Low Stress Pumping Tests to Evaluate Mass Flux in a Highly Permeable Aquifer

Low stress pumping tests were applied to estimate permeability and mass flux during vertical aquifer profiling (VAP) of a prolific glacial outwash aquifer system. The low stress pumping tests were used because the prior estimates of permeability were expected to be higher than the effective range of direct-push injection logging (DPIL)—greater than 10^-2centimeters per second (cm/sec). 

To collect permeability data efficiently, the testing was completed in conjunction with groundwater sample collection during VAP activities using sonic drilling methodology. The low stress pumping tests used flow rates between 20 and 30 liters per minute (L/min) and were performed during the drilling fluid purge until drawdown reached a steady state. Permeability estimates derived from the low stress pumping tests as well as confirmatory pneumatic slug tests were compared with estimates obtained from historical long term constant-rate pumping tests. Results indicated that a higher degree of hydraulic resolution across the aquifer can be achieved by the low stress pumping tests; however, they also suggest a lower overall range of aquifer permeability—this is likely due to several factors. This testing proved to be efficient and provided accurate permeability estimates for the mass flux mapping that will support the remedial design goals.