Specific Problems Related to Partially Penetrating Wells in Confined Aquifers

Partial penetration, especially for confined aquifers, may significantly affect the associated well(s) hydraulics due to the incidence of vertical flow in the vicinity of the well. This induces additional head losses, affects the potential pumping rate, and the related peizometeric head distribution around the well. Closed form analytical solution is beyond manual computations due to complicated integrations and summations in addition to dealing with a large number of variables. The main objective of this paper is to provide engineers with a simplified, yet accurate, solution to three specific problems, of common occurrence. Defining the effective aquifer thickness, in case of partial penetration for confined aquifers, is one problem. In case of unknown aquifer thickness, the performed analysis recommends to define the effective thickness as a multiple of the screen length, which in turn, is time dependant. Multiple values of 2, 3, and 4 are found to correspond to pumping periods of 1, 3, and 10 days, regardless of the pumping rate. Determining the optimum screen length for maximum well yield is a second problem. A screen design chart has been prepared while taking into consideration empirically-derived well capacity equation. Detecting the zone of influence of a partially penetrating pumping well is the last studied problem. The peizometric head at any radius can be estimated from proposed influence zone charts that require the pre knowledge of five well and aquifer parameters. All results are postulated based on programming of Hantush equation for partially penetrating wells.