Land application of industrial wastewater with high levels of nitrogen requires adequate management practices to prevent groundwater pollution by nitrates. In this study a predictive computerized model was developed for nitrate leachate concentrations resulting from land application of wastewater onto crop systems including poplars. The study included a literature review, development of a computer program that could serve this purpose, and a field investigation to test the validity of the computed predictions. The literature review focused on poplar water and nitrogen uptakes, and suggested that mature poplars could uptake up to 400 lb of nitrogen /acre/year and 2 3 million gallons of water per acre per year. The computer model, based on 10-day water and nutrient balances, takes into account a number of parameters such as wastewater quality, evapotranspiration and precipitation data, irrigation volumes, soil water holding capacities, fertilization, crop nutrient uptakes and crop coefficients. This study involves a number of assumptions selected to give conservative (i.e., worst case approach) model predictions. Attempts to validate the model were conducted through soil and groundwater sampling along with precipitation data collection in four distinct fields in Brooks, Oregon, from October 1996 to April 1997. The variations in nitrogen soil profiles from October to April helped determine the amount of nitrogen leaving the soil, and groundwater samples from 5 feet deep wells gave nitrate concentrations in groundwater below the root zone. A sensitivity analysis of the program demonstrated how important nitrogen and water uptakes values were to the model predictions. An increase of 1% in nitrogen uptake or of 0.4% in crop coefficients generated 1% decrease in nitrogen concentration of the leachate. These results are important to consider when adopting highly uncertain literature values for crop uptakes -especially with poplars. The field validation of the model showed promising results in terms of estimating average yearly leachate concentrations in nitrogen resulting from land application of wastewater, but also suggested that more groundwater wells were needed to obtain a statistically significant validation of the model. These preliminary field results indicate that the model can provide an indication of groundwater nitrogen concentration trends but needs to further verified to be used confidently as a predictive tool. / Graduation date: 1998

Deep injection wells (DIW) in Florida are regulated by the U.S. Environmental Protection Agency (USEPA) and the state of Florida through the Underground Injection Control regulations contained within the Safe Drinking Water Act. Underground injection is defined as the injection of hazardous waste, nonhazardous waste, or municipal waste below the lowermost formation containing an underground source of drinking water within one-quarter mile of the wellbore. Municipalities in Florida have been using underground injection as an alternative to surface disposal of treated domestic wastewater for nearly 40 years. The research involved collecting data as of September, 2007 on all the Class I DIWs in the state of Florida and evaluating the differences between them. The analysis found regional differences in deep well practice and canonical correlation analyses concluded that depth below the USDW is the most significant factor to prevent upward migration of the injected fluid. / by Jie Gao. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.