Groundwater Development Investigations

Groundwater 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.

ER 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.

Electrical resistivity profile across piedmont Virginia terrain

Fracture Traces superimposed onto aerial photography

Example of fracture and joint patterns in outcrop on Cadillac Mountain, Acadia National Park

Above: 60 GPM (YES!!)

 300 GPM !!! (That' a Weir...)