Groundwater Flow Through a Constructed Treatment Wetland

This study is an analysis of the flow of water through a constructed treatment wetland at Wright-Patterson AFB, OH. The purpose of the treatment wetland is to biodegrade perchloroethylene, which is present in the groundwater as a contaminant. Contaminated water enters the bottom of the wetland and flows upward, exiting the wetland from a weir at one end. The wetland is designed for water to move vertically through the soil layers composing the wetland. The main purpose of this study is to characterize the water flow through the different layers of soil in the wetland. In this study, hydraulic parameters are measured and then used to build a numerical model of the wetland system. The model is then run to simulate flow through the wetland, in order to develop a residence time distribution function (RTDF). The RTDF tells us what fraction of water (and contaminant) molecules can be expected to be in the wetland for a given time. This information is needed to predict the overall extent of contaminant degradation within the system. It was determined that for the fraction of influent water that ultimately flowed out the weir, the mean residence time was 1.6 days.