The Impact of Well-Field Configuration on Plume Persistence
It is now recognized that most sites with large groundwater contaminant plumes will require many decades before cleanup will be achieved under current methods and standards. Conceptually, the factors that contribute to plume persistence have long been established, including uncontrolled source zones, dispersed reservoirs of dissolved (present in lower-permeability zones) and sorbed contaminant, and hydraulic-related factors such as non-optimal remedial well-field performance. Of these potential factors, hydraulic phenomena associated with configuration and operation of the well field employed for remedial operations have received minimal attention. The objective of this research is to investigate the influence of well-field configuration on contaminant mass removal and reduction in contaminant mass discharge (CMD). Mathematical modeling, implemented using MODFLOW and MT3D, was conducted to simulate scenarios with different well-field configurations in both homogenous and heterogeneous aquifers. The system was designed such that contaminant was present as only aqueous and sorbed mass (no separate organic-liquid sources). The impacts of several variables on the results are investigated, including pumping rate, layer thickness, and vertical dispersivity. The results are assessed in terms of the relationship between reductions in CMD and reductions in contaminant mass.