SIMULATED RECOVERY OF LIGHT, NONAQUEOUS PHASE LIQUID FROM UNCONFINED HETEROGENEOUS AQUIFERS

A multiphase flow model (ARMOS) was used to evaluate the effects of su bsurface heterogeneities on the recovery of light, nonaqueous phase li quids (LNAPLs or simply ''oil''). Stochastic inputs for the model incl uded the saturated hydraulic conductivity (K-sw), van Genuchten alpha and n, the water saturation at field capacity (S-m), and the maximum r esidual oil saturations in the saturated (S-or) and the unsaturated zo nes (S-og). The turning bands method was used to generate stochastic s oil parameters representing three hypothetical sandy loam soils. Oil r ecovery in the three heterogeneous cases was compared to an ''equivale nt'' homogeneous soil with effective parameters computed as the geomet ric means of the stochastic parameters. Distributions of the free oil plumes were described over time using statistical and spatial moment a nalyses. Due to the smoothing effect of the flow process, the predicte d well oil thickness (H-o) and free oil specific volume (V-of) were le ss variable than the input stochastic parameter In(K-sw). However, H-o and V-of became more variable as free oil volume diminished and the o il distribution was controlled more by soil variability than gradients in the fluid levels. At the onset of oil recovery, the free oil area was greater in all three heterogeneous soils than the homogeneous soil . Nevertheless, soil heterogeneities did not greatly affect oil recove ry or trapping in the saturated and unsaturated zones. Heterogeneities may have had a greater influence on oil recovery if a smaller spill h ad been studied or if the vertical dimension had been simulated explic itly. The results suggest that the geometric mean soil properties prov ide a useful estimate of the potential for oil recovery from oil spill s that span a large number of correlation scales.