Report of Investigations No. 141 Hydrogeology of the Edwards Aquifer, Austin Area, Central Texas

UT Librarie

Kaon properties and cross sections in nuclear medium

Results for the $\pi + N \to \Lambda, \Sigma + K$ reactions in nuclear matter of Ref. nucl-th/0004011 are presented. To evaluate the in-medium modification of the reaction amplitude as a function of the baryonic density we introduce relativistic, mean-field potentials for the initial, final and intermediate mesonic and baryonic states in the resonance model. These vector and scalar potentials were calculated using the quark meson coupling model. Contrary to earlier work which has not allowed for the change of the cross section in medium, we find that the data for kaon production at SIS energies are consistent with a repulsive $K^+$-nucleus potential.Comment: 5 pages, 3 postscript figures included, uses iopart.cls and iopart10.clo (included), presented by K.T. at the 5th International Conference on Strangeness in Quark Matter, July 20 - 25, 2000, Berkeley, California, to be published in the proceedings, J. Phys. G. An explanation has been added in Sec. 3 with a new figur

Hydrogeology of Barton Springs, Austin, Texas

The major point of discharge of the Edwards aquifer between the Colorado River and the ground-water flow divide near Kyle, 15 miles south of Austin, is Barton Springs; it comprises five major springs. The Balcones Fault Zone southwest of Austin is the principal zone of recharge to the aquifer. Changes in water levels of wells in the area show good correlation with changes in spring discharge, indicating good interconnection. The potentiometric surface of the aquifer shows a shift from conditions of high flow to low flow. During low flow groundwater flow lines are concentrated in the eastern portion of the Balcones Fault Zone. Water-levels are also significantly lower. The water levels of wells in the Rollingwood area do not follow that pattern. Overall hydrologic parameters of the aquifer were estimated by applying recession curve analyses to hydrographs of the spring discharge and of water-level declines in the potentiometric surface throughout the aquifer. Additionally, a two-dimensional ground-water flow model was constructed for the northeastern part of the aquifer in order to simulate the observed water-level fluctuations in well 58-42-915. The average value of transmissivity inferred from the model agrees well with results based on the recession curve analysis. Storativity, however, differed by about one order of magnitude. The water chemistry of the springs varies also between high-flow and low-flow discharge. The concentrations of Na, Cl, SO4, and Sr increase during low flow, indicating influx from the 'bad-water' zone (water from downdip Edwards with 1000 ppm total dissolved solids or more). This inflow of water from the 'bad-water' zone during low flow is also documented by the water chemistry of well 58-50-216, approximately two miles south of Barton Springs; during dry periods there is a large increase in total dissolved solids in that well. Even though the chemical composition of Barton Springs changes with varying discharge, the general water chemistry in the Edwards limestone aquifer remains constant. The aquifer contains calcium-bicarbonate water that evolves to a sodium-sulphate water and then a sodium-chloride water as it moves dondip. In some locations, however, leakage from the Glen Rose Formation increases the sulphate and strontium concentrations. This leakage occurs along large displacements of faults, where the Edwards Formation is adjacent to the Glen Rose Formation. In addition, carbonate equilibria of selected samples from the aquifer, springs, and creeks were calculated. Creek water is saturated with respect to calcite and dolomite during conditions of approximate steady state flow. During floods after heavy rainfall the water chemistry of most of the creeks, except for Barton Creek, indicate undersaturation with respect to calcite and dolomite. Saturated spring water which occurs only during very high discharge could result because spring flow is sustained to a major part by saturated flood water from Barton Creek. The influx of highly saturated 'bad-water' appears to have little effect on the saturation state of water from Barton Springs.Geological Science

Hydrodynamic Development of the Palo Duro Basin and Other Mechanisms Creating Possible Transient Flow Conditions

Characterization of the regional flow regime in the Palo Duro Basin is assisted by numerical groundwater flow models as described by INTERA (1984), Senger and Fogg (1984), and Wirojanagud and others (1984). In general, the models which incorporate the available hydrogeologic information simulate hydraulic head distribution and fluxes under steady-state conditions. The computed heads are then compared to measured heads in order to evaluate the adequacy of the conceptual model. The conceptualized flow regime in the Palo Duro Basin is generally assumed to represent a steady-state, gravity-driven flow system of the type described by Hubbert (1940). Groundwater flow is governed by the fluid potential along the topographic surface and permeability of the hydrostratigraphic units. In the Palo Duro Basin, extensive modification of the topography as a result of tectonic and geomorphologic processes has occurred within the last 15 million years (McGookey, 1984; Gustavson and others, 1981). Accordingly, it is possible that hydraulic heads observed in the Deep-Basin Brine aquifer represent transient conditions and that they are still equilibrating to modifications of topography in the past. Significant hydrocarbon occurrences in the Texas Panhandle suggest other possible mechanisms creating transient flow conditions as a result of reservoir pressure decline due to hydrocarbon production. The purpose of this study is to investigate transient flow conditions and to identify possible flow patterns resulting from changing hydrologic conditions with time. For this purpose, the model herein is used to simulate possible groundwater flow patterns caused by different tectonic and geomorphologic processes. The hydrodynamic development of the basin is crucial to the origin and hydrochemical evolution of the fluid in the deep basin. Changing hydraulic head distributions with time result in changes of groundwater flow paths. Consequently, transport of chemical constituents could have traveled along ancient pathways much different than is suggested by the present-day hydraulic head distribution observed in the basin.Bureau of Economic Geolog

Monte-Carlo simulation of localization dynamics of excitons in ZnO and CdZnO quantum well structures

Localization dynamics of excitons was studied for ZnO/MgZnO and CdZnO/MgZnO quantum wells (QW). The experimental photoluminescence (PL) and absorption data were compared with the results of Monte Carlo simulation in which the excitonic hopping was modeled. The temperature-dependent PL linewidth and Stokes shift were found to be in a qualitatively reasonable agreement with the hopping model, with accounting for an additional inhomogeneous broadening for the case of linewidth. The density of localized states used in the simulation for the CdZnO QW was consistent with the absorption spectrum taken at 5 K.Comment: 4 figures, to appear in J. Appl. Phy

Testing Lorentz Invariance by Comparing Light Propagation in Vacuum and Matter

We present a Michelson-Morley type experiment for testing the isotropy of the speed of light in vacuum and matter. The experiment compares the resonance frequency of a monolithic optical sapphire resonator with the resonance frequency of an orthogonal evacuated optical cavity made of fused silica while the whole setup is rotated on an air bearing turntable once every 45 s. Preliminary results yield an upper limit for the anisotropy of the speed of light in matter (sapphire) of \Delta c/c < 4x10^(-15), limited by the frequency stability of the sapphire resonator operated at room temperature. Work to increase the measurement sensitivity by more than one order of magnitude by cooling down the sapphire resonator to liquid helium temperatures (LHe) is currently under way.Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 28-July 2, 201

Statistical hadronization of charm: from FAIR to the LHC

We discuss the production of charmonium in nuclear collisions within the framework of the statistical hadronization model. We demonstrate that the model reproduces very well the availble data at RHIC. We provide predictions for the LHC energy where, dependently on the charm production cross section, a dramatically different behaviour of charmonium production as a function of centrality might be expected. We extend our predictions for charm production towards the threshold energies, where charm is expected to be measured at the future FAIR facility.Comment: 4 pages, 3 figures; proceedings of QM200

Identification of Recharge-Discharge Areas of the Palo Duro Basin, Texas Panhandle

This report presents the preliminary results of research to identify the recharge and discharge areas of the major aquifers in the Palo Duro Basin. Recharge has been investigated by studying the isotopic compositions of surface and shallow ground waters in New Mexico and Texas. Discharge studies have focused on identifying the source of the brine discharged in springs and seeps along the outcrop of Permian rocks east of the Caprock Escarpment.Bureau of Economic Geolog

Wellhead Protection Strategies for Confined-Aquifer Settings

Improper management of contamination sources has resulted in numerous cases of groundwater contamination of public water supply wells. One approach toward preventing contamination of public water supplies is to protect the areas that recharge precipitation and surface water to the aquifer near the wells. This zone of protection is referred to as a wellhead protection area (WHPA). The potential for contamination is typically less in a confined aquifer than in an unconfined aquifer. Nevertheless, contamination of confined aquifers has occurred. Wellhead protection areas should be developed for all aquifer settings. A confined aquifer is an aquifer overlain by low-permeability strata. The presence of the low permeability material reduces the risk of a surface contaminant reaching a producing well. The potential for contamination of a confined aquifer is controlled by two factors: (1) The presence of permeable pathways (for example, faults, fractures, permeable sands, or unplugged abandoned boreholes) that permit contaminant migration and (2) the existence of appropriate hydrologic conditions (for example, downward flow) that cause contaminants to migrate through the low-permeability strata. Confined aquifers occur pervasively from coast to coast in the United States. The coastal plain aquifers along the Atlantic Ocean and Gulf of Mexico represent some of the largest confined aquifer systems in the United States. There are numerous other smaller aquifers which exhibit confined conditions.Bureau of Economic Geolog