||Risk-based corrective action (RBCA) is rapidly becoming an accepted approach for the remediation of contaminated sites. Under a RBCA approach, the risks to human health and the environment associated with a contaminated site are evaluated and appropriate corrective measures are taken as needed to reduce risk to acceptable levels. A series of standard guides of RBCA have been developed by American Society for Testing and Materials (ASTM). The major tasks of this study were to (1) perform the sensitiveness analysis to evaluate the effectiveness of each input parameter on the calculated risks, (2) application of Monte Carlo simulation using a statistic software (@RISK) to analyze the distribution probability of inhalation risk, (3) conduct a risk evaluation and risk calculation at a chlorinated-compound contaminated site. |
Results from the sensitiveness analysis show that the major factors, which play important roles in the risk evaluation including sources of air pollution, vapor transportation rate, pollutant volatilization rate, length and direction of wind, distance of pollutant transport, width of pollution source, and groundwater flow velocity. Results from the Monte Carlo simulation show that the carcinogenic risk is about 15×10-6 when the accumulation rate is 95% via inhalation. Moreover, the carcinogenic risk is about 31×10-6 when the accumulation rate is 95% via ingestion. The calculated risk levels are higher than the requirement for minimum target risk level (cancer risk of 1x10-6) described in Taiwan’s “Soil and Groundwater Remediation Act”. Results also show that the hazard index of non-carcinogenic risk is about 0.5 via the route of inhalation, which is higher than the minimum target risk level of 1. Moreover, the hazard index of non-carcinogenic risk is about 1.3 via the route of ingestion, which is lower than the acceptable level of 1.
Results from the case study show that the major pollutant exposure routes at this chlorinated-compound contaminant site include inhalation of contaminant vapor and groundwater ingestion. Therefore, the input parameters affect the calculated risks include daily intake of drinking water, groundwater infiltration, groundwater flow velocity, aquifer depth, and distance of pollutant transport. Based on the results of risk assessment, it is very important for the decision makers to incorporate remedial activities including institutional controls, engineering controls, and remediation programs from RBCA results. This study provides a streamlined process and guidelines of developing the risk-based decision-making strategy for contaminated sites in Taiwan.