Hydraulic Behavior of soil contaminated with Trichloroethylene (TCE)

Hydraulic conductivity and retention are important characteristics of porous environment in relation to imposed contaminants. Retention curve and hydraulic conductivity are dependent on soil characteristics and soil solution. When Chlorinated pollutants enter to groundwater will contaminate it due to its compounds. Thus preventing them to enter soil and water is crucial to avoid any contamination. In order to investigate the hydraulic behavior of Trichloroethylene in soil, the retention of Trichloroethylene and water were determined. Determining the saturated hydraulic conductivity and estimating the unsaturated hydraulic conductivity by Mualem -van Genuchten, Mualem - Brooks- Corey and Mualem- Kosugi models in the two-phase NAPL-air systems were further objectives of this study.

In this study, the hydraulic behavior of both Trichloroethylene fluid and water were examined. In order to draw the water and Trichloroethylene retention curves in SiL soil the hanging water column method was used. The constant head method was employed to determine the saturated hydraulic conductivity. The Soil retention parameters for Trichloroethylene and water were obtained based on van Genuchten, Brooks-Corey and Kosugi retention models, using the RETC program. The unsaturated hydraulic conductivity, for both fluids as a function of Matric potential was obtained based on Mualem -Brooks-Corey, Mualem -van Genuchten and Mualem-Kosugi models. The performances of these models were assessed by some statistics including ME, RMSE, EF, CD and CRM.

The obtained results indicated that in a certain amount of liquid phase, Trichloroethylene has lower retention and larger hydraulic conductivity compared to water in soil. According to lower surface tension and viscosity of Trichloroethylene compared to water, the saturated hydraulic conductivity of Trichloroethylene and water were 136.75 and 94.5 cm/day, respectively. For water, the van Genuchten retention model demonstrated highest EF (0.93) and lowest RMSE (0.018) values compared to Trichloroethylene fluid. The other two models were also provided more efficiency for water than Trichloroethylene. In the case of Trichloroethylene, the van Genuchten and Brooks-Corey models showed highest efficiency. Generally, the accuracy of all three models for Trichloroethylene was less than water.

The validation results of hydraulic models shows that the van Genuchten model provides better prediction for retention in soil compared to Kosugi and Brooks-Corey models in the two-phase air-water and air-Trichloroethylene system. Trichloroethylenefluid according to its higher hydraulic conductivity and lower retention compared to water, if enters to soil would have faster movement to the groundwater as a consequence of high infiltration rate to aquifer.