| Current aquifer characterization methodologies do not provide enough information to allow for accurate forecasting of contaminant transport in the subsurface. The existing techniques either measure the aquifer parameters on the intermediate field scale or on a small laboratory scale. However, they do not provide porous media characterization on scales corresponding to the grid scales typically used in groundwater contamination models. In addition, the existing tests establish a horizontally dominant flow pattern and thus do not provide information on vertical hydraulic conductivity. Finally, the disturbed zone around the well, created through the well installation process by augering and then backfilling the annulus with foreign porous material, may have significantly different hydraulic properties than the aquifer and may, therefore, bias the test results.;The dipole-flow test with a tracer (DFTT), a new single-borehole test combining a small scale dipole-flow test and tracer test, may mitigate or eliminate many of the above described problems affecting existing single-borehole tests. Proposed and investigated in numerical experiments by Ruud and Kabala (1996), the DFTT uses a straddle-packer assembly to isolate two chambers in a well, and a pump to create the dipole-flow pattern around the well. After the pressure distribution in the subsurface reaches steady state, an innocuous tracer is released in the injection chamber and its breakthrough curve is recorded in the extraction chamber.;As part of this work, two DFTT devices, one for the saturated and another for the unsaturated zone, have been designed, constructed, and tested. During testing, protocols for conducting the DFTT were developed. Laboratory tests have been conducted to quantify the Taylor dispersion inherent in the equipment and found that it is not significant.;The saturated zone device was successfully field tested at the Lizzie Intensive Study Area, located near Greenville in the coastal plain of North Carolina, and operated by the North Carolina Department of Environment and Natural Resources, Division of Water Quality. Preliminary field tests of the saturated zone DFTT were conducted in both recirculating and non-recirculating modes on wells situated in confined and unconfined formations at the Lizzie field site. These DFTTs represent the first small-scale, single-borehole tracer tests ever conducted. |
