Light nonaqueous phase liquid (LNAPL) saturation and movement in the subsurface are controlled by soil capillary characteristics, permeability, and fluid properties. Where free-product occurs in monitoring wells, LNAPL saturations in the formation vary significantly as a function of the observed thickness in the monitoring well and soil type. Fine-grained soils generally exhibit lower LNAPL saturations than coarse-grained material for the same observed thickness in a monitoring well. MAGNAS3MAGNAS3. HydroGeoLogic, Inc., Herndon, VA, 1992; Huyakorn, P. S.; Panday, S.; Wu, Y. S. J Gontam. Hydrol. 1994, 16, 190-130, a three-dimensional, finite-element model that can simulate movement of three active phases (air, water, and LNAPL), was used to investigate LNAPL recovery in three different soil types and using several recovery designs to examine the effect of these factors on LNAPL recovery. The results of this analysis show that, because the relative mobility of LNAPL decreases with decreasingsaturation and because the intrinsic permeability of fine-grained soil is less than that of coarse-grained soil, free-product pumping or skimming has less likelihood of success in fine-grained soil. Recovery in fine-grained soils was minimal, withsignificant reductions in LNAPL saturation occurring only within about 10-15 ft of the well. Recovery of LNAPL in coarse-grained soils was simulated to be much more successful, with approximately 95 of the original hydrocarbon recovered through fluidpumping. The results of the modeling further shows that, for any soil type, recovery decreases LNAPL saturation and mobility near the well with the effect diminishing with distance. Therefore, a zone of decreased LNAPL permeability is formed near recovery wells that acts to impede additional recovery from greater distances. Increases in the hydraulic recovery rate (i.e., not considering volatilization) can be realized in all of the soils studied through vacuum enhanced free-product recovery.
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