Determining the thickness of LNAPL-impacted soils considering water table fluctuations

ABSTRACT: Monitoring of the water table and apparent thickness of Light Non Aqueous Phase Liquid (LNAPL), at an observation well, was carried out over a period of 4 months prior to in situ treatment of contaminated soils. Data collected from the monitoring program was used to determine the thickness of soils impacted by LNAPL, as well as the vertical location of impacted soils within the geological formation. The thickness of impacted soils was determined by considering the presence of the free phase of LNAPL in the soils and the residual LNAPL potentially contained in the soils. This determination was performed by taking into account water table fluctuations which can affect the location of the free phase of LNAPL and residual LNAPL in the soils. Determining total thickness of soils impacted by a LNAPL is a useful element during the assessment of the impacted soil volumes and could allow a better precision of in situ treatment of soils. Moreover, this evaluation could be used to determine how deep the water table should be lowered, through pumping, in order that the impacted soils become located in an unsaturated zone and can be then subjected to an in situ treatment by ventilation or by thermal approach.