Study On Groundwater Environment Impact Of A Hazardous Waste Landfill In Sichuan

Hazardous wastes usually have one or more characteristics such as corrosiveness,flammability,toxicity or infectivity,and they can damage the ecological environment through the air,water and soil,and thus harm human health.At present,the disposal methods for hazardous wastes in China mostly use landfill technology.During the landfill process,a large amount of leachate containing highly toxic substances will be generated.Once a leakage accident occurs,the surrounding groundwater environment will be seriously affected.Taking a hazardous waste landfill in Sichuan Province as the research object,the paper investigated and assessed the present situation of groundwater environment in the research area,and then analyzed the potential pollution sources of the landfill,and finally predicted the potential impact on the groundwater environment by using the numerical simulaton method which verified by the flow of water.According to the result of the impact on the groundwater environment,the paper put forward relevant prevention and control measures which can provide a certain reference for protecting the groundwater environment of similar landfills.The paper mainly obtained the following understandings and conclusions:(1)Pollution source characteristics: on the basis of the results of landfill leachate test,compare the water quality parameters of the same project's main pollutants in the country and the characteristics of the industries,the paper identified the main characteristics of the project's leachate are Cd,Pb,Ni and As;And the analysis of different contaminated scenes showed that the infiltration quantities of landfill in the normal(effective impervious)and abnormal conditions(ineffective anti-seepage area is 5 % and 10 %)are 0.0013 L/d,112.5 L/d,and 225 L/d,respectively.(2)Hydrogeological conditions: the main aquifer in the study area are the Quaternary loose layer and the Cretaceous Guankou Formation which affected little by tectonic activities,and their permeabilities are about 5m/d and 2.5 m/d,respectively.The ater depth is 0.3~14.9 m.And the permeability coefficient of thevadose zone in the study area is 0.1536 m/d,resulting in the weak antifouling performance of study area.The atmospheric precipitation is the main supply source of groundwater which will discharge to the lower reaches of the Yuejiang River,excreted in a small amount of groundwater will discharged in the form of evaporation and artificial mining.(3)Groundwater environment quality: the groundwater quality evaluation results of single index and the Nemerow index method show that the individual monitoring wells within the water level have a water quality class of IV and the dry season water quality class are of Grades I to III.Among them,the water quality of Class IV is mainly due to the escherichia coli exceeding standard which influenced by residents' lives;the aerated zone evaluation results of the standard index method show that the content of heavy metals in the soil are lower than the secondary standard value of the soil environmental quality standard.(4)Prediction results of different scenes: on the basis of the verified flow field simulation,Cd was selected as the prediction factor.Using Darcy's law,the theoretical time for the leachate to penetrate the impermeable layer under normal conditions is about 100 years,and the simulation predicted that the pollutant Cd will only affect the local water quality and will not cause the water quality to exceed the standard after the leachate enter the aquifer.In the abnormal condition of anti-seepage failure,the Cd pollution bound(concentration ? 0.005 mg/L)caused by the 10% impervious failure is about 1.5 times of the 5% impervious failure at different times,and the concentration value is also relatively higher.,At 7300 days,the Cd pollution didn't exceeded the standard,but its pollution impact range(concentration values between0.0001 mg/L and 0.005 mg/L)has spread to the residential area near the downstream Yuejiang River.(5)Prediction result of monitoring well in abnormal condition: the concentration of Cd in the monitoring wells W03 and W04 near the landfill is lower than the standard value of Class III(0.005 mg/L),and the downstream well W04 responded to the pollution is about 60 to 100 days.That is to say,the existing monitoring wells of underground water quality have relatively weak effect on monitoring groundwater pollution,and can not easily find leakage of leachate in time.