The application of ground penetrating radar for mapping fractures in plutonic rocks within the Whiteshell Research Area, Pinawa, Manitoba, Canada

Abstract Ground penetrating radar (GPR) has been applied in the Canadian Nuclear Fuel Waste Management Program to map structural features in the granitic and gneissic rock of the Canadian Shield. Field results confirm the theoretical analysis, which shows that useful signal penetration in excess of 60 m is possible in near-surface rocks of low electrical conductivity containing fresh and dilute groundwater. Effective probing distances are drastically reduced (less than 20 m) at greater depth (> 400 m) because of increased electrical conductivity associated with saline groundwaters. GPR has been applied successfully on profiles on outcrops and from boreholes. Examples of mapping low-dip fracture features in granitic and gneissic outcrops in the Whiteshell Research Area and in the tunnel and boreholes of the Underground Research Laboratory are presented. Results of a near-surface crosshole tomogrpahy survey in combination with surface radar reflection profiling are discussed in terms of combined effectiveness in mapping the continuity of fracture features below an overburden-covered area around and between boreholes. Hydraulic transmissivity values and water flow rates determined from hydraulic pump tests at discrete fracture intervals in the boreholes support evidence for the fracture interconnectivity interpreted from the radar surveys.