Application of multiphase transport models to field remediation by air sparging and soil vapor extraction.

The design and operation of air sparging and soil vapor extraction (AS/SVE) remediation systems remains in large an art due to the absence of reliable physically based models that can utilize the limited available field data. In this paper, a numerical model developed for the design and operation of air sparging and soil vapor extractions systems was used to simulate two field case studies. The first-order mass transfer kinetics were incorporated into the model to account for contaminant mass transfer between the water and air (stripping), NAPL and water (dissolution), NAPL and air (volatilization), and water and soil (sorption/desorption), the model also accounted for soil heterogeneity. Benzene, toluene, ethyl benzene and xylenes (BTEX) were the contaminants of concern in both case studies. In the second case study, the model was used to evaluate the effect of pulsed sparging on the removal rate of BTEX compounds. The pulsed sparging operation was approximated assuming uniform contaminant redistribution at the beginning of the shut-off period. The close comparison between the observed and simulated contaminant concentration in the aqueous phase showed that the approximation of the pulsed sparging operation yielded reasonable prediction of the removal process. Field heterogeneity was simulated using Monte Carlo analysis. The model predicted about 80-85% of the contaminant mass was removed by air-water mass transfer, which was similar to the average removal obtained by Monte Carlo analysis. The analysis of the removal/rebound cycles demonstrated that removal rate was controlled by the organic-aqueous distribution coefficient K(oc). Due to the lack of site-specific data, the aerobic first-order biodegradation coefficients (k(bio)) were obtained from a literature survey, therefore, uncertainty analysis of the k(bio) was conducted to evaluate the contribution of the aerobic biodegradation to total contaminant removal. Results of both case studies showed that biodegradation played a major role in the remediation of the contaminated sites.

[1]  Jonathan F. Sykes,et al.  Compositional simulation of groundwater contamination by organic compounds: 1. Model development and verification , 1993 .

[2]  Say Kee Ong,et al.  Water-to-Air Mass Transfer of VOCs: Laboratory-Scale Air Sparging System , 1998 .

[3]  Gordon A. Fenton,et al.  Simulation and analysis of random fields , 1990 .

[4]  R. Schwarzenbach,et al.  Environmental Organic Chemistry , 1993 .

[5]  Jonathan F. Sykes,et al.  Modeling the transport of volatile organics in variably saturated media , 1989 .

[6]  George F. Pinder,et al.  A Multiphase Approach to the Modeling of Porous Media Contamination by Organic Compounds: 1. Equation Development , 1985 .

[7]  George F. Pinder,et al.  A Multiphase Approach to the Modeling of Porous Media Contamination by Organic Compounds: 2. Numerical Simulation , 1985 .

[8]  M. Yavuz Corapcioglu,et al.  A compositional multiphase model for groundwater contamination by petroleum products: 1. Theoretical considerations , 1987 .

[9]  Mark L. Brusseau,et al.  Transport of Organic Chemicals by Gas Advection in Structured or Heterogeneous Porous Media: Development of a Model and Application to Column Experiments , 1991 .

[10]  J. McCray,et al.  Numerical Simulation of Air Sparging for Remediation of NAPL Contamination , 1997 .

[11]  K. Reddy,et al.  Effect of groundwater flow on remediation of dissolved-phase VOC contamination using air sparging. , 2000, Journal of hazardous materials.

[12]  Susan E. Powers,et al.  An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems: Transient mass transfer rates , 1992 .

[13]  M. Yavuz Corapcioglu,et al.  A compositional multiphase model for groundwater contamination by petroleum products: 2. Numerical solution , 1987 .

[14]  D. LaBrecque,et al.  Air sparging in a sandy aquifer (Florence, Oregon, U.S.A.): Actual and apparent radius of influence , 1995 .

[15]  Jonathan F. Sykes,et al.  Compositional simulation of groundwater contamination by organic compounds: 2. Model applications , 1993 .

[16]  R. Mohtar,et al.  Factors affecting air sparging remediation systems using field data and numerical simulations. , 2002, Journal of hazardous materials.

[17]  J. Massmann.  Applying groundwater flow models in vapor extraction system design , 1989 .

[18]  Linda M. Abriola,et al.  A numerical model (MISER) for the simulation of coupled physical, chemical and biological processes in soil vapor extraction and bioventing systems , 2000 .

[19]  A. Corey.  Mechanics of Immiscible Fluids in Porous Media , 1986 .

[20]  Peter A. Forsyth,et al.  Mechanisms Controlling Vacuum Extraction Coupled With Air Sparging for Remediation of Heterogeneous Formations Contaminated by Dense Nonaqueous Phase Liquids , 1995 .

[21]  Charles S. Sawyer,et al.  Optimal flow rates and well locations for soil vapor extraction design , 1998 .

[22]  D. J. McKay,et al.  Neutron Moisture Probe Measurements of Fluid Displacement During In Situ Air Sparging , 1996 .

[23]  Alan J. Rabideau,et al.  Field Performance of Air-Sparging System for Removing TCE from Groundwater , 1999 .

[24]  Emil O. Frind,et al.  Nonequilibrium mass transfer between the vapor, aqueous, and solid phases in unsaturated soils during vapor extraction , 1994 .

[25]  William G. Gray,et al.  General conservation equations for multi-phase systems: 1. Averaging procedure , 1979 .

[26]  M. Marley,et al.  The Application of In Situ Air Sparging as an Innovative Soils and Ground Water Remediation Technology , 1992 .

[27]  R. Mohtar,et al.  Field and numerical analysis of in-situ air sparging: a case study. , 2000, Journal of hazardous materials.

[28]  Kurt D. Pennell,et al.  An Experimental Investigation of Rate‐Limited Nonaqueous Phase Liquid Volatilization in Unsaturated Porous Media: Steady State Mass Transfer , 1995 .

[29]  Mark L. Brusseau,et al.  The influence of sorbate-organic matter interactions on sorption nonequilibrium , 1989 .