Laboratory Investigation of DNAPL Migration Behavior and Distribution at Varying Flow Velocities Based on Light Transmission Method

The migration and distribution of dense non-aqueous phase liquid (DNAFL) in subsurtace are attectea ny many factors. We selected PCE as the substitute contaminant, and performed several well-controlled two-dimensional sandbox experiments to investigate the effect of flow velocity on DNAPL infiltration and redistribution. Light transmission method (LTM) was used to monitor the transport process of DNAPL in the sandbox and quantitatively measure DNAPL saturation. The spatial moments based on measured DNAPL saturation were used to describe the average spatial behavior of DNAPL plume at various times. Experimental results showed a strong correlation between results obtained by LTM and the known amounts of DNAPL added into the sandbox (R2 >0.98). The LTM accurately reflected the infiltration and redistribution processes. The results of DNAPL saturation and first moment (mass center) showed that the increased velocity promoted not only lateral but also vertical migration, leading to an inclined percolation path. Also vertical migration reacted more sensitive to flow velocity. The second moment (spread variance) showed that the increased velocity promoted lateral and vertical spread, increasing the pollution scope. The histogram of DNAPL saturation showed a unimodal distribution at low flow velocity, but showed a bimodal distribution at lager flow velocity, and the distance between two peaks became higher with the increasing flow velocity.