Construct Risk Assessment System Of Groundwater Environment

With the rapid economic development over the past four decades,China has almost completed the industrialization process which cost hundreds of years in western developed country.However,this high speed development in short time makes the ecosystem under great pressure.The groundwater environmental problems have become more obvious.As one of the most important part of environmental risk management,the groundwater environmental risk assessment is an important technique for the prevention and control of groundwater pollution.Otherwise,the global,scientific and united groundwater environmental risk theory method doesn't exist.Further research still be needed to build systematic and comprehensive groundwater environmental risk system and method.To solve the existing problems,this research redefined the groundwater environmental risk based on the environmental system risk chain.Moreover this research built and discussed the process of the groundwater environmental risk assessment system.Eventually,Zhehai slag,which is the most important environmental risk rooted in the history,was used as a typical case study to do the groundwater environmental risk assessment.The main achievements were shown as follow:1.This research redefined the groundwater environmental risk.Based on the characteristic of environmental risk transformation,the groundwater environmental risk can be expressed as:The human activities or both human activities and environmental process act on groundwater that is the receptors and vectors of the risk may cause potential chain hazards through a variety of related environmental factors.Eventually the environmental events happen and make human society and nature to pay the losses.2.This new groundwater environmental risk assessment system had been built based on the redefining of the groundwater environmental risk.The main purpose and key point of the system are groundwater environmental risk management and environmental hydrogeological conditions,respectively.The mainly six steps by using the system idea of risk chain included pollution load and model identifying,process simulation and damage representing,mitigation measures and results verification based on the simulation analysis of risk process.This work also identified,estimated and managed three groundwater risks including value loss risk,pollutants transportation risk and health risk3.This research discussed groundwater environmental risk assessment method.This method is based on the process simulation.Message list was used to express the pollutant load and one or multigroup risk situation was built through risk model identifying to establish the groundwater solute transport model and obtain the spatial-temporal distribution data of pollutants,respectively.And then,based on the value losing message,the risk parameters of soil,surface water and crops and metering-effecting model,the value losing degree,possibility of pollutants migration and health hazard of groundwater had been proposed in this research.At the same time,the criterion can be estabilished by using the lowest reasonable and feasible principle to judge the acceptable level of risk.Eventually,the management strategy had been built.And technology selection and scheme comparison had been used to design and verify the project.4.A case study of groundwater environmental risk assessment in Zhehai slag,which is the most important history left environmental risk,had been done by using the system.The main results were shown as follow:The result of distinguishing the pollution load and identifying the risk model showed the pollutants migrated to groundwater through soil.And they were easy to transport to soil,corps and rivers nearby.This migration process may reduce the value of groundwater,increase the risk of pollutant transport and health hazard.Otherwise,the depth of pollutants migration was limited.There are two aquiclude layers which can adsorb the pollutants under the Zhehai slag.The thickness and permeability coefficient of the aquiclude layers were 10-30cm and 1×10^-88 cm/s,respectively.The monitoring results indicated the shallow groundwater,surface water,crops and soil had already be contaminated.Otherwise,the deep groundwater and depth of soil contamination were limited.Zhehai slag would cause continuous loss of groundwater drinking value.And Zhehai slag was transporting the risk to soil,surface water,crops and health.The simulation results showed the pollution halo migrate to deep down.The most migration distance is about 1574 m.And the pollute area is about 815,60000 m².In the monitoring well,the concentration of Zn is 36.7 mg/L which is exceeded at 1300 day.The pollutants migrated from groundwater to soil,surface water and crops.Moreover the concentration of Zn is 504.06 mg/kg,1.02 mg/L and 100.5 mg/kg at 650^th,1824 ^thh and1223^th,which over the human health acceptable value showing as 500 mg/kg,1mg/L and 100 mg/kg.Especially,the concentration over the onewas more than the acceptable value at 1133^th.The risk adjustment shown the risk of groundwater in Zhehai slag was acceptable.The amount of the slag would continue to contaminate the downstream environment.Therefore,the protection is necessary.Natural aquiclude layers limited the possibility and pathway of pollutants migration to deep.The pollutants only migrated in Quaternary as horizontal migration as the amount of water was limited.The pollution of slag could be controlled by many mature technologies such as hydraulic capture.Based on the in-site control theory,the research proposed the project of‘source controlling,pathway interdicting and flow closuring'.And this project had been proofed the effectivity by professional theory.In this project,the ecological restoration was used as source controlling.The vertical barrier project at east and south carried out the pathway interdicting.And the hydraulic capture at south carried out the flow closuring.Moreover,the simulation results indicated in the five decades period,the amount of leachate decreases-101.5 m³/d.The capture rate of groundwater is 88.9%.The maximum migration distance decreases from 1574 m to 165m.The pollution area decreases from 0.81 km² to 0.14 km².The pollution could be effectively controlled as the stacking area decreases from 0.9 km² to 0.05 km².By the effect verification in one year,the in-site treatment and control project achieved the expect goal.The monitoring results indicated the amount of leachate decreased 41000 m³ and the capture rate was 66.73%.The concentration of pollutants kept decreasing outside the eastern hydraulic curtain project.The concentration of Zn and Cd decreased 100 times at the most.Moreover,the concentration of pollutants differed by 500 times between monitoring point in outside and inside southern hydraulic curtain project.Additionally,the concentration of Zn and Cd decreased 3-4 times in wells in downstream area.5.This research had verified the feasibility of the groundwater environmental risk assessment.The risk assessment process was the identification process of risk.This system satisfied the requirement of the environmental management and support the accomplishment of environmental protection.Moreover,this system would fit the location planning of important pollutants,pollution controlling,comprehensive disposal and other environmental protection fields.The highlights of this research included as follow:1.Based on the environmental risk chain,the groundwater environmental risk had been proposed.Moreover,groundwater environmental risk assessment system and methods had been built.2.Zhehai slag was used as a case study to design,implement and verify the process of groundwater environmental risk management by using this risk assessment system.Eventually,the disposition problem of environmental risk in Zhehai slag left over by history had been broken through in this work.All the results of this work might enrich the application cases and theoretical system of groundwater environmental risk assessment.Additionally,they can also provide some technical references for prevention and control of heavy metals pollution and groundwater.