Geology topics

P. A. Macfarlane

Publications and source records attributed to P. A. Macfarlane.

5 recordsLinked to original sources

USGS2009

New insights into the hydrostratigraphy of the High Plains aquifer from three-dimensional visualizations based on well records

Regional aquifers in thick sequences of continentally derived heterolithic deposits, such as the High Plains of the North American Great Plains, are difficult to characterize hydrostratigraphically because of their framework complexity and the lack of high-quality subsurface information from drill cores and geophysical logs. However, using a database of carefully evaluated drillers' and sample logs and commercially available visualization software, it is possible to qualitatively characterize these complex frameworks based on the concept of relative permeability. Relative permeability is the permeable fraction of a deposit expressed as a percentage of its total thickness. In this methodology, uncemented coarse and fine sediments are arbitrarily set at relative permeabilities of 100% and 0%, respectively, with allowances made for log entries containing descriptions of mixed lithologies, heterolithic strata, and cementation. To better understand the arrangement of high- and low-permeability domains within the High Plains aquifer, a pilot study was undertaken in southwest Kansas to create three-dimensional visualizations of relative permeability using a database of >3000 logs. Aggregate relative permeability ranges up to 99% with a mean of 51%. Laterally traceable, thick domains of >80% relative permeability embedded within a lower relative permeability matrix strongly suggest that preferred pathways for lateral and vertical water transmission exist within the aquifer. Similarly, domains with relative permeabilities of <45% are traceable laterally over appreciable distances in the sub-surface and probably act as leaky confining layers. This study shows that the aquifer does not consist solely of local, randomly distributed, hydrostratigraphic units, as suggested by previous studies. ?? 2009 Geological Society of America.

Geosphere↗

USGS2006

Remote sensing and geophysical investigations of glacial buried valleys in northeastern Kansas

Aquifers found in glacial buried valleys are a major source of good-quality ground water in northeastern Kansas. The extent and character of many of these deposits are not precisely known, so a detailed study of the buried valleys was undertaken. Test drilling, Landsat imagery, shallow-earth temperature measurements, seismic refraction, surface electrical resistivity, and gravity data were used to evaluate two sites in Nemaha and Jefferson Counties. Tonal patterns on springtime Landsat imagery and winter/summer anomalies in shallow-earth temperatures were quick and inexpensive methods for locating some glacial buried aquifers and suggested areas for more intensive field studies. Reversed seismic refraction and resistivity surveys were generally reliable indicators of the presence or absence of glacial buried valleys, with most depth determinations being within 25% of test-drilling results. The effectiveness of expensive test-hole drilling was greatly increased by integrating remote sensing, shallow-earth temperature, seismic, and resistivity techniques in the two buried valley test areas. A gravity profile allowed precise definition of the extent of one of the channels after the other techniques had been used for general information.

Kansas↗

USGS2006

Helping Students make the transition from novice learner of ground-water concepts to expert using the Plume Busters software

Environmental and earth science students are novice learners and lack the experience needed to rise to the level of expert. To address this problem we have developed the prototype Plume Busters?? software as a capstone educational experience, in which students take on the role of an environmental consultant. Following a pipeline spill, the environmental consultant is hired by the pipeline owner to locate the resulting plume created by spill and remediate the contaminated aquifer at minimum monetary and time cost. The contamination must be removed from the aquifer before it reaches the river and eventually a downstream public water supply. The software consists of an interactive Java application and accompanying HTML linked pages. The application simulates movement of a plume from a pipeline break throug h a shallow alluvial aquifer towards the river. The accompanying web pages establish the simulated contamination scenario and provide students with background material on ground-water flow and transport principles. To make the role-play more realistic, the student must consider cost and time when making decisions about siting observation wells and wells for the pump-and-treat remediation system.

Journal of Geoscience Education↗

USGS2004

Strontium isotope geochemistry of groundwater in the central part of the Dakota (Great Plains) aquifer, USA

The Dakota aquifer of the central and eastern Great Plains of the United States is an important source of water for municipal supplies, irrigation and industrial use. Although the regional flow system can be characterized generally as east to northeasterly from the Rocky Mountains towards the Missouri River, locally the flow systems are hydrologically complex. This study uses Sr isotopic data from groundwater and leached aquifer samples to document the complex subsystems within the Dakota aquifer in Nebraska and Kansas. The interaction of groundwater with the geologic material through which it flows has created spatial patterns in the isotopic measurements that are related to: long-term water-rock interaction, during which varying degrees of isotopic equilibrium between water and rock has been achieved; and the alteration of NaCl fluids by water-rock interaction. Specifically, Sr isotopic data distinguish brines from Kansas and western Nebraska from those in eastern Nebraska: the former are interpreted to reflect interaction with Permian rocks, whereas the latter record interaction with Pennsylvanian rocks. The Sr isotopic composition of groundwater from other parts of Nebraska and Kansas are a function of the dynamic interaction between groundwater and unlithified sediments (e.g., glacial till and loess), followed by interaction with oxidized and unoxidized sediments within the Dakota Formation. This study illustrates the power of combining Sr chemistry with more conventional geochemical data to obtain a more complete understanding of groundwater flow systems within regional aquifer systems where extensive monitoring networks do not exist. ?? 2003 Elsevier Ltd. All rights reserved.

Applied Geochemistry↗

USGS1998

Noble gases, stable isotopes, and radiocarbon as tracers of flow in the Dakota aquifer, Colorado and Kansas

A suite of chemical and isotope tracers (dissolved noble gases, stable isotopes of water, radiocarbon, and CI) have been analyzed along a flow path in the Dakota aquifer system to determine likely recharge sources, ground water residence times, and the extent of mixing between local and intermediate flow systems, presumably caused by large well screens. Three water types were distinguished with the tracers, each having a very different history. Two of the water types were found in south-eastern Colorado where the Dakota is poorly confined. The tracer data suggest that the first group recharged locally during the last few thousand years and the second group was composed of ground water that recharged earlier during a cooler climate, presumably during the last glacial period (LGP) and mixed aged water. The paleotemperature record archived in this groundwater system indicates that south-eastern Colorado was about 5??C cooler during the LGP than during the late Holocene. Similar temperature changes derived from dissolved noble gases in other aquifer systems have been reported earlier for the south-western United States. The third water type was located down gradient of the first two in the confined Dakota in western and central Kansas. Groundwater residence time of this water mass is on the order of 104-105 yrs and its recharge location is near the Colorado and Kansas border down gradient of the other water types. The study shows the importance of using multiple tracers when investigating ground water systems.A suite of chemical and isotope tracers (dissolved noble gases, stable isotopes of water, radiocarbon, and CL) were analyzed along a flow path in the Dakota aquifer system to determine likely recharge sources, ground water residence times, and the extent of mixing between local and intermediate flow systems. Three water types were distinguished with the tracers, each having a very different history. Two of the water types were located in south-eastern Colorado where the Dakota is poorly confined. The third water type was located down gradient of the first two in the confined Dakota in western and central Kansas.

Journal of Hydrology↗