Monday, April 29, 2013: 2:30 p.m.
Regency East 1 (Hyatt Regency San Antonio)
Intensive application of inorganic compounds (N,P,K) for agriculture benefits leads to increased percolation into the subsurface and can end up in the groundwater. High levels of nitrate in the groundwater pose a serious health hazard if it reaches the drinking water supply. The U.S. EPA has established the MCL for NO3 to be 10mg/L (measured as NO3-N). Previous studies have analyzed the fate and transport of agriculture-derived chemicals on groundwater quality using in-situ methods, column test or numerical simulations. However, these techniques may take a long time and are difficult to maintain a controlled environment. The experimental approach to study the transport of nutrients derived from agriculture related activities, for unsaturated soils under different soil saturation levels, is presented. The level of saturation in a sand-clay mixed soil related activities in the laboratory under centrifugation. A 7.0 mM NH4NO3 solution was used to study the transport of nitrate through the soil mixture. The solution was pumped into the soil with the volumetric flow rate controlled by an external pump which is connected to a steady-state centrifugation-unsaturated flow apparatus (UFA). Three saturation levels (SH=0.85, SM=0.43, and SL=0.28) were chosen to represent high, medium and low saturations, respectively. Nitrate breakthrough curves were plotted and adsorption coefficients, Kd, were then calculated for the high, medium, and low saturation level; they were 13.5 μg/mg, 2.9 μg/mg, and -8.8 μg/mg, respectively. The data shows a relationship exists between the saturation level and adsorption coefficient for the given soil suggesting that nitrate will be sorbed more efficiently under higher saturation levels. Future work will include analysis of the sorbtion of soil mixture with fly-ash. An additional relationship of transport parameters such as dispersion and correlation to saturation level is also of interest for contaminant mass transport.
