Characterisation of a Multi-Layer Aquifer Using Open Well Borehole Dilution Tests
Abstract
Multilayer aquifers are commonly characterized using wells that penetrate several layers. The drawndown behaviour of such wells during hydraulic tests is the result of complex interactions between the separate layers, via the wells. Therefore, conventional analysis (e.g. Theis response) provides only bulk parameters; also these bulk parameters may depend on the observation well layout, as well as the aquifer properties. Isolating individual layers for hydraulic testing using packers is the conventional way around this problem; however, packer testing is difficult, expensive, and time consuming. We describe an alternative approach to characterizing a multi-layer aquifer system using the open-well borehole dilution technique, combined with a conventional open-well pumping test. The open well borehole dilution technique involves introducing a saline tracer into the observation wells, and monitoring the tracer as it is flushed out during the pumping test, e.g. using a conductivity sonde. By modelling the movement of water within the borehole and between bore hole and the aquifer, dilution depth profiles are converted into instantaneous vertical borehole flow velocities for each section of the observation well. The vertical flow velocities in the observation wells are then matched to those generated from forward modeling of the multi-layer aquifer system `shorted' by the observation wells, thus yielding information on the hydraulic properties of the constituent layers. An example of the application of this approach to a multi-layer Chalk aquifer in NE England is presented.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.H21C1355W
- Keywords:
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- 1828 Groundwater hydraulics;
- 1829 Groundwater hydrology;
- 1847 Modeling;
- 1859 Rocks: physical properties;
- 1895 Instruments and techniques: monitoring