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This article in JEQ

  1. Vol. 29 No. 2, p. 540-550
    Received: Dec 4, 1998

    * Corresponding author(s): ghodrati@nature.berkeley.edu
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A Multiplexed Fiber Optic Miniprobe System for Measuring Solute Transport in Soil

  1. Masoud Ghodrati *,
  2. Fernando Garrido,
  3. Chris G. Campbell and
  4. Michael Chendorain
  1. Division of Ecosystem Sciences, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, 94720-3110.



A fiber optic miniprobe (FOMP) system has been recently developed, capable of measuring solute breakthrough curves (BTCs) in situ and in real time at a single point within the soil matrix. We have multiplexed this system to allow continuous operation of up to 20 of these FOMPs simultaneously. The system was used to measure replicated multipoint BTCs of a fluorescent tracer in a large silica sand column, and allowed verification of the multiplexed FOMP system's ability to measure transport at a point scale. We performed seven miscible displacement studies (runs) generating 140 BTCs to examine system performance, transport variability measured at a small scale, and the sensitivity of that variability to changes in initial pulse concentration (Co). The convective-dispersive equation (CDE) was adequate to describe transport in the silica sand (r2 > 0.96). However, tails observed in all the BTCs were attributed to an immobile phase by fitting several BTCs to a resident concentration form of the mobile-immobile model (MIM). The mass recovery of the tracer ranged from 73 to 127% with an average of 98%. Changes in column averaged transport parameters for the seven miscible displacement studies were minimal; however, there appears to be no consistency in transport at the measurement scale of the probes. Small changes in Co were not found to significantly alter or change the variability in transport parameters. The multiplexed fiber optic system was found to be an accurate tool for small-scale characterization of solute transport in soil.

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