Lise Slagstad's thesis
by
Lise Slagstad, MSE
University of Texas at Austin, 1997
Supervisor: Russell T. Johns
Larry W. Lake
A common method for withdrawal of light non-aqueous phase liquid (LNAPL) from an aquifer
is the pump-and-treat method, either by single-pump or dual-pump systems. This method
involves pumping water and LNAPL from the aquifer, and the subsequent treatment of the
produced water.
This work develops a three-phase model for segregated flow describing the variation of the
thicknesses of the LNAPL layer and the water-layer, and a two-phase diffuse flow model
including the capillary pressure and relative permeabilities describing the water saturation
distribution. Both models are for a dual-pump system.
Dimensionless groups were determined for both models, and from the sensitivity analysis
the sensitivity of the models to each of their dimensionless groups was found. It
was found that the segregated flow model was most sensitive to the dimensionless
water thickness at the exterior, Ne. The diffuse flow model was most
sensitive to the endpoint mobility ratio, Mo, and the Bond number,
Nb.
The segregated flow model can be used to estimate how far the LNAPL spill extends. Both
models can estimate the volume of the LNAPL spill for the case when only water is flowing.
The segregated flow model was validated by showing that the analytical and the numerical solution
for the limiting cases of no water flow or no LNAPL flow were the same.
Furthermore, the diffuse
flow model was shown to agree with the segregated flow model at high bond numbers. That is, the
difference between the two models approaches zero as the grid was refined and the bond number
increased.
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