ANALYSIS OF SPRING DISCHARGE FOR CHARACTERIZATION OF GROUNDWATER FLOW IN THE BLUE RIDGE PROVINCE, VIRGINIA

Low discharge (<6gal/min) springs are ubiquitous in the fractured crystalline rocks of the Blue Ridge Province of the Eastern United States. Many of these springs flow perennially with little variation in discharge between seasons and are often used as potable water sources. Establishment of a springhead protection program requires a better understanding of the source and flow paths for these springs. It is anticipated that three or more flow regimes may be responsible for the discharge at the springs in the Province. These regimes include: variable phreatic flow through highly heterogeneous regolith and saprolite, interconnected fracture pathways within the crystalline bedrock, and a porous media type flow along intensely fractured fault planes.

Investigation of the various flow pathways is being approached using surface resistivity measurements, analysis of spring-flow hydrographs and chemical water analyses to reveal the source of the water discharged at the springhead. Recent investigations incorporating these techniques indicate that the sources for these springs is likely connected to flow along high-transmissivity fault planes or interconnected fractures associated with thrusting. Additionally, the Blue Ridge groundwater system is very heterogeneous with large, complex variations in bedrock, saturation, and available water resources. Multiple flow pathways produce characteristic recession curves on springflow hydrographs. Springflow hydrographs collected in a Floyd County, VA study area reveal one or two dominate pathways that may respond quickly to rainfall events. Recent surface resistivity imaging surveys combined with chemical groundwater characterization indicate a deeper source of water and possible mixing of shallow and deeper water for the same spring.

Correct characterization of groundwater systems will help lead to source water protection strategies that predict or prevent groundwater contamination in this region.