Partially penetrating slug tests in an unweathered till layer

Abstract

This research improves field based estimates of aquitard compressibility and permeability. A semianalytical model of partially penetrating, overdamped slug tests achieves this objective. The short term solution is an existing fully penetrating model, the long term solution is the polar residue of an inverse Laplace transform, and an exponential spline function patches the solutions together. Large amplitude slug test data from ten pairs of partially penetrating monitoring wells installed in an unweathered till at Scituate Hill in eastern Massachusetts calibrate the model. The deposit is bound by weathered till and the Dedham Granite fracture zone, and both are far more permeable than the unweathered till. The calibrated till permeability of 8.4 × 10–16 m2 is about 25% less than existing model calibrations that include boundary recharge in permeability values. The calibrated till compressibility of 5.1 × 10–10 Pa–1 reflects the proper inclusion of recharge as a long term source of groundwater, rather than the unrealistically large compressibility calibrations required by fully penetrating models.