Design of a field scale project for surfactant enhanced remediation of a DNAPL contaminated aquifer
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This dissertation describes a new methodology for the use of numerical modeling in the design and interpretation of field-scale surfactant remediation of an unconfined aquifer contaminated with DNAPLs, dense non-aqueous phase liquids. A three-dimensional, multi-component, multi-phase simulation study was conducted incorporating extensive laboratory and field data. UTCHEM, the University of Texas CHEMical flood simulator, was used to model the aquifer, groundwater, contaminants, and injected chemicals. The primary objective of this research was to develop and apply engineering methods, especially flow and transport modeling, to optimize the removal of contaminants using surfactant enhanced aquifer remediation (SEAR), including the effect and importance of such processes as adsorption, solubilization/mobilization, dispersion/diffusion, gravity, and viscous forces upon remediation efficiency. Partitioning tracer tests were included in the project, both preceding and following the surfactant remediation, to establish the volume of DNAPL present to be remediated and to determine the effectiveness of this process in removing the DNAPL source. Field surfactant floods and tracer tests were conducted at a site in Hill AFB, which allowed validation of the test design methodology, including the value of simulation in this process. The simulations accurately predicted tracer breakthrough times, tracer peak times and concentrations, and performance of the tracer “tail” or concentration decline critical for moment analysis and DNAPL volume determination. The simulations also were critical in determining the appropriate injection and extraction rates, injection concentrations, and time required for each segment of the test. Surfactant was injected successfully in the field, as evidenced by no loss in hydraulic conductivity during the test, low adsorption and high surfactant recovery, a dramatic increase in contaminant production at surfactant breakthrough, and successful treatment of produced fluids by existing facilities. Hydraulic control was designed by tuning rates of injection/extraction/hydraulic control wells and was confirmed in the field results by high recovery of injected chemicals and low concentrations of tracers in monitoring wells north and south of the test area. This field test resulted in 98.5% DNAPL recovery and a reduction in TCE concentration in the produced water from 900 mg/l down to 10 mg/l at the end of the test.