Response to pumping of wells in sloping fault zone aquifers

Abstract

A number of short-term variable discharge pumping tests were conducted on sloping fault zones cutting serpentinites from a thrust complex in north Portugal. The fault zones were identified and geometrically characterized by geological mapping, interpretation of aerial photographs and electromagnetic survey. The evolution of specific drawdowns obeyed two different laws: (1) specific drawdown-time points fitted to straight lines in log–linear scatter plots. In these cases, test data were interpreted by the Cooper–Jacob method, as if fault zones were regular confined porous media aquifers; (2) specific drawdown-time points fitted to straight lines in bilinear scatter plots. Because the available theoretical models were unable to match the observed data, a new approach was developed. The approach introduces the concept of impermeable barrier with variable effective position, a barrier that is represented by the upper limit of the fault zone aquifer. The mechanics of the method is still based on the concepts and formulae of confined porous media aquifers, including the framework of the image well theory. The calculated transmissivities (T=7×10 −7–2×10 −4 m 2/ s) and storage coefficients ( S=2×10 −5–6.1×10 −4) are within those commonly found for confined aquifers in fractured rocks.