EFFECTIVE PARAMETERS OF NATURAL AND ENHANCED DISSOLUTION AS APPLIED TO FIELD SCALE REMEDIATION
|T. Saba and T.H. Illangasekare, Civil and Environmental Engineering department, University of Colorado, Boulder, CO 80309-0428||
The rate of mass transfer from entrapped waste chemicals in the form of nonaqueous phase liquids (NAPLs) determines the concentrations of dissolved organics in aqueous plumes and the time needed for cleanup using pump and treat schemes. Mass transfer rates as enhanced by surfactants, co-solvents, or thermal means also determine the effectiveness of remediation schemes.
The mass transfer rate coefficients that characterize dissolution are generally determined under residual entrapment at the macroscopic scale in one-dimensional soil columns. In field sites, the natural heterogeneities in combination with unstable flow of NAPLs (e.g. fingering of DNAPLs) produce complex entrapment saturation distributions. In the field scale modeling of dissolution, both under natural and enhanced conditions, it is necessary to determine the mass transfer rate coefficients under heterogenous aquifer conditions and complex source distributions.
The results of an investigation where techniques will be developed to determine the effective mass transfer coefficients at the field scale are presented. These methods will have the applicability in field upscaling of technologies such as surfactant-enhanced and thermally-enhanced dissolution.
Experiments were conducted in two large flumes (4.4 m x 1.1 m and 2.2 m x 1.1 m). A light organic test fluid, p-xylene, was entrapped in a variety of heterogeneous formations. Aqueous samples taken from observation ports downstream of the entrapment zone were analyzed using gas chromatography to determine dissolved organic concentrations.
Breakthrough curves were analyzed to assess the impact of water flow patterns, increase in solubility due to temperature, and buoyancy forces created by temperature gradients on dissolution enhancement. The experiments we modeled using a three-dimensional flow and transport model to determine effective mass transfer coefficients at various observation scales. Based on these analysis, theories will be developed to predict effective mass transfer rate parameters in models used in the design and evaluation of field remediation techniques that use surfactant and thermally enhance dissolution.
Key words: organic waste, NAPL dissolution, enhanced dissolution, parameter upscaling
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