John Walton | University of Texas at El Paso (UTEP) (original) (raw)

Papers by John Walton

Journal of Environmental Engineering, 1990

Groundwater, 2008

Multivariate statistical methods (MSMs) applied to ground water chemistry provide valuable insigh... more Multivariate statistical methods (MSMs) applied to ground water chemistry provide valuable insight into the main hydrochemical species, hydrochemical processes, and water flowpaths important to ground water evolution. The MSMs of principal component factor analysis (FA) and k‐means cluster analysis (CA) were sequentially applied to major ion chemistry from 211 different ground water–sampling locations in the Amargosa Desert. The FA reduces the number of variables describing the system and finds relationships between major ions. The CA of the reduced system produced objective hydrochemical facies, which are independent of, but in good agreement with, lithological data. The derived factors and hydrochemical facies are innovatively presented on biplots, revealing composition of hydrochemical processes and facies, and overlaid on a digital elevation model, displaying flowpaths and interactions with geologic and topographic features in the region. In particular, a distinct ground water c...

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995

UNDERGROUND EXCAVATIONSRADIOACTIVE WASTE 295A huge-scale steel model silo with a pyramidal hopper... more UNDERGROUND EXCAVATIONSRADIOACTIVE WASTE 295A huge-scale steel model silo with a pyramidal hopper showed that the stress state of the material stored is influenced significantly by the wall flexibility and boundary conditions. The measured wall pressures were very different from pressures predicted by traditional theories and existing design codes. This is because most traditional theories were developed for rigid-wall circular silos and ignored the effects of interaction between stored material and structure. The causes of the observed pressure redistribution are explained. (Authors) 956345 Civil reuses of underground mine openings: a summary of international experience D.

Journal of Geotechnical and Geoenvironmental Engineering, 1997

Leakage through flaws in geomembranes was examined with laboratory experiments and modeling. Math... more Leakage through flaws in geomembranes was examined with laboratory experiments and modeling. Mathematical models were developed using analytical and numerical solutions to calculate leakage through flaws. The models were verified with laboratory experiments. ...

Applied Geochemistry, 2006

A conceptual model for the chemical evolution of near-field water chemistry in the proposed high-... more A conceptual model for the chemical evolution of near-field water chemistry in the proposed high-level nuclear waste repository at Yucca Mountain, Nevada is presented. This model considers the effects of differential solubility in flowing water that is subject to evaporation or condensation. The results of a simplified numerical implementation of the model are used to predict the aqueous chemistries produced from a variety of source waters under two bounding assumptions of separation. The model predicts that, under some conditions the most soluble ions will not always be present in solution. The more soluble ions may precipitate at different locations than ions of slightly less solubility leading to a highly complex system containing different brine compositions at different locations.

Journal of Environmental Engineering, 1998

Influence of Carbonation on Leaching of Cementitious Wasteforms. [Journal of Environmental Engine... more Influence of Carbonation on Leaching of Cementitious Wasteforms. [Journal of Environmental Engineering 124, 463 (1998)]. Md. Sazzad Bin Shafique, John C. Walton, Neyda Gutierrez, Robert W. Smith, Anthony J. Tarquin. Abstract. ...

Materials Research Society Symposium Proceedings, 2008

In the long run, nuclear waste packages at the Yucca Mountain repository are likely to evolve int... more In the long run, nuclear waste packages at the Yucca Mountain repository are likely to evolve into a combination of corroded materials mixed with relicts of intact Alloy-22 and other waste package materials. Different rates of corrosion, due to physical and chemical disturbances in the environment of the repository, will lead to different times of penetration between waste packages and at different locations on the same waste package. Radionuclides are released from waste packages by dissolution and transport in water. In this paper, we shed some light on the effect of residual heat release, and other physical processes that take place in the waste package during penetration times, on radionuclide release. We develop a flow-through conceptual model for a probable serious failure in which multiple penetrations allow water to flow through a partially failed waste container. This model demonstrates that evaporation at hotter protected areas creates a capillary pressure gradient that causes water to flow with its dissolved and suspended contents toward these relict protected areas, effectively preventing radionuclide release. We derive a dimensionless group to estimates the minimum size of the covered areas required to sequester radionuclides and prevent release, and explore the implication of the flow-through model on the Yucca Mountain repository performance.

Journal of Arid Environments, 2005

Timing and amount of solar radiation were examined as factors influencing the distribution of sev... more Timing and amount of solar radiation were examined as factors influencing the distribution of seven perennial plants on a small mountain located in the Chihuahuan Desert. Average direct beam solar radiation fluxes at differing times throughout the day and year were estimated with computer calculations. Principal components analysis was used to reduce the number of solar radiation parameters and include the maximum available information with a manageable number of variables. The remaining solar radiation parameters were compared to plant distributions using redundancy analysis and generalized additive models. Unimodal, bimodal, and monotonic responses were all found depending upon the species and solar radiation parameter. Niche separation at this location depends upon the timing as well as the amount of solar radiation.

Desalination, 2001

Thermal desalination by salinity-gradient solar ponds (SGSP) is one of the most promising solar d... more Thermal desalination by salinity-gradient solar ponds (SGSP) is one of the most promising solar desalination technologies. Solar ponds combine solar energy collection with long-term storage and can provide reliable thermal energy at temperature ranges from 50 to 90°C. Solar-pond-powered desalination has been studied since 1987 at the E1 Paso Solar Pond Project, El Paso, Texas. From 1987 to 1992, the research mainly focused on the technical feasibility of thermal desalination coupled with solar ponds. Since 1999, the research has focused on long-term reliability, improvement of thermodynamic efficiency, and economics. During this period, a small multi-effect, multi-stage flash distillation (MEMS) unit, a membrane distillation unit, and a brine concentration and recovery system (BCRS) were tested over a broad range of operating conditions. The most important variables for the MEMS operation were flash range, concentration level of reject brine, and circulation rate of the fast effect. The brine concentration and recovery system is part of the goal of developing a systems approach combining salinity-gradient solar pond technology with multiple process desalination and brine concentration. This systems approach, called zero discharge desalination, proposes concentrating brine reject streams down to near NaCI saturated solutions and using the solution to make additional solar ponds. In addition to presenting the test results on the MEMS and BCRS units, this paper also presents a summary of solar pond operation experiences obtained from the 16-year operation at the E1 Paso solar pond.

Accurate estimates of groundwater recharge are necessary components for understanding longterm su... more Accurate estimates of groundwater recharge are necessary components for understanding longterm sustainability of groundwater resources and predictions of groundwater flow rates and flow directions. Amargosa Desert regional groundwater studies show that the surface runoff infiltration occur in the arroyos following runoff producing storms, and this infiltration is considered to be a major source of groundwater recharge. The present study attempts to investigate how water chemistry evolves during the surface runoff and infiltration processes, in the southern Amargosa Desert. In this ongoing study, four surface runoff samplers (SRS) were installed at two different arroyos in the southern Amargosa Desert to capture the surface runoff water. The sampling process included sediment, precipitation, and SRS water samples. In total, four SRS, six sediment, and two precipitation samples were collected between September, 2009 and January, 2010. Analysis of chloride and the stable isotopes of wa...

Journal of Environmental Engineering, 1994

Solidification and/or stabilization with cementitious materials prior to burial is one option for... more Solidification and/or stabilization with cementitious materials prior to burial is one option for disposal of liquid hazardous and radioactive wastes. A common design for disposal of cementitious waste forms is to pour the material into large belowground vaults. The leaching performance of partially degraded monolithic vaults is examined quantitatively for facilities located in humid to semiarid climates. Development of perched water on the vault roof leading to fracture flow through the structure is predicted for a wide range of climate and design conditions. Leaching controlled by diffusion in matrix blocks out to fractures is examined parametrically in relation to water flux rate and crack spacing. Depending upon the parameters examined, release rate may be controlled by water flux rate (advection controlled) or diffusion. Under some circumstances, contaminant release rates and exit concentrations are predicted to be inversely related. In this situation, minimization of release does not result in the l...

Applied geochemistry, 2006

MRS Proceedings

Theory of a mechanistic model for estimating the maximum rate of uniform corrosion for a steel or... more Theory of a mechanistic model for estimating the maximum rate of uniform corrosion for a steel or copper container in a saturated repository environment is described. Four oxidants that are considered are oxygen, sulfate, radiolysis products, and water. Rates of corrosion from oxygen and sulfate reduction are assumed limited by the rate of inward diffusion of the oxidant through the rock, packing, and corrosion product layers surrounding the container. Reduction of water is limited by kinetic processes as influenced by mass transfer of products and reactants, temperature, and pH. Substantial changes in the system resulting from the corrosion process are predicted to occur over time.

Journal of Environmental Engineering, Nov 1, 1994

Groundwater geochemical data from 211 sampling locations in the Amargosa Desert region are analyz... more Groundwater geochemical data from 211 sampling locations in the Amargosa Desert region are analyzed to better understand the general flow system and climate-induced changes in recharge around Fortymile Wash near Yucca Mountain. Major ion groundwater chemistry was examined using the multivariate statistical methods of principal component analysis and k-means cluster analysis. These analyses showed several groundwater signatures, or potential flowpaths; the most pronounced tracked the entire length of Fortymile Wash. Carbon-14 data from 98 sampling locations in the region, corrected with carbon-13 data, are presented. Corrected carbon-14 dating of groundwater beneath Fortymile Wash shows ages between 8,000 years BP in the upper canyon region and 14,000 years BP in the lower region near the Amargosa Desert. This range in ages corresponds to the end of the Pleistocene and early Holocene epochs, marking the end of Wisconsin glaciation and the start of the current interglacial period. In contrast, groundwater adjacent to Fortymile Wash appears to be older. The trend of increasing groundwater age beneath Fortymile Wash with increasing distance from the source suggests that the average reach of runoff events and recharge diminished over time as the climate became warmer and dryer. Stable isotopic hydrogen-2 data and oxygen-18 data from 115 and 118 sampling locations, respectively, from the same region are interpreted in relation to the global meteoric water line. The hydrogen-2 and oxygen-18 signatures are similar to carbon-14 corrected by carbon-13 and principal component analysis signatures, and are evidence of changes to the groundwater system as the climate became warmer and dryer during the past 14,000 years.