The large-diameter time-domain reflectometry soil water sensors placed horizontally in a structured loamy soil are very sensitive to rapid preferential percolation events. Their readings on these occasions rise considerably, often becoming higher than the native soil's porosity. The effect is caused by gaps between the native soil and the sensors. The geometry of the gaps, even if filled with soil slurry at installation, is not exactly reproducible, which leads to sensor-to-sensor variability of readings. Field calibration in percolation-free periods lead to non-unique trajectories rather than monotonous calibration curves, which can be commented in terms of soil heterogeneity and the dual porosity theory. Data of two typical percolation events are presented. Sensors of this type can be used for detection of preferential flux.

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Doležal F., Matula S., Moreira Barradas J.M. (2015): Rapid percolation of water through soil macropores affects reading and calibration of large encapsulated TDR sensors. Soil & Water Res., 10: 155-163.The electromagnetic soil water content sensors are invaluable tools because of their selective sensitivity to water, versatility, ease of automation and large resolution. A common drawback of most their types is their preferential sensitivity to water near to their surfaces. The ways in which the drawback manifests itself were explored for the case of large Time-Domain Reflectometry (TDR) sensors Aqua-Tel-TDR (Automata, Inc., now McCrometer CONNECT). Their field performance was investigated and compared with the results of field and laboratory calibration. The field soil was loamy Chernozem on a carbonate-rich loess substrate, while the laboratory calibration was done in fine quartz sand. In the field, the sensors were installed horizontally into pre-bored holes after being wrapped in slurry of native soil or fine earth. Large sensor-to-sensor variability of readings was observed. It was partially removed by field calibration. The occurrence of percolation events could be easily recognised, because they made the TDR readings suddenly rising and sometimes considerably exceeding the saturated water content. After the events, the TDR readings fell, usually equally suddenly, remaining afterwards at the levels somewhat higher than those before the event. These phenomena can be explained by the preferential flow of water in natural and artificial soil macropores around the sensors. It is hypothesised that the percolating water which enters the gaps and other voids around the sensors accumulates there for short time, being hindered by the sensors themselves. This water also has a enlarged opportunity to get absorbed by the adjacent soil matrix. The variance of TDR readings obtained during the field calibration does not differ significantly from the variance of the corresponding gravimetric sampling data. This suggests that the slope of the field calibration equation is close to unity, in contrast to the laboratory calibration in quartz sand. This difference in slopes can be explained by the presence or absence, respectively, of gaps around the sensors. A typical percolation event and dry period records are presented and analysed. Sensors of this type can be used for qualitative detection of preferential flow and perhaps also for its quantification. The readings outside the percolation events indicate that the sensor environment imitates the native soil reasonably well and that the field-calibrated sensors can provide us with quantitative information about the actual soil water content.

Báťková K., Matula S., Miháliková M., Chala A.T., Moreira Barradas J.M., Mekonnen G.B. (2014): Testing of activated carbon for water and non-volatile LNAPL quantitative determination in porous media under laboratory conditions. Soil & Water Res., 9: 161-168.Activated carbon is a highly porous form of carbon, which has an exceptionally large surface area. Activated carbon material has been artificially processed as a set of plates, within which two different types of pores are present: micropores (< 2 nm) and transport pores (macropores > 50 nm and mesopores 2-50 nm). The transport pores bring molecules of different substances (organic compounds) into the micropores, which are basically the active centres where the adsorption takes place. Activated carbon, due to its high adsorption potential, is used in many applications such as air, water, wastewater or chemical purification. In this study, the pelletized activated carbon (Silcarbon SC40) was tested for water and non-volatile LNAPL (Light Non-Aqueous Phase Liquid; medicinal mineral oil used in this study) determination in a porous medium (silica sand). The experiments were carried out under controlled laboratory conditions. Three different sets of experiments were carried out: (i) the water or LNAPL adsorption from pure media (water or LNAPL liquids); (ii) the water or LNAPL adsorption from pure media (water or LNAPL vapours); (iii) water and/or LNAPL adsorption from the porous material at different sampling intervals. Furthermore, the water/LNAPL contents of the porous media were determined on the basis of the water/LNAPL contents of sampled Silcarbon SC40. The results confirmed the suitability of the Silcarbon SC40 for water/LNAPL sampling from the porous media under laboratory conditions. The method is suitable for detection of water and/or LNAPL in a liquid or gaseous phase and also for water and/or LNAPL quantitative determination. For the quantitative determination a calibration of this method would be required.Keywords: activated carbon; LNAPL; silica sand; Silcarbon SC40; sampling interval Organic contaminants are one of the most common substances contaminating the vadose and saturated zones of soil and rock environments. Light NonAqueous Phase Liquids (LNAPLs) represent a group of organic substances that are relatively insoluble in water and are less dense than water (US EPA 2012). The LNAPLs move through the vadose zone towards the ground water level; its lateral movement can start even before the LNAPL reaches the ground water level due to the capillary fringe and saturated conditions above the ground water level (Cohen & Mercer 1990). Quite a lot of effort has been invested in studies of LNAPL behaviour in homogeneous conditions (Lenhard et al. 1993;Ostendorf et al. 1993;Eckberg & Sunada 1984). However, LNAPL transport within heterogeneous media has not been investigated thoroughly and requires further research (Schroth et al. 1998). In the past, research was aimed at applications in the petroleum industry. Recently however preferences have ...