Optimization Study of a Pump - and - Treat System At Massachusetts Military Reservation

The Massachusetts Military Reservation is located in the western portion of Cape Cod. World War II and the period immediately afterward saw the most intense military activity on the base. During this time, chemicals leached into the groundwater and contaminated the aquifer. One of the larger regions, or plumes, of groundwater contamination is the Chemical Spill 10 (CS10) plume, a region in which maximum contaminant levels of trichloroethene and perchloroethene are exceeded. The treatment system that is in place at the CS-10 site consists of pump-and-treat technology. The newest component of the system is known as the Southern Southwest Remedial Design (SSRD). It includes three extraction wells, one in the in-plume section, and two along leading edges, and a lengthening of two existing infiltration trenches. For the current analysis, a MODFLOW model of the system developed by the Jacobs Engineering Group Inc. was modified in order to facilitate display and manipulation within the preprocessor Visual MODFLOW. This simplified version of the model was calibrated to the pre-pumping steady state water table elevations at the site. It served as a more manageable representation of the CS-10 system. With this model as a basis, the software MODOFC was implemented to perform an optimization of groundwater extraction rates. The results of the optimization procedure led to the recommendation to activate only the most centrally located of the three SSRD wells. The results were subjected to a drawdown analysis, which confirmed that their effects are within an acceptable threshold of impact to the aquifer. Consequently, it is recommended that contaminant transport analysis be performed with the wells performing at the rates optimized in this study for comparison with the Jacobs Engineering Group's final SSRD design. Thesis Supervisor: Peter Shanahan, Ph.D. Lecturer, Department of Civil and Environmental Engineering