Influence of hydrogeological and operational parameters on well pumping capacity

Abstract

Numerous studies have analyzed how groundwater levels respond to pumping depending on aquifer and well characteristics. This study investigates how, conversely, the pumping capacity of a well depends on hydrogeological and operational conditions. The analysis is based on an analytical solution that considers wellbore storage and skin effects. The solution depends on aquifer transmissivity, aquifer storativity, well radius, well surface casing radius, skin layer transmissivity, pumping duration, and maximum allowable head change. We first conduct a sensitivity analysis of dimensionless pumping capacity to the three dimensionless parameters on which it depends. The results show strongly nonlinear relationships and an important effect of wellbore storage for small dimensionless pumping durations. Since the primary (dimensional) parameters are the ones that one ultimately needs to characterize or engineer in practice, we also conduct a sensitivity analysis of the primary system. The results show that, besides being trivially linearly related with the maximum allowable head change, pumping capacity (defined as a volume) is almost linearly related with aquifer transmissivity and pumping duration. Given the broad natural range of transmissivity values, transmissivity is the most critical parameter to determine for the estimation of pumping capacity. In contrast, pumping capacity is little sensitive to aquifer storativity and well radius, and so the precise determination of these parameters is less critical. Finally, we investigate the relationship between pumping capacity and specific capacity, the latter being a commonly used indicator of the productivity of wells. Our analysis confirms the previously acknowledged limitation of specific capacity for predicting pumping capacity when the duration of the specific capacity test is much smaller than the operational pumping duration. The theoretical insights gained from this study will assist groundwater scientists and engineers in their research, planning, and design activities.