Millions of Canadians rely on private groundwater wells to access drinking water, which presents many challenges including a lack of government regulations, and limited resources for maintenance, monitoring, management, and protection. These challenges result in an increased risk of acute gastrointestinal illness in private well users. The goal of this work is to improve the understanding of drivers of E. coli fate and transport in groundwater using a data-driven approach to better inform well owners and policy makers. Specifically, the objectives include: exploratory analysis of the physical and human drivers of private well contamination; advancing the understanding of the relationships between land use-land cover and E. coli presence in wells; assessment of rainfall intermittency patterns as a driver of contamination, as an alternative to standard lag times; and, the development of data-driven explanatory models for E. coli contamination in private wells that move towards a novel coupled-systems approach. This research utilizes a large dataset with 795,023 contamination observations, 253,136 unique wells, and over 33 variables (i.e., microbiological, hydrogeological, well characteristic, meteorological, geographical, and testing behaviour) across Ontario, Canada between 2010 and 2017. Data used includes the Well Water Information Database, Well Water Information System, Daymet, Provincial Digital Elevation Model, Ontario Land Cover Compilation, Southern Ontario Land Resource Information System, and Roads Network. Data analysis methods range from univariate and bivariate analyses to supervised and unsupervised machine learning techniques, including regression, clustering, and classification. This work has contributed important understandings of the relationships between E. coli contamination and well and aquifer characteristics, seasonality, weather, and human behaviour. Specifically, increased well depth reduced, but did not eliminate, likelihood of contamination; wells completed in consolidated material increased likelihood of contamination; the most significant driver of contamination was identified as land use - land cover, which was categorized into four classes of E. coli contamination potential for wells, ranging from very high to low; latitude was found to drive seasonality and consequent weather patterns, leading to the creation of geographically-based seasonal models; liquid water (i.e., rainfall, snow melt) was a key driver of contamination, where increased water generally increased presence of E.coli while causing decreasing prevalence; time of year, not habit, drove user testing, generally peaking in July; and, a surrogate measure of well user stewardship was identified as driving time to closest drop-off location. Further, this work has contributed methodological advancements in identifying drivers of groundwater contamination including: utilizing literature confidence ratings alongside regression analyses to supply strategic direction to policy makers; demonstrating the value of large datasets in combination with innovative machine learning techniques, and subject matter expertise, to identify improved physically-based understandings of the system; and, highlighting the need for coupled-systems approaches as physical models alone do not capture human behaviour-based factors of contamination. / Thesis / Doctor of Engineering (DEng) / There are millions of people globally relying on private groundwater to access drinking water. Unfortunately, these wells come with many challenges including a lack of government regulations, and limited resources for maintenance, management, and protection. These challenges also result in an increased risk of illness in private well users. Groundwater research is often limited by lack of numerical data, making it extremely difficult to understand how groundwater and contaminants are transported. This research utilizes a large dataset with 795,023 contamination observations, 253,136 unique wells, and over 33 variables (i.e., well and aquifer characteristics, human behaviours, weather-related) across Ontario, Canada between 2010 and 2017. The work in this thesis utilizes a data-driven approach, using various machine learning techniques combined with subject matter expertise, to uncover trends and insights into when and how contamination events occur in private wells, to inform policy makers and empower well users.

80 pp. / Arizona: Know Your Water. A consumer's guide to water source, quality, regulations and home water treatment. / This well owners guide presents detailed sections to assist the reader in becoming familiar with water quality concepts, drinking water guidelines and water testing. The reader can also become familiar with Arizona specific aquifers, conditions and activities that determine ground water quality. Well owners can also review and become familiar with well construction, components and maintenance needed for the safe and proper function of their wells. Finally, a section on water treatment technologies and selection, based on water quality conditions is presented. Well owners will be able to refer to this section for the selection of water treatments, should they choose to improve the water quality of their wells. Includes numerous illustrations.

Vattenförsörjningen på Gotland består till stor del av vattenuttag från täkter baserade på grundvatten både ur allmänna täkter och enskilda brunnar. Gotlands grundvatten är på grund av berggrunden och ofta tunna jordlager känsligt för föroreningar och förändringar i klimatet. Idag är datainsamlingen gällande grundvattenkemin begränsad och det är önskvärt att informationen och kunskapen om Gotlands grundvatten ökar. Detta gäller framför allt Gotlands 14000 enskilda vattentäkter där analysresultaten idag inte är tillgängliga för myndigheter att använda i exempelvis miljömålsuppföljningar och i vattenförvaltningsarbetet. Därför syftar detta arbete till att ta fram ett förslag på hur ett tillgängliggörande av analysresultat kan gå till och vilka användningsområden som finns för dessa, och förhoppningsvis ligga till grund för ett praktiskt genomförande på Gotland. Vattenlaboratoriet på Gotland, SGU (Sveriges Geologiska Undersökning) och Länsstyrelsen fick svara på riktade frågor gällande deras del i detta arbete. Sammanställningen gjordes utifrån deras svar och resulterade i två förslag och ett medgivandeformulär. Slutsatsen är att det i dagsläget finns möjlighet att applicera och starta en datainsamling av analysresultat som kan vara till betydande hjälp i vattenförvaltningsarbetet på Gotland. Det kommer att underlättas framöver när Vattenlaboratoriet får nytt datasystem. / The water supply on Gotland mainly consists of withdrawal from groundwater wells both for public and private use. The groundwater on Gotland is especially vulnerable for contamination and effects of climate change because of the geology and thin soil layer. The data collection regarding the quality of the groundwater is limited today and it is desirable that information and knowledge about the groundwater improves. Primarily, this concerns Gotland’s 14000 private wells where analysis results are not available for authorities to use, for example, for work with environmental goals and water management. Therefore, this work aims to produce a proposition on how to make analysis results available and which use and applications they can have, and hopefully this can be a starting point for a practical implementation on Gotland. The Water laboratory on Gotland, SGU (Geological Survey of Sweden) and the County Administrative Board answered a questionnaire about their area of work and involvement in this. The answers provided a basis for this work, resulting in two suggestions on how to make the analysis results available and in a consent form. In summary, it is possible to start to collect data on analysis results, which can be of importance and use in the water management on Gotland. This will be more easily implemented and easier when the Water laboratory get their new computer system.

Background: An estimated 1.27 million people per year are experiencing acute gastrointestinal illness (AGI) due to private water sources, which are federally unregulated drinking water sources in the US (Murphy et al., 2017). Previous studies have found a relationship between drinking water source (domestic well or publicly supplied water) and waterborne disease. Although some work has been done to characterize the quality of water in karstic terrain, and karst is considered to be a risk factor for pathogenic contamination of domestic wells, little work has been done to assess the relationship between karst and incidence of enteric disease. There is also little known about the socio-demographic factors of populations in the US using domestic wells. Although studies have also shown an association between rain, antecedent rain, and waterborne illness, the relationship is not well defined. Objective: The dissertation uses spatiotemporal and epidemiologic methods to characterize domestic well users in Pennsylvania, determine the relationship between use of domestic wells and cases of illness, and investigate an interactive effect between rain and drought on county level occurrence of reporting of illness. This work includes illness due to Salmonella, Campylobacter, Giardia, and Cryptosporidium as reported to the PA department of health. The population of interest is the estimated 12.8 million people who lived in PA from 2010-2019, of which an estimated 3.5 million used a domestic well. Aim 1: Determine whether populations of Pennsylvania that rely on domestic wells are more socially vulnerable than those with access to public water supply or wastewater treatment. Hypothesis: Census tracts that are generally more socially vulnerable are also more likely to lack access to public water supply. Aim 2: Determine presence of spatial clusters of reportable enteric diseases (Salmonella, Campylobacter, Giardia, or Cryptosporidium) between 2010 and 2019 in PA, and whether those clusters are associated with drinking water source (whether a domestic well or publicly supplied water). Hypothesis 1: Enteric disease in PA for the 2014 - 2018 time period cluster in time and space. Hypothesis 2: The incidence risk ratio of reported enteric disease will be positively associated with the proportion of households utilizing domestic wells. Aim 3: Determine the effects of rain and drought on weekly counts of reportable enteric illness (Salmonella, Campylobacter, Giardia, or Cryptosporidium) in PA, 2010-2019. Hypothesis 1: County level weekly enteric illness incidence rates are positively associated with total rain (cm) in prior week(s). Hypothesis 2: The incidence rate of reportable enteric illness by county is associated with an interaction between total rain (cm) in the prior week by county and drought conditions as measured by the Palmer Drought Severity Index in the same week the rain is measured preceding disease onset. Methods: Using county and zip code tabulation area incidence data on enteric illnesses made available from the Pennsylvania Department of Health for the years 2010 to 2019, this thesis investigated the potential relationships between rain, drought conditions, use of private wells, and the occurrence of karstic terrain and illness. The social characteristics of those who do not have access to public water supply were also explored. This was done in three parts, all utilizing ecologic study designs. Aim 1: We assessed how social vulnerability measures co-occur with domestic well use and also how those patterns change over space using a profile regression method. Aim 2: We examined the spatial patterns, by Zip Code Tabulation Area using a Poisson Spatial only SaTScan analysis with 5% of the state population without Philadelphia allowing for hierarchical clusters, and temporal patterns, using the R software trending package to develop a season adjusted negative binomial model to assess outbreaks, of weekly reported enteric illnesses. The weekly county incidence rates for each illness were also assessed by percentage of a county that did not have access to public water supply and presence of karst using a zero-inflated negative binomial model with random intercept for county. Philadelphia was excluded because they did not share their data. To assess the second hypothesis, that the incidence risk ratio of reported enteric disease is positively associated with the proportion of households utilizing domestic wells, a zero-inflated negative binomial model with a random intercept for county was utilized to determine if there was an association. This same model was expanded as assessment of an association between illness rates and percentage of a county underlain by karst. Aim 3: We assessed multiple time lags using a zero-inflated negative binomial model with random intercept for county to determine if there was an relationship between county level weekly rainfall (cm) and drought, as measured by the Palmer Drought Severity Index, on the weekly incidence rates of these four reportable enteric illnesses. Philadelphia was excluded, because they did not share their data. If both the amount of rain and the level of drought were found to be related to the number of cases of illnesses, an interaction was assessed for that lag time.Results: Aim 1: Measures of social vulnerability have 15 distinct profiles or clusters in the state of PA. These clusters occur spatially heterogeneously across the state. Five distinct population-profiles are more likely to rely on a domestic well. Two of these profiles are also more likely to experience social vulnerability when measured at the census tract level. In general, census tracts with higher proportions of homeowners, lower proportions of those without a high school diploma, lower median per capita income, and higher proportions of children under the age of 5 and 17 are more likely to rely on an unregulated drinking water source than populations with greater proportions of their population having a high school diploma, higher median per capita income and lower proportions of their population consisting of people under the age of 5 and 17. Aim 2: All four pathogens, which were assessed, have spatial heterogeneity in the state of Pennsylvania. All pathogens had higher incidence rates in the summer and lowest rates in the winter. However, most outbreaks occurred in the wintertime. A positive association was found between quartile of area of a county not served by public water supply and incidence rates of campylobacteriosis [IRR = 1.35 (95%CI 1.21, 1.51 p < 0.001)], cryptosporidiosis [IRR = 1.33 (95%CI 1.07, 1.66, p < 0.05)], and giardiasis [IRR = 1.25 (95%CI 1.11, 1.42, p < 0.01)]. An association was also observed between the quartile of area of a underlain by karst and incidence rates of campylobacteriosis [IRR = 1.21 (95%CI 1.08, 1.35, p <0.01)] and cryptosporidiosis [IRR = 1.36 (95%CI 1.09, 1.69, p < 0.01)]. Aim 3: There was at least one lag time (weeks between weekly measure of rain and specimen collection) where the amount of rain was positively associated with counts of campylobacteriosis, salmonellosis, and giardiasis. We also evaluated potential associations between enteric disease and rain as well as previous drought conditions (wetness or lack thereof) with various time-lags for 66 counties of PA for a 10-year time, Philadelphia is not included in this analysis because their data was not shared. In the case of Salmonella, there were four different lag times with an increase in incidence (weeks 4, 5, 11 and 12) and Giardia had two different lag times that showed an increase in incidence (weeks 12, and 14 ). At week 11 for cases due to Campylobacter, there was also an assessed interaction, while both rain and drought, as measured by the weekly Palmer Drought Index (PDI) had a positive relationship with risk, the relationship changed direction and was protective [IRR = 0.9997 (95%CI 0.9997, 0.9999, p < 0.01)]. Conclusions: The key findings are: 1. There are distinct profiles of domestic well users that differ by measures of social vulnerability. Two types of census tracts in PA are likely to have a high number of domestic wells and experience high social vulnerability traits. 2. Enteric illnesses due to Salmonella, Campylobacter, Giardia and Cryptosporidium, have patterns of clustering spatially across the state, and have a strong relationship with season. 3. There is a positive association between the area of a county not served by public water supply and incidence rates of campylobacteriosis, cryptosporidiosis, and giardiasis. 4. There is a positive association between the area of a county underlain by karst and incidence rates of campylobacteriosis and cryptosporidiosis. 5. That rain and drought (wetness) conditions weeks to several weeks prior, affect the incidence rate ratio of cases of Giardia, Cryptosporidium, Campylobacter, and Salmonella in Pennsylvania. The relationship between rain and drought conditions and illness varies by organism type which could be attributed to incubation period, reporting time, transport time in the environment and exposure sources (drinking water, food, recreation). There was evidence of an interactive effect between rain and drought conditions for cases of campylobacteriosis, with an 11-week lag time. / Epidemiology

The US Safe Drinking Water Act (SDWA), established in 1974, has improved water quality nationwide through the introduction of maximum contaminant levels, source water protection, and treatment guidelines and requirements. Despite the obvious success many important water quality issues are not covered by regulation. These include the following four topics in this dissertation: 1) Support infrastructure for private well users, 2) Identification and analysis of contaminants in private wells, 3) Leaks or corrosion within building plumbing, and 4) The role of citizen scientists in addressing water quality concerns. Private wells, which provide water for approximately 13% of the population (42.5 million people), are not subject to any federal regulation and well users are responsible for ensuring their own water safety. When water quality issues do arise, state or local organizations can provide critically important support. For instance, in North Carolina (NC) local health departments (LHDs) are required to have private well programs that enforce statewide well construction standards, offer water testing services, and provide well water outreach and assistance. Little is known about the effectiveness of such programs, however, so this work conducted a survey of all NC LHDs to determine their capacity for well water outreach and identify differences among programs around the state. All LHDs reported overseeing the construction of new wells as required by law. However, services provided to existing well users were offered infrequently and/or inconsistently offered. Lack of uniformity was observed in the number of LHD staff and their assigned responsibilities; the costs and availability of well water testing; and the comfort of LHD staff communicating with well owners. While the total number of staff was lower in LHDs in rural counties, the number of outreach activities and services offered was typically not related to the number of well users served. Variations in structure and capacity of well programs at LHDs has created unequal access to services and information for well users in NC. Such gaps in NC, which has among the most stringent state guidelines for well water support, suggests the need to examine conditions in other states nationwide. While direct support to private well users is more common at the state and local levels, the scientific information and resources needed by these officials can be supplemented at the federal level or through academia, especially with respect to emerging contaminants, which many officials may not yet have experience with. For instance, following Hurricane Florence in 2018, dam failures and flooding of coal ash disposal and reuse sites in NC prompted concerns about potential contamination of well water with hexavalent chromium. There is also widespread naturally occurring Cr(VI) in the groundwater however, and methods accessible to state and local officials to identify sources are needed. Literature was reviewed related to source tracking techniques and they were applied to Cr(VI) data we collected from 1,265 private wells across 22 NC counties. Almost two thirds of private wells tested (62.0%) exceeded the Cr(VI) public health goal of 0.07 ppb, with concentrations ranging from <0.02-13.9 ppb (median=0.12 ppb). In the literature review, we identified 33 Cr(VI) groundwater tracking techniques from 51 publications and only 5 techniques were used in more than 12 papers. All papers used different combinations of techniques. We applied these techniques to our well sampling data, and inconclusive results were reported for 7 techniques, while three techniques suggested potential geogenic sources whereas three techniques indicated anthropogenic Cr(VI) sources. Specifically looking at coal ash, two techniques did not support coal ash as a primary source and three were inconclusive. Overall, these techniques did not agree as to the origins of Cr(VI) in well water. This may be due to the fact that these techniques primarily focused on regional scale identification, rather than household-level occurrence. This study demonstrates the difficulty and complexity in identifying and distinguishing the source(s) responsible for Cr(VI) in well water. In addition to private wells, another gap in the SDWA framework involves corrosion of plumbing within a home or private building. The Lead and Copper Rule (LCR) was the first SDWA legislation to include sampling at the tap in private buildings, although these results are only used to inform control of the corrosivity of the water at the treatment plant. Thus, there is no maximum level of lead or copper enforced at the consumers tap, and protection against excessive private plumbing corrosion is not required. A survey conducted about a decade ago suggested that recent efforts to increase temperatures of hot water systems to better control Legionella bacteria might also be increasing pinhole leaks in copper plumbing. Recently, an overseas large building experienced at least 300 pinhole leaks in a hot water recirculation system that frequently exceeded > 65°C in 2018. The occurrence of leaks along the top of the pipes where thick deposited of metal oxides were not visibly protective, was not consistent with conventional patterns of failure, but seemed to be a manifestation of an unusual type of hot water pitting due to the presence of cathodic iron or manganese oxide suggested in prior literature. A macro-cell apparatus was developed and tested to mechanistically test this novel hot water pitting corrosion mechanism experimentally. Cathodic manganese oxides deposits were shown to drive pitting corrosion on a part of the pipe surface without deposits. Pitting occurred over a wide range of pH and was worst at a high ratio of sulfate to bicarbonate. While iron oxide coatings tested in this work did not behave cathodically, as suggested in prior literature, further research could determine if some iron oxides might behave similarly to the manganese oxide tested in this work. Past failures to follow provisions of the SDWA has undermined trust in water safety nationally. Collaborations between citizens and scientists can sometimes expose problems with water safety. Over the last decade we have helped consumers evaluated their concerns using citizen science collaborative approaches. We documented and summarized several case studies conducted by the U.S. Water Study team at Virginia Tech that had varying degrees of success in exposing problems with water supplies via citizen science collaborations. The case studies start with a discussion of work in Flint, MI (lead and Legionella bacteria) in 2015 and St. Joseph, LA in 2016 (lead and iron). Later cases included: Enterprise, LA (lead and iron), Denmark, SC (lead, iron, and Halosan), Chicago, IL (lead), Moore, OK (arsenic), Santa Barbara, CA (copper), anonymous town in SC (Acanthamoeba), and Harrisonburg, VA (Legionella). Approaches, challenges and outcomes of each case study are reviewed along with lessons learned. Overall, this dissertation explored water quality issues which, for various reasons, fall outside of the existing SDWA regulatory framework. The importance of well water support was emphasized by documenting inequalities between local health departments well services and by critically reviewing literature to find a lack of scientific guidance for source determination for an important emerging contaminant. Development of a novel apparatus for monitoring of chemistry related hot water pitting allows for a better understanding of this mechanism and provides a baseline of guidance for avoiding or mitigating such problems in the future. Finally, the use of citizen science to address past water quality concerns and that considers reasonable expectations for future work was evaluated. / Doctor of Philosophy / In the United States, drinking water is usually collected and treated by a local drinking water treatment plant before being sent out to all customers within a city or community. Since the 1970's, the US Environmental Protection Agency (EPA) has regulated treatment plants to make sure they do not send out water that could be potentially dangerous to the health of those drinking, cooking, or bathing with it. These EPA regulations have helped deliver cleaner and cleaner water across the country, but they do not protect every aspect of drinking water for every person in the US. This dissertation covers four topics that EPA regulations do not cover including: 1) Support systems for people getting their water from private wells, 2) Understanding dangers to safe water in unregulated private wells, 3) Leaks in plumbing within a building, and 4) The role of citizens working closely with scientists to determine if their water is safe. More than 1 in 10 people in the US get their drinking water from private wells, and EPA regulations do not protect the safety of that water. Instead, consumers are on their own to make sure it is safe to drink. When water that could be dangerous is discovered, state or local governments are important sources where residents can get help in treating it. For instance, in North Carolina (NC), local county health departments are required to have programs focused on private wells. The goals of these programs are to make sure new wells are built according to legal codes, offer to test well water for residents, and answer questions people have about their well water. No one has ever determined how well how well health departments meet these goals. This work sent a survey to each health department in NC to figure out how much each was doing and identify any differences between counties. All health departments were checking new wells to make sure they were installed according to state law. But all health departments did not provide support or answer questions of people who had older wells. Some of the differences were due to the number of staff working on these problems, costs charged for well water testing, and the confidence with which staff answered well water questions. Well users in different NC counties get a different level of service as a result. The fact that these differences exist in NC, a state believed among the best in supporting private well owners, suggests a need for a similar analysis in other states. Local health departments and state agencies are more likely to work directly with people concerned about their well water. College or federal government researchers can still help support these groups. Extra support is important when contaminants that state or local officials haven't experienced before become concerning. In one example, after Hurricane Florence in NC in 2018, sites where coal power plants had been throwing away their coal ash became flooded, and coal ash was introduced into floodwaters. Coal ash has been known to contain Cr(VI), which can is believed to increase chances of cancer if consumed in drinking water. Cr(VI) also occurs naturally, when it is leached from rocks in groundwater. Figuring out where Cr(VI) found in a private well is from is difficult. To determine methods of figuring out the sources of Cr(VI) we reviewed scientific literature and documented the methods that had been used before to determine Cr(VI) sources. Then, we conducted a sampling campaign across the state, and sampled 1,265 private wells from 22 different NC counties. Cr(VI) was found in many of the wells we tested, and nearly 2/3 had Cr(VI) above the level established by the NC state government as a potential health concern. From previous literature, we reviewed 51 papers and found 33 methods that had been used to determine the source of Cr(VI) in groundwater. Only five of these methods were used by more than 12 papers and while many papers used more than one method, no papers used the same grouping of methods. When we used the methods from the literature to see how the results compared between methods, they did not all agree. Three said that Cr(VI) was coming from natural sources, three indicated it came from industry, and seven made no prediction. Overall, this study shows how difficult it can be to find out the source of Cr(VI) that occurs in private wells. Leaks in copper plumbing inside of a home or building are also not covered at all by EPA laws. The Lead and Copper Rule (LCR), passed in 1991, does include testing the water coming out of peoples' faucets for copper. But those testing results are only used to make changes at the water treatment plant to make the water less corrosive. Over the last 10-20 years, scientists have become worried that pipes may be at risk of forming more leaks, when higher hot water temperatures are used to prevent the growth of dangerous bacteria that can grow in plumbing. In one large building outside the US, at least 300 leaks were found in hot water pipes, costing large amounts of money to fix. In the past, most leaks like this were at the bottom of pipes, under settled particles with iron and manganese oxides in them. In this building though, leaks were at the top of pipes, where there was no deposit, which was very surprising. One reason for this could have been a type of reaction from past studies where iron or manganese coatings cause a reaction which forms leaks in nearby copper pipe. No experiments have ever proven this reaction though. Our study made a lab setup to learn more about this reaction and proved that it is possible and was due to manganese oxide. We found the most corrosion occurred in water with high pH and high levels of sulfate. Iron oxide particles did not cause the reaction in our study, but it is possible that other types of iron oxide could still have a role in making the reaction happen. Past examples of cities or towns not following EPA rules has caused distrust in public drinking water. Citizens and scientists working closely together have sometimes been able to find out about such problems and get them fixed. Over the last 10 years, we have helped people learn more about their water concerns by working with them to take and analyze water tests. We documented a number of those cases which had different levels of success. The first case we talk about is Flint, MI in 2015, then St. Joseph, LA in 2016. Later cases include cities in Louisiana, South Carolina, Illinois, Oklahoma, California, and Virginia, with a number of different water risks. The first two cases caused drastic and quick changes to water safety and drinking water emergencies were declared. But after that the response was less urgent. If scientists want to pursue work with citizens who have concerns, they will need to be ready for keep working on it for a long time, and face disagreement from agencies and government groups who provide the water. Overall, this work tried to help people, who were not being protected by government rules, or who felt that they were being harmed by governments or companies who were breaking the rules. Many of these problems make people worried about their water, or create worries that are not necessary, or cost consumers a lot of money. More work is needed to address this type of problem.

The Safe Drinking Water Act ensures that public systems provide water that meets health standards. However, no such protection exists for millions of Americans who obtain water from private wells. Concern for safety is warranted as most wells draw from underground aquifers, and studies demonstrate that groundwater is affected by a range of contaminants, most often nitrate. Oregon's Domestic Well Testing Act (DWTA) links well testing to property sales, enabling continuous data collection by the State. This research addresses a need for identifying datasets for characterizing exposure to private well contaminants by evaluating DWTA data for use in a sentinel surveillance system. Validation of DWTA data was accomplished by developing a land use regression (LUR) model based on agricultural nitrogen inputs and soil leachability to predict nitrate concentrations in well water. Geographic information systems (GIS) were used to advance methods for high resolution spatial modeling of fertilizer and manure nitrogen with statewide coverage. Hazard mapping with these datasets suggests that nearly half of recently drilled wells are susceptible to nitrate contamination. Spearman's rank correlation demonstrated a significant correlation between LUR-predicted nitrate levels and levels reported in the DWTA dataset. These results suggest that DWTA data is valid for use in a sentinel surveillance system, such that evidence of nitrate contamination in a single well may indicate an area-wide health hazard. However, a low fraction of variance explained by the LUR model highlighted the need for specific improvements to datasets crucial for understanding nitrate contamination in well water, including the DWTA. / Graduation date: 2012