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

Geologic and Hydrologic Investigations Reese Air Force Base, Lubbock, Texas

The Bureau of Economic Geology has conducted a characterization of the geology and hydrology of the Ogallala and Blackwater Draw Formations at Reese Air Force Base to establish baseline information for better delineation of contamination on the base. Analysis of five cores revealed two predominant depositional facies: eolian sands and fluvial gravels. The gravels seem to extend continuously across the base and likely constitute the primary water-bearing unit, potentially serving as the main pathway for contaminant migration in the groundwater beneath the base. Continuous water-level recorder data from water-supply wells and monitoring wells on the base indicated a mix of confined and unconfined conditions. The degree of confinement may be influenced by the wells' proximity to the playa lakes on the base or by the relationship of the water levels in the wells to the top of the water-bearing gravel unit. This variability in confinement suggests a hydrological setting that is more intricate than typically recognized for the Ogallala aquifer.Bureau of Economic Geolog

Effects of Hydrostratigraphy and Basin Development on Hydrodynamics of the Palo Duro Basin, Texas

A two-dimensional groundwater flow model was developed along a cross-section through the Palo Duro Basin to understand regional groundwater flow paths and investigate factors influencing underpressuring below the Evaporite aquitard, as well as recharge and discharge mechanisms to and from the Deep-Basin Brine aquifer. Steady-state flow simulations were employed to examine the effects of lithostratigraphy and topography on groundwater flow. Additionally, transient flow simulations were used to describe changes in regional hydrodynamics resulting from various tectonic and geomorphologic processes. The groundwater flow pattern in the Palo Duro Basin is characterized by a shallow groundwater flow system primarily controlled by topography. Deeper flow regimes recharge in the New Mexico area and pass beneath the Pecos River into the deep section of the Palo Duro Basin. The Evaporite aquitard effectively separates the deeper flow regime from the more rapidly circulating shallow aquifer system, although leakage through the aquitard is significant and could contribute up to 27 percent of the water passing through the deep section. Within the Deep-Basin Brine aquifer, groundwater flow patterns are strongly influenced by the spatial distribution of more permeable strata, such as granite-wash deposits, which facilitate drainage of the deep aquifer system more readily than recharge occurs.Bureau of Economic Geolog

Hydrology of an Evaporite Aquitard Permian Evaporite

Permian evaporite strata of the Palo Duro Basin, Texas Panhandle, are considered to have low permeabilities but are capable of some leakage. Cross-sectional and areal modeling of regional groundwater flow in the Palo Duro Basin indicates leakage from the Upper aquifer through the Evaporite aquitard that contributes approximately 30 percent of the water in the underlying Deep-Basin Brine aquifer. The regional estimate of permeability of the aquitard (˜ 10^-4 md) is in general agreement with laboratory testing of salt permeability. Oxygen and hydrogen isotopic composition and the Cl/Br ratio of the deep-basin brines also suggest leakage through the aquitard. Isotopically nonequilibrated meteoric waters are found to depths of 8,000 ft. Leakage through the aquitard may occur as either matrix or fracture flow. According to petrographic and geochemical studies of the evaporite strata, halite dissolution and minor recrystallization occurred predominantly during Permian time. Post-Permian waters may have altered the top of the Evaporite aquitard. Fracturing is prevalent in the rock strata in the basin; the greatest density of fracturing occurs in areas with tectonic deformation. The potential for leakage may be greatest in these areas.Bureau of Economic Geolog

Geologic and Hydrologic Investigations Reese Air Force Base, Lubbock, Texas

The Bureau of Economic Geology has characterized the geology and hydrology of the Ogallala and Blackwater Draw Formations at Reese Air Force Base to provide baseline information for better delineation of contamination on the base. Examination of five cores identified two predominant depositional facies: eolian sands and fluvial gravels. The gravels appear to be continuous across the base and may represent the major water-bearing unit; therefore, they may be the prime conduit for contaminant migration in the groundwater beneath the base. Continuous water-level recorder data from water-supply wells and monitoring wells on the base indicated typically confined and unconfined conditions. The degree of confinement may be controlled by the wells' proximity to the playa lakes on the base or by the relation of the water levels in the wells relative to the top of the water-bearing gravel unit. This variability in the degree of confinement indicates a more complex hydrologic setting than is normally recognized for the Ogallala aquifer.Bureau of Economic Geolog

Geology and Hydrology of the Northern Segment of the Edwards Aquifer with An Emphasis on the Recharge Zone in the Geogetown, Texas, Area

In March 1986, the Bureau of Economic Geology was contracted by the Texas Water Development Board to conduct geologic and hydrologic investigations of the northern segment of the Edwards aquifer along the Balcones Fault System in the Georgetown-Round Rock area, particularly to elucidate the processes and areas of recharge for the Edwards in the Georgetown area. Geological mapping, combined with analysis of fractures in Comanche Peak, Edwards, and Georgetown limestones (Edwards aquifer strata) in the vicinity of Georgetown and Round Rock, Texas, was conducted to provide data useful in identifying potential recharge areas, assessing local groundwater flow, and enhancing our understanding of the geology of the Balcones Fault Zone. Cretaceous Comanche Peak, Edwards, Georgetown, Del Rio, Buda, Eagle Ford, and Austin strata dip gently (1°) eastward and are overlain in some places by terrace deposits and alluvium. Several major normal faults, downthrown to the east, strike northward across the area. Gentle flexures, possibly related to faulting, parallel the faults. Minor normal faults and joints are most abundant in areas adjacent to major faults and flexures. These fractured-strata zones likely parallel the length of the faults or flexure axes and may be as wide as 1.6 km. Most minor faults strike between 340°-040°, have displacements less than 2 m, and dip from 40°-80° both eastward and westward. Most joints strike between 340°-020° and 260°-300°, and fracture densities range from 4 joints per meter to 1 joint per 5 meters in 1 to 2-meter-thick beds.Bureau of Economic Geolog

A cognitive tool for ethical decision-making: A case for ACED IT

The present study examined two forms of a cognitive tool (ACED IT map), which is designed to facilitate ethical decision-making, along with expressive writing. Results demonstrated that participants completing the original ACED IT were more likely to identify: 1) more steps to implementing a solution, 2) more barriers to solution implementation, and 3) more solutions to those barriers, than participants who completed the modified ACED IT, engaged in expressive writing, and those in the control group. These findings suggest that cognitive tools such as ACED IT may be of considerable value for individuals who are presented with ethical dilemmas

Pressure and ethical decision-making

Performance pressure degrades performance on many types of tasks. Mounting evidence, however, suggests that pressure may not affect ethical decision-making. For the present study, participants analyzed an ethical dilemma using a cognitive tool (ACED IT), expressive writing, or a control task, and their decisions were compared for participants in high and low pressure conditions. Perceptions of moral intensity were also measured

Proteome analysis of Arabidopsis thaliana by two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry

In the present study we show results of a large-scale proteome analysis of the recently sequenced plant Arabidopsis thaliana. On the basis of a previously published sequential protein extraction protocol, we prepared protein extracts from eight different A. thaliana tissues (primary leaf, leaf, stem, silique, seedling, seed, root, and inflorescence) and analysed these by two-dimensional gel electrophoresis. A total of 6000 protein spots, from three of these tissues, namely primary leaf, silique and seedling, were excised and the contained proteins were analysed by matrix assisted laser desorption/ionisation time of flight mass spectrometry peptide mass fingerprinting. This resulted in the identification of the proteins contained in 2943 spots, which were found to be products of 663 different genes. In this report we present and discuss the methodological and biological results of our plant proteome analysis

Ethical decision-making interrupted: Can cognitive tools improve decision-making following an interruption?

This study examined the effects of interruptions and the use of cognitive decision-making tools on ethical decision-making. Participants completed a structured cognitive tool, an unstructured decision-making technique, or no decision-making technique, and half of the participants were interrupted during the decision-making task, whereas half were allowed to complete the decision-making task without interruption. Results revealed that 1) participants who completed the structured cognitive tool (ACED-IT map) performed better on a number of markers of ethical decision-making, 2) interruptions reduced participants’ plan quality, and 3) participants who were interrupted, and who completed the structured cognitive tool exhibited perceptions that suggested that they felt better prepared to handle the ethical dilemma. These results could have important implications for professionals in jobs that experience frequent interruptions, particularly those in management positions