Use and Limitations of Short and Medium Duration Pumping Tests in Understanding Hard Rock Fracture Aquifers - An Example from Kerala

Short and medium duration pumping test data from a well-field, in conjunction with outcrop fracture pattern studies, are used to understand the nature of a system of fracture aquifers in a metamorphic terrain in Kerala State. Satellite imagery shows a minor E - W lineament intersecting a major regional NNW - SSE lineament in the area. Drawdown and time lag data indicate greater connectivity along the minor lineament compared to the major one. The E - W elongation of the drawdown contours correlates with dominant E - W fracture sets seen on outcrops. The NNW - SSE fracture zone probably forms a regional conduit for groundwater flow, with the degree of hydraulic. connectivity modified locally by other intersecting fracture zones. A large-scale heterogenity in the form of an E-W fracture zone is indicated in this area. The pumping tests give responses similar to double-porosity and semi-confined models. Some data suggest localised linear flow near pumped well. Heterogeneity in fracture distribution results in a complex response to pumping. Celtain broadly-defined zones and groundwater flow conditions are discernible within this heterogeneity.