COLLABORATIVE RESEARCH: EVALUATION OF THE EFFECTS OF PHYSICAL AND GEOCHEMICAL HETEROGENEITY ON VIRUS TRANSPORT IN AQUIFERS (SGER )

PI: C. Welty, Co-PI: Ronald W. Harvey, USGS Denver
PI: Joseph N. Ryan, University of Colorado Boulder

Funding Source: NSF Environmental Engineering

The purpose of this project is to obtain initial data to quantify virus transport in physically and geochemically heterogeneous, unconsolidated aquifer materials under carefully controlled laboratory conditions and to incorporate the observational results in a stochastic model of virus transport in aquifers. This work is considered to be "high risk" in that the hypotheses set forth based on related work and heuristic arguments not previously tested. Initial results obtained under this effort will be utilized in a full proposal to NSF at a later time.

The long-term goal of the proposed work is to advance the understanding of mechanisms governing transport of pathogenic viruses heterogeneous aquifer materials for application to environmental engineering design. The near-term objectives of this SGER proposal are twofold. The first objective is to test the hypotheses, using carefully controlled laboratory column studies, that the following local-scale virus transport parameters are correlated to physical aquifer heterogeneity (as characterized by hydraulic conductivity) and the degree of geochemical heterogeneity (as characterized in a model system by percentage ferric oxyhydroxide surface coatings): (a) collision frequency, or single collector efficiency (h0), (b) collision efficiency (ac), (c) detachment rate coefficient (kdet), and (d) surface inactivation rate coefficient (kds). The second objective is to utilize the observational findings to develop a stochastic model of virus transport in physically and geochemically heterogeneous media, where large-scale aquifer properties are defined by a geostatistical representation of hydraulic conductivity and degree of geochemical heterogeneity, and local-scale aquifer-virus interactions are characterized by the observational laboratory results.

To test the hypotheses that virus transport properties are correlated to the hydraulic conductivity and geochemical heterogeneity of the porous medium, "synthetic" porous media will be created by purchasing quartz sand available in eight well-sorted size fractions and coating the sand with desired percentages of ferric oxyhydroxides. The synthetic sand and bacteriophage virus PRD1 will be used in a series of column studies designed to determine local-scale transport parameters for columns containing sands of differing hydraulic conductivity and percentage surface coatings. The observational findings will be incorporated in a streamline-based stochastic model to evaluate (1) the effect of coupling of local-scale virus transport phenomena with a three-dimensional random-field model of aquifer hydraulic conductivity, including the effect of geochemical heterogeneity, and (2) the importance of the effect of this local-scale interaction on large-scale virus transport in heterogeneous media.

Future work will include evaluating a suite of viruses to test the influence of virus size and isoelectric point on the developed correlations. Future efforts will also include testing the developed models by running field experiments at the USGS Cape Cod site.

This is a collaborative research proposal that involves investigators at three institutions. Dr. Claire Welty (UMBC) is supervising model development and application. Dr. Joseph N. Ryan (University of Colorado) and Dr. Ronald W. Harvey (U.S. Geological Survey) are supervising column experiments in Boulder. Drs. Reed M. Maxwell and Andrew F.B. Tompson of Lawrence Livermore National Laboratory have provided advice on revised streamline model development.


STOCHASTIC ANALYSIS OF VIRUS TRANSPORT IN AQUIFERS

PI: C. Welty, Co-PI: Ronald W. Harvey, USGS Denver

Funding Source: NSF Hydrologic Science Program

Objectives

The objective of the work is to develop a three-dimensional stochastic model of virus transport in aquifers. The hypothesis to be tested is that the stochastic spectral approach provides an improved representation of field-scale virus transport compared to other currently available models. The scope of work as stated in the proposal includes three parts: (1) deriving the three-dimensional field-scale (mean) governing equations for free virus transport and mass conservation of attached viruses, and the effective parameters in those governing equations, by applying spectral stochastic analysis to the chosen local-scale processes; (2) assessing the magnitude and relative importance of the derived effective field parameters and the effects of the complex dependence of these effective field parameters on local-scale processes by carrying out illustrative numerical simulations of the coupled mean equations; and (3) comparing the theoretical results to the best set of observational data available to assess model performance.

Project Findings to Date

A stochastic mean model of virus transport has been developed by linking a system of local-scale free-virus transport and attached virus conservation equations found in the current literature with a random-field representation of aquifer and virus transport properties. The effects of spatial variability in aquifer hydraulic conductivity and virus transport (attachment, detachment, and inactivation) parameters on large-scale virus transport have been evaluated. The resultant mean equations for free and attached viruses have been found to differ considerably from the local-scale equations on which they are based, and include such effects as a free virus effective velocity that is a function of aquifer heterogeneity as well as virus transport parameters. Stochastic mean free virus breakthrough curves have been compared with local model output in order to observe the effects of spatial variability on virus transport.

Significant findings include: (1) stochastic model breakthrough occurs earlier than local model breakthrough, and this effect is most pronounced for the least conductive aquifers studied, (2) a high degree of aquifer heterogeneity can lead to virus breakthrough actually preceding that of a conservative tracer, (3) as the mean hydraulic conductivity is increased, the mean model shows less sensitivity to the variance of the natural-logarithm hydraulic conductivity and mean virus diameter, (4) incorporation of a heterogeneous colloid filtration term results in higher predicted concentrations than a simple first-order adsorption term for a given mean attachment rate, and (5) the mean model is more sensitive to the inactivation rate of viruses associated with solid surfaces than to the inactivation rate of viruses in solution.

Validation of the stochastic mean model is being carried out by
implementation of a streamline method for three-dimensional simulation of virus transport in heterogeneous media. The model uses a Lagrangian coordinate transform along dominant flow pathways or streamlines, yielding a series of independent, one-dimensional transport simulations. Transport equations for free and attached colloid are solved simultaneously as a function of space and time along each streamline. Any number of geostatistical techniques may be used to generate the input hydraulic conductivity distribution. Coupling of hydraulic conductivity variability with colloid filtration is carried out by mathematical specification of functional correlations between hydraulic conductivity and (1) colloid collision (sticking) efficiency, (2) single collector efficiency, (3) grain size and effective porosity, and (4) detachment. The model can be used to predict virus transport at any scale.

Presentations and Publications

Rehmann, L. L. C., C. Welty, and R.W. Harvey. Stochastic Mean Simulation of Virus Transport in Aquifers EOS Trans. AGU, 79(17), Spring Meeting Suppl., S144, 1998.
(Presentation by L. L. C. Rehmann received outstanding AGU student paper award).

Rehmann, Linda L. C. , A Spectral Stochastic Model of Virus Transport in Aquifers. Ph.D. Dissertation, Drexel University, May 1998, 225 p.

Rehmann, L. L. C., C. Welty, and R. W. Harvey, Stochastic Analysis of Virus Transport in Aquifers, Water Resources Research, 35(7), 1987-2006, 1999.

Rehmann, L. L. C., C. Welty, and R. W. Harvey, (Invited talk presented by C. Welty), A Stochastic Approach to Modeling Virus Transport in Aquifers, European Geophysical Society Meeting, April 20, 1999, The Hague.

Rehmann, L.L.C. (Invited talk) Beyond the Keyhole Approach: Understanding virus transport in heterogeneous aquifers using stochastics. International Symposium on Subsurface Microbiology,Vail, Colorado, August 27, 1999.

Ren, J. A. Packman, and C. Welty, Correlation of Colloid Collision Efficiency with Hydraulic Conductivity of Silica Sands. EOS Trans AGU, Fall Meeting Suppl. 1999.

C. Welty, Seminar to Lawrence Livermore National Lab, 5/4/99

C. Welty, Seminar to Technical University of Munich, 7/15/99

L. L.C. Rehmann, Seminar to Princeton University, 11/19/99

C. Welty, Seminar to CalTech, 2/9/00

Ren, J. A. Packman, and C. Welty, Correlation of Colloid Collision Efficiency with Hydraulic Conductivity of Silica Sands. Water Resources Research, 36(9), 2493-2500, 2000.

Ren, J., A. I. Packman, and C. Welty. Variation in Colloid Collision Efficiency Due to the Size of Collector Media. (Presented by J. Ren),"Colloid 2000", 74th Colloid and Surface Science Symposium, Sponsored by the ACS Division of Colloid and Surface Chemistry, Lehigh University, Bethlehem, Pennsylvania, June 18-21, 2000.

Rehmann, L. L. C., C. Welty, and R. W. Harvey, Reply to Comment by T.R. Ginn on Stochastic Analysis of Virus Transport in Aquifers, Water Resources Research, 36(7), 1983-1984, 2000.

Maxwell, R. M. and C.Welty, Simulation of the Impact of Geologic Heterogeneity on Colloid Transport in Riverbank Filtration, presented at the Second International Conference on Riverbank Filtration, Düsseldorf, Germany, November 2 -4 , 2000.

Maxwell, R. M., C.Welty, and R. W. Harvey. Simulation of Biocolloidal Transport in Three-Dimensionally Heterogeneous Geologic Media Using a Streamline Approach. Fall 2000 Meeting of the American Geophysical Union, San Francisco, Dec. 15 - 19, 2000. EOS Trans AGU, Fall Meeting Suppl. 2000.

Maxwell, R. M. and C.Welty, Simulation of the Impact of Geologic Heterogeneity on Colloid Transport in Riverbank Filtration, Proceedings of the Second International Conference on Riverbank Filtration, Düsseldorf, Germany, November 2 -4 , 2000; IAWR, International Association of the Waterworks of the Rhine Series "Rhein-Themen 4", DIN-A5, pp. 241-250, 2001.

Tompson , A. F. B. ,M. Lee Davisson, R. M. Maxwell, G. Bryant Hudson, Claire Welty, S. F. Carle, and Nina D. Rosenberg. On the Fate of Artificial Recharge in a Coastal Aquifer. Submitted to The First International Conference on Salt Water Intrusion and Coastal Aquifers--Monitoring, Modeling, and Management. Essaouira, Morocco, April 18-25, 2001.

Ren, J., A. I. Packman, and C. Welty. Analysis of an observed relationship between colloid collision efficiency and mean collector grain size, Colloid and Surfaces A: Physicochemical and Engineering Aspects, 191, 133-144, 2001.

R.M. Maxwell, Seminar to Orange County Water District, 2/13/01.

C. Welty, Seminar to University of Delaware, 3/8/01.

Maxwell, R. M., C.Welty, and A.F.B. Tompson. "Streamline-based Simulation of Virus Transport Resulting from Long Term Artificial Recharge in a Heterogeneous Aquifer." Presented on December 13, 2001 at the Fall Meeting of the American Geophysical Union, San Francisco, Abstract in Eos Trans. AGU, 82(47), Fall Meeting Suppl., H42E-08, 2001.

Maxwell, R. M. , C. Welty, and A.F.B. Tompson. "Streamline-Based Simulation of Cryptosporidium Transport in Riverbank Filtration", presented at the Second USGS/EPA STAR Cryptosporidium Removal by Bank Filtration
Meeting, September 9 - 10, 2003, USGS HQ, Reston VA.

Maxwell, R. M., C. Welty, and A.F.B. Tompson. Streamline-based simulation of virus transport resulting from long-term artifical recharge in a heterogeneous aquifer, Advances in Water Resources, 26(10), 1075-1096, 2003.

Availability of Materials

  • Dissertation - Available through Interlibrary Loan from Drexel University's Hagerty Library; Available for purchase from University Microfilms in Ann Arbor, Michigan http://www.umi.com/; Limited photocopies available from C. Welty - Send requests to weltyc@umbc.edu
  • Journal articles - Send reprint requests to weltyc@umbc.edu
  • Code for mean virus transport - Hard copy is printed in appendix of L. L. C. Rehmann's dissertation; electronic copy is available upon request from C. Welty at weltyc@umbc.edu.

This material is based upon work supported by the National Science Foundation under Grant No. 9725086. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.