Evolution Mechanism And Health Risk Of Groundwater Environmental Geochemistry In Sunan Mining Area

Mining cities are ecotone areas where people and nature interact,and human activities such as mining,industrial and agriculture severely restricted the sustainable development of groundwater resources in China.At present,most of the groundwater environmental studies conducted in mining areas focus on the characteristics of major ions,metalloids and trace elements in pore water flow systems and contamination studies,while there are few studies on the environmental geochemical evolution mechanisms and health risks of bedrock fractures and karst water flow systems.Therefore,the systematic groundwater environmental study of geochemical evolution mechanism,source apportionment and health risk in mining areas not only further understands the formation and evolution mechanism of groundwater environmental geochemistry,but also has important guiding significance for the groundwater environmental pollution control and expansion of groundwater resources availability in mining cities.Based on the groundwater environment in the Sunan Mining Area,244 water samples were collected between 1985 and 2021,and 93 additional groundwater samples were collected on site.A study on the spatial-temporal evolution mechanism of groundwater environmental geochemistry,identification of groundwater reactive geochemical transport pathways,spatial dependence of groundwater environmental geochemistry,and human health and ecological risk evaluation based on positive definite matrix factor source analysis was conducted by using indoor water chemistry tests,geochemical simulations,isotope analysis,theoretical model calculations and multivariate statistical analysis,combined with the measurement results of major ions,metalloids,trace elements and isotopes(δ²H/δ¹⁸O,δ³⁴S,δ⁸⁷Sr/δ⁸⁶Sr).The following major results had been achieved:（1）Mining process was divided into three time periods:the early mining period（before2011 year）,the middle mining period（2012-2016）and the late mining period（2017-2021）in combination with human mining activities.The water chemical phases of loose pore water mining at the early stage,middle stage and late stage are Cl·SO₄-Na·Ca,HCO₃-Na·Ca and SO₄-Na·Ca respectively,with calcite and gypsum dissolution,desulfurization as well as calcite,gypsum and dolomite dissolution respectively.The water chemical phases of the Permian sandstone water mining at the early stage,middle stage and late stage are SO₄-Na,HCO₃·SO₄-Na and HCO₃-Na respectively,with pyrite oxidation,pyrite oxidation and gypsum dissolution,as well as carbonate dissolution and desulfation respectively.The chemical phases of carboniferous limestone water mining at the early stage,middle stage and late stage are SO₄·HCO₃-Na·Mg,HCO₃·SO₄-Na·Ca and HCO₃-Na respectively,with halite dissolution and carbonate dissolution mainly,gypsum dissolution and carbonate dissolution,as well as carbonate dissolution mainly respectively.In addition,the intensity of the geochemical action of loose water and carboniferous limestone water is higher in the north than in the south in all periods,and gradually decreases with time as a whole.In sandstone water,sulfate dissolution decreases with time,while carbonate dissolution and cation exchange increase with time as a whole.The distribution of the intensity of geochemical interactions in the region is complicated by the heterogeneity of the sandstone water-richness.（2）An exponential whitening function and gray situational decision method fused with water source discriminative model in the mining process were established,and the unknown water samples in the mining process were identified,and the comprehensive accuracy rates were 83.3%,70.8%and 80.0%in the early,middle and late stages of mining,respectively.The exponential whitening function in the model emphasizes the non-zero value of the function at adjacent levels compared with the linear whitening function,which effectively avoids the lack of effective information due to high weighting.The integration of the model with the gray situational decision method with Critic weighting has the advantages of overcoming the inability of a single factor to reflect all water source information,the high volatility of data and the strong correlation of variables.（3）The isotopic signatures ofδ²H/δ¹⁸O,δ³⁴S andδ⁸⁷Sr/δ⁸⁶Sr indicate that halite dissolution is the main reason for the enrichment of ¹⁸O and Cl^-in the water bodies,sulfate mainly from evaporite mineral dissolution and pyrite oxidation,and strontium mainly from silicate and carbonate mineral dissolution.Four reactive geochemical transport pathways were identified in combination with mineral phase characterization and inverse simulation,mainly including the process of recharge of mine water by loose water,Carboniferous limestone water and Ordovician limestone water,hydraulic connection between Carboniferous and Ordovician limestone aquifers mainly through faults or fractures,surface collapse ponding water,mutual circulation recharge between Hui River water and loose water,and possible connection between shallow and deep aquifers through fractures or faults generated by mining.（4）The multivariate system in the groundwater environment of the Sunan mining area shows spatial dependence,and its controlling factors affect the water utilization and agricultural crop growth of local residents.The results indicate that cation exchange,halite dissolution and silicate dissolution contribute to high concentrations of variables such as K⁺+Na⁺,TDS and EC in loose water in the western and southern part of the study area,sandstone water in the Zouzhuang mine,and Carboniferous water in the central part of the study area and Ordovician water in the Qianyingzi mine.Mining factors cause high concentrations of variables such as As,Sb and B in loose water in the northern part of the study area,sandstone water in Zouzhuang mine,Carboniferous water in the western part of the study area and Ordovician water in Qianyingzi mine.Mineral weathering dissolution causes high concentrations of variables such as Ca²⁺,Mg²⁺,Fe and Mn in loose water of Qidong mine,sandstone water of the southern part of the study area,Carboniferous water of the southern part of the study area and Ordovician water of Taoyuan mine and Qidong mine.（5）The environmental quality of groundwater in the mining area of Sunan was affected by both natural and artificial pollution sources,and the impact of natural sources is relatively large,among which agricultural sewage discharge,coal gangue percolation pollution and mine pit drainage are the main artificial pollution sources.The drinking water route is the main exposure route for all population health risks,where As and Co are the dominant elements for non-carcinogenic and carcinogenic risks.As,Cr and Cu are the dominant elements of potential ecological risk,loose water in the areas around Qinan,Taoyuan and Qianyingzi mines are medium ecological risk areas.In sandstone water,which is mostly affected by coal mining,all areas are high ecological risk zones except for the southern part of the Qinan mine.The high ecological risk zone of Carboniferous limestone water is in the Zouzhuang mine.Ordovician limestone water is a high risk area in the central part of Taoyuan coal mine and the eastern part of Zouzhuang.Figure[103]Table[48]Reference[294]...