MULTIFLUID FLOW IN BEDDED POROUS-MEDIA - LABORATORY EXPERIMENTS AND NUMERICAL SIMULATIONS

Understanding light nonaqueous-phase liquid (LNAPL) movement in hetero geneous vadose environments is important for effective remediation des ign. We investigated LNAPL movement near a sloping fine- over coarse-g rained textural interface, forming a capillary barrier. LNAPL flow exp eriments were performed in a glass chamber (50 cm x 60 cm x 1.0 cm) us ing two silica sands (12/20 and 30/40 sieve sizes). Variable water sat urations near the textural interface were generated by applying water uniformly to the sand surface at various flow rates. A model LNAPL (So ltrol(R) 220) was subsequently released at two locations at the sand s urface. Visible light transmission was used to quantitatively determin e water saturations prior to LNAPL release and to observe LNAPL flow p aths. Numerical simulations were performed using the Subsurface Transp ort Over Multiple Phases (STOMP) simulator, employing two nonhystereti c relative permeability-saturation-pressure (k-S-P) models. LNAPL move ment strongly depended on the water saturation in the fine-grained san d layer above the textural interface. In general, reasonable agreement was found between observed and predicted water saturations near the t extural interface and LNAPL Bow paths. Discrepancies between predictio ns based on the van Genuchten/ Mualem (VGM) and Brooks-Corey/Burdine ( BCB) k-S-P models existed in the migration speed of the simulated LNAP L plume and the LNAPL Bow patterns at high water saturation above the textural interface. In both instances, predictions based on the BCB mo del agreed better with experimental observations than predictions base d on the VGM model. The results confirm the critical role water satura tion plays in determining LNAPL movement in heterogeneous vadose zone environments and that accurate prediction of LNAPL flow paths depends on the careful selection of an appropriate k-S-P model. (C) 1998 Elsev ier Science Limited. All rights reserved.