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THE QUANTIFICATION OF AQUEOUS TRACERS IN LABORATORY AQUIFER MODELS USING A LIGHT TRANSMISSION VISUALIZATION METHOD - 3
Citation:
BRATT, C. L., M. BROOKS, M. BOB, AND A. L. WOOD. THE QUANTIFICATION OF AQUEOUS TRACERS IN LABORATORY AQUIFER MODELS USING A LIGHT TRANSMISSION VISUALIZATION METHOD - 3. Presented at East Central University's Academic Excellence Day, Ada, OK, April 18, 2007.
Impact/Purpose:
To inform the public.
Description:
The quantification of solute concentrations in laboratory aquifer models has been largely limited to the use of sampling ports, from which samples are collected for external analysis. One of the drawbacks to this method is that the act of sampling may disturb plume dynamics and does not provide a continuous distribution of sampling points over the entire model. As an alternative approach, this study demonstrated the use of light transmission visualization (LTV) methods to spatially characterize the distribution of fluorescein disodium salt over the entire model in a flowing medium. A 4 x 6 inch Hele-Shaw model was used to simulate two-dimensional flow through a homogenous porous medium. The model was placed over a 5x7 inch planar light source and a 16-bit monochromatic charged couple device camera (CCD camera) equipped with a 492 nm filter was used for imaging. Light intensity values at individual pixels within the images were converted into solute concentrations using an internal calibration curve created by imaging serially diluted tracer at known concentrations. Mass balance measurements, which were obtained by converting the intensity at each pixel to measurements of mass and then summing up the total mass of tracer within the image, ranged from approximately 94 – 99% of the injected fluorescein mass. A spectrophotometer was used to create an external calibration curve, the slope of which was compared to the internal calibration curve. The difference between these two slopes (12%) suggests that it may be possible to quantify tracers inside a model using external analyses. The effect of boundary layers around trapped air on the transport of the fluorescein tracer through the model was also observed.