[en] With the increased emphasis by Department of Energy personnel on assessing the environmental impact of past waste disposal practices at all of its facilities, there has been an associated increase in characterization activities that focus on delineating site-specific groundwater flow regimes and contaminant migration pathways. At the Oak Ridge Y-12 Plant, the complex geologic and hydrologic relationships require a more detailed understanding of the three-dimensional properties of groundwater flow regimes than can be obtained by conventional monitoring activities. Thus, as part of groundwater characterization activities conducted by the Environmental Surveillance Section staff of the Y-12 Plant Environmental Management Department, five existing deep core holes were instrumented with multiport monitoring systems to provide greatly enhanced resolution of the hydraulic and hydrochemical properties of the groundwater system within Bear Creek Valley. With a multiport system, it is possible to measure hydraulic head and hydraulic conductivity and collect water samples from multiple levels within a single borehole. In this report, multiport data collected during fiscal years (FYs) 1990 and 1991 are summarized