Présentations Colloques

Determining the location and magnitude of volumetric groundwater fluxes in depth discrete intervals along open rock boreholes in a fractured aquifer is important for the management of contaminated sites and efficiency assessment of geothermal heat exchange systems. Measurements made under natural gradient conditions provide insight into the ambient flow system and determine long term plume behavior that drastically improve decision making capabilities. A recent study demonstrates an active distributed temperature sensing method (active DTS) applied in sealed boreholes can locate and differentiate zones with variable groundwater flow in fractured bedrock aquifers (Coleman et al., 2015). This presentation highlights an advancement of the field deployment and mathematical approach to provide quantitative estimates of groundwater fluxes along the full borehole length using active DTS. Validation of this technique requires a second, independent method such as the point dilution method (PDM). This method is well-established and provides flux estimates derived from the dilution of a tracer within intervals isolated by straddle packers. A new PDM system was developed by G360 at the University of Guelph, Canada by modifying a straddle packer system to allow both the application of the PDM, and to perform multiple, high resolution hydraulic tests such as rising and falling head, and constant head step tests in the same 1.07 m long interval without removing the packers. Hydraulic tests, especially constant head step tests, are conducted to avoid non-linear flow to improve estimation of apparent hydraulic. The active DTS and PDM techniques were applied in the same 12.50 cm diameter borehole at the Bedrock Aquifer Research Station on the University of Guelph campus. Seven intervals, accounting for 80% of the entire borehole transmissivity, presented volumetric fluxes ranging from 2 to 3000 m day, demonstrating large variability in local fractured zone flux. These same intervals have noticeable heat dissipation in the active DTS temperature profiles yielding corroboration of methods.