Investigation for three-dimensional DNAPL migration and dissolved phase concentration changes in porous media by water table fluctuation

A number of two-dimensional DNAPL migration studies in groundwater have been performed by other researchers. To date, however, three-dimensional study has not been done and study considering water table fluctuation are currently lacking as well. In this study, well controlled three-dimensional laboratory experiment was performed to investigate migration of TCE, NAPL saturation and morphological DNAPL pool in the groundwater. The 20ml TCE (Trichloroethylene) and Oil Red O was used to visualize TCE that was used in this study. The column (43cm diameter and 40cm height) is big enough so free-phase TCE cannot reach column wall or bottom. Previous study at Wonju-si, Gangwon-do, South Korea shows TCE concentration changes proportional to rainfall intensity (Seasonal variation). The main objective of this study is to clarify variation of NAPL migration and dissolved NAPL concentration by water table changes. Water samples were collected at three-dimensional points (at each 3cm vertical depth and 7cm lateral depth) and gas phase TCE and effluent samples were also analyzed. At the end of the experiment, sand layers were removed one by one and pictures of cross-sectional area at various depths were taken. The dyed areas where free-phase TCE exist were analyzed by modal counting. The result shows that the free-phase TCE infiltrates through the unsaturated zone and accumulated around water table spreading laterally, some of TCE migrate through the saturated zone until all free-phase TCE is adsorbed on the sand grains or dissolved into water. And after water table rising, some point shows reduced concentration by dilution with fresh water but the highest concentration of TCE is higher than the concentration that is sampled before the water table rising. (Highest TCE concentration before water table rising: 443.28 ppm, after water table rising: 779.1 ppm) This means, remediation action should be taken with considering seasonal rainfall variation. NAPL saturation and the depth that residual TCE exists can be measured by TCE concentration at various points.This subject is supported by Korea Ministry of Environment as 'The GAIA Project (173-092-009)'.