A retail establishment in an area underlain by blue gneiss, a hard metamorphic rock not known for its water bearing capacity except along fractures and joints, needed an on-site water well to supply its water use and emergency use requirements. GTS was asked to survey the five acre property to determine where to best locate a water well. The regulatory setbacks from property lines, buildings, roads and lots, and septic systems limited greatly the available locations for a water well.

GTS recommended a two step investigation consisting of a fracture trace survey and a VLF WADI survey. The fracture trace survey uses high resolution aerial photography to seek out subsurface fractures and joints that are visible as subtle linear or near linear features on the photographs. The WADI survey uses special very low frequency (VLF) transmitters, which are located around the world. The radio energy travels through the upper crust of the earth and concentrates along fractures and joints in the bedrock, which is also where groundwater can concentrate. GTS used an ABEM WADI VLF meter to collect measurements along several profiles crossing the site. The fracture trace information indicated that there were two major directions of fracture development so the VLF profiles were oriented roughly perpendicular to these fracture directions. VLF stations located geographically along the fracture directions were also selected as radio sources.



The VLF profiles located five major intersections of fractures or joints within the property boundaries. Only the weakest of these fracture intersections was located in one of the few areas where a well could be drilled without violating setback restrictions. GTS recommended to the client that the best location was sufficiently desirable that a setback waiver should be sought and special wellhead protection construction should be used to place the well in the best location.






METHODS
Electrical Resistivity
Terrain Conductivity
Very Low Frequency
Spontaneous Potential
Seismic Refraction
Ground Penetrating Radar
Magnetometry
Vibration Monitoring
Soil Resistance Testing


CASE HISTORIES
Archaeology
Bedrock Delineation
Ground Penetrating Radar
Groundwater Availablity
Mining 1
Mining 2
Sinkhole Investigations
Sinkhole Investigations 2
Soil Resistance Testing
Underground Storage Tanks
Vibration Monitoring




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