FLOW TO A WELL OF FINITE DIAMETER IN A HOMOGENEOUS, ANISOTROPIC WATER-TABLE AQUIFER

A Laplace transform solution is presented for the problem of flow to a partially penetrating well of finite diameter in a slightly compressi ble water table aquifer. The solution, which allows for evaluation of both pumped well and observation piezometer data, accounts for effects of well bore storage and skin and allows for the noninstantaneous rel ease of water from the unsaturated zone. For instantaneous release of water from the unsaturated zone the solution approaches the line sourc e solution derived by Neuman as the diameter of the pumped well approa ches zero. Delayed piezometer response? which is significant during ti mes of rapidly changing hydraulic head, is included in the theoretical treatment and shown to be an important factor in accurate evaluation of specific storage. By means of a hypothetical field example it is de monstrated that evaluations of specific storage (S-s) using classical line source solutions may yield values of S-s that are overestimated b y a factor of 100 or more, depending upon the location of the observat ion piezometers and whether effects of delayed piezometer response are included in the analysis. Theoretical responses obtained with the pro posed model are used to suggest methods for evaluating specific storag e.