Non-aqueous-phase-liquid breakthrough during evaporative drying of clay barriers.
In this study, an attempt has been made to model a real field scenario, whereby an initially almost saturated clay liner in a waste site is gradually drying, due to evaporation at its lower boundary. A detailed conceptual model that deals with the penetration and breakthrough of non-aqueous-phase-liquid (NAPL) in clay liners is introduced. Water content of clay samples was monitored during ambient evaporation through apertures at the base of sample holders. Clay drying rate served as the primary parameter for the NAPL breakthrough study. The interconnection between drying rates, structural damage formation (cracks and suction) and NAPL penetration is especially addressed. The processes taking place in the clay samples during drying appear to be associated with the capillary effects between the different fluid phases in the vicinity of either the NAPL-clay or the clay-air boundaries. A conceptual model of NAPL penetration and breakthrough of the clay layer has been considered, based on both indirect and direct observations of structural damages produced on either clay boundaries. A mutual interaction between these two boundaries is suggested and discussed. NAPL breakthrough is suggested to take place through cracks initiated on the upper soil surface.
Numerical modelling on fate and transport of nitrate in an unsaturated system under non-isothermal condition
Nitrate pollution in groundwater arising from wastewater and fertiliser application through vadose zone is a major problem and it causes a prime risk to groundwater-based drinking water supplies. In this study, a one-dimensional numerical model is developed to investigate the nitrogen species transport in unsaturated porous media along with mass transfer of oxygen from gaseous phase to aqueous phase. Further, the temperature-dependent nitrogen transformation rates, oxygen solubility in an aqueous phase from gaseous phase, and oxygen diffusion coefficient have been successfully incorporated. Results suggest that the temperature-dependent oxygen diffusion coefficient is significant in case of temperature variation between 30 and 45 °C, whereas the temperature-dependent oxygen solubility and transformation rate are found to be the critical parameters influencing the nitrogen species transport when the temperature variation is between 10 and 30 °C. In the temperature range between 30 and 45 °C, the model performance marginally improved compared with that of the same under isothermal condition. But in the case of variation between 10 and 30 °C, the nitrate nitrogen concentration has higher variation during non-isothermal conditions when compared with isothermal conditions. Moreover, the results suggest that the dissolved oxygen concentration is also significantly affected by non-isothermal conditions.
Eimeria odocoilei n. sp. from the mule deer Odocoileus h. hemionus in Washington.
SYNOPSIS. Eimeria odocoilei n. sp. is described from feces of a mule deer Odocoileus h. hemionus in Washington. Its oocysts are 26 to 28 by 22 to 26 μ. It is the second species of Eimeria described from this host.