in the Piedmont and the Valley and Ridge Provinces of Virginia is stored in the
saprolite zone of the subsurface (the area between the subsoil and hard bedrock).
In some cases, this zone can reach tens of meters in thickness and, depending
upon locality, has the potential to store an enormous volume of water. This serves
as the reservoir of groundwater in fractured bedrock settings. Accessing this
reservoir of water is achieved by drilling wells in precise locations that
intersect interconnected, highly transmissive, fractured zones of the deeper bedrock.
Bedrock fractures are
often manifested as straight-line features (lineations) in the surface and are
mapped via Fracture Trace Analysis of stereo-aerial photographs. The number, length
and orientation of these fractures are important aspects in groundwater prospecting.
True North identifies these features and often follows this up by conducting a method
of geophysics known as High Resolution Electrical Resistivity (ER) Imaging.
surveys measure relative resistivity values in the deep bedrock and are used to
verify the occurrence of observed lineations, to expose water-bearing fractures
that go undetected by fracture trace analysis and as a tool to determine final
drilling locations. These surveys are usually conducted where large volumes of
water are desired, or where fracture trace analysis has been unsuccessful.
resistivity profile across piedmont Virginia terrain
Traces superimposed onto aerial photography
of fracture and joint patterns in outcrop on Cadillac Mountain, Acadia National
300 GPM !!! (That' a Weir...)