Determining aquifer coefficients from residual drawdown data

Abstract

Hantush's equation for the drawdown in a leaky, infinite aquifer, adapted to the residual drawdown, is used to obtain a least sum of squares fit to the residual drawdown measurements in an observation well by iteratively adjusting the transmissivity, storativity, and leakage factor. First estimates for the least squares method are obtained by first fitting the equation, with a fixed high value of the leakage factor, to two points of the data; this is followed by a number of fits to three points, each fit yielding a set of values for the three aquifer coefficients; the set which yields the least sum of squares is selected as first estimate to the main routine. An application to data from a pump test at Chatham, New Brunswick, is shown as an example.