Constraining permeabilities in a large-scale groundwater system through model calibration

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Abstract

The range of field estimates of permeabilities in rocks of the Atikokan Research Area (ARA), Canada, has been reduced by calibrating a groundwater flow model of the ARA. The flow model was calibrated to the recharge component of the water balance and to measured freshwater heads in boreholes. A good match between field and simulated recharge, and between measured and simulated heads was obtained with two different permeability-depth distributions that differed by up to two orders of magnitude in places. Solute transport simulation of the distributions of total dissolved solids (TDS), chlorides (CI) and oxygen-18 (18O) in groundwater in the area was performed to further refine the permeability estimates. Vertical average linear groundwater velocities from the calibrated flow model were used in one-dimensional solute transport models of the system to generate depth-concentration profiles of TDS, CI and 18O. Recharge-, midline- and discharge-area models of both the fracture zones and the rock mass were employed. The midline area is the narrow zone that separates the recharge (downward flow) area from the discharge (upward flow) area. Groundwater flow is essentially horizontal in the midline area. 'Envelopes' formed by the simulated profiles that were created with the velocities of one simulation case more tightly enclosed the field data (TDS, Cl, 18O) than those of another simulation case, indicating that velocities of the former simulation case better represent the hydrodynamics of the real system. The models demonstrate that the scatter of TDS, CI and 18O field data for the ARA is consistent with the groundwater flow model predictions and can be explained by the complexity arising from different hydraulic regimes (recharge, midline, discharge) and hydrogeologic environments (fracture zones, rock mass) of the regional flow system. Solute transport simulation of hydrochemical constituents can aid in refining and constraining permeabilities in large-scale groundwater systems.

Original languageEnglish
Pages (from-to)1-20
Number of pages20
JournalJournal of Hydrology
Volume224
Issue number1-2
DOIs
StatePublished - 12 Oct 1999

Keywords

  • Canada
  • Fractured rock
  • Groundwater flow
  • Permeabilities
  • Simulation
  • Solute transport

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