The different characteristics of aquifer parameters and their implications on pumping-test analysis

Abstract

The concepts of two-way coordinates and one-way coordinates are used to describe the different characteristics of two key aquifer parameters, transmissivity and storativity, under constant-rate pumping conditions. A two-way coordinate is such that the conditions at a given location are influenced by changes in conditions on either side of that location; a one-way coordinate is such that the conditions at a given location are influenced by changes in conditions on only one side of that location. Results from sensitivity analysis indicate that storativity has the characteristics of two-way coordinates, but transmissivity has the characteristics of one-way coordinates, i.e., its information can be transferred mainly from upstream to downstream. An upstream observation well can produce information on storativity both upstream and downstream, but it can produce little information on transmissivity downstream. These characteristics of the aquifer parameters have important implications on pumping-test designs and interpretation. For example, to estimate the parameters of an anomalous zone in an aquifer, an observation well should be located downstream but near the zone. It should not be placed upstream if the parameters downstream are to be estimated. An observation well which can provide adequate information for estimating storativity may not provide adequate information for estimating transmissivity, and vice versa. The aquifer area represented by estimated storativity may be different from that represented by estimated transmissivity.