of bedrock overlain
by unconsolidated material called regolith. Included in the regolith
are: saprolite, which is a layer of earthy, decomposed rock developed
by weathering of the bedrock; soil that develops on the upper part
of the saprolite; and alluvium, which is mainly confined to stream
valleys and may overlie soil, saprolite, and bedrock.
the crystalline rocks formed under intense heat and pressure, they
have few primary pore spaces, and the porosity and permeability
of the unweathered and unfractured bedrock are extremely low. This
does not mean, however, that these rocks will yield no water. Ground
water can be obtained from two sources: (1) the regolith, and (2)
fractures in the rock. Locally, where the crystalline rocks consist
of marble, the dissolving action of slightly acidic ground water
has created solution openings that yield large volumes of water.