NUMERICAL SIMULATIONS EVALUATING THE EFFECT OF VERTICAL JOINTING AND RECHARGE ON THE DEVELOPMENT OF PROTO-CONDUITS IN LIMESTONE AQUIFERS AT DEPTH

A discrete random aperture, variably-saturated, three-dimensional numerical model has been developed to evaluate the geochemical evolution of proto-conduits in limestone aquifers. Kinetic and equilibrium mass action relationships are integrated into the reactive chemistry solution to account for calcite and dolomite dissolution along vertical and horizontal fracture planes and atmospheric and soil enhanced PCO2 boundary conditions. In addition to the solute transport of aqueous species, sediment transport is also considered with equations adopted from surface water observations and theory.

Simulations are presented which illustrate the effects of different vertical jointing scenarios and recharge on the development of proto-conduits at depth along bedding planes. Results illustrate that depending upon the frequency, distribution and orientation of vertical fractures, relative to the mean groundwater flow direction, notably different horizontal conduits develop at depth. Simulations also demonstrate the importance of characterizing vertical fractures in field studies to increase the potential of understanding the flow network at depth.