Investigation of groundwater flow zones and contaminant transport in Solid Waste Storage Area 5 at Oak Ridge National Laboratory, Oak Ridge, Tennessee. Environmental Restoration Program

摘要

An understanding of subsurface transport processes is essential to produce realistic predictions of future contaminant discharge from Solid Waste Storage Areas (SWSAs) at Oak Ridge National Laboratory (ORNL). Locating groundwater flow zones (permeable pathways) and determining the relative contributions of primary vs secondary contaminant sources are critical to the proper selection and evaluation of remedial actions. Because groundwater discharge from SWSA 5 contributes significant amounts of (sup 3)H and (sup 90)Sr to the White Oak Creek watershed, an area on the southeastern edge of SWSA 5 was chosen for an investigation aimed at understanding and characterizing the subsurface movement of contaminants. Preliminary data collected in 1991 indicated that the vertical distribution of (sup 3)H (0.02 to 279 (mu)Ci/L) observed over the sampled interval (O to 10 ft deep) may be a result of upward diffusion from a hydraulically dominant fracture (or fractured zone) below the sampled interval. The investigation continued this year (1992) with the primary objective of defining where the most permeable zones exist in the subsurface and how they relate to the vertical extent of (sup 3)H. An open borehole was drilled on the southeastern edge of SWSA 5 through the upper zones of soil and saprolite and then through interbedded shales and limestones to a depth of about 26 ft. Two methods were used to determine permeable zones within the borehole. In addition, samples were collected monthly from a nearby well and seep (where tritiated groundwater discharges) to determine seasonal variability in the transport of (sup 3)H and (sup 90)Sr from the study area.