Lyndsay B. Ball

Controls on groundwater flow in a semiarid folded and faulted intermountain basin

The major processes controlling groundwater flow in intermountain basins are poorly understood, particularly in basins underlain by folded and faulted bedrock and under regionally realistic hydrogeologic heterogeneity. To explore the role of hydrogeologic heterogeneity and poorly constrained mountain hydrologic conditions on regional groundwater flow in contracted intermountain basins, a series of 3-D numerical groundwater flow models were developed using the South Park basin, Colorado, USA as a proxy. The models were used to identify the relative importance of different recharge processes to major aquifers, to estimate typical groundwater circulation depths, and to explore hydrogeologic communication between mountain and valley hydrogeologic landscapes. Modeling results show that mountain landscapes develop topographically controlled and predominantly local-scale to intermediate-scale flow systems. Permeability heterogeneity of the fold and fault belt and decreased topographic roughness led to permeability controlled flow systems in the valley. The structural position of major aquifers in the valley fold and fault belt was found to control the relative importance of different recharge mechanisms. Alternative mountain recharge model scenarios showed that higher mountain recharge rates led to higher mountain water table elevations and increasingly prominent local flow systems, primarily resulting in increased seepage within the mountain landscape and nonlinear increases in mountain block recharge to the valley. Valley aquifers were found to be relatively insensitive to changing mountain water tables, particularly in structurally isolated aquifers inside the fold and fault belt.

Automatic mapping of the base of aquifer — A case study from Morrill, Nebraska

AbstractWhen a geologist sets up a geologic model, various types of disparate information may be available, such as exposures, boreholes, and (or) geophysical data. In recent years, the amount of geophysical data available has been increasing, a trend that is only expected to continue. It is nontrivial (and often, in practice, impossible) for the geologist to take all the details of the geophysical data into account when setting up a geologic model. We have developed an approach that allows for the objective quantification of information from geophysical data and borehole observations in a way that is easy to integrate in the geologic modeling process. This will allow the geologist to make a geologic interpretation that is consistent with the geophysical information at hand. We have determined that automated interpretation of geologic layer boundaries using information from boreholes and geophysical data alone can provide a good geologic layer model, even before manual interpretation has begun. The workfl...

Semiautomatic mapping of permafrost in the Yukon Flats, Alaska

Thawing of permafrost due to global warming can have major impacts on hydrogeological processes, climate feedbacks, arctic ecology, and local environments. To understand these effects and processes, it is crucial to know the distribution of permafrost. In this study we exploit the fact that airborne electromagnetic (AEM) data is sensitive to the distribution of permafrost, and demonstrate how the distribution of permafrost in the Yukon Flats, Alaska is mapped in an efficient (semi-automatic) way, using a combination of supervised and unsupervised (machine) learning algorithms, i.e. Smart Interpretation and K-means clustering. Clustering is used to sort unfrozen and frozen regions, and Smart Interpretation is used to predict the depth of permafrost based on expert interpretations. This workflow allows, for the first time, a quantitative and objective approach to efficiently map permafrost based on large amounts of AEM data.

ELECTROMAGNETIC METHODS TO DELINEATE HIGH CONDUCTIVITY IN SHALLOW AQUIFERS, EAST POPLAR OIL FIELD AREA, NORTHEASTERN MONTANA

Airborne, ground, and borehole geophysical studies by the U.S. Geological Survey (USGS), in cooperation with the Fort Peck Assiniboine and Sioux Tribes, have been used to delineate areas of saline groundwater in shallow (<40 meters) unconfined aquifers underlying the East Poplar oil field in northeastern Montana. In the 20 years since the first delineation of saline groundwater, the quality of water from wells completed in the shallow aquifers has changed markedly. The current estimated extent of saline-water plumes based on integrated geophysical and hydrologic studies differs from that delineated in the early 1990s. Ground electromagnetic surveys began in the mid-1990s using an EM-34 (10, 20, and 40 meter vertical and horizontal loops) to measure subsurface electrical conductivity. Results from the EM surves indicated broad areas of high conductivity, which when integrated with results from groundwater quality samples, led to estimates of more than 12 square miles of saline groundwater. In 2004; an airborne electromagnetic survey funded by the Ft. Peck tribes was conducted over a 106 square-mile area that included most of the southeast East Poplar oil field. These surveys provided a foundation for developing a hydrogeologic framework and saline plume mapping over a large area. These surveys, in conjunction with water quality analyses, led to the determination that handling and disposal of brine produced with oil in the East Poplar oil field area resulted in contamination of not only the deeper aquifers, but also shallower areas some of which are near the Poplar River. The integrated interpretation of hydrogeological and geophysical studies has increased the understanding of the subsurface glacial hydrostratigraphy which controls groundwater flow and migration of saline waters. In one area (termed the Biere area near Biere well #1-22), Pioneer Natural Resource (PNR) voluntarily designed and built a plume capture and remediation system consisting of fifteen saline, groundwater removal wells, five crude oil recovery wells and a deep, 7,800 foot, USEPA Class V, injection well. The brine remediation system became fully operational in August 2008 and is operating at an average daily rate of 5,100 barrels per day (214,200 gallons/day). As of January 2015 the system has removed 8,798,390 barrels (369,532,380

Airborne electromagnetic data and processing within Leach Lake Basin, Fort Irwin, California: Chapter G in Geology and geophysics applied to groundwater hydrology at Fort Irwin, California

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