@article{showers_genna_mcdade_bolich_fountain_2008, title={Nitrate contamination in groundwater on an urbanized dairy farm}, volume={42}, ISSN={["0013-936X"]}, DOI={10.1021/es071551t}, abstractNote={Urbanization of rural farmland is a pervasive trend around the globe, and maintaining and protecting adequate water supplies in suburban areas is a growing problem. Identification of the sources of groundwater contamination in urbanized areas is problematic, but will become important in areas of rapid population growth and development. The isotopic composition of NO3 (delta15N(NO3) and delta18O NO3), NH4 (delta15N(NH4)), groundwater (delta2H(wt) and delta18O(wt)) and chloride/bromide ratios were used to determine the source of nitrate contamination in drinking water wells in a housing development that was built on the site of a dairy farm in the North Carolina Piedmont, U.S. The delta15N(NO3) and delta18O NO3 compositions imply that elevated nitrate levels at this site in drinking well water are the result of waste contamination, and that denitrification has not significantly attenuated the groundwater nitrate concentrations. delta15N(NO3) and delta18O(NO3) compositions in groundwater could not differentiate between septic effluent and animal waste contamination. Chloride/ bromide ratios in the most contaminated drinking water wells were similar to ratios found in animal waste application fields, and were higher than Cl/Br ratios observed in septic drain fields in the area. delta18O(wt) was depleted near the site of a buried waste lagoon without an accompanying shift in delta2H(wt) suggesting water oxygen exchange with CO2. This water-CO2 exchange resulted from the reduction of buried lagoon organic matter, and oxidation of the released gases in aerobic soils. delta18O(wt) is not depleted in the contaminated drinking water wells, indicating that the buried dairy lagoon is not a source of waste contamination. The isotope and Cl/Br ratios indicate that nitrate contamination in these drinking wells are not from septic systems, but are the result of animal waste leached from pastures into groundwater during 35 years of dairy operations which did not violate any existing regulations. Statutes need to be enacted to protect the health of the homeowners that require well water to be tested prior to the sale of homes built on urbanized farmland.}, number={13}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Showers, William J. and Genna, Bernard and McDade, Timothy and Bolich, Rick and Fountain, John C.}, year={2008}, month={Jul}, pages={4683–4688} }
 @article{bergslien_fountain_2008, title={Examining the utility of epoxy replicas of single, natural fractures in dolostone for visualization experiments}, volume={16}, ISSN={["1435-0157"]}, DOI={10.1007/s10040-007-0223-8}, number={1}, journal={HYDROGEOLOGY JOURNAL}, author={Bergslien, Elisa and Fountain, John}, year={2008}, month={Feb}, pages={43–53} }
 @article{bergslien_fountain_2006, title={The effect of changes in surface wettability on two-phase saturated flow in horizontal replicas of single natural fractures}, volume={88}, ISSN={["1873-6009"]}, DOI={10.1016/j.jconhyd.2006.06.009}, abstractNote={By using translucent epoxy replicas of natural single fractures, it is possible to optically measure aperture distribution and directly observe NAPL flow. However, detailed characterization of epoxy reveals that it is not a sufficiently good analogue to natural rock for many two-phase flow studies. The surface properties of epoxy, which is hydrophobic, are quite unlike those of natural rock, which is generally assumed to be hydrophilic. Different surface wettabilities result in dramatically different two-phase flow behavior and residual distributions. In hydrophobic replicas, the NAPL flows in well-developed channels, displacing water and filling all of the pore space. In hydrophilic replicas, the invading NAPL is confined to the largest aperture pathways and flow frequently occurs in pulses, with no limited or no stable channel development, resulting in isolated blobs with limited accessible surface area. The pulsing and channel abandonment behaviors described are significantly different from the piston-flow frequently assumed in current modeling practice. In addition, NAPL never achieved total saturation in hydrophilic models, indicating that significantly more than a monolayer of water was bound to the model surface. Despite typically only 60-80% NAPL saturation, there was generally good agreement between theoretically calculated Young-Laplace aperture invasion boundaries and the observed minimum apertures invaded. The key to determining whether surface wettability is negligible, or not, lies in accurate characterization of the contaminant-geologic media system under study. As long as the triple-point contact angle of the system is low (<20 degrees), the assumption of perfect water wettability is not a bad one.}, number={3-4}, journal={JOURNAL OF CONTAMINANT HYDROLOGY}, author={Bergslien, Elisa and Fountain, John}, year={2006}, month={Dec}, pages={153–180} }
 @article{israel_showers_fountain_fountain_2005, title={Nitrate movement in shallow ground water from swine-lagoon-effluent spray fields managed under current application regulations}, volume={34}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2004.0338}, abstractNote={ABSTRACTRapid increases in the swine (Sus scrofa domestica) population in the 1990s and associated potential for nitrate N pollution of surface waters led the state of North Carolina to adopt stringent waste management regulations in 1993. Our objectives were to characterize (i) nitrate N movement from waste application fields (WAFs) in shallow ground water, and (ii) soil, hydrologic, and biological factors influencing the amount of nitrate N in the adjacent stream. A ground water monitoring study was conducted for 36 mo on a swine farm managed under new regulations. Water table contours and lack of vertical gradients indicated horizontal flow over most of the site. Nitrate N concentrations in water from shallow wells in WAFs averaged 30 ± 19 mg L−1 and δ15N ratios for nitrate N were between +20 and +25 per mil. Nitrate N concentration decreased from field‐edge to streamside wells by 22 to 99%. Measurement of δ18O and δ15N enrichment of nitrate in ground water throughout the WAF–riparian system indicated that denitrification has not caused significant 15N enrichment of nitrate. Over a 24‐mo period, δ15N ratios for nitrate N in the stream approached δ15N ratios for nitrate N in ground water beneath WAFs indicating delivery of some waste‐derived nitrate N to the stream in shallow ground water. Nitrate N concentrations in the stream were relatively low, averaging 1 mg L−1 Dilution of high nitrate N water in shallow horizontal flow paths with low nitrate N water from deeper horizontal flow paths at or near the stream, some denitrification as ground water discharges through the stream bottom, and some denitrification in riparian zone contributed to this low nitrate N concentration.}, number={5}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Israel, DW and Showers, WJ and Fountain, M and Fountain, J}, year={2005}, pages={1828–1842} }
 @article{bergslien_fountain_giese_2004, title={Characterization of the surface properties of epoxy-type models used for multiphase flow studies in fractured media and creation of a new model}, volume={40}, ISSN={["1944-7973"]}, DOI={10.1029/2003wr002780}, abstractNote={Epoxy models have been used as analogs for fractured rock surfaces in many laboratory investigations of multiphase flow processes. However, there is no agreement on how well or poorly such an analog replicates the surface chemistry of geologic materials, nor is there a satisfactory analysis of the surface properties of epoxy. This paper addresses the issue of accurately characterizing the surface chemistry of a typical epoxy used in laboratory multiphase flow studies and comparing that surface to a polystyrene surface and a radio frequency glow discharge treated polystyrene surface. Surface properties were determined using direct contact angle measurements of polar and apolar liquids on flat test samples. The epoxy was determined to have surface properties as follows: γ = 62.3, γLW = 39, γAB = 23.3, γ⊕ = 0, and γ = 23.3 mJ/m2, where γ is the total surface tension of the solid, γLW is the Lifshitz‐van der Waals (LW) surface tension component, γAB is the Lewis acid base (AB) surface tension component, γ is the electron‐donor (negative) parameter, and γ⊕ is the electron‐acceptor (positive) parameter. Values of γ < 27.9 mJ/m2 indicate a hydrophobic surface, which means that epoxy is not a good analog for most geologic materials. This study also explores the use of radio frequency glow discharge plasma to add hydroxyl functionality to polymer surfaces producing a material with alterable surface properties and the same optical and casting properties as epoxy. Using this method, the degree of alteration of the surface chemistry of polymer fracture models can be controlled, allowing the creation of models with a variety of different wettabilities. The resultant models were found to be durable, long lasting, and a potentially very useful alternative to the more typical epoxy models.}, number={5}, journal={WATER RESOURCES RESEARCH}, author={Bergslien, E and Fountain, J and Giese, R}, year={2004}, month={May} }