Hydraulic tomography: Development of a new aquifer test method

Hydraulic tomography (i.e., a sequential aquifer test) has recently been pr oposed as a method for characterizing aquifer heterogeneity. During a hydra ulic tomography experiment, water is sequentially pumped from or injected i nto an aquifer at different vertical portions or intervals of the aquifer. During each pumping or injection, hydraulic head responses of the aquifer a t other intervals are monitored, yielding a set of head/discharge (or recha rge) data. By sequentially pumping (or injecting) water at one interval and monitoring the steady state head responses at others, many head/discharge (recharge) data sets are obtained. In this study a sequential inverse appro ach is developed to interpret results of hydraulic tomography. The approach uses an iterative geostatistical inverse method to yield the effective hyd raulic conductivity of an aquifer, conditioned on each set of head/discharg e data. To efficiently include all the head/discharge data sets, a sequenti al conditioning method is employed. It uses the estimated hydraulic conduct ivity field and covariances, conditioned on the previous head/discharge dat a set, as prior information for next estimations using a new set of pumping data. This inverse approach was first applied to hypothetical, two-dimensi onal, heterogeneous aquifers to investigate the optimal sampling scheme for the hydraulic tomography, i.e., the design of well spacing, pumping, and m onitoring locations. The effects of measurement errors and uncertainties in statistical parameters required by the inverse model were also investigate d. Finally,the robustness of this inverse approach was demonstrated through its application to a hypothetical, three-dimensional, heterogeneous aquife r.