TCE gas concentration variation in the unsaturated zone under the influence of fluctuating water table

Abstract:

Common residual DNAPLs (Dense non-Aqueous Phase Liquids) in subsurface are TCE, PCE, and chlorinated solvents. Because DNAPLs were remained or trapped in soil pore while these swept through the subsurface environment.

Soil gas sampling is one of the methods to identify the residual source existence in the field contaminated by DNAPLs. However, the concentration of soil gas samples is changeable depending on water table fluctuation. This trend was shown in Woosan Industrial Complex (WIC) site in Korea. To understand this phenomenon in the field laboratory experiments were performed under controllable condition.

Continuous soil gas extraction and sampling method was conducted at the laboratory with several different cases. Three cases assume the experimental conditions which were 1) only residual source of TCE exists in vadose zone; 2) only dissolved source of TCE in water exists; 3) not only residuals source but also dissolved source exist in the usual position.

 A two-dimensional model tank was used for the laboratory scale test. The STOMP-WOA model program was also operated to calculate the TCE gas concentration changes. The concentration represented changes opposite to the water table change as the concentration increased when water table decreased. STOMP simulation results showed the similar trend with laboratory test results.