E. Scott Bair

Regional and local hydrology of a created riparian wetland system

The hydrology of a created riparian wetland system was characterized for local and regional conditions. Three methods, two laboratory and onein situ, were used to calculate the hydraulic conductivity of the wetland substrate. Hydraulic conductivity values and measured vertical gradients were used to estimate seepage loss to ground water. Surface-water inflow and outflow dominated the hydrologic budget for the wetland. Precipitation, seepage loss, and evapotranspiration were minor components of the hydrologic budget. Water seeping from the wetland into the ground-water-flow system has characteristics of a local ground-water-flow system. Ground-water modeling and particle tracking show that water originating from the wetland seeps into the ground water and flows in the local ground-water system to the southeast portion of the site. Ground-water travel times were estimated to range from 700 to 1,200 days before being discharged to the Olentangy River.

Variable-density flow in the midcontinent basins and arches region of the United States

Basins in the midcontinent basins and arches region of the United States are typical of many sedimentary basins containing a diverse assemblage of lithologies that have been deformed at various stages in their geologic history and now transmit fluids of varying density. On the basis of the synthesis of geologic data from more than 500 wells, specific-gravity data from more than 1800 samples, fluid-pressure data from nearly 40 deep wells, and hydraulic-conductivity data from core analyses of more than 35 wells, the midcontinent basins and arches region is conceptualized as a layered, heterogeneous, hydrologically mature region containing 11 hydrostratigraphic units that have undergone various periods of deformation and comprise a sequence of aquifers and confining layers with fluid-density variations ranging from freshwater to brine. An interpretative, threedimensional, steady state, variable-density, finite difference flow model was constructed to organize the field data and to evaluate various controls on regional flow patterns. Simulation results indicate that flow directions in the shallow hydrostratigraphic units are controlled by local surface elevations. The deeper flow systems, however, show the influence of regional structural features, such as the Cincinnati Arch, that control the locations of regional groundwater divides. The amount of downward cross-formational flow into the older hydrostratigraphic units is greatest along the area of the Cincinnati and Findlay Arches where the Mt. Simon Sandstone is relatively shallow and fracturing and faulting are more common. Spatial variations in fluid density are a significant influence on vertical cross-formational flow in regions where salt-bearing units are present.

Role of salinity‐derived variable‐density flow in the displacement of brine from a shallow, regionally extensive aquifer

Portions of many regional-scale aquifers in midcontinent sedimentary basins exhibit large salinity gradients that significantly impact the velocity field and solute distribution through time. A two-dimensional, numerical transport model was constructed to examine the role of salinity-derived variable-density flow on changes in the velocity field and solute distributions in a near-surface, regionally extensive aquifer as brine is displaced by infiltrating meteoric water. The Silurian-Devonian carbonate aquifer in the western portion of the Appalachian Basin was used as a framework to insure that realistic flow velocities and salinities were used in the assessment. The variable-density effects on brine displacement are observed by examining the differences in the velocity fields and solute distributions produced by uniform-density and variable-density simulations. The effects include the change from an intraformational displacement pattern to a cross-formational displacement pattern with the development of flow reversals and partitioning of regional flow cells into smaller flow cells. Variable-density effects also are manifest in the solute distributions by slowing the displacement of brine and influencing the magnitude of the salinity gradient. A sensitivity analysis used to examine the influence of flow and transport parameters on the transient development and migration of salinity gradients shows that increasing cross-formational leakage into the regional aquifer causes flow velocities to decrease, which magnifies the influence of the variable-density behavior by slowing the displacement of brine. The sensitivity analysis also shows that increasing the value of dispersivity causes an increase in the variable-density effects. However, the effects of variable-density flow are relatively insensitive to changes in values of horizontal and vertical anisotropy assigned to the aquifer or to the presence of an overlying transmissive layer.

Developing Analytical and Communication Skills in a Mock-Trial Course Based on the Famous Woburn, Massachusetts Case

A mock trial in which undergraduates serve as expert witnesses and law students serve as their attorneys is an effective vehicle for developing quantitative skills and enhancing written and oral communication skills. I have developed an interdisciplinary course based on the book A Civil Action. The book deals with the legal struggle of families in Woburn, Massachusetts, who sued two corporations alleging that improperly handled industrial chemicals entered the groundwater system, were captured by two municipal wells, and prolonged ingestion of the contaminated water caused leukemias and other health disorders. Students analyze aerial photographs, well logs, streamflow records, permeability tests, and water-level and water-quality data from the trial to complete assignments that become exhibits in the mock trial. Assignments include construction of geologic cross sections, potentiometric maps, hydrographs, flood recurrence graphs, and calculation of hydraulic gradients, groundwater velocities, and contaminant travel times. Trial transcripts and newspaper articles serve as background materials for a term paper. Based on the computational assignments, background readings, and a discussion of professional ethics, students compose an expert opinion from the viewpoint of their client and are deposed by opposing counsel. A jury of undergraduates is impaneled for the one-day mock trial in which the law students make opening statements and closing arguments, and conduct direct examinations and cross examinations of the scientific experts. The course teaches students how to develop and defend their opinions, how to question the opinions of others, the limitations of data collection and analysis, and the importance of integrating computational and communication skills.

Regional hydrodynamics of the proposed high-level nuclear-waste repository sites in the Texas Panhandle

Abstract Bedded salt in the Palo Duro Basin area of the Texas Panhandle is being evaluated as possible host rock for a high-level nuclear-waste repository. The two potential sites are underlain by three major hydrostratigraphic units: a shallow freshwater aquifer system developed in the Tertiary Ogallala Formation and the Triassic Dockum Group, a thick shale and evaporite aquitard developed in an Upper Permian evaporite sequence, and a deep-basin brine aquifer system predominantly developed in the Wolfcamp Series and the Pennsylvanian System. Water level, shut-in pressure, and specific-gravity data from inventoried wells, drill-stem tests, and long-term pumping tests were used to construct potentiometric surfaces, potentiometric profiles, and pressure-depth diagrams. Water in the Ogallala and Dockum aquifers predominantly flows horizontally and discharges to springs and wells. Equipotential patterns on potentiometric profiles indicate that some water may be moving downward from the Ogallala into the Dockum across an intervening confining unit, as well as moving downward from the Dockum across the shale and evaporite aquitard and into the deep-basin aquifer system. This is corroborated by the slope of pressure-depth data which indicate the potential for regional downflow in the shale and evaporite aquitard. Equipotential patterns and pressure-depth data indicate predominantly horizontal flow in the deep-basin aquifer system which is influenced by permeability variations related to facies changes. Hydraulic gradients are flatter in the more permeable shelf, shelf margin, and fan-delta facies and steeper in the less permeable deep-basin facies.

Regional depressurization and its impact on the sustainability of freshwater resources in an extensive midcontinent variable‐density aquifer

Regional depressurization due to groundwater withdrawal from a large confined midcontinent aquifer may cause significant changes in the regional flow field and solute distributions through time. This study addresses the effects of depressurization in the Silurian-Devonian carbonate aquifer in the western flank of the Appalachian Basin in Ohio, where salinity-derived variable-density flow effects are significant. This complex hydrogeologic environment is examined using an interpretative, transient, numerical flow and transport model to examine the hydrodynamics involved in the salinization process, to simulate changes in the velocity field and solute distributions over the past 100-year period, and to forecast the effects of three different depressurizing scenarios over the next 100-year period. The results indicate that large-scale depressurization can lead to significant changes in the regional flow patterns, resulting in changes in solute distributions and salinization of a portion of the aquifer. Depressurization creates vertical flow gradients within the carbonate aquifer that transport brine from underlying and overlying shale units into the updip freshwater portion of the aquifer. Model results show the development of flow reversals in the downdip portions of the aquifer that facilitate transport of brine from the deeper portions of the carbonate aquifer. These processes result in significant water quality degradation in the updip portion of the aquifer, which is extensively used for municipal, industrial, and domestic water supplies. Our results indicate the need to monitor water levels, pumping rates, and water quality so that future management decisions regarding the sustainability of the resource are based on complete and accurate field data.

The use of stochastic simulations and geophysical logs to characterize spatial heterogeneity in hydrogeologic parameters

Characterization of the spatial distribution of hydrogeologic parameters in an aquifer is important to understanding the hydrodynamics of a groundwater flow system. The operational procedure presented in this paper uses core permeability and porosity data and geophysical logs to characterize hydrogeologic parameters, especially hydraulic conductivity (K). The procedure is illustrated with a geostatistical analysis of the permeability distribution along a 120 km cross section of the Milk River aquifer in Alberta, Canada. Geologic and hydrogeologic data from aquifers come in a variety of forms. In deep, regional aquifers, the most ubiquitous form usually is geophysical logs that are used to determine spatial variations in the thickness, porosity, and permeability as well as other rock properties of hydrostratigraphic units. Several methods of deriving hydraulic conductivity values from geophysical logs are evaluated with respect to the Milk River aquifer. Based on a statistical evaluation, a direct relation between porosity and permeability was selected. Once the hydrogeologic data were analyzed and evaluated, a stochastic approach using Bayesian updating with Cholesky decomposition is used to describe the spatial heterogeneity of hydraulic conductivity. This approach produces random-correlated fields of hydraulic conductivity that are conditioned at specific locations by the geophysically derived hydraulic conductivity values. The conditioned, random-correlated fields of hydraulic conductivity are a description of relatively small-scale heterogeneity in the hydraulic conductivity field that can be used in a numerical transport model as a detailed, spatial description of hydraulic conductivity.