Evaluating the Relationship Between Source Zone Metrics and Down-Gradient Plume Response as a Function of Mixed DNAPL Mass Removal
Abstract
The influence of source zone architecture on down-gradient plume and flux-averaged effluent concentrations as a function of source depletion was evaluated through a series of 2-D aquifer cell experiments contaminated with a mixed dense non-aqueous phase liquid (DNAPL) consisting of a 1:1 molar ratio of trichloroethene (TCE) and tetrachloroethene (PCE). The aquifer cells (1.0 m length x 48 cm height x 1.4 cm internal thickness) were packed with different size fractions of quartz sands, and low permeability lens configurations were varied to achieve alternative varied source zone saturation distributions. DNAPL saturation distributions were quantified using a light transmission system and characterized by the ganglia-to-pool ratio (GTP, 0 to infinity) and pool fraction (0 to 1), where saturations less than 0.13 represent discrete ganglia and saturations equal to or greater than 0.13 are considered to represent "pools". Flux-averaged effluent dissolved-phase TCE and PCE concentrations were monitored continuously, while down-gradient plume samples were collected periodically from 25 side-ports. Results from these studies indicated that TCE was preferentially depleted during aqueous phase dissolution from the mixed DNAPL source zone, while PCE was preferentially depleted during surfactant flooding with a 4% (w/w) solution of polyoxyethylene (20) sorbitan monooleate (Tween 80, a nonionic, food-grade surfactant). Batch experiments were conducted to investigate this competitive solubilization of PCE and TCE from the DNAPL mixture in the presence of surfactant. Results indicate that PCE is preferentially solubilized relative to TCE in micellar solutions of Tween 80 and Aerosol MA-80I, demonstrating that a Raoult’s Law convention is not applicable to these systems. In contrast to the PCE and TCE data, results obtained using a 1:1 molar mixture of decane and dodecane in the same micellar solutions indicate that the amount of decane or dodecane solubilized in the aqueous phase was proportional to the mole fraction in the NAPL, consistent with a Raoult’s Law. It is hypothesized that the deviations from Raoult’s Law observed for PCE and TCE were caused by preferential solubilization of PCE within the hydrophobic core of the micelles. Work is on-going to quantify the preferential solubilization observed in the batch experiments, which will facilitate the incorporation of this relationship into multiphase compositional simulators. These simulators will then be used to improve the understanding of the inter-relationships between the initial source zone architecture, mass removal, reductions in mass flux and plume evolution in multi-component contaminated subsurface systems.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H24A..04C
- Keywords:
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- 1803 HYDROLOGY / Anthropogenic effects;
- 1831 HYDROLOGY / Groundwater quality;
- 1834 HYDROLOGY / Human impacts