Table 2 - Summary of selected technologies used to characterize groundwater flux and velocity in fractured rock.

Method Scale Examples Instrumentation/Description
Darcy-based methods
  • generally, ~10 m to ~100m separation between wells
  • local to regional investigations common
  • risk of misleading interpretation unless the equivalent porous medium (EPM) assumption is validated
  • conventional site investigation based on water level survey and estimation of hydraulic conductivity (K)
  • wells and water level tapes or sondes
  • measure head in wells for gradient across domain and obtain domain K value - data collection requires minutes per well
  • packer testing may be performed to characterize hydraulic properties of fractures to support Darcy calculations
Tracer tests
  • meters to kilometers
  • dye tracers (Aley, 2002)
  • tracer poured into well or recharge site
  • tracer detected by water sampling or with passive solid sorbent samplers
  • isotopes (Cook, 2020)
  • active injection followed by water sampling
  • sampling only following tracer introduction by spill or natural source
  • salts (Luhmann et al., 2012)
  • active injection followed by water sampling
  • colloids (McKay et al., 2000)
  • active injection with a two-well injection-withdrawal system
  • dissolved gases (e.g., He, SF6) (Gupta et al., 1994; Vulava et al., 2002)
  • active injection followed by water sampling
Single borehole techniques
  • centimeter-scale measurements geared to locations where fractures cross the borehole
  • larger scale flow patterns possible with multiple wells and complimentary information from other methods
  • borehole dilution and FVPD (Brouyere et al., 2008)
  • packers to isolate the borehole section of interest, tracer injection system, sampling/datalogging
  • Flute liner
  • pressure log
  • temperature profile (Peheme et al., 2010)
  • pressure profiling during installation can identify depths of major fractures
  • temperature profiling next to liner to identify zones of high water-flux - with heating and subsequent return to background temperatures, flow rates may be inferred
  • FRPFM (fractured rock PFM) (Levison and MacDonald, 2014)
  • instrument supplied by vendor, suspended in well for days to weeks, packer system required
  • return to vendor for analysis
  • ORP (oxidation-reduction profiling)
  • (Sale et al., 2020)
  • sensors suspended in borehole and passively sense variations in water redox chemistry with depth - depths of greatest variations suggest depths of water flux from fractures
  • requires datalogger for longer-term data collection
  • IWPVP
  • (Osorno et al., 2018)
  • instrument positioned across fracture for testing
  • requires injection system and datalogger