Use of Physics Based Management Optimization for Groundwater Remedy Design - 18671
Numerical modeling coupled with formal mathematical optimization techniques was used to design a groundwater remedy strategy to address a carbon tetrachloride (CCl{sub 4}) plume covering several square miles. The optimization approach, methodology, and project costs are described. The site consists of a large grain elevator in Nebraska. CCl{sub 4} was used as a fumigant and subsequently impacted soils and groundwater. Remedy design focused on the more diffuse plume, which extended approximately 4.5 miles down gradient of the source area. An eleven-layer model was developed and calibrated to observed groundwater conditions. This model was linked with formal optimization techniques to identify the best design capable of meeting client specified requirements and well location limitations. The planned system included requirements on the location of extraction and injection wells, total system flow rate, number of management periods, and specific constraints limiting further plume expansion. A separate trinitrotoluene (TNT) contaminant plume from a third party was located vertically above the leading edge of the CCl{sub 4} plume within the same aquifer. A further constraint imposed was that the design could not affect or cause additional migration of the TNT plume. Optimal system design was determined using HydroGeoLogic's Physics Based Management Optimization (PBMO{sup TM}) system. Over 38,000 candidate solutions consisting of different combinations of pumping and injection wells locations and rates, were evaluated through flow modeling coupled with either particle tracking or fully convective-dispersive transport simulations to determine the optimal design. Planning for installation of the optimal design is underway. Simulations were completed on a distributed computing platform consisting of 3 Quad Core PCs. Flow and particle tracking simulations required less than 2 minutes per simulation. Coupled flow and transport simulation run times were generally between 30-40 minutes per simulation. The total costs for developing the groundwater flow model and completing the subsequent optimal design were approximately $400,000. (authors)