Study On Groundwater Pb Pollution Risk Prediction Of Shizuishan Industrial Park Of Ningxia

Groundwater, with stable water supply conditions and good water quality, has been akind of absolutely necessary water resource to human society, but the negative impact of theglobal economic construction on the environment has led to the trend of heavy metalcontamination in groundwater aggravating year by year.Once the heavy metal contaminants enter the aquifer，which will not only pollute thewater environment, but also endanger humans and all kinds of creatures seriously. At present,researches on heavy metal contamination of groundwater in China greatly are lagging behindits contamination rate, which not only directly leads to the deterioration of soil andgroundwater environment, also causes many environmental, ecological, social problems.Shizuishan Industrial Park of Ningxia has many industrial and mining enterprises, includingNingxia Hengli Steel Wire Rope Factory near to the Yellow River which has high productionof metal products and brings the worrying problems of waste pollution with the expansion ofscale in recent years. The area is located in the most northern part of the Yinchuan Plain, andprevious studies are not high, so there is an urgent need for risk analysis of groundwaterheavy metal contamination. Base on the former achievements, combining the hydrogeologicalconditions in the study area, the first use of the popular MODFLOW software to establish agroundwater flow numerical model and water quality model to predict the risk of groundwaterheavy metal contamination. The whole thesis can be divided into five main parts as follows:Part I: the overview of the purpose and significance of this study, the introduction of thestatus quo of groundwater heavy metal pollution and the progress of evaluation and predictionof groundwater heavy metal pollution by the use of MODFLOW, and putting forward someproblems which need further research.The second part introduces the natural geographical and hydrogeological profiles ofresearch area, analyzes and evaluates the potential risk of heavy metal pollution ofgroundwater. Part III: the establishment of groundwater flow numerical model in the study area, and ananalysis of model sensitivity.Part IV: the research of migration transformation mechanism of pollutants, includingadsorption, dispersion effect.Part V: On the basis of these studies, using MT3DMS to establish a water quality modelto predict the risk of heavy metal pollution in groundwater. The following conclusions:1. Combining with the results of previous studies and field survey data, an analysis of thestructure of unconfined aquifer and groundwater characteristics of the study area.Groundwater types in this area are mainly pore water in loose rock, and phreatic aquiferlithology is mainly sand and gravel, sand, loam. The thickness of unconfined aquifer becomesthinner from west to east and it is underlain by Tertiary sandstones and sandy mudstone. Theaquifer is rich in groundwater and buried deeply, main receives the west side of the Helanpiedmont lateral runoff, the major excretion of unconfined aquifer is artificial mining. ThePhreatic Water flows wholly from west to east, southwest to the northeast on the whole, thehydraulic gradient is very small. The average value of TDS is1111.75mg/L indicating thegroundwater belongs to the brackish water, and water chemistry type is quite complex. Theconcentration of Pb²⁺in three samples exceeds the standard，the maximum of which is0.035mg/L, which is3.5times more than the "drinking water health standards"（GB5749-2006）limit, so the situation is very serious.2. Taking advantage of MODFLOW to establish the numerical model of groundwaterflow in the study area, and the numerical model were calibrated, the fit is less than0.441meters, indicating that the numerical model can objectively describe the motion characteristicsof the groundwater flow.3. Using the above model, the orthogonal test method is used to analyze the influencedegree of the hydrogeological parameters of the simulation results, the analysis of range andvariance indicated that the specific yield than hydraulic conductivity impact on the modelmore significantly. Comparison analysis of the principle and calculation process withtraditional methods indicates that the reliability and superiority of orthogonal test method in the analysis of the groundwater flow numerical model parameter sensitivity. The totalsensitivity of the model is0.51m, which indicates this model is relatively stable, can be usedto research of prediction of water level and solute transport.4. Through the adsorption test to determine the adsorption equilibrium parameters ofmedium on Pb²⁺; finally, determining the degree of dispersion is5meters according to theresults of previous studies in the Yinchuan plain.5、Taking advantage of MT3DMS to establish the water quality model of research area toforecast the impact scope and degree of groundwater lead pollution in the groundwater flowwithin the next20years. The prediction result shows the concentration of contaminants willincrease significantly with the time of pollutants solute injecting the groundwater increasesand its influence will gradually expand. Pollutants are migrating in all directions in the aquifer,but its main trend spread to the southeast of pollution sources. The maximum range ofpollutant planar diffusion is about150meters, and the impact area is about12615square meters after20years, and the peak concentration is0.006mg/L which has notexceeded the standard, but the concentration grows with the mode of Power function, so thereis the need to strengthen water quality monitoring. Assuming that the slag field has accidentcases, the pollutant concentrations grows with the mode of line and will be up to0.011mg/Lafter20years which has exceeded the upper limit value of “drinking water health standards”（GB5749-2006） indicating that it has caused a certain degree of pollution. The presence ofadsorption desorption has a great influence on contaminant migration, which not only controls the spread of pollutants, but also inhibits the rise of concentration of pollutants. Therefore,there is a need to strengthen the study of the adsorption and desorption of vadose zone andaquifer medium to heavy metal pollutants on research of heavy metal pollution ofgroundwater prediction in the future.