Browsing by Subject "Hydrogeology"

Now showing 1 - 5 of 5
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    Characterizing groundwater flow in the Twin Cities metropolitan area, Minnesota a chemical and hydrostratigraphic approach.
    (2012-06) Tipping, Robert G.
    Historic chemical and isotopic data for groundwater within the 11 county Twin Cities Metropolitan Area, extended (TCMAx) were used to distinguish three regional groundwater types based on similar chemical and isotopic composition: 1.) recent waters, characterized by detectable tritium, elevated chloride and/or the presence of anthropogenic compounds; 2.) waters with elevated strontium to calcium plus magnesium ratios; and 3.) naturally elevated chloride-distinct from recent waters based on carbon-14 dating and low chloride to bromide ratios where sufficient data exists. The three-dimensional distribution of these hydrochemical facies were compared to permeability of unconsolidated sediments, the distribution of macropores within sedimentary (Paleozoic) bedrock, and the regional distribution of vertical hydraulic head gradient. Results of this investigation demonstrate that groundwaters within the TCMAx can be broadly categorized by chemical composition, and that their distribution is controlled both by regional differences in subsurface permeability and natural hydraulic head gradients, and by regional changes in hydraulic gradient due to high-capacity pumping. Chloride content and chloride to bromide ratios, in particular, can be used to identify the presence of recently recharged groundwater in bedrock aquifers and further characterize the movement of these recent waters through bedrock macropores. Urban groundwater systems present unique challenges for resource management and scientific investigations due in large part to the transient nature of hydraulic head gradients and changing landuse. For urban planners charged with groundwater resource management, results in this thesis demonstrate the utility of having groundwater hydrochemical types fully integrated with a hydrogeologic framework model in a three-dimensional geographic information system (GIS) environment, where age and chemical quality of groundwaters can be compared with other, more familiar factors, such as locations and pumping levels of high capacity wells. For groundwater modelers of urban aquifers, these same results can guide conceptual models of recharge to bedrock aquifers and constrain model calibration to produce flux estimates in agreement with flowpaths indicated by the distribution of recent waters.
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    Hydrochemical Signatures of Glacial Meltwater on Volcán Chimborazo, Ecuador
    (2017-11) McLaughlin, Rachel
    Glacier recession in the tropical Andes is generating significant concern over future water availability for domestic use, irrigation, and hydropower. Sparse data sets, extreme heterogeneity in climate patterns, and the limited understanding of groundwater and ecohydrological processes in these catchments make predicting the hydrologic response to glacier retreat difficult. Here I examine a glaciated watershed on Volcán Chimborazo, Ecuador. I use geospatial analysis and recent geologic studies to evaluate the vegetation and geologic factors that influence the hydrologic response of the watershed. Additionally, I utilize hydrochemical and stable isotope signatures to investigate how melt and groundwater contributions to streamflow have changed over time along with possible meltwater-groundwater connections. A new landcover map of Volcán Chimborazo, generated using object based image analysis, reveals a significant increase in the upper limit of vegetation on the mountain and expansion of crop and pasture land since 1978. Geologic cross-sections, based on recent studies, show that near surface geology is dominated by glacial deposits and underlain by relatively young volcanic bedrock. Results from a hydrochemical mixing model (HBCM) combined with discharge measurements reveal spatial variability in groundwater discharge and suggest that groundwater discharge during the dry season has decreased from 2012-2017. Short time scale variability is clearly influenced by precipitation, but long-term discharge trends remain uncertain. Lastly, stable isotope and solute concentrations in samples suggest groundwater in the study watershed is recharged by precipitation falling at high elevations where ice and snow may dominate the hydrologic system.
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    Hydrogeologic Monitoring at University of Minnesota Outreach, Research and Educational Park (UMore Park), 2011
    (2012-01) Groten, Joel T.; Alexander, E. Calvin
    The mining of the gravel resource and subsequent development at the University of Minnesota Outreach, Research and Educational Park (UMore Park) may potentially impact the groundwater quality at, and around UMore Park. In order to provide a pre-mining baseline against which to monitor potential water quality changes, monitoring of water quality in selected monitoring wells began in 2009 (Anger and Alexander, 2010.) Anger and Alexander (2010) reviews the previous work defining the hydrogeology of the UMore Park site and installing the existing monitoring wells. This report updates and Anger and Alexander (2010) with monitoring data obtained through June 2011.
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    Karst Hydrogeologic Investigation of Trout Brook, Dakota County, Minnesota
    (2013-02) Groten, Joel T.; Alexander, E. Calvin
    Trout Brook in the Miesville Ravine County Park of Dakota County is the trout stream with the highest nitrate concentration in the karst region of southeastern Minnesota. Water quality data from 1985 and 1995 (Spong, 1995) and from 2001, 2002, 2006 and 2010 by the Dakota County Soil and Water Conservation District (SWCD) (2010) document an increasing level of nitrate in Trout Brook. A karst hydrogeologic investigation was designed to measure nitrate levels at sampling points along the stream and to increase our understanding of the source and movement of nitrates throughout the length of Trout Brook. Eighteen springs and seeps have been located in the Main Branch and tributaries of Trout Brook. A previously unreported flowing section and stream sieve, Weber Sieve, were found above what had been thought to be the head of perennial flow in the East Branch of Trout Brook. Two new sinkholes developed after the 14-15 June 2012 flood in a field northeast of the East Branch of Trout Brook. This investigation included regular monitoring of major anions in the streams and springs, synoptic stream flow measurements, a dye trace of a sinking stream in the Trout Brook drainage, and continuous temperature monitoring at two springs. The initial assumption was that the majority of the baseflow of Trout Brook was from discrete springs. However, synoptic baseflow and nitrate measurements show that only 30-40 percent of the total flow in Trout Brook is from discrete springs, and the rest appears to be from distributed groundwater discharge directly into the stream. Both the discrete springs and the distributed recharge occur along reaches of Trout Brook that drain the significant high transmissivity zone near the bottom of the regionally important Shakopee aquifer. Dye traces have confirmed flow-paths from Weber Sieve to LeDuc and Bridgestone Springs and have begun to define springsheds for these head water springs. The temperatures of two springs were monitored for 7.5 months. The observed small, seasonal temperature fluctuations at the springs seem to be due to the air temperature while storms that result in flooding and surface runoff cause larger, short-term temperature fluctuations. Nitrate concentrations and chloride/bromide ratios decreased systematically from the upstream springs to the downstream springs. The nitrate concentrations have been increasing at four springs from 1985 to 2012 and at two surface sampling points from 2001 to 2012. The nitrate concentration of another surface sampling point increased from 2001 to 2006 but decreased from 2006 to 2012. Snowmelt and rainfall runoff was sampled on 2 March 2012 and showed no detectable nitrate in the runoff from a watershed with no row-crop agriculture, but elevated nitrate was detected in an adjacent watershed with row-crop agriculture. All of these trends illustrate the dominance of agricultural sources of nitrate in Trout Brook.
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    Optimizing borehole Heat exchanger spacing to maximize advective heat transfer
    (2013-09) Meester, Jennifer
    This generalized study provides first order insights into the effect of heat advection on ground source heat pump (GSHP) system operation and the optimization of spacing between borehole heat exchangers (BHE) using groundwater flow and heat transport models. In these systems, there is a threshold Péclet number, the ratio of heat advection rate to heat conduction rate, beyond which the efficiency of heat transfer between the BHEs and the aquifer is significantly increased, thus lowering the temperature drop of the circulating fluid in the BHE and increasing the overall efficiency of the BHE system. This threshold Péclet number depends on the groundwater flow rate and effective thermal diffusivity (among other factors) of the system and, for the given conditions, is approximately 2 with a 1% change in BHE outlet temperature and approximately 11 with a 5% change. In GSHP systems with standardized spacings between BHEs, groundwater heat advection can cause negative thermal interactions between heat exchangers, which can be eliminated and in some situations replaced with positive thermal interactions by optimizing the spacing between BHEs. Above the threshold Péclet number, there is specified spacing between heat exchangers that will allow for the utilization of the previous season's heat injection or extraction, a half year transport distance. For the GSHP system simulated in this study, the BHE spacings for optimization are 6.65 m and 13.8 at groundwater flow velocities of 2.5 x 10-5 m/s and 5 x 10-5 m/s, respectively. It may also be possible to space the heat exchangers at a distance that captures heat after a year and a half of transport (for systems with only slight heat advection dominance), but more simulations are necessary to investigate the results of such a strategy.