The steady-state dipole-flow test for characterization of hydraulic conductivity statistics in a highly permeable aquifer: Horkheimer Insel Site, Germany

Over the last decade the dipole-flow test (DFT) evolved from the general id ea of using recirculatory flow to evaluate aquifer properties, to the devel opment of prototype instrumentation and feasibility studies, to a reliable tool for characterization of aquifer heterogeneity. The DFT involves the in terpretation of head in recirculatory flow between injection and extraction sections (chambers) in a single well isolated from each other by a multipa cker system. In this study, the steady-state dipole flow test (DFT) has bee n used to characterize the statistics of horizontal hydraulic conductivity (K,) of the highly permeable, heterogeneous, and thin aquifer at the Horkhe imer Insel site, Germany. In previous studies, K-r estimates were based on the steady-state head difference between chambers. A new by-chamber interpr etation is proposed that is based on drawdown within each individual chambe r. This interpretation yields more detailed information on structure of het erogeneity of the aquifer without introducing complexity into the analysis, The DFT results indicate that K-r ranges from 49 to 6000 m/day (mean In K- r [(m/s)] similar to - 4, and variance of In K-r [(m/s)] similar to 1-2), D escriptive statistics from the DFT compare well with those from previous fi eld and laboratory tests (pumping, borehole flowmeter, and permeameter test s and grain-size analysis) at this site. It is shown that the role of confi ning boundaries in the DFT interpretation is negligible even in this case o f a thin (< 4 m thick) aquifer, This study demonstrates the flexibility of the DFT and expands the potential application of this method to a wide rang e of hydrogeologic settings.