Stratabound pathways of preferred groundwater flow: An example from the Copper Ridge Dolomite in East Tennessee

The Copper Ridge Dolomite of the Upper Cambrian Knox Group underlies a site at Oak Ridge, Tennessee under consideration by the Department of Energy (DOE) for a below ground waste disposal facility. The Copper Ridge was studied for DOE to understand the influence of lithology on deep groundwater flow. Three facies types are distinguished which comprise laterally continuous, 1 to 4 m thick rock units interpreted to represent upward-shallowing depositional cycles having an apparently significant effect on groundwater flow at depth. Rock core observations indicate one of the recurring facies types is characterized by thin to medium-bedded, fine-grained dolostone with planar cryptalgal laminae and thin shaley partings. Distinctive fracturing in this facies type, that may have resulted from regional structural deformation, it considered to be responsible for weathering at depth and the development of stratabound pathways of preferred groundwater flow. In addition, geophysical data suggest that one occurrence of this weathered facies type coincides with an apparent geochemical interface at depth. Geophysical data also indicate the presence of several fluid invasion horizons, traceable outside the study area, which coincide with the unweathered occurrence of this fine-grained facies type. The subcropping of recurrent zones of preferred groundwater flow at the weathered/unweathered interface may define linear traces of enhanced aquifer recharge paralleling geologic strike. Vertical projection of these zones from the weathered/unweathered rock interface to the ground surface may describe areas of enhanced infiltration. Tests to determine the role of stratigraphic controls on groundwater flow are key components of future investigations on West Chestnut Ridge. 14 refs., 13 figs

Discovery, interception, and treatment of a groundwater plume: Oak Ridge National Laboratory

A radiological groundwater plume was discovered to be discharging into a surface stream and portions of the storm drain network at Oak Ridge National Laboratory (ORNL). A CERCLA removal action was initiated to address the discharges. The plume was found to be migrating 65 degrees oblique to the overall hydraulic gradient and was identified only after historic data were analyzed and field tests were performed under the working hypothesis of stratabound flow and transport. A detailed geologic and hydrologic analysis was performed that accurately predicted the 3-dimensional plume configuration from a single point datum where significantly elevated contaminant levels were found in a bedrock core hole. Subsequent sampling found that direct discharges of contamination existed in the stream only in the location of the predicted stratum. The affected storm drain outfall discharges were suspected to be the major contributors to {sup 90}Sr surface water risk from ORNL. Thus, the selected removal action focused on eliminating the known seepage to the storm drain network. Intercept system operations reduced the total surface water {sup 90}Sr flux by about 90%. Ongoing investigations seek to identify the source of the plume with the hope that the intercept system may eventually be deactivated. However, the efficiency of the system exceeded expectations and demonstrated that a good understanding of the hydrodynamics is a prerequisite to success. The relatively trouble free operation of the system also indicates that simple technologies can serve as effective measures to address immediate problems

Characterizing groundwater at Oak Ridge National Laboratory hazardous waste sites

The Oak Ridge National Laboratory (ORNL) is a large multipurpose US Department of Energy research facility located in East Tennessee on the Oak Ridge Reservation (ORR). The legacy of fifty years of operations at ORNL includes a variety of contaminated inactive facilities, research areas, and former waste disposal areas. At ORNL the majority of wastes were buried in shallow trenches above the water table. Groups of geographically contiguous areas, referred to as waste area groupings (WAGs), were defined for the Environmental Restoration Program so that a suitable monitoring system could be established. Thirteen WAGs at ORNL have been identified as potential sources of groundwater contamination. The main objective of the work described in this paper was to develop a systematic means for analyzing routine groundwater monitoring data from all WAGs to facilitate interpretation at a scale larger than individual monitoring points, to look for patterns that suggest general principles. In particular we wanted to determine whether specific geologic formations have discernable groundwater chemical signatures. The description of geologic formations in terms of their groundwater chemical signatures can be used in several practical ways. Positioning of down gradient sampling locations can be evaluated by comparing contaminant source and down gradient geochemistries. The geochemistry of contaminated seeps and springs can be used to suggest a likely stratigraphic association to the contaminant source. Also, the contaminant source location geochemistry and knowledge of the geologic unit`s potential for strata-bound flow can be used to predict exit pathways from contaminant sources

Use of DOE site selection criteria for screening low-level waste disposal sites on the Oak Ridge Reservation

The proposed Department of Energy (DOE) site selection criteria were applied to the Oak Ridge Reservation, and the application was evaluated to determine the criteria's usefulness in the selection of a low-level waste disposal site. The application of the criteria required the development of a methodology to provide a framework for evaluation. The methodology is composed of site screening and site characterization stages. The site screening stage relies on reconnaissance data to identify a preferred site capable of satisfying the site selection criteria. The site characterization stage relies on a detailed site investigation to determine site acceptability. The site selection criteria were applied to the DOE Oak Ridge Reservation through the site screening stage. Results of this application were similar to those of a previous siting study on the Oak Ridge Reservation. The DOE site selection criteria when coupled with the methodology that was developed were easily applied and would be adaptable to any region of interest

Source Areas Investigation Plan and Recommendation for Removal Actions at Waste Area Grouping 5 at Oak Ridge National Laboratory, Oak Ridge, Tennessee. Environmental Restoration Program

This Source Area Investigation Plan and Recommendation for Removal Action (SAIP/RRA) was prepared in support of the regulatory working group for Oak Ridge National Laboratory (ORNL) Waste Area Grouping (WAG) 5. The purpose of the plan is to focus the investigation of and initiate potential groundwater seepage control actions for contaminant source areas at WAG 5. The SAIP/RRA addresses four discrete groundwater discharge areas (seeps) in or near WAG 5 that have been identified as significant contributors to the contaminant flux released from ORNL at White Oak Dam. Combined, these four seeps (designated Areas A, B, C, and D) contribute 25--50% and 20--45% of the total flux of tritium and strontium-90, respectively, in the White Oak Creek watershed. To reduce the release of contaminants from these areas and prevent further degradation of surface water, non-time-critical removal actions are proposed at the two areas characterized by discrete seeps: Areas C and D. An Engineering --Evaluation/Cost Analysis will be initiated to identify and evaluate feasible removal actions for these areas. Further investigation activities are planned at all four areas, and will emphasize, identifying and characterizing the contaminant source terms and migration pathways