Effects of repeated drainage and imbibition on the contamination behavior of a LNAPL and on its S-p relation

Four drainage/imbibition cycles on an initially fully saturated 50 cm-tall Toyoura sand column contaminated with a Light Non-Aqueous Phase Liquid (LNAPL) were performed. Saturation distributions of both water and LNAPL on the three-phase system were measured following the Simplified Image Analysis Method (SIAM). Clear differences were observed in the saturation values at the same points during each cycle, most importantly between the first and second cycles, but also noticeable on the latter two. To better understand the changes, we analyzed the variation in the LNAPL's S-p relation after five consecutive LNAPL drainage/imbibition cycles using a Tempe Cell system. It was found that the changes in LNAPL residual saturation values, Srf, followed a logarithmic relationship with the number of cycles, knowledge that helps us improve our understanding of the behavior of these contaminants when subject to dynamic conditions in subsoil.