Research For Groundwater Contamination Risk Assessment Methodology Of Uncontrolled Landfill Site

Landfill leachate poses a great contamination risk to groundwater adjacent touncontrolled landfill sites. Groundwater contamination risk assessment is of greatsignificance to the prevention, control and effective management of landfill leachateand groundwater. Based on researches of the related theory and methodology aimingat groundwater pollution risk assessment, this study was conducted on the concept ofgroundwater pollution risk, which selected uncontrolled landfill sites as the risksource and groundwater source, and chose the spring water, the pumping well, and themonitoring well as the risk receptor. Based on the integration thought of risk source,vadose zone, aquifer and risk receptor, two methods are established for groundwatercontamination risk assessment: the overlay index method and the process-basedsimulation method. This assessment enriched the methodology system of groundwaterpollution risk assessment.Risk evaluation method, based on the overlay index method, contained fiveaspects: the landfill site risk, exposure of evaluation objects, pollution resistanceability of vadose zone, aquifer vulnerability and groundwater harmfulness. Then arisk assessment index system was established. The value of each evaluation index wasdetermined which is ranging from1to10. With this method, analytical hierarchyprocess (AHP) was used to determine the proportion of each evaluation index.Accordingly a comprehensive index risk assessment model was developed. The riskassessment model based on the overlay index method is simple, easy to use. Besides,the associated parameters are easily obtained. But the indicators selection andproportion calculation of the main links have many subjective factors, so theevaluation results have some uncertainty. This method is applicable to the brief riskevaluation of the landfill groundwater pollution which is insufficient of data.Based on the systematical structure analysis of groundwater pollution byuncontrolled landfill site on the process-based simulation method and constructed, arisk assessment theory frame of groundwater pollution, and a pollutants transporting &transforming mathematical risk assessment model upon process modeling weredeveloped. The groundwater contamination risk evaluation factors were identified andgroundwater pollution risk levels were classified according to the pollution range andextent of chloride ions (Cl-). The theory realized the integration of risk assessment,simulation and early warning of groundwater pollution. This method has theadvantages of quantified simulation results and more accurate evaluation results, etc.However, the evaluation indexes are more and the index parameters are difficult toobtain. Therefore, this method is suitable for the brief landfill groundwater pollutionrisk evaluation with relatively complete of field data.Take north heaven simple landfill groundwater pollution risk evaluation as anexample, two risk assessment methods established in this study were used to conductthe groundwater pollution risk assessment for the surrounding three monitoring wells.The results showed that the conclusion of the two risk evaluation methods wasunanimous. The conclusions are:(1) monitoring well’s pollution risk level is high,(2)pollution monitoring well has medium risk level; and (3) the monitor well pollutionrisk level is low. These results prove that the two kinds of risk evaluation methodsestablished in this research are scientific and reasonable.