10.2190/XJDL-WXFG-QALQ-P8TM XJDLWXFGQALQP8TM 1 LESSONS FOR ENVIRONMENTAL MANAGERS IN CHOOSING AND APPLYING MODELS FOR GROUNDWATER TRANSPORT AND REMEDIATION: A CASE STUDY 1 26 20050531 20050531 20050531 20050531 XJDLWXFGQALQP8TM.pdf http://baywood.metapress.com/link.asp?target=contribution&id=XJDLWXFGQALQP8TM 1 SARA SAYLER WILLIAM F. MCTERNAN SCOTT A. WARD Tinker Air Force Base Oklahoma State University, Stillwater A case study is presented which highlights the large discrepancy in projected environmental remediation requirements resulting exclusively from the selection and application of alternative modeling approaches for a contaminated groundwater system. Initially, a state of the practice numerical modeling system was employed to determine the final contaminant concentrations and plume configurations which could be expected in future years. These methods and models have become almost standard practice in these types of situations. In this particular application, however, the final model configuration was much more complex than was allowed by the collected data and by the aquifer system being modeled. Internal auto-calibration techniques were needed to calibrate critical field collected data with model results. The resultant model although calibrated projected contaminant plumes in excess of remediation goals well beyond regulatory property lines. Projected costs of remediation were in excess of 4 million USD. The projected concentrations and plume configurations following calibration did not, however, agree with time series data established during an extended monitoring program. These collected data suggested a much slower rate of plume migration. Inspection of the initial transport model suggested that the auto-calibration procedures resulted in parameter values far in excess of those measured by a variety of agencies and individuals. An alternative set of analytical procedures were employed to evaluate the statistically possible range of input parameters possible from aggregate measured data and to employ these data in various modeling configurations to define plume configurations and travel times beneath the study area. Geostatistical analysis and Monte Carlo simulations were employed together with relatively simple analytical transport codes in this effort. The results, statistically more robust than those derived in the initial effort, show a significantly reduced plume footprint in future years, with a corresponding reduction in projected remediation costs. The original 4 million USD estimate was reduced to approximately $155,000 USD. Most significantly, these results and projections are based upon techniques that are consistent with the measured data. This case study illustrates the types of technical concerns confronting environmental managers. By necessity, models frequently must be applied to help amplify complex conditions. If the wrong model is selected or if it is improperly configured, however, the resulting analysis may be woefully incorrect resulting in the expenditure of needless resources that may not provide adequate environmental protection. This article develops one set of methodologies available to address these concerns. L. Smith, R. A. Freeze, and J. Massmann, Geostatistical Approach to Site Characterization and Risk Assessment Related to Groundwater Contamination at Hazardous Waste Sites, in Risk Assessment for Groundwater Pollution Control, W. F. McTernan and E. Kaplan (eds.), American Society of Civil Engineers, New York, 1990. J. W. Mercer, L. R. Silka, and C. R. Faust, Modeling Ground-Water Flow at Love Canal, New York, Journal of Environmental Engineering, 109:4, pp. 924-942. G. T. Yeh, AT123D: Analytical Transient One- Two- and Three-Dimensional Simulation of Waste Transport in the Aquifer System, Environmental Sciences Division Publication No. 1439, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1981. American Petroleum Institute, Risk/Exposure Assessment Decision Support System (DSS), Washington, D.C., 1994. U.S. Environmental Protection Agencym, Bioscreen: User Manual, Subsurface Protection and Remediation Division, Ada, Oklahoma, 1997. C. J. Newell, R. K. McLeod, and J. R. Gonzales, BIOSCREEN Natural Attenuation Decision Support System: User's Manual Versions 1.3 and 1.4, U.S. Environmental Protection Agency, Ada, Oklahoma, 1996. A. W. Harbaugh, A Generalized Finite-Difference Formulation for the U.S. Geological Survey Modular Finite Difference Ground-Water Flow Model, United States Geological Survey, Open-File Report 91-494, Reston, Virginia, 1992. C. Zheng, A Modular Three-Dimensional Transport Model for Simulation of Advection, Dispersion and Chemical Reactions of Contaminants in Groundwater Systems, United States Environmental Protection Agency, Ada, Oklahoma, 1990. S. Christenson and L. Carpenter, Ground-Water Quality of the Central Oklahoma (Garber-Wellington) Aquifer, proceedings of the United States Geological Survey, Open-File Report 92-116, February 20, 1992. D. L. Parkhurst, S. Christenson, and G. N. Briet, Ground-Water-Quality Assessment of the Central Oklahoma Aquifer, Oklahoma: Geochemical and Geohydrologic Investigations, United States Geological Survey, Open-File Report 92-642, 1992. J. S. Havens, Geohydrology of the Alluvial and Terrace Deposits of the North Canadian River from Oklahoma City of Eufaula Lake, Central Oklahoma, United States Geological Survey, Water-Resources Investigation Report 88-4234, 1989. N. J. Gantos, T. Fox, N. J. Gupta, M. Kelley, and G. Yu, Work Plan and Data Compilation for the Base-Wide Model at Tinker Air Force Base (AFB), Contract No. DAAL03-91-C-0034, Battelle Memorial Institute, Columbus, Ohio, 1994. Palisades Corporation, @RISK. Risk Analysis and Simulation Add-In for Microsoft Excell, Newfield, New York, 2000. A. G. Journel and C. Huijbregts, Mining Geostatistics, Academic Press, London, 1978. E. Englund and A. Sparks, Geostatistical Environmental Assessment Software, User's Guide, U.S. Environmental Protection Agency, EPA 600/8-91/008, Las Vegas, Nevada, 1991. R. M. Cooper and J. D. Istok, Geostatistics Applied to Groundwater Contamination I: Methodology, Journal of Environmental Engineering, 111:2, 1988. P. Goovaerts, Geostatistics for Natural Resources Evaluation, Oxford University Press, New York, 1997. American Society of Civil Engineers, Review of Geostatistics in Geohydrology. I: Basic Concepts. II: Applications, Journal of Hydraulic Engineering, 116:5, pp. 612-658, 1988. E. H. Isaaks and R. M. Srivastava, An Introduction to Applied Geostatistics, Oxford University Press, New York, 1989. J. D. Dean, P. S. Huyakorn, A. S. Donigian, K. S. Voos, R. W. Schanz, Y. J. Meeks, and R. F. Carsel, Risk of Unsaturated/Saturated Transport and Transformation of Chemical Concentrations (RUSTIC). Volume I: Theory and Code Verification, U.S. Environmental Protection Agency, EPA 600/3-89/048a, Athens, Georgia, 1989.