Observations in Granite Quarries Facilitate Understanding the Hydrogeology of the Georgia Piedmont

Abstract

Because the crystalline bedrock of the Piedmont Province in Georgia is so poorly exposed, it can be difficult to readily understand how water flows in the subsurface and why bedrock well yields in the Piedmont are so variable. Quarries provide an easy way to visually observe how the hydrogeology in this terrain operates. There are numerous quarries in the Elberton area and elsewhere that show excellent exposures of both the overlying regolith and bedrock, the principal components of the aquifer system of the Piedmont. Within the exposed bedrock, it is readily apparent that water is transmitted in only a few fractures. Most fractures show evidence of little or no water movement. Fractures that yield relatively large amounts of water are mostly shallow, are generally extensive, and appear to be connected to the overlying regolith, the principle reservoir for groundwater. Deeper fractures appear to transmit little water, perhaps because they are less abundant and have smaller apertures due to the overlying lithostatic load. Even those fractures that appear to transmit relatively large amounts of water may actually have very small apertures. Calculations using the cubic flow law indicate that fracture apertures for typical flow rates are quite small, with very small fracture porosities, despite their appearance at the surface of the quarry to the contrary.