Influence of textural and wettability variations on predictions of DNAPL persistence and plume development in saturated porous media Thomas J. Phelan a,1 , Lawrence D. Lemke a,1 , Scott A. Bradford b,2 , Denis M. O’Carroll a,1 , Linda M. Abriola c, * a Department of Civil and Environmental Engineering, University of Michigan, 181 EWRE, 1351 Beal Ave., Ann Arbor, MI 48109-2125, USA b George E. Brown, Jr. Salinity Laboratory, US Department of Agriculture, Agricultural Research Service, 450 Big Springs Rd., Riverside, CA 92507, USA c School of Engineering, Tufts University, 105 Anderson Hall, 200 College Ave., Medford, MA 02155, USA Received 18 December 2003; accepted 4 February 2004 Abstract Numerical simulations examine the migration, entrapment, and mass recovery behavior of DNAPLs in aquifer systems with coupled textural and wettability variations. Permeability fields of varying degrees of heterogeneity (i.e., differing r 2 lnðkÞ ) were gen- erated with sequential Gaussian simulation, using geostatistical parameters derived from core grain size measurements in a sandy glacial outwash aquifer. Organic-wet mass fraction, a representative metric for wettability, was correlated to porous media per- meability. A multiphase flow simulator incorporating wettability-dependent constitutive relationships for capillary behavior is used to generate residual saturation distributions for tetrachloroethene (PCE) spill events in these synthetic aquifers. Simulated saturation distributions then serve as initial conditions for compositional simulations of PCE dissolution, to examine the effect of coupled wettability and permeability variations on DNAPL mass recovery. Simulations reveal considerable differences in predicted depth of organic liquid penetration, extent of vertical spreading, and magnitude of maximum entrapped saturation for the various modeled scenarios. These differences are directly linked to observable variations in effluent concentration and mass recovery predictions in the aqueous phase flushing simulations. Results suggest that mass recovery behavior may be highly realization dependent and not closely correlated with geostatistical parameters. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Multiphase flow; DNAPL; Wettability; Heterogeneity; Numerical model; Source zone remediation 1. Introduction The accidental or intentional introduction of low solubility organic compounds into the subsurface has led to widespread contamination of groundwater re- sources. These contaminants are often released as a separate, immiscible phase known as a nonaqueous phase liquid (NAPL). Of particular concern is the behavior of dense nonaqueous phase liquids (DNAPLs), which migrate through the vadose and saturated zones under gravitational and pressure forces, leaving behind pooled or entrapped residual organic liquid mass [52,75]. This pooled and entrapped organic liquid has the potential to contaminate significant volumes of groundwater over lengthy time scales due to its low aqueous phase solubility. The fate and transport of DNAPL contaminants is known to be controlled by spatial heterogeneity in physical and chemical properties. Numerical [13,24, 30,43,47], laboratory [75], and field [55] studies have examined the effect of spatial variability in physical properties on the flow and entrapment of immiscible liquids in the saturated zone. Other studies have inves- tigated the effect of spatial variability on source zone * Corresponding author. Fax: +1-617-627-3819. E-mail addresses: tphelan@engin.umich.edu (T.J. Phelan), ldlemke@engin.umich.edu (L.D. Lemke), sbradford@ussl.ars.usda.gov (S.A. Bradford), denismo@engin.umich.edu (D.M. O’Carroll), linda.abriola@tufts.edu (L.M. Abriola). 1 Fax: +1-734-763-2275. 2 Fax: +1-909-342-4963. 0309-1708/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.advwatres.2004.02.011 Advances in Water Resources 27 (2004) 411–427 www.elsevier.com/locate/advwatres