The agricultural production of peppermint has been shown to contribute significant quantities of nitrate-nitrogen to groundwater recharge. In an effort to provide new tools for increasing nitrogen efficiency within peppermint production, three research questions were proposed: i) How should plant tissue samples be collected to achieve the greatest precision when using the mint stem nitrate test for nitrogen management?; ii) What is the consumptive use of water by peppermint in the post-harvest period?; and iii) How does irrigation uniformity affect nitrate loading to groundwater when N is supplied through chemigation? In the first investigation, structured field experiments were designed and conducted on commercial peppermint fields to isolate potential environmental, management, and sampling influences on stem nitrate test results. The most significant effects observed were those of the type of stem material collected (a 441% effect at p<0.001) and the number of stems collected to estimate the field mean concentration. It was found that the variance of the sample population and the number of stems required for a given sampling error could be greatly reduced by only collecting stems from within the plant canopy. Less pronounced but statistically significant differences in stem nitrate concentrations were produced by variations in solar radiation on hourly (a 17% effect at p<0.05) and daily (a 29% effect at p<0.01) scales. In an analysis of stem nitrate spatial variability, a purely random distribution of stem nitrate concentrations was observed on the 1-150 m scale. For the second investigation, a field study was conducted to measure the consumptive use of peppermint in the post-harvest period and to develop crop coefficients (Kc) used to predict evapotranspiration rates. The soil water balance was measured on two fields with a neutron moisture probe over an 80 day period. Over the 49 days following harvest, a cumulative consumptive use of 96 mm was observed. Basal crop coefficients increased from near zero to approximately 0.40 within 40 days post-harvest. The third, and final, investigation developed a simple heuristic statistical model to explore the effective adequacy of chemical application as influenced by the uniformity of irrigation. To perform this analysis, an expression was presented whereby irrigation distribution parameters for the normal, or Gaussian, model could be derived from common irrigation design terms. The results of this model indicate that the effective chemical adequacy is greatly compromised when the irrigation uniformity coefficient is low and/or the design irrigation adequacy is high. / Graduation date: 1998

Radon-222 gas has unique properties allowing it to be used as an indicator for the presence of organic phase liquids in the saturated zone. It naturally occurs in soils. It is radioactive, making quantitative detection straight forward. A noble gas, it is chemically inert and does not react with aquifer media. Finally, radon has an affinity to concentrate in nonaqueous phase liquids. A proposed linear equilibrium partitioning model was tested by batch equilibration with the pore fluid to establish the deficit in aqueous radon concentrations that results from its partitioning into the residual saturation of the organic phase (Soltrol-220). Five sets of experiments were run on columns with 0.0, 1.0, 2.5, 5.0, and 8.0 percent residual soltrol fractions. The model was found to accurately represent the partitioning process. A one-dimensional physical model was run to see if the data from the partitioning experiments could be successfully applied to predict the aqueous radon concentrations in a more complex situation. The results indicate that radon-222 has great potential to be used as a means of detecting and quantifying the presence of residual organic phase liquids in the saturated zone. / Graduation date: 1995

Assessment of the environmental impacts of an agricultural production system requires information on both soil water quality and solute flux. Passive Capillary Samplers (PCAPS), which sample water from the vadose zone using fiber glass wicks, have shown potential to provide both flux and solute concentration in unsaturated zone sampling but have not been tested under long-term, natural, rainfall conditions. The objectives of this study are to (1) evaluate PCAPS operation under non-steady, natural rain and irrigation fed conditions, (2) determine the samplers ability to estimate recharge, and (3) estimate the loss of nutrients resulting from agricultural production. 32 PCAPS and 78 suction cup samplers were installed below the root zone at 16 commercial fields in Lane County, Oregon. PCAPS' were installed in positions using ground penetrating radar such that PCAPS' were placed in homogeneous or concave profile locations. Two PCAPS and six suction cups were installed at each site. Rain gages and TDR probes were installed at eight of the 16 sites. These data were used to develop a mass balance for each of the eight special study sites. Comparison to mass balance data indicates that the PCAPS flux measurements were within 10% of the mass balance estimated recharge. Surface runoff of potential drainage water during periods of high rainfall was a point of concern for estimated recharge discrepancies because runoff was not measured. The saturated hydraulic conductivity was shown to be the most influential design parameter for matching wick and soil types. On the other hand, the incident flux, rather than conductivity, determined the ultimate ground water recharge. PCAPS collection was found to be significantly correlated (average R��=0.75) to the mass balance monthly estimated recharge. To estimate the mean monthly recharge at each site with a 30% bound on the mean and 95% confidence level, 20 PCAPS would be required at each site. PCAPS were found to be superior to suction cup samplers for estimating ground water recharge concentrations because PCAPS were able to sample both flux and resident concentrations. Mint and row crop, organic and inorganic, production systems contributed to the largest adverse environmental impacts with average recharge concentrations for mint and row crop of 24 mg L����� and 28 mg L�����, respectively. Orchard and blueberry production systems had little impact with their seasonal concentrations averaging below the EPA water quality standard. Amounts of percolation were key in determining which management systems were inefficiently operated. Over-irrigation during the summer lead to increased losses of nitrogen for the mint production systems in the summer as well as the winter. Over-fertilization was important for creating significant differences in seasonal mass losses of nitrogen from row crop production systems. Overall, the PCAPS estimated nitrogen loss was 12% lower than that calculated using a simplified nitrogen mass balance approach. Best management practice suggestions concerning irrigation, fertilization and cover cropping were provided as a direct result of the findings of the project. With technical support and increase in concern over nitrate contamination, farmers should be able to control leaching losses without the use of quotas or allotments. / Graduation date: 1995

The objective of this research was to evaluate the treatment efficiency of a nitrate-contaminated soil by combined technologies of the injection of palladized nanoiron slurry and electrokinetic remediation process. First, nanoiron was prepared by two synthesis processes based on the same chemical reduction principle yielding products of NZVI-A and NZVI-B, respectively. Then they were characterized by various methods. Micrographs of scanning electron microscopy have shown that a majority of these nanoparticles were in the range of 50-80 nm and 30-40 nm, respectively. Results of nitrogen gas adsorption-desorption show that NZVI-A and NZVI-B are mesorporous (ca. 30-40 &#x00C5;) with BET surface areas of 128 m2/g and 77 m2/g, respectively. Results of X-ray diffractometry have shown that both types of nanoiron were poor in crystallinity. Results of zeta-potential measurements indicated that NZVI-A and NZVI-B had the same isoelectric point at pH 6.0. Although NZVI-A and NZVI-B were found to be superparamagnetic, their magnetization values were low. Poly acrylic acid (PAA), an anionic dispersant, was employed for stabilizing various types of nanoiron. Then Palladium¡]ca. 1 wt% of iron¡^ was selected as catalysis to form palladized nanoiron¡]Pd/Fe¡^. Results have demonstrated that an addition of 1 vol. % of PAA during the nanoiron preparation process would result in a good stabilization of nanoiron and nanoscale Pd/Fe slurry. Batch tests were carried out to investigate the effects of pH variation on degradation of nitrate aqueous solutions. Experimental results have indicated that palladized nanoiron outperformed nanoiron in treatment of nitrate in this study. Apparently, an employment of catalyst would enhance the treatment efficiency. Further, an exponential increase of the reaction rate was found for the systems at low pH. The final stage of this study was to evaluate the treatment efficiency of combined technologies of the injection of palladized nanoiron¡]Pd/Fe¡^ slurry and electrokinetic remediation process in treating a nitrate-contaminated soil. Test conditions used were given as follows: (1) slurry injection to four different positions in the soil matrix; (2) electric potential gradient: 1 V/cm; (3) daily addition of 20 mL of palladized nanoiron (4 g/L) slurry to the injection position; and (4) reaction time: 6 days. Test results have shown that addition of palladized nanoiron slurry to the anode reservoir yielded the lowest residual nitrate concentration in soil. Namely, about 99.5% removal of nitrate from soil. On the other hand, the acidic condition of soil matrix around the anode reservoir would enhance the degradation of nitrate therein. Based on the above findings, the treatment method employed in this work was proven to be a novel and efficient one in treating nitrate contaminated soil.

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

The potential for leachate movement out of a sanitary landfill was evaluated and simulated by a computer program model. Landfill operations and geohydrological conditions in the area were investigated in order to develop a conceptual model of the system and to obtain numerical data for the development of the simulation.The landfill is operated in a 20 to 27 foot thick clay till which overlies a 10 foot thick, continuous sand and gravel aquifer. Monitor wells located around the site indicate minimal changes in groundwater quality to this date. This is attributed to the slow movement of leachate through the confining layer which would take at least 5 to 10 years.Numerical parameters not readily determined were varied in 16 simulations. This procedure allowed analysis of the different plumes developed as well as observation of the program’s sensitivity to such changes. In simulations of five years from the time leachate would enter the aquifer, leachate plumes were developed which extended a mile and one half down the hydrologic gradient from the landfill. Varying the parameters led to fairly consistant conclusions regarding the effects of the landfill.Ball State UniversityMuncie, IN 47306

Wetland-based treatment systems are often implemented as a method to remove unwanted substances from contaminated groundwater. Wetlands are effective due to the high biological activity that naturally takes place in the rhizosphere and soil. In support of a demonstration surface wetland system at a site in Columbus, Georgia, laboratory-scale wetland systems were designed to study the effect of different carbon sources and their biodegradability, COD:N ratio and temperature on the rate and extent of nitrate reduction of nitrate-bearing groundwater. Nitrate reducing bacteria are ubiquitous in surface and subsurface wetlands but a major limiting factor for these systems is carbon availability. Two major carbon sources were investigated in both continuous-flow and batch systems: a natural source, hay and a commercial source, MicroC GTM, a concentrated carbohydrate mix. Between these two carbon sources, the nitrate removal rate was not significantly different as long as sufficient biodegradable carbon was provided. The effect of both hydraulic retention time (HRT) and COD:N ratio on nitrate removal were investigated in continuous-flow systems. The specific nitrate removal rate in open to the atmosphere batch reactors was estimated at 0.55 mg N/mg biomass VSS-day. The effluent nitrate concentration in a continuous-flow system maintained with an HRT of 5 days at room temperature (22 to 23°C) was less than 3 mg nitrate-N/L. The COD:N ratio was kept at 6:1 for the majority of the experiments (approximately twice the theoretical requirement) to ensure sufficient carbon loading. Lower COD:N ratios of 5, 4, 3, 2, 1, and 0.5 were also investigated in the continuous-flow system and the minimum required carbon loading to achieve an effluent nitrate concentration below 10 mg N/L for an influent groundwater nitrate concentration between 65 and 70 mg N/L was determined to be 5:1 COD:N. The effect of temperature on the nitrate removal rate was also investigated at 22, 15, 10 and 5°C. As expected, the rate of nitrate reduction decreased with the decrease in temperature, especially below 10°C. Overall, the surface wetland is a feasible solution to treating nitrate-bearing groundwater even at relatively low ambient temperature values, provided that sufficient, biodegradable carbon is present.

published_or_final_version / Applied Geosciences / Master / Master of Science

The assumption of perfect stratification in an aquifer has been widely used in solute-transport modeling studies. This assumption is especially useful for applied studies where limited site characterization data are available, but geologic well logs indicate significant layering. Chapter 3 investigates the issue of vertical sampling density via a sensitivity analysis of the number of aquifer layers used in a model of tracer transport through a heterogeneous synthetic aquifer. Tracer breakthrough in the synthetic aquifer is predicted by layered models. Given a variance of ln K of 2 and an exponential covariance function, sampling the synthetic aquifer at more than 12 elevations did not produce any significant improvement in the predictions. Even six sampling points, however, produced more accurate predictions of transport compared to a full-aquifer, homogeneous approach employing a local-scale dispersivity. Chapter 4 presents and interprets data from a dual-well, forced-gradient tracer experiment conducted in a confined aquifer underlying a contaminant source zone of a Superfund site. Tracer breakthrough was monitored at an extraction well and at four levels of a centerline monitoring well. A perfectly stratified numerical transport model based on multi-level data successfully predicted tracer breakthrough at the extraction well. Given the added vertical resolution associated with the layered model, it was possible to use dispersivity values more than an order of magnitude lower than the value used in a vertically integrated model. It is expected that the multi-layer model would allow for more robust analyses of solute transport at the site. In Chapter 5, TCE elution during the same dual-well experiment is predicted with a stratified numerical model incorporating rate-limited desorption, rate-limited diffusion, and rate-limited dissolution of nonaqueous phase liquid (NAPL). Based on model results, initial mass calculations, and other indirect lines of evidence, it is concluded that NAPL is the primary cause of rate limitations for TCE transport at the site. NAPL presence is the primary reason a large pump-and-treat system at the site has failed to reduce contaminant concentrations to federal drinking water standards. Alternative remediation technologies are thus necessary for restoring the aquifer, especially in the contaminant source zone.

Thesis (MTech. degree in Environmental management.)-Tshwane University of Technology, 2008. / Aims to generate information on the quality of water from boreholes and the Steelpoort river in order to ascertain the level of pollution within the vicinity of Vantech mine. The information is envisaged to help a better water management within the area. The following objectives were pursued: to measure water quality parameters ; to investigate the extent of the pollution plume movement ; to study the composition and geological factors in the area in relation to mobility of groundwater and to determine the impacts of Geo hydrological characteristics.