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Liquid-release tests, performed in boreholes above an underground opening constructed in unsaturated fractured rock, are used in this study to evaluate seepage into a waste emplacement drift. Evidence for the existence of a capillary barrier at the ceiling of the drift is presented, based on field observations (including spreading of the wetting front across the ceiling and water movement up fractures exposed in the ceiling before seepage begins). The capillary barrier mechanism has the potential to divert water around the opening, resulting in no seepage when the percolation flux is at or below the seepage threshold flux. Liquid-release tests are used to demonstrate that a seepage threshold exists and to measure the magnitude of the seepage threshold flux for three test zones that seeped. The seepage data are interpreted using analytical techniques to estimate the test-specific strength of the rock capillary forces ({alpha}{sup -1}) that prevent water from seeping into the drift. Evaporation increases the seepage threshold flux making it more difficult for water to seep into the drift and producing artificially inflated {alpha}{sup -1} values. With adjustments for evaporation, the minimum test-specific threshold is 1,600 mm/yr with a corresponding {alpha}{sup -1} of 0.027 m.

This report covers progress made at Oak Ridge National Laboratory (ORNL) on research and development projects that contribute to the advancement of fossil energy technologies. Projects on the ORNL Fossil Energy Program are supported by the U.S. Department of Energy (DOE) Office of Fossil Energy, the DOE National Energy Technology Laboratory (NETL), the DOE Fossil Energy Clean Coal Technology (CCT) Program, the DOE National Petroleum Technology Office, and the DOE Fossil Energy Office of Strategic Petroleum Reserve (SPR). The ORNL Fossil Energy Program research and development activities cover the areas of coal, clean coal technology, gas, petroleum, and support to the SPR. An important part of the Fossil Energy Program is technical management of all activities on the DOE Fossil Energy Advanced Research (AR) Materials Program. The AR Materials Program involves research at other DOE and government laboratories, at universities, and at industrial organizations.

The primary hypothesis of this work is that surface-active chemicals and/or microorganisms present in the unsaturated zone can significantly alter interfacial phenomena governing the migration of DNAPLs, thereby affecting the accessibility of a DNAPL during remediation efforts. The surface-active materials are present in complex NAPL mixtures and are produced through microbial metabolic processes. The overall goal of this proposed research is to understand the role of and changes in interfacial phenomena on the accessibility of DNAPL in the vadose zone.

This report summarizes progress from the Laboratory Directed Research and Development (LDRD) program during fiscal year 2000. In addition to a programmatic and financial overview, the report includes progress reports from 244 individual R and D projects in 13 categories.