Abstract

Plumes of contamination emanate from nonaqueous-phase liquid sources as its constituents slowly dissolve into passing groundwater. For a large, well-characterized source, an aggressive technology such as steam flooding can accelerate cleanup. Steam is injected through a series of wells within and around a source area, and the steam zone grows radially around each injection well. The steam front drives the contamination to a system of groundwater pumping wells in the saturated zone and soil vapor extraction wells in the vadose zone. The movement of steam in the subsurface is governed primarily by soil heterogeneity and gravity. Steam is buoyant in groundwater and tends to migrate upward unless injected below a continuous confining layer. Groundwater pumping rates and vacuums typical of steam flooding are generally low compared to the steam injection rate and pressure and have limited influence over the lateral growth of the steam zone. To overcome these limitations, a system of air injection wells can be used to direct the steam zone growth. This paper presents results of sand-box experiments using air injection to prevent the outward growth of a steam zone between extraction wells with a discontinuous confining layer limiting the upward migration of steam. These experiments were numerically modeled with the multiphase nonisothermal code T2VOC. When confined vertically, the experiments and modeling show that outward migration of the steam front can be effectively controlled by placing air injection wells opposite steam injection wells. This technique can direct steam zone growth toward difficult access sources and away from areas where steam is not desired. Control of a proposed full-scale steam flood of the M-Area settling basin at the Savannah River Site was modeled using this method and the results are presented in this paper.

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