Considerations for robust compositional simulations of subsurface nonaqueous phase liquid contamination and remediation

Abstract

A nonisothermal compositional model has been developed for examining nonaqueous phase liquid contamination and remediation scenarios. The governing mass balance equations and constraints have been presented, and various type of compositional formulations available have been examined. An efficient and robust formulation has been developed that addressed certain issues related to groundwater situations and overcomes numerical difficulties encountered with previous formulations. The proposed formulation collapses to that corresponding to the multiphase flow equation set when interface mass transfer is neglected. Numerical implementation of the formulation has been discussed, and example problems have been presented for benchmark and verification. The present formulation outperforms other currently used formulations for the isothermal case studied and performs at least as well as its counterparts for the nonisothermal case. Characteristics of the simulator that hinder convergence for difficult problems have been identified, and directions for even further improvements have been noted. phase mass transfer, can also be used to evaluate the effectiveness of gas venting and air sparging as feasible remedial measures for contaminated sites. Finally, models that also include nonisothermal effects can examine the effectiveness of processes such as hot water flooding and steam injection as viable remediation schemes. Permeability ko, m 2 Porosity •b Soil compressibility, Pa -1 Standard fluid molar densities Pw, mat m -3 ion, mat m-3 Pa, mat m -3 Component molecular weights Mw, kg mat -1 Mn, kg mat -1 Ma, kg mat-1 Component campressibitities

Constraining a compositional flow model with flow‐chemical data using an ensemble‐based Kalman filter

“…Panday et al . [] presented a comprehensive nonisothermal compositional model for rigorous treatment of strongly coupled and highly nonlinear flow and transport applications. Analysis of their model formulation suggests that if interface mass transfer is neglected, then the governing equations are simplified to the standard, but substantially faster, multiphase flow scenario.…”

Organic contaminant transport and fate in the subsurface: Evolution of knowledge and understanding

“…Plume concentrations generally display long tailing that can be due to rate‐limited mass transfer from the NAPL [ Brusseau , ; Zhang and Brusseau , ], rate‐limited diffusion within the NAPL [ Brusseau , ], decreased effective solubility as a constituent becomes depleted in a NAPL mixture [ D'Affonseca et al ., ; Frind et al ., ], nonlinear, rate‐limited sorption/desorption [ Armstrong et al ., ; Johnson et al ., ], and/or back‐diffusion out of low‐permeability zones [ Ball et al ., ; Brown et al ., ; Brusseau , ; Chapman and Parker , ]. Many multiphase, multicomponent transport numerical models have been developed assuming equilibrium partitioning of constituents between fluid phases [ Abriola and Pinder , ; Adenekan et al ., ; Baehr and Corapcioglu , ; Huang et al ., ; Moortgat et al ., ; Panday et al ., ; Sleep and Sykes , ]. However, there has also been great interest in characterizing the role of nonequilibrium mass transfer on contaminant fate.…”

Numerical modelling of multiphase flow and transport processes in landfills

“…An overview of possible combinations of primary variables in multiphase systems is given by Panday et al (1995). Suitable sets of primary variables may consist of phase saturations or pressure.…”