Unsaturated Zone Studies at the Proposed Low-Level Radioactive Waste Disposal Facility, Eagle Flat Basin, Texas

dc.creatorScanlon, Bridget R.
dc.creatorXiang, Jiannan
dc.creatorGoldsmith, Richard S.
dc.description.abstractHydrologic studies were conducted to characterize unsaturated zone processes at the proposed low-level radioactive waste disposal site and surrounding area in southern Hudspeth County, Texas. The study area is in northwest Eagle Flat basin, which is within the Basin and Range Physiographic Province. Fractured Cretaceous bedrock crops out to the southeast of the site. The thickness of the basin-fill sediments at the proposed site ranges from 164 feet (50 m) to approximately 656 feet (200 m). Northwest Eagle Flat basin is an internally drained basin that drains through the ephemeral Blanca Draw into Grayton Lake playa. The climate in the study area is subtropical arid and the long-term average annual rainfall is 12.6 inches (320 mm). Unsaturated zone studies were conducted in ephemeral stream and interstream geomorphic settings. In addition to studies of areas typical of these settings, the impact of pseudofissures, an earth fissure, and borrow pits on shallow zone unsaturated processes was also investigated. To evaluate unsaturated zone processes, 57 boreholes were drilled in the various geomorphic settings for collection of soil samples and installation of monitoring equipment. Soil samples were analyzed in the laboratory for particle size, water content, water potential, and chloride concentration. Water potential data are used to evaluate the direction of the driving force for water movement. Chloride concentration data provide information on water fluxes because chloride concentrations are inversely proportional to water flux; low chloride concentrations indicate high water fluxes because chloride is flushed through the soil, whereas high chloride concentrations indicate low water fluxes because chloride is concentrated by evapotranspiration. In addition to laboratory analyses, a monitoring program was initiated by installing neutron probe access tubes in the different geomorphic settings to monitor water content. Field psychrometers were installed to a depth of 60.7 feet (18.5 m) in the interstream setting to monitor water potential and temperature. Hydraulic conductivity was also measured in the field using permeameter tests, constant-head borehole infiltration tests, and multistep constant-head borehole infiltration tests.
dc.description.departmentBureau of Economic Geology
dc.relation.ispartofContract Reports
dc.subjectunsaturated zone
dc.subjectradioactive waste
dc.subjectwaste disposal
dc.subjectEagle Flat Basin
dc.titleUnsaturated Zone Studies at the Proposed Low-Level Radioactive Waste Disposal Facility, Eagle Flat Basin, Texas

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