Risk Assessment Of Groundwater Pollution Based On Process

As a fundamental work of rational groundwater exploitation, utilization and protection, groundwater pollution risk assessment is an important approach for groundwater management and pollution control. Based on researches of the related theory and methodology and aimed at groundwater pollution risk assessment, the paper used multi-technologies which included data collection, field investigation, physical and numerical simulation, combined pollution load, migration and transformation processes of pollutant in unsaturated zone with groundwater value, and constructed risk assessment theory and methodology of groundwater pollution based on the processes. The theory and methodology implemented coupling the pollutant migration and transformation simulation with the pollution risk assessment. Furthermore, it was successfully applied to the groundwater pollution risk assessment in Luanhe Delta. The main research results were as follow:(1) Based on the concept of groundwater pollution risk and the integration between the soil-unsaturated zone-groundwater system and the pollution load-process-receptor system, the paper synthetically analyzed the influence factors among pollution load, antipollution capacity of unsaturated zones, pollutant migration and transformation processes and the groundwater functions and constructed a risk assessment theory frame of groundwater pollution based on processes. The theory achieved the integration among risk assessment, simulation and early warning of groundwater pollution.(2) Led by the risk assessment theory of groundwater pollution based on processes and combined mechanism with risk assessment, the assessment method coupling the process model about pollutant migration and transformation in soil-groundwater system with the risk assessment index model was established. It enriched the methodology system of groundwater pollution risk assessment. (3) The theory and method of risk assessment for groundwater pollution based on processes was achieved successfully in Luanhe Delta and 32 relevant maps were drawn. Some achievements have been adopted by one of the key projects of China Geological Survey Bureau- Investigation and Assessment of Groundwater Pollution in Luanhe Delta. The results provided reference for the migration and transformation of pollutants and prevention and control of groundwater pollution in the area. Regional research results were as follow:①The antipollution capacity of the soil-groundwater system in Luanhe Delta was weak. This led that the declining quality of shallow groundwater and serious pollution. The typical pollutants of soil-groundwater system in Luanhe Delta were ammonia-N, nitrite-N, nitrate-N(Generally named"three N") and petroleum. Oversize rate of three N was 47.3% and that of benzopyrene detection was 7.8% in groundwater. Pollutants passed through vadose zones and entered groundwater by means of intermittent or continuous infiltration.②Through the systematic analysis on behaviour characteristics of three N and petroleum pollutants in the soil-vadose zone and groundwater and researches on their kinetic processes of convection/dispersion, adsorption/desorption, degradation and plant accumulation, the paper established the related kinetic models and obtained the moisture and solute transportation parameters.③The migration and transformation process model about nitrogen and petroleum pollutants in soil-groundwater system were established and migration and transformation rule of the two pollutants in vadose zones were ascertained. According to the model calculation results, the migration and transportation rates of the two pollutants and the input quantity of groundwater were obtained. The migration rate of nitrate -N were much quicker than those of ammonia-N and nitrite-N and the input quantity of groundwater was 0.996kg/ha2·a. The migration rate of petroleum pollutants on condition of intermittent infiltration, only 3.65cm/a, was much slower than that on condition of continuous infiltration.④Based on the migration and transportation models of three N and petroleum pollutants and combined the antipollution capacity of groundwater, the influence of the two pollutants on groundwater were assessed. The assessment results showed that the influence degree of three N on groundwater became gradually weakening from the north to the south in Luanhe Delta. Thereinto the easily polluted areas mainly distributed in Tangshan city and the north part of Luanxian County. The strongly polluted areas of petroleum pollutants mainly distributed in the petroleum exploitation area in the south of Liuzan Town located in coastal alluvial plains.⑤The groundwater pollution risk was assessed in Luanhe Delta. The assessment results showed that the high risk areas of groundwater pollution mainly distributed in the east part of Yutian County, the west part of Fengrun district, Tangshan City and the north part of Fengnan district, which all located in the pluvial fan of mountain fronts. The moderate risk areas included the north part of Fengrun district, Luannan County, Leting County and most of Changli County. The low risk areas mainly distributed in Yutian County, the south part of Fengnan district, Tanghai County, the south part of Leting County, coastal district of Changli County and Qinhuangdao City, all located in alluvial-pluvial plains along the coasts.⑥Compared with the traditional assessment method, the risk assessment method of groundwater pollution based on processes was more comprehensive in index selection and the assessment results could reflect the risk degree of groundwater pollution more accurately.These researches enrich the risk assessment theory and methodology of groundwater pollution and have important theoretical and practical significance for groundwater management and pollution prevention. The research results are the basis of the shallow groundwater protection in Luanhe Delta.