Use of particle tracking to improve numerical model calibration and to analyze ground-water flow and contaminant migration, Massachusetts Military Reservation, western Cape Cod, Massachusetts

A steady-state, three-dimensional numerical model coupled with a particle-tracking algorithm was developed to simulate the complex hydrogeologic conditions affecting ground-water flow and contaminant migration in the Cape Cod aquifer beneath the Massachusetts Military Reservation, Massachusetts. The known extents of the contaminant plumes beneath the reservation were incorporated into a particle-tracking analysis to improve model calibration. Particle tracking was used to evaluate the effects of simulated changes in hydraulic properties and in simulated hydrologic boundaries such as ponds and streams.

The model simulations made during the calibration process indicated that changes in simulated hydraulic properties and hydrologic boundaries resulted in small changes in the water-table and pond altitudes and in streamflows, yet had a substantial effect on model-calculated groundwater flowpaths. Therefore, the characterization of contaminant migration using a model calibrated only on the basis of ground-water heads and flux may be inaccurate.

The results of model simulations for the analysis of the effects of pumping and recharge on ground-water flow and contaminant migration indicated that ground-water flowpaths were greatly affected by subtle shifts in hydraulic gradients. These changes in the ground-water-flow system in response to hydrologic stresses such as pumping and recharge can be determined by the use of a particle-tracking analysis.