A dual-tube direct-push method for vertical profiling of hydraulic conductivity in unconsolidated formations
- applications
- case studies
- Douglas County Kansas
- ground water
- hydraulic conductivity
- hydrology
- instruments
- Kansas
- monitoring
- movement
- permeability
- pollutants
- pollution
- pore water
- preferential flow
- remediation
- sampling
- slug tests
- soil mechanics
- soils
- spatial variations
- unconsolidated materials
- United States
- unsaturated zone
- direct-push methods
A new direct-push procedure has been developed for the purpose of conducting discrete-interval slug tests to define vertical variations in hydraulic conductivity (K.) This approach is an extension of existing dual-tube methods developed for soil sampling. In this procedure, nested rods (tubes) are simultaneously advanced to predetermined test intervals. The inner rods are then removed and a screen is inserted into the formation for slug testing and possible water sampling. Once testing and sampling are completed, the screen is retrieved, the inner rods reinserted, and the system is advanced to the next test interval. A series of field tests were performed in a highly permeable sand and gravel aquifer to assess the effectiveness of this new approach. Dual-tube profiling results were compared to multilevel slug tests conducted in conventional monitoring wells for intervals in which hydraulic conductivity ranged from 175 ft/day to over 800 ft/day. An initial evaluation found that the dual-tube profiling results were in good agreement (< or =12 percent difference) with K values obtained from multilevel slug tests in the closest monitoring well. Two more-detailed profiles demonstrate that the dual-tube method can effectively delineate small-scale vertical and horizontal variations in hydraulic conductivity. This field assessment shows that the dual-tube method is an accurate and efficient procedure for obtaining information about spatial variations in hydraulic conductivity. This information can be useful for selecting intervals for well installations, for assessment of various remediation alternatives, and for identifying preferential flow paths and other features that can control contaminant movement in the subsurface. The information is obtained without the need for permanent wells. Because this is a direct-push procedure, drill cuttings are eliminated and the volume of development water generated is significantly reduced.
