A downhole colun technique for field measurememnt of transport parameters

The paper presents a new method for the characterization of dispersive and adsorptive properties of natural sedimentary deposits at a field site in the Perch Lake Basin using a downhole technique. The potential capabilities of the proposed method were evaluated by conducting a dual-tracer test in a series of downhole field columns using non-reactive (3H) and reactive (85Sr) tracers. The observed breakthrough curves were analysed using linear and non-linear mass transport equations. The dispersivity values obtained by analysing 3H (range 0.2-1.1 cm) are in good agreement with those reported for 131I radial injection experiment at the same site (range 0.4-1.5 cm). The distribution coefficient (KdSr) values obtained from analysis of breakthrough curves at four depths using the linear equilibrium model ranged from 6.22 to 7.39 mL.g-1. These values are in good agreement with those obtained by separation of pore waters from sediments (5.0-6.6 mL.g-1) and half of those obtained by batch experiments on core sediments (12.8-14.9 mL.g-1). These values compare favorably with the KdSr determined for Sr migrating in a 25-year-old radioactive waste plume (mean of 10 mL.g-1) at a nearby site. The model identification problem was addressed by constructing linear and non-linear equilibrium transport models. The non-linear models based upon Freundlich and Langmuir isotherms showed some improvement over the linear model in fitting experimental data. It was concluded, however, that for simulating radio-strontium behaviour