Theses and Dissertations at Montana State University (MSU)
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Item An investigation of coliform contamination in private well water on the Crow Reservation(Montana State University - Bozeman, College of Agriculture, 2019) Three Irons, Emery UP; Chairperson, Graduate Committee: Scott Powell; Margaret Eggers (co-chair)The Crow reservation has a rural population that depends on home well water for domestic use. Many of the home wells do not have a suitable well cap, allowing a potential pathway of bacterial contamination of groundwater. Fecal coliform is associated with acute health problems, such as gastrointestinal illness, diarrhea, and cramps. Therefore, total coliform contamination of well water is an important health concern among Crow home well users. This research examines patterns in total coliform contamination among home well samples with respect to a suite of well and local aquifer characteristics thought to influence vulnerability to contamination, including well protection factors. Well and aquifer characteristics considered in this research include: the geologic production formation, local land cover, and distance to the nearest river. Well protection factors include: cap type, cap condition, depth of completion and time since completion (or age). One hundred water quality samples were collected from home wells along the Little Big Horn River in 2017, and available data on the character of those wells and aquifers were collected for comparison with the patterns in fecal coliform contamination among the samples. Presence/absence of coliform contamination was assessed using the Colilert IDEXX Quanti-Tray 2000 method. Spatial variations in the characteristics of wells and aquifers were characterized through a combination of well logs, the National Land Cover Dataset, and the National Hydrography Dataset. Logistic regression was used to identify potential relationships between probability of coliform contamination and characteristics of associated wells and aquifers. Logistic regression models suggested two notable and statistically significant (? = 0.05 level) relationships: (1) wells completed in alluvium and farther from the river had a higher probability of total coliform contamination, and (2) wells with old style caps had a higher probability of total coliform contamination. The government of the Crow tribe can decide how to use the results for mitigation efforts and awareness for homeowners with contaminated wells. Also, the Crow Water Quality Project should archive and consider these results for future research, planning, development, and management.Item Groundwater nitrate transport and residence time in a vulnerable aquifer under dryland cereal production(Montana State University - Bozeman, College of Agriculture, 2013) Miller, Christine Ross; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, W. Adam Sigler, E. N. J. Brookshire, Clain A. Jones, Douglas Jackson-Smith and Gary S. Weissmann were co-authors of the article, 'Groundwater nitrate transport and residence time in a vulnerable aquifer under dryland cereal production' submitted to the journal 'Journal of geophysical research - biogeosciences' which is contained within this thesis.Selection of agricultural management practices to reduce nitrate leaching from soils can only be successful if both nitrate loading rates from soils to shallow aquifers and groundwater residence times are quantified. Elevated nitrate concentrations in shallow unconfined aquifers are commonly observed in agricultural areas as a result of increased N inputs. In the Judith River Watershed (JRW) in central Montana, USA, notably high nitrate concentrations in groundwater and stream water have exceeded the U.S. EPA drinking water standard of 10 mg L -1 for at least two decades. This large (24,400 ha) watershed drains immediately into the Missouri River, a tributary of the Mississippi River. Over an eleven month period in 2012, we measured groundwater and surface water nitrate concentrations across a hydrologically isolated strath terrace. We use the resulting data to constrain nitrate accumulation dynamics in the shallow aquifer. Nitrate is relatively conservative in this location, as it is high in groundwater (17.57 +/- 4.29 mg L -1; all groundwater samples pooled together), and remains high in streams and springs that drain the landform (15.67 +/- 9.45 mg L -1; all surface water and spring samples pooled together). We use a numerical model to simulate the character of nitrate accumulation in the aquifer as a whole, in order to evaluate how the entire period of cultivation has contributed to current nitrate concentrations, and begin to predict response times for effects of land use change. We consider the effect of groundwater residence time and travel time on nitrate loading using particle tracking in a three dimensional model aquifer. We find no correlation with nitrate concentrations in groundwater and emerging surface waters, and suggest approaches for improving both the geometry of the model and the selection of sites in future work. Overall, our results imply that groundwater residence times are several decades at most, suggesting that similar timeframes will be needed to reduce overall nitrate concentrations in groundwater and emergent streams to below drinking water standards. Preliminary evaluation of several management scenarios suggests that both increased fertilizer use efficiency and rotational strategies may be needed to prevent the loss of soil N to groundwater.