Analysis Of Groundwater Pollution Characteristics And Mechanism In Some Area Of Xichang

The research area is located in the northwest of Xichang.The topography is high in the West while low in the East.The west is the Mopan Mountain area and the east is the river crossing this area from north to south.According to the test results by local environmental protection department,some ions are exceeding the standard in the groundwater in this area which has affected the normal production and life of local residents.Therefore,it is of great significance to find out the characteristics of groundwater pollution and to study the mechanism of groundwater pollution in this area,which can provide theoretical support for local groundwater prevention and control.On the basis of previous research,this article makes a deep study on the characteristics of supplement,runoff and discharge of groundwater recharge in the research area by means of hydrogeology and hydrological geochemistry,hydro-geochemistry and other theoretical method;through the leaching experiment of soil sampling and groundwater samples,combined with flame atomic spectrophotometric method and ion chromatography method,the analysis of soil and groundwater in the research area was carried out;the chemical characteristics of groundwater in the research area were analyzed by means of mathematical statistic analysis,proportional coefficient analysis and correlation analysis;the groundwater quality was evaluated by using single index evaluation method,Nemerow index and fuzzy comprehensive evaluation method.Based on the Kriging spatial interpolation principle,this article also analyzed the pollution source in the research area;the Modflow software was used to simulate and predict the excess ion Mn²⁺in the groundwater.The following understandings and conclusions are obtained:?1?Through the analysis of the geological environment and hydro-geological conditions in the research area,it is found that there are Yangtianwo rupture,Beiyan rupture and Shiguan Mountain rupture;the rupture trends are mainly north-south direction,northeast-southwest direction and northwest-southeast direction.The third and fourth series of the regional strata are distributed from the lower Proterozoic to the Cenozoic,and the main surface of the research area is covered by the fourth series.The south-east shows the Neogene of the Triassic group,and the northwestern part of is a small high group of Triassic.The groundwater types are loose accumulation layer pore water and bedrock fissure water.Among them bedrock fissure water includes clastic rock type fissure water and magmatic type fissure water;the main recharge sources of groundwater in the research area are atmospheric precipitation,which is drained by the gully and fissure in the western mountainous area.?2?The dispersion coefficients of cations Mg²⁺?1.074?,Ca²⁺?0.73?,and Na⁺+K⁺?1.074?changed significantly in the research area,which indicating that they were greatly affected by different human factors and environmental factors in each region of the research area.The dispersion coefficients of anions Cl^-and SO₄^2-were1.93 and 1.32 respectively,of which Cl^-was the highest among all elements,and it was the largest change in the spatial range of the research area.It was also related to groundwater dynamic conditions in the research area.Because of the difference between groundwater flow and flow rate between different areas in the research area,the Cl^-migration rate and enrichment degree behave differently in different regions,which resulting in a clear difference in Cl^-between different regions.Through the analysis of the TDS contour distribution map,the overall TDS content is between100mg/L-200mg/L,and the mineralization of ground water is small;through analyzing the distribution of ionic isoline of chemical composition of groundwater in the research area,we found that Na⁺+K⁺is mainly concentrated in the landfill area,and its content in the landfill area is significantly higher than in other areas;the changing trends of Ca²⁺and Mg²⁺are the similar.The content of Ca²⁺and Mg²⁺within the scope of the mining area and around the landfill is significantly higher than in other areas of the research area;the content of major anions such as HCO₃^-,Cl^-and SO₄^2-of groundwater in open-cast mining areas is generally higher than that in landfills,which indicating that the anion content in the research area is greatly affected by the mining area.;?3?Correlation analysis between TDS and each component in the research area shows that the correlation between Ca²⁺and TDS is the highest,which showing a highly correlated condition;the degree of correlation between other components and TDS is Mg²⁺>SO₄^2->HCO₃^->Cl^-.At the same time,it can be seen that each component ion has a positive correlation with TDS.By drawing Piper trilinear chart,it can be seen that the water type of the water samples in the research area is dominated by bicarbonate water,and sulfuric acid-type water and chloride-type water appear locally.There are obvious differences in different locations of the water samples.In the upper reaches of the research area,bicarbonate water is the main source.Along the direction of groundwater flow,the chemical type of groundwater is gradually changed from bicarbonate water to bicarbonate chloride type water and chloride sulfuric acid type water or chloride bicarbonate water.?4?The groundwater quality in the research area was evaluated by using the single-index evaluation method,the Nemerow index method,and the fuzzy comprehensive evaluation method for the 20 water samples detected for the first time during the wet season.The results showed that there were 2 water samples in the?class,6 water samples in?type,7 samples in?The results showed that there were2 water samples in the?class,6 water samples from?type,?water quality of 7samples,and 5 water samples of?type,and 5 water samples in?type;the pollution indicators are mainly NO₃^-and NO₂^-,and followed by SO₄^2-and Mn²⁺;In the water samples,the polluted water samples were collected again in the same spatial location during the dry season,and the soil samples and soil samples were collected again.Combined with the leaching experiments of soil sample and comprehensive verification of the relevant literature,the contaminant of water samples in front and back and in the underground water of soil samples were contrastively analyzed.The main sources of nitrogen are nitrogen-containing organic compounds in local farmland with fertilizer and pesticide irrigation.The main sources of pollution in SO₄^2-and Mn²⁺are the residue with enough S-element-rich in the local mining area and the landfill material with Mn²⁺produced by the inhabitants.?5?Modflow software was used to simulate and predict the migration of excessive ionized manganese in groundwater.It can be known from the predicted simulated migration results that manganese is diffused around the pollution source as the center.The dominant direction of diffusion is the South-East,which is consistent with the direction of groundwater flow in the research area.In the main direction of groundwater flow and manganese element migration,an approximate ellipse pollution stripe is formed,and the influence on the surrounding groundwater quality is increasing.With the increasing pollution plume,the Mn²⁺has a great influence on river water in the ninth year after the first sampling.