Fulltext

Identification of zones of preferential groundwater tracer transport using a mobile downhole fluorometer

Flynn, Raymond ; Schnegg, Pierre-Andre ; Costa, Roberto ; Mallen, German ; Zwahlen, François

In: Hydrogeology Journal, 2005, vol. 13, no. 2, p. 366-377

Add to personal list
    Title
    • Identification of zones of preferential groundwater tracer transport using a mobile downhole fluorometer
    Author
    • Flynn, Raymond. Hydrogeology Centre, University of Neuchatel, Emil Argand 11, 2007, Neuchatel, Switzerland
    • Schnegg, Pierre-Andre. Geomagnetism Group, Geological Institute, University of Neuchatel, Emil Argand 11, 2007, Neuchatel, Switzerland
    • Costa, Roberto. Geomagnetism Group, Geological Institute, University of Neuchatel, Emil Argand 11, 2007, Neuchatel, Switzerland
    • Mallen, German. Department of Hydrology, Gesellschaft für Strahlenforschung, Ingoldstäter Landstrasse 1, 85764, Neuherberg, Germany
    • Zwahlen, François. Hydrogeology Centre, University of Neuchatel, Emil Argand 11, 2007, Neuchatel, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:317809
    Summary
    A mobile downhole fluorometer was used to detect zones of preferential groundwater tracer transport into an observation well. Identification of such zones is not possible if individual samples are collected over the well's entire screened interval. Laboratory-based tests using the fluorometer, and a purpose-built apparatus demonstrated that the fluorometer could be used with tracers to characterise well water flow regimes. During field investigations in a porous aquifer, the fluorometer monitored tracer concentrations in an observation well with a 12-m-long screen, 10m down the hydraulic gradient from a fully penetrating injection well. Test results showed that the tracer occurred in the observation well over a discrete 2.5-m-thick interval. Single-well dilution test and vertical-flow data indicated that water entered the well at additional depths, but no tracer was detected at these levels. A numerical model reproducing dilution test concentration profiles indicated that water entered the well in many of these horizons at comparable velocities to those in the tracer-bearing zone. These data suggest that groundwater flow direction varied with depth in the aquifer under investigation. Moreover, simulations of tracer arrival indicated that the tracer distribution observed in the observation well was derived from a horizon that may be no thicker than 0.5m