Development of an Integrated Risk Analysis System (ARCTRA) for Runoff Related Heavy Metal Contaminant in Unsaturated Zone

TL;DR: In this article, an integrated analytical runoff and contaminant transport risk analysis system (ARCTRA) is developed for assessing the environmental risks associated with heavy metal transport in the unsaturated zone.

Abstract: An integrated analytical runoff and contaminant transport risk analysis system (ARCTRA) is developed for assessing the environmental risks associated with heavy metal transport in the unsaturated zone. The ARCTRA system considers three processes: rainfall runoff, soil erosion and solute transport in soil. A corresponding analytical solution is applied for each process. Particularly, a Monte Carlo simulation is integrated to quantify the uncertainties associated with key model parameters after model sensitivity analysis. Moreover, the Fuzzy Set risk assessment method is employed to quantify incomplete-type uncertainties associated with the site conditions, environmental quality guidelines and health impact criteria based on the Monte Carlo Probability Simulation. Fuzzy membership functions are established considering the environmental-guideline-based risk (ER) and health risk (HR) to obtain a generalized risk level through a fuzzy rule base. An integrated risk value can be then obtained to evaluate and rank the risk level of a contaminated site. Finally, a user interface was developed for the ARCTRA system based on the VB program code in Excel to facilitate technology transfer and to provide a user-friendly system to assist in the processing of input and calculation of results. The ARCTRA system developed in this study can be used to systematically assess the heavy metal in the unsaturated zone caused by rainfall-runoff process and support effective management of the contaminated site. The developed ARCTRA system was verified through compassion analysis against existing models. Specifically, the rainfall-runoff section was compared with the PCSWMM model which simulates the runoff formation under given rainfall conditions. In the soil erosion part, an analytic solution from the Hairsine-Rose model was studied to conduct a comparative analysis of the concentration of heavy metal dissolved in the surface runoff. And, the ARCTRA module for analyzing transport of contaminants in the soil is examined against the STANMOD and the HYDRUS model. Two real cases were studied in this thesis. Pb and Zn were studied in the case studies. The results of the ARCTRA and other existing models were obtained based on the real case data and compared with monitoring data The model verification and validation indicates the developed ARCTRA system is useful in assessing the risks of heavy metals in the soil caused by the rainfall-runoff process.