Pumping test data interpretation and drift inflow assessment by finite-difference radial modelling

Abstract

A digital radial (r-z-t) finite-difference model for the simulation of constant-discharge pumping-tests in multilayered ground is described. The model is particularly useful for the interpretation of multiport piezometer data since the drawdown at each port can be independently simulated on the r-z-t grid. Unlike conventional methods of pumping-test interpretation, where flow and ground properties are usually averaged over one or two layers, the radial (r-z-t) model allows a detailed approximation of the vertical variation in ground hydraulic properties.

A case study is described in which the radial (r-z-t) model is applied to the interpretation of multiport piezometer data from two pumping-tests carried out in a site investigation for a proposed new surface drift. The resulting permeability distribution is then used as input data to model inflows to the proposed drift under construction. Three-dimensional inflows to a short length of unlined drift open section are approximated using steady-state radial (r-z) flow models. Use of the numerical modelling techniques result in a better understanding of the groundwater system than that obtained from conventional analytical techniques.