Portfolio for GEOL 488/888: Groundwater Geology

Groundwater Geology is a course that draws undergraduate and graduate students from multiple units, including the College of Arts and Sciences, Institute for Agriculture and Natural Resources, and Civil and Environmental Engineering. The course material focuses on groundwater as a resource, and includes the use of computer programming (Python programming language) to analyze groundwater data. Many students who enroll in the course are new to either geosciences or Python, despite the fact that it is an advanced course. The course has been redesigned recently to include materials suitable for a groundwater engineering course, because it is newly offered with sections listed by the Department of Civil and Environmental Engineering. This has provided opportunities for course updates, but also challenges due to the hybrid nature of engineering classes, since the department is split between two campuses. By focusing on course objectives and using backward design for assignments and assessments, the Spring 2023 student cohort was successful in mastering the course materials and made excellent strides in applying Python programming to groundwater applications

Risk and Cost Assessment of Nitrate Contamination in Domestic Wells

This study combines empirical predictive and economics models to estimate the cost of remediation for domestic wells exceeding suggested treatment thresholds for nitrates. A multiple logistic regression model predicted the probability of well contamination by nitrate, and a life cycle costing methodology was used to estimate costs of nitrate contamination in groundwater in two areas of Nebraska. In south-central Nebraska, 37% of wells were estimated to be at risk of exceeding a threshold of 7.5 mg/L as N, and 17% were at risk of exceeding 10 mg/L as N, the legal limit for human consumption in the United States. In an area in northeastern Nebraska, 82% of wells were at risk of exceeding the 10 mg/L as N legal threshold. Reverse osmosis Point-of-Use (POU) treatment was the option with the lowest costs for a household (3–4 individuals), with an average of $4–$164 total regional cost per household per year depending on the threshold for treatment. Ion exchange and distillation were the next most cost-effective options. At the community level (~10,000 individuals), a reverse osmosis Point-of-Entry (POE) treatment system was the most expensive option for a community due to high initial costs and ongoing operation and maintenance costs, whereas the biological denitrification system was least expensive due to economies of scale. This study demonstrates integrated modeling methods to assess water treatment costs over time associated with groundwater nitrate contamination, including quantification of at-risk wells, and identifies suitable options for treatment systems for rural households and communities based on their cost

Influence of Irrigation Drivers Using Boosted Regression Trees: Kansas High Plains

Groundwater levels across parts of western Kansas have been declining at unsustainable rates due to pumping for agricultural irrigation despite water-saving efforts. Accelerating this decline is the complex agricultural landscape, consisting of both categorical (e.g., management boundaries) and numerical (e.g., crop prices) factors that drive irrigation decisions, making integrated water budget management a challenge. Furthermore, these factors frequently change through time, rendering management strategies outdated within relatively short time scales. This study uses boosted regression trees to simultaneously analyze categorical and numerical data against annual irrigation pumping to determine the relative influence of each factor on groundwater pumping across both space and time. In all, 45 key water use variables covering approximately 19,000 groundwater wells were tested against irrigation pumping from 2006 to 2016 across five categories: (1) management/policy, (2) hydrology, (3) weather, (4) land/agriculture, and (5) economics. Study results showed that variables from all five categories were included among the top 10 drivers to irrigation, and the greatest influence came from variables such as irrigated area per well, saturated thickness, soil permeability, summer precipitation, and pumping costs (depth to water table). Variables that had little influence included regional management boundaries and irrigation technology. The results of this study are further used to target the factors that statistically lead to the greatest volumes of groundwater pumping to help develop robust management strategy suggestions and achieve water management goals of the region. Plain Language Summary Water use for crops has lowered groundwater levels in western Kansas. Past studies have shown that this water use is driven by many factors spanning policy, economics, and the physical environment. Because of this complexity, it has been difficult to fully understand which factors most drive irrigation use relative to each other. This study uses a machine-learning model to rank the influence of 45 factors on irrigation pumping. These factors are analyzed over space (∼19,000 wells across western Kansas) and time (2006–2016). Based on this study, drivers to water use include total irrigated area, summer rainfall, and depth to the water table. Factors that have little influence include management district boundaries and irrigation system type. These results are used to make water management suggestions for the region

The long term effect of agricultural, vadose zone and climatic factors on nitrate contamination in Nebraska\u27s groundwater system

A four-decade dataset (1974–2013) of 107,823 nitrate samples in 25,993 wells from western and eastern parts of Nebraska was used to assess long-term trends of groundwater nitrate concentration and decadal changes in the extent of groundwater nitrate-contaminated areas (NO3-N≥10 mg N/L) over the entire state. Spatial statistics and regressions were used to investigate the relationships between groundwater nitrate concentrations and several potential natural and anthropogenic factors, including soil drainage capacities, vadose zone characteristics, crop production areas, and irrigation systems. The results of this study show that there is no statistically significant trend in groundwater nitrate concentrations in western Nebraska, in contrast with the increasing trend (p \u3c .05) to the east. The spatial extent and nitrate concentrations in contaminated groundwater in center pivot-irrigated areas was less than in gravity-irrigated areas. Areas with a thicker vadose zone and larger saturated thickness of the aquifer have relatively lower nitrate concentrations. The results of a classification and regression tree (CART) model indicate the difference in the influence of physical factors on groundwater nitrate concentrations between western and eastern Nebraska, namely that groundwater nitrate concentrations correspond with vadose zone thickness, effective hydraulic conductivity, and saturated thickness in the west, while in eastern Nebraska, concentrations are correlated with average percent sand in the topsoil (0–150 cm), well depth, and effective hydraulic conductivity

Risk and Cost Assessment of Nitrate Contamination in Domestic Wells

This study combines empirical predictive and economics models to estimate the cost of remediation for domestic wells exceeding suggested treatment thresholds for nitrates. A multiple logistic regression model predicted the probability of well contamination by nitrate, and a life cycle costing methodology was used to estimate costs of nitrate contamination in groundwater in two areas of Nebraska. In south-central Nebraska, 37% of wells were estimated to be at risk of exceeding a threshold of 7.5 mg/L as N, and 17% were at risk of exceeding 10 mg/L as N, the legal limit for human consumption in the United States. In an area in northeastern Nebraska, 82% of wells were at risk of exceeding the 10 mg/L as N legal threshold. Reverse osmosis Point-of-Use (POU) treatment was the option with the lowest costs for a household (3–4 individuals), with an average of $4–$164 total regional cost per household per year depending on the threshold for treatment. Ion exchange and distillation were the next most cost-effective options. At the community level (~10,000 individuals), a reverse osmosis Point-of-Entry (POE) treatment system was the most expensive option for a community due to high initial costs and ongoing operation and maintenance costs, whereas the biological denitrification system was least expensive due to economies of scale. This study demonstrates integrated modeling methods to assess water treatment costs over time associated with groundwater nitrate contamination, including quantification of at-risk wells, and identifies suitable options for treatment systems for rural households and communities based on their cost

Assessing agricultural risk management using historic crop insurance loss data over the Ogallala Aquifer

Much of the agricultural production in the Ogallala Aquifer region relies on groundwater for irrigation. In addition to declining water levels, weather and climate-driven events affect crop yields and revenues. Crop insurance serves as a risk management tool to mitigate these perils. Here, we seek to understand what long-term crop insurance loss data can tell us about agricultural risk management in the Ogallala. We assess patterns and trends in crop insurance loss data from the U.S. Department of Agriculture Risk Management Agency. Indemnities, or insurance payments, totaled $22 billion from 1989–2017 for the 161 counties that overlie the Ogallala Aquifer. We focused on the top ten weather and climate-driven causes of crop loss for the Ogallala, which comprised at least 92% of total indemnities. Drought, hail, and heat were the leading causes of crop loss for the region, and varied over space and time. For example, drought is a significant cause of loss across all seasons, while hail is more prevalent in the spring and summer. Spatially heterogeneous patterns emerged showing larger hail indemnities in the northern Ogallala versus larger drought indemnities in the southern portion. We performed a Mann-Kendall trend analysis of county-level annual loss cost values (the ratio of indemnities to liabilities). Drought and excess moisture showed significant increasing loss cost trends in the western counties of the Ogallala. In contrast, hail showed significant decreasing trends in the northern and eastern portions. These results suggest the northern counties of the Ogallala may perceive hail as a greater risk, and may be better equipped to handle drought losses as compared with the southern Ogallala. Crop insurance loss data play a role in integrating long-term trends with near-term management practices, and providing relevant risk information in producers’ operational to tactical decision making processes

A Hydrometeorological Assessment of the Historic 2019 Flood of Nebraska, Iowa, and South Dakota

During early 2019, a series of events set the stage for devastating floods in eastern Nebraska, western Iowa, and southeastern South Dakota. When the floodwaters hit, dams and levees failed, cutting off towns, while destroying roads, bridges, and rail lines, further exacerbating the crisis. Lives were lost and thousands of cattle were stranded. Estimates indicate that the cost of the flooding has topped $3 billion as of August 2019, with this number expected to rise. After a warm and wet start to winter, eastern Nebraska, western Iowa, and southeastern South Dakota endured anomalously low temperatures and record-breaking snowfall. By March 2019, rivers were frozen, frost depths were 60-90 cm, and the water equivalent of the snowpack was 30-100 mm. With these conditions in place, a record breaking surface cyclone rapidly developed in Colorado and propagated eastward, producing heavy rain towards the east and blizzard conditions toward the west. In areas of eastern Nebraska, western Iowa, and southeastern South Dakota, rapid melting of the snowpack due to this rain-on-snow event quickly led to excessive runoff that overwhelmed rivers and streams. These conditions brought the region to a standstill. In this paper, we will provide an analysis of the antecedent conditions in eastern Nebraska, western Iowa and southeastern South Dakota, the development of the surface cyclone that triggered the historic flooding, along with a look into the forecast and communication of flood impacts prior to the flood. The study used multiple datasets, including in-situ observations and reanalysis data. Understanding the events that led to the flooding could aid in future forecasting efforts

Transition Pathways to Sustainable Agricultural Water Management: A Review of Integrated Modeling Approaches

Agricultural water management (AWM) is an interdisciplinary concern, cutting across traditional domains such as agronomy, climatology, geology, economics, and sociology. Each of these disciplines has developed numerous process-based and empirical models for AWM. However, models that simulate all major hydrologic, water quality, and crop growth processes in agricultural systems are still lacking. As computers become more powerful, more researchers are choosing to integrate existing models to account for these major processes rather than building new cross-disciplinary models. Model integration carries the hope that, as in a real system, the sum of the model will be greater than the parts. However, models based upon simplified and unrealistic assumptions of physical or empirical processes can generate misleading results which are not useful for informing policy. In this article, we use literature and case studies from the High Plains Aquifer and Southeastern United States regions to elucidate the challenges and opportunities associated with integrated modeling for AWM and recommend conditions in which to use integrated models. Additionally, we examine the potential contributions of integrated modeling to AWM — the actual practice of conserving water while maximizing productivity

The long term effect of agricultural, vadose zone and climatic factors on nitrate contamination in Nebraska\u27s groundwater system

A four-decade dataset (1974–2013) of 107,823 nitrate samples in 25,993 wells from western and eastern parts of Nebraska was used to assess long-term trends of groundwater nitrate concentration and decadal changes in the extent of groundwater nitrate-contaminated areas (NO3-N≥10 mg N/L) over the entire state. Spatial statistics and regressions were used to investigate the relationships between groundwater nitrate concentrations and several potential natural and anthropogenic factors, including soil drainage capacities, vadose zone characteristics, crop production areas, and irrigation systems. The results of this study show that there is no statistically significant trend in groundwater nitrate concentrations in western Nebraska, in contrast with the increasing trend (p \u3c .05) to the east. The spatial extent and nitrate concentrations in contaminated groundwater in center pivot-irrigated areas was less than in gravity-irrigated areas. Areas with a thicker vadose zone and larger saturated thickness of the aquifer have relatively lower nitrate concentrations. The results of a classification and regression tree (CART) model indicate the difference in the influence of physical factors on groundwater nitrate concentrations between western and eastern Nebraska, namely that groundwater nitrate concentrations correspond with vadose zone thickness, effective hydraulic conductivity, and saturated thickness in the west, while in eastern Nebraska, concentrations are correlated with average percent sand in the topsoil (0–150 cm), well depth, and effective hydraulic conductivity

Risk and Cost Assessment of Nitrate Contamination in Domestic Wells

This study combines empirical predictive and economics models to estimate the cost of remediation for domestic wells exceeding suggested treatment thresholds for nitrates. A multiple logistic regression model predicted the probability of well contamination by nitrate, and a life cycle costing methodology was used to estimate costs of nitrate contamination in groundwater in two areas of Nebraska. In south-central Nebraska, 37% of wells were estimated to be at risk of exceeding a threshold of 7.5 mg/L as N, and 17% were at risk of exceeding 10 mg/L as N, the legal limit for human consumption in the United States. In an area in northeastern Nebraska, 82% of wells were at risk of exceeding the 10 mg/L as N legal threshold. Reverse osmosis Point-of-Use (POU) treatment was the option with the lowest costs for a household (3–4 individuals), with an average of $4–$164 total regional cost per household per year depending on the threshold for treatment. Ion exchange and distillation were the next most cost-effective options. At the community level (~10,000 individuals), a reverse osmosis Point-of-Entry (POE) treatment system was the most expensive option for a community due to high initial costs and ongoing operation and maintenance costs, whereas the biological denitrification system was least expensive due to economies of scale. This study demonstrates integrated modeling methods to assess water treatment costs over time associated with groundwater nitrate contamination, including quantification of at-risk wells, and identifies suitable options for treatment systems for rural households and communities based on their cost