Performance evaluations of pump-and-treat system using advection-dispersion analysis: Effects of clay layer on remediation duration

To evaluate the effects of a clay layer on the performance of pump-and-treat remediation, an advection-dispersion analysis assuming non-sorption was calculated by changing five parametric variables, namely, the length of the clay layer, the thickness of the clay layer, the hydraulic conductivity of the clay layer, the effective molecular diffusion coefficient of the contaminants, and the contamination duration. The simulation procedure consisted of firstly contaminating the analysis domain, and then cleaning up this contaminated domain by a pump-and-treat system in order to consider strictly the contamination conditions of a clay layer at a real contaminated site. From the calculation results, the pump-and-treat remediation was found to be effective if at least one of the following two conditions was satisfied, namely, the hydraulic conductivity of the clay layer was greater than 5.0 x 10(-5) cm/s or the thickness of the clay layer was less than 3 m. In addition, the contamination duration was an important parameter in evaluating the applicability of this pump-and-treat remediation to contaminated sites. For cases in which the contamination duration was short, the contamination conditions of the clay layer easily became heterogeneous such that the remediation duration was much longer than the contamination duration. It is necessary to note that contaminated sites may not always be remedied in a short period of time, even if the sites are discovered early.