Multifluid flow in bedded porous media: laboratory experiments and numerical simulations M. H. Schroth a , *, J. D. Istok a , J. S. Selker a , M. Oostrom b & M. D. White b a Departments of Civil and Bioresource Engineering, Oregon State University, 202 Apperson Hall, Corvallis, OR 97331, U.S.A. b Pacific Northwest National Laboratory, Environmental Technology Division, K9-33, Richland, WA 99352, U.S.A. (Received 15 June 1997; revised 1 October 1997; accepted 1 December 1997) Understanding light nonaqueous-phase liquid (LNAPL) movement in heterogeneous vadose environments is important for effective remediation design. We investigated LNAPL movement near a sloping fine- over coarse-grained textural interface, forming a capillary barrier. LNAPL flow experiments were performed in a glass chamber (50 cm 3 60 cm 3 1.0 cm) using two silica sands (12/20 and 30/40 sieve sizes). Variable water saturations near the textural interface were generated by applying water uniformly to the sand surface at various flow rates. A model LNAPL (Soltrolt 220) was subsequently released at two locations at the sand surface. Visible light transmission was used to quantitatively determine water saturations prior to LNAPL release and to observe LNAPL flow paths. Numerical simulations were performed using the Subsurface Transport Over Multiple Phases (STOMP) simulator, employing two nonhysteretic relative permeability–saturation–pressure (k – S – P) models. LNAPL movement strongly depended on the water saturation in the fine-grained sand layer above the textural interface. In general, reasonable agreement was found between observed and predicted water saturations near the textural interface and LNAPL flow paths. Discrepancies between predictions based on the van Genuchten/ Mualem (VGM) and Brooks–Corey/Burdine (BCB) k – S – P models existed in the migration speed of the simulated LNAPL plume and the LNAPL flow patterns at high water saturation above the textural interface. In both instances, predictions based on the BCB model agreed better with experimental observations than predictions based on the VGM model. The results confirm the critical role water saturation 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. q 1998 Elsevier Science Limited. All rights reserved Keywords: multifluid flow, LNAPL, capillary barrier, numerical simulation, constitutive relations. 1 INTRODUCTION Light nonaqueous-phase liquids (LNAPLs) are common contaminants in soil and groundwater systems. Petroleum products spilled at the soil surface, and/or leakages from underground fuel storage facilities followed by vertical product migration through the vadose zone, are common LNAPL sources. While many investigations over the past decade have focused on the movement of LNAPLs in homogeneous porous media (e.g. Eckberg and Sunada, 7 Abdul, 1 Lenhard et al., 22,23 Cary et al., 4,5 Høst-Madsen and Jensen, 13 Ostendorf et al., 36 Van Geel and Sykes, 54 and Schroth et al. 45 ), the understanding of LNAPL behavior in heterogeneous subsurface environments is still incom- plete. Tools have been developed to predict the migration of LNAPLs through the subsurface, but their evaluation is currently hindered by the limited availability of quantitative experimental data, especially in heterogeneous porous media. Commonly encountered forms of geological heterogeneity Advances in Water Resources Vol. 22, No. 2, pp. 169–183, 1998 q 1998 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0309-1708/98/$ - see front matter PII: S 0 3 0 9 - 1 7 0 8 ( 9 7 ) 0 0 0 4 3 - 2 169 *Corresponding author.