Centrifuge physical modelling of light nonaquaeous phase liquid (LNAPL) transport in an unsaturated sand is discussed with regard to the similitude of the resulting three-fluid flow. Three model series are reported: the first to establish a reproducible unsaturated moisturesuction profile; the second to examine the modelling of models methodology for evaluating similitude of an LNAPL release into an unsaturated fine sand; and the third to prototype-scale data sets for 1000 L surface LNAPL releases at two different rates. Results show that a slower release rate produces deeper LNAPL penetration, and the reasons for this behaviour are discussed. An inexpensive and readily available numerical code called SWANFLOW was used to independently simulate the prototype release rates, and the results are compared with the centrifuge data. The numerical simulations produced compatible predictions of short-term oil transport but did not predict the observed longer term fate of the LNAPL in this highly nonlinear imbibitiondrainage problem. A numerical code that incorporates hysteresis between the imbibition and drainage curves would be expected to produce more complete long-term predictions. Key words: centrifuge modelling, numerical simulation, LNAPL fate, unsaturated sand.
The infiltration of a light nonaqueous phase liquid (LNAPL) into an unsaturated porous medium will result in varying amounts of water, LNAPL, and air within the soil voids. A simple and reliable method of determining the percent saturation of each fluid is needed to analyze laboratory infiltration experiments. This note reviews the available methodologies for determining the oil content in porous media and presents an experimental study of a simple and reliable method for determining water and oil contents in an unsaturated fine to medium sand. Key words: fluid saturations, oil content, gravimetric, extraction, assay.
Although field compaction techniques and specifications for achieving a homogeneous clay barrier are well known, changes in borrow materials due to weathering or stratifications can lead to variability in the performance of such compacted barriers. Field density testing can give an indication of barrier quality but quality control should also incorporate hydraulic conductivity testing. Hydraulic conductivity testing on a daily basis is a difficult task. This paper outlines a methodology for barrier control testing by centrifugation and discusses why centrifuge testing is superior to bench testing with elevated gradients. The use of centrifugation for evaluating barrier diffusion and possible long-term change in hydraulic conductivity is also discussed.
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