Role of the Capillary Fringe in Groundwater Petroleum Cleanup

A petroleum contaminant plume, Diesel No. 2 in this case, atop shallow groundwater had been under cleanup for more than two decades using traditional methods of bailing, skimmers, and other techniques that reduced the plume-free product depth to mostly sheen over the plume footprint of about $\mathrm{1,300}{\mathrm{m}}^2$. It was assumed that the plume had been essentially cleaned up and was no longer a risk in the shallow poor-quality groundwater, which was perched atop an aquitard, protecting potable aquifers below. After this long period of cleanup, the petroleum pool began to significantly thicken as the shallow groundwater surface levels began to rise. Based on this field case, it is shown that the significant plume increase in thickness was attributable to the capillary fringe behavior.