Browsing by Subject "Aquifer"

Now showing 1 - 4 of 4
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    C-29 Geologic Atlas of Clay County, Minnesota [Part A]
    (Minnesota Geological Survey, 2014) Bauer, Emily J.
    Surface and subsurface geology of Clay County, Mn., also includes data-base information, subsurface stratigraphy, bedrock topography, depth-to-bedrock and sand distribution models.
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    Geological mapping and 3D model of deposits that host ground-water systems in the Fargo-Moorhead region, Minnesota and North Dakota
    (Minnesota Geological Survey, 2005) Thorleifson, L. H.; Harris, K.L.; Berg, J.; Tipping, R.G.; Malolepszy, Z.; Lusardi, B.A.; Setterholm, D.; Anderson, F.
    The objective of the current project is to present an updated and enhanced depiction of the sediments and rocks within which ground-water systems occur across the Fargo-Moorhead region, to support further assessment of currently utilized and potentially usable ground-water resources in the region. To do so, existing geologic maps from North Dakota and Minnesota were compiled, interpreted, and integrated to produce two maps, one depicting the uppermost unconsolidated deposits (Surficial Geology; 1: 200,000), and the other depicting the uppermost rocks (Bedrock Geology; 1: 400,000). These maps were merged with a new interpretation of bedrock elevation and a compilation of readily available digital drillhole data for approximately 30,000 sites to produce a three-dimensional (3D) depiction of subsurface geology, extending from the land surface down to the top of the granites and other igneous and metamorphic basement rocks of Precambrian age that underlie the entire region.
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    Geospatial Analysis of Transmissivity and Hydraulic Conductivity Across Minnesota: Using the County Well Index and Specific-Capacity Data
    (2022-12) Full, Jonathan
    Numerous hydrogeologic studies have been performed across Minnesota; however, they focus on small regions of the state. The Minnesota Conductivity Calculator (MCC) was developed to better observe spatial variations in hydraulic conductivity. This work strives to capture the variations of hydraulic conductivity across a variety of domains, scaling from a small neighborhood of wells to large provinces spanning across the state. The MCC leverages data from the Minnesota County Well Index (CWI) to determine transmissivity and hydraulic conductivity at 170,975 wells. Then, lognormal ordinary kriging was performed with the hydraulic conductivity data to visualize spatial variations. The MCC can be used to efficiently produce maps of hydraulic conductivity across the state, which is useful for a number of groundwater management purposes, including groundwater modeling.
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    Water temperature as a tracer in karst aquifers.
    (2011-07) Luhmann, Andrew James
    Water temperature at springs generally provides useful information concerning aquifer geometry and recharge. Temperature monitoring at 25 springs and cave streams in southeastern Minnesota has shown four distinct thermal patterns that can be interpreted in terms of heat exchange effectiveness along a flow path and the nature of recharge. The patterns provide information about the size of the flow path, recharge type and duration, and aquifer depth. Water temperature is generally an interactive tracer, where heat exchange rapidly occurs when water and aquifer rock are at different temperatures. In a multi-tracer experiment at Freiheit Spring, MN, uranine, chloride, and δD breakthrough curves were essentially identical and conservative. In contrast, the water temperature interacted with the aquifer as it moved along the flow path, producing a damped, lagged thermal signal at the spring. However, both the conservative and nonconservative tracers provide useful geometrical information. By summing discharge between the initial increase in stage produced by a pressure pulse and the chloride peak, the conduit volume is estimated as 51 m3. Using a heat transport simulation to reproduce the modified thermal signal requires a planar flow path with a hydraulic diameter of 7 cm. Both methods together suggest a bedding plane flow path that is 3.5 cm high by 10 m wide, in agreement with the observed spring geometry. The different tracers provide complementary information and stronger constraints on flow path geometry than could be obtained using a single tracer. Finally, numerical simulations were run to determine variables controlling thermal retardation in karst conduits. The lag of a thermal peak in the water is proportional to a conduit's length; is proportional to the square root of recharge duration, rock thermal conductivity, rock specific heat, and rock density; and is inversely proportional to a conduit's hydraulic diameter, velocity, water specific heat, and water density. These individual relationships were then combined to form one collective function, which, when plotted against thermal peak lag produced a line in log-log space. The relationship between the thermal peak lag and the combined function potentially enables estimates of conduit geometry using thermal peak lag data.