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Moisture monitoring in large diameter boreholes

Description: The results of both laboratory and field experiments indicate that the neutron moisture gauge traditionally used in soil physics experiments can be extended for use in large diameter (up to 15 cm) steel-cased boreholes with excellent results. This application will permit existing saturated zone monitoring wells to be used for unsaturated zone monitoring of recharge, redistribution and leak detection from waste disposal facilities. Its applicability to large diameter cased wells also gives the soil physicist and ground-water hydrologist and new set of monitoring points in the unsaturated zone to study recharge and aquifer properties. 6 refs., 6 figs., 2 tabs.
Date: November 19, 1985
Creator: Tyler, S.
Partner: UNT Libraries Government Documents Department

The role of fracture coatings on water imbibition into unsaturated tuff from Yucca Mountain

Description: Studies dealing with fracture flow at Yucca Mountain have generally assumed that any water flowing down in a fracture will be absorbed by the porous matrix. However, a thin lining of low permeability material on the fracture walls may significantly impede imbibition into the matrix of unsaturated tuff. In this research, imbibition was measured across the fracture surfaces in the laboratory. Samples were collected from surface outcrops of Tiva Canyon and Topopah Spring members of the Paintbrush tuff near Yucca Mountain. Sorptivity, a convenient measure of imbibition, was used to investigate the changes in hydraulic properties as a result of fracture coatings. Results from experimental analysis of Topopah Spring tuff showed decreased sorptivity across coated fracture surfaces. Statistically, the coatings on the Tiva Canyon samples do not significantly affect sorptivity. Scanning Electron Microscope analysis shows that coatings on the s grit Tiva Canyon samples are made up of iron, aluminum and to some extent magnesium. Coating material on the Topopah Spring samples is made up of calcium, magnesium, aluminum and iron. Coating significantly reduces the sorptivity for the Topopah Spring tuff. Numerical results are presented to show the effect of fracture coatings on water infiltration down a vertical fracture in simulated tuff. For the Topopah Spring tuff, the wetting front in the coated fracture travels deeper in the fracture and less into the matrix compared to the wetting front in the uncoated fracture. For the Tiva Canyon tuff, the wetting front in the uncoated fracture travels deeper in the fracture and less into the matrix as compared to the wetting front in the coated fracture.
Date: November 1, 1995
Creator: Chekuri, V.S.; Tyler, S.W. & Fordham, J.W.
Partner: UNT Libraries Government Documents Department

Hydrogeologic characterization of wells HTH-1, UE18r, UE6e, and HTH-3, Nevada Test Site

Description: Monitoring for the migration of contaminants in groundwater or for the proper design of nuclear test emplacement holes at the Nevada Test Site (NTS) requires proper placement and completion of monitoring wells. This is only possible if the hydrogeologic system is understood in a regional and local context, necessitating data from existing wells and boreholes. Though the NTS Groundwater Characterization Project will be drilling wells, their great expense limits the number of new wells. However, there are many existing boreholes and wells on the NTS which have not been completely evaluated hydrologically. Some of these are incorporated in the Long Term Hydrologic Monitoring Program (LTHMP) of the US Environmental Protection Agency (EPA), others are related to the testing programs. In all cases, additional site investigation in necessary to properly interpret the hydrogeologic data from these wells. Monitoring wells on the NTS are poorly characterized with regard to aquifers penetrated, vertical hydraulic gradients, and vertical variations in water quality. One of the goals of the well validation program was to gain a thorough understanding of the parameters needed to interpret the source and fate potential hazardous and radioactive substances that may be detected in these wells in the future. One of the most critical parameters for monitoring is the knowledge of what aquifer or geologic unit is being sampled when a water sample is collected. Pumped water samples are weighted most heavily to the water quality of the most productive (highest transmissivity) aquifer penetrated by the well.
Date: June 1, 1991
Creator: Lyles, B.F.; McKay, W.A.; Chapman, J.B. & Tyler, S.W.
Partner: UNT Libraries Government Documents Department

Radiological impact of uranium tailings and alternatives for their management

Description: Uncontrolled tailings piles are mobile sources of fugitive dust that may produce a practically uncleanable adjacent environment. A practical procedure for managing solid tailings is addition of surface moisture, mechanical and gravitational separation of slimes, and storage of slimes below solution tailings. Presently practical alternatives for tailings management are variations of two basic methods - surface below-ground disposal. Isolation of tailings by natural materials such as clay lenses and combinations of overburden, top soil, vegetation and rip-rap may provide both minimization of exposure and stability. Experimental measurement of radon flux over two inactive tailings, acid and carbonate leached tailings resulted in average specific flux values of phi infinity approx. = 0.64 and phi infinity approx. = 0.30 (pCi Rn-222/m/sup 2/ sec) / (pCi Ra-226/g), respectively. The average diffusion coefficient for these tailings were, respectively, 2.4 x 10/sup -3/ and 5.7 x 10/sup -4/ cm/sup 2//sec. Tailings covered with native soil of clay-silt-sand mixture to a depth of 225 cm resulted in attenuation of flux with diffusion coefficients of 3.69 x 10/sup -3/ and 3.60 x 10/sup -3/ cm/sup 2//sec for ACID and ALKO sites, respectively. By means of the UDAD code dose commitments were estimated for inhalation of particulates and radon and for external exposure under three degrees of surface moisture on the tailings. Based on these analyses and assumption that the dose contribution from ingestion pathway is comparable in magnitude to that of inhalation, both compliance with the 25 mrem/year limit and reduction of flux to background level is feasible. Stability of alternative decommissioned tailings over the predictable future is discussed.
Date: January 1, 1979
Creator: Momeni, M.H.; Kisieleski, W.E.; Tyler, S.; Zielen, A.; Yuan, Y. & Roberts, C.J.
Partner: UNT Libraries Government Documents Department

Random numbers spring from alpha decay

Description: Congruential random number generators, which are widely used in Monte Carlo simulations, are deficient in that the number they generate are concentrated in a relatively small number of hyperplanes. While this deficiency may not be a limitation in small Monte Carlo studies involving a few variables, it introduces a significant bias in large simulations requiring high resolution. This bias was recognized and assessed during preparations for an accident analysis study of nuclear power plants. This report describes a random number device based on the radioactive decay of alpha particles from a /sup 235/U source in a high-resolution gas proportional counter. The signals were fed to a 4096-channel analyzer and for each channel the frequency of signals registered in a 20,000-microsecond interval was recorded. The parity bits of these frequency counts (0 for an even count and 1 for an odd count) were then assembled in sequence to form 31-bit binary random numbers and transcribed to a magnetic tape. This cycle was repeated as many times as were necessary to create 3 million random numbers. The frequency distribution of counts from the present device conforms to the Brockwell-Moyal distribution, which takes into account the dead time of the counter (both the dead time and decay constant of the underlying Poisson process were estimated). Analysis of the count data and tests of randomness on a sample set of the 31-bit binary numbers indicate that this random number device is a highly reliable source of truly random numbers. Its use is, therefore, recommended in Monte Carlo simulations for which the congruential pseudorandom number generators are found to be inadequate. 6 figures, 5 tables.
Date: May 1, 1980
Creator: Frigerio, N.A.; Sanathanan, L.P.; Morley, M.; Clark, N.A. & Tyler, S.A.
Partner: UNT Libraries Government Documents Department

Leak detection systems for uranium mill tailings impoundments with synthetic liners

Description: This study evaluated the performance of existing and alternative leak detection systems for lined uranium mill tailings ponds. Existing systems for detecting leaks at uranium mill tailings ponds investigated in this study included groundwater monitoring wells, subliner drains, and lysimeters. Three alternative systems which demonstrated the ability to locate leaks in bench-scale tests included moisture blocks, soil moisture probes, and a soil resistivity system. Several other systems in a developmental stage are described. For proper performance of leak detection systems (other than groundwater wells and lysimeters), a subgrade is required which assures lateral dispersion of a leak. Methods to enhance dispersion are discussed. Cost estimates were prepared for groundwater monitoring wells, subliner drain systems, and the three experimental systems. Based on the results of this report, it is suggested that groundwater monitoring systems be used as the primary means of leak detection. However, if a more responsive system is required due to site characteristics and groundwater quality criteria, subliner drains are applicable for ponds with uncovered liners. Leak-locating systems for ponds with covered liners require further development. Other recommendations are discussed in the report.
Date: September 1, 1983
Creator: Myers, D.A.; Tyler, S.W.; Gutknecht, P.J. & Mitchell, D.H.
Partner: UNT Libraries Government Documents Department

Chloride-mass-balance for predicting increased recharge after land-use change

Description: The chloride-mass-balance (CMB) method has been used extensively to estimate recharge in arid and semi-arid environments. Required data include estimates of annual precipitation, total chloride input (from dry fallout and precipitation), and pore-water chloride concentrations. Typically, CMB has been used to estimate ancient recharge but recharge from recent land-use change has also been documented. Recharge rates below a few mm/yr are reliably detected with CMB; however, estimates above a few mm/yr appear to be less reliable. We tested the CMB method against 26 years of drainage from a 7.6-m-deep lysimeter at a simulated waste-burial ground, located on the Department of Energy s Hanford Site in southeastern Washington State, USA where land-use change has increased recharge rates. Measured drainage from the lysimeter for the past 26 years averaged 62 mm/yr. Precipitation averaged 190 mm/yr with an estimated chloride input of 0.225 mg/L. Initial pore-water chloride concentration was 88 mg/L and decreased to about 6 mg/L after 26 years, while the drainage water decreased to less than 1 mg/L. A recharge estimate made using chloride concentrations in drain water was within 20 percent of the measured drainage rate. In contrast, recharge estimates using 1:1 (water: soil) extracts were lower than actual by factors ranging from 2 to 8 or more. The results suggest that when recharge is above a few mm/yr, soil water extracts can lead to unreliable estimates of recharge. For conditions of elevated recharge, direct sampling of pore water is the preferred method, because chloride concentrations are often 20 to 50 times higher in directly-sampled pore water than in pore-water extracts.
Date: February 23, 2004
Creator: Gee, G.W.; Zhang, Z.F.; Tyler, S.W.; Albright, W.H. & Singleton, M.J.
Partner: UNT Libraries Government Documents Department