Groundwater Environmental Quality Evaluation And Tailing Pond Leakage Analysis In Gejiu Mining Area

With the accelerating pace of the country's industrialization,exploitation of mineral resources is more and more serious,and the scale of tailings storage has also increased.The environmental pollution caused by the tailings has aroused widespread concern in the society.Groundwater contaminated by tailings will bring great damage to its downstream ecological environment and human health.The eastern area of Gejiu tin mine,which includes the mining area and the karst spring water discharge points and occupies the area of about 837 km²,is taken as a research object.Based on the chemical characteristics of water environment in the research area,this paper analyzes the characteristics of the karst spring water and the tailings pore water and the differences between the two and the formation characteristics of groundwater as well as evaluates the quality of water environment in the area scientifically and comprehensively.Based on extensive review of relevant literature and field investigation,16 pore water samples of tailings and 7 karst spring water samples were collected.The content of 10 constant anions and cations,14 heavy metal elements?including As,Se?and the comprehensive indexes of PH,TDS were determined.According to the results,this paper carried on the study work of evaluation chemical characteristics of the water environment and water quality and drew the following conclusions:1.The pore water of tailings and karst spring show their respective characteristics and the great differences between them in the type of hydrochemical,comprehensive index of water environment,the content and correlation of major ions and heavy metal elements,in other words,the karst spring water is less affected or even uncontaminated by the tailings water.In terms of formation characteristics,karst spring water is mainly controlled by the dissolution of carbonate rock and salt rock,while tailings water is accredited to the results of mining industrial wastewater and domestic sewage.2.The single-factor index method was used to evaluate the water quality of each sample.The results showed that:in the karst spring water,the As element of Shuitouquan?STQ?in Zhadian Village and the pH of Jinhu Park?JHGY?exceeded the standard,so it could be judged as Single-factor pollution;For the pore water of tailings,there are 14 evaluation indexes that exceed the standard,among which SO₄^2-,TH,NH₄⁺,TDS,Mn and F^-are the main pollutants in tailing pond.The improved Nemero index method is used to comprehensively evaluate the water quality and the results showed that:among the 7 groups of karst springs,only the water of Chadian Village?STQ?exceeds grade III and the other can be used as a drinking water source,and the overall water quality is better.Among the pore water of tailings,only Beiyin Hill tailings?BYS?,the Xinjian tailings?XJK?,Qiliu village?QLZ?do not exceed grade III?These tailings ponds have been closed for many years?,the quality of the pore water of the tailings is poor.3.Taking the typical Wujiaotang tailings pond as an example in Gejiu mining area,the maximum amount of tailings water seeping out from the clay layer and entering the lower limestone layer is31.55m³/d by the numerical simulation software-Visual MODFLOW.Compared with the daily reception of the tailings water emissions,leakage emissions accounted for only 2%,that is to say,the most of the pollutants still gathered in tailings pond.4.The results of indoor infiltration experiments show that the permeability of tailing sand-tailings powder ranges between 10^-2cm/s¹0^-6cm/s and that of clay layer ranges between 10^-6cm/s¹0^-9cm/s,the semi permeable tailings and the weak permeable clay layers constitute the physical water barrier under the tailings pond.In the tailings,the hardpans layer formed by secondary mineral cementation and high content of iron oxides in the clay layer have the ability of adsorbing and precipitating polluted ions and heavy metals,which combine to form a chemical adsorption precipitation barrier.After the pollutants in the tailings water experienced“multiple-layer interception”by the tailings layer and the clay layer,the damage to the environment in the part of the Karst spring water has been dramatically reduced.5.Acid mine drainage is found not to exist in the mining area,which is the result of neutralization reaction between carbonate and acid mine drainage,indicating that the Gejiu mining area has strong natural repair ability for acid mine drainage.