THE VALUE OF SIMPLE EQUILIBRIUM APPROXIMATIONS FOR ANALYSING PUMPING TEST DATA

Abstract

The aim of this Editors’ Message is to highlight the merits of simple equilibrium formulae for analysing pumping test data. It is not the intention to argue that equilibrium approaches should replace the standard non-equilibrium methods where the latter can be applied properly. However, the reality is that good test data are unavailable for the vast majority of the world’s wells, and even where time-drawdown data are available, the non-equilibrium methods involving curve-matching or fitting straight lines are often misapplied, with little understanding of the inherent assumptions. Therefore, equilibrium approximations are indeed useful (1) as an initial estimate of transmissivity (T) in the absence of good test data, and (2) for comparison with, and therefore checking on, the results obtained from non-equilibrium analyses even where there are good time-drawdown data. Regarding (2), it may be the case that the equilibrium T value can be discounted because of leaky conditions, recharge boundaries, or whatever, but at least the process of comparing the results with the non-equilibrium analysis will encourage the hydrogeologist to think about these issues. It is possible that the wide availability of software for interpreting pumping-test data, enabling automatic fitting of straight lines or matching of type curves, discourages some hydrogeologists from giving proper thought to the analysis.