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 modeling of biological clogging on transport of nitrate in an unsaturated porous media
AbstractIn order to 
better understand nitrogen species transport and transformation in the saturated zone, it is essential to predict the contaminant concentration in the unsaturated zone as the concentration profiles estimated from unsaturated zone forms as the input for estimation of contaminant concentration in the saturated zone. Since the nitrogen transformations occur in the presence of bacteria, there is a need to account the influence of biological clogging to develop comprehensive model of nitrogen species transport. In this study, a one-dimensional numerical model is developed to investigate the nitrogen species transport in an unsaturated porous media along with microbial clogging process. Results suggest that hydraulic conductivity is enhanced initially due to increase in the water content followed by a significant reduction at larger simulation time resulting from bioclogging. As bioclogging mitigates the hydraulic conductivity significantly, a considerable delay is observed in the ammonium nitrogen and nitrate nitrogen transport with reference to the system without bioclogging. In addition, the effect of oxygen mass transfer coefficient on biological clogging was evaluated. Numerical results suggest that as the oxygen mass transfer is decreased the ammonium nitrogen and nitrate nitrogen concentration travels a larger depth. Further numerical results strongly suggest that nitrogen species transport in the unsaturated zone is significantly affected by the presence of biological clogging.
NOTE ON THE EFFECT OF TIME ON THE DRYING SHRINKAGE OF CLAYS1
The drying shrinkage or clays were studied to determine how quickly different types can be dried and to note whether or not the time of drying influences the amount of shrinkage. Three shales, two ball clays and one fire-clay were tested and the following conclusions reached: (a), drying time depends largely on water content; (b), the structure of the clay is an important factor; (c), the amount of total shrinkage is proportional to the water content; (d), the amount of total shrinkage is not influenced by the rapidity of drying.