Change in flow velocity around a well in a porous aquifer after pumping

This study compares the results of natural tracer tests before and after a pumping test in an alluvial aquifer. Changes in flow velocity demonstrate that intense well development (like that produced by an intense pumping test) can change natural aquifer properties around the well, which must be taken into account when designing and interpreting tracer tests to derive natural aquifer transport properties within 8-9 m of an injection well. These hydrogeological changes occur because pumping tests (in this case, with a rate of 77 l/s) extract the finest part of the reservoir (i.e., silt and very fine sand) around the well, causing a negative skin effect. An important groundwater reservoir is present in the alluvial plain of Treviso (Veneto region, NE Italy). Previous hydrogeological studies on the unconfined aquifer system have provided some qualitative and quantitative data for its hydrostructural and hydrodynamic assessment. In our study, tracer tests indicate that well development has increased local flow velocities 3.1 m from injection well B and that these changes are visible up to 8.4 m from the injection well.