Study On Risk Assessment And Control Of Groundwater Environment In Qianan County,Jilin Province

This thesis combined the selected topics of the Shenyang Geological Survey Center of the China Geological Survey project ?Regional Water Resource Survey and Evaluation Methods and Groundwater Ecological Water Level Threshold Survey and Research?(DD20190340)to research environmental geology issues such as groundwater salinization,soil salinization,and excessive fluoride and arsenic in Qian‘an County,Jilin Province.The research aimed to determine:(1)If the water quality of deeper aquifers is still recommended as a management alternative against F and As under gradual contamination;(2)The success or otherwise of groundwater salinity and soil salinization mitigation projects;(3)The potential impact of the Hadashan Water Control and Irrigation Project(HWCIP)on the groundwater environment(salinization)in Qianan County.These goals were achieved by appraising the impact of natural and human activities on the groundwater environment using a temporal assessment of groundwater quality,human health risk,groundwater salinity,and soil salinization in Qianan County from the 1980 s to the 2010 s.Data from field surveys,water quality monitoring,water level monitoring,climate,water use statistics and remote sensing were used.Basic theories of geology,hydrogeology,and hydrogeochemistry are applied.The technical methods used include descriptive statistics,correlation matrix,spatial and remote sensing analysis,laboratory analysis,geochemical modelling,human health risk assessment(HHRA),trend analysis and groundwater flow modelling(GWFM).The main conclusions obtained are as follows:(1)The water quality and change law of groundwater in upper Pleistocene(Q3)phreatic aquifer,lower Pleistocene(Q1)confined aquifer and Neogene(N)confined aquifer in the region was revealed.Except for major elements such as sodium and magnesium,trace elements fluoride and arsenic,most of the water quality parameters are basically within the recommended limits.Sodium can affect taste,magnesium can be removed by boiling,but fluoride and arsenic require special handling.Arsenic is the most significant heavy metal pollutant in groundwater in the research area with concentrations in 2001 and 2010 s in Q3,Q1 and N aquifers exceeding the recommended limit by 11.36% to 25.25%.(2)The groundwater quality status in three aquifers and the health risk assessment of drinking water were evaluated.Groundwater quality is ranked as N>Q1>Q3 from good to poor according to the physical and chemical characteristics of groundwater,water quality index,heavy metal pollution index and hazard index(HI),and groundwater in deeper aquifers is the preferred source of drinking water.From the 1980 s to the 2010 s,the average Total dissolved solids(TDS)of groundwater in all aquifers increased over time.(3)The sources and influencing factors of groundwater salinity are analyzed.The temporal effects of depth to groundwater level and precipitation over time on groundwater salinity are not obvious,except in shallower areas;evaporation has a greater impact on groundwater salinity;and the physical characteristics of soil lithology,landforms and geology also affect the salinity of groundwater.(4)The law of average decrease of saline-alkali land in the region and its causes are revealed.Groundwater salinity increased slightly in the study area,and analysis of soil salinization from the 1980 s to the 2010 s showed a decrease in the affected area.This is mainly due to the conversion of land to dryland and rice paddies.The downward trend in evaporation and the general decline in the groundwater level are also responsible for the decrease in saline-alkali land in the region.The policy-driven,proactive alkaline land recovery program is the most important driver of salinized land reduction,highlighting the success of the salinization mitigation program.(5)A numerical simulation model of groundwater was constructed and the groundwater level was predicted.Under the HWCIP irrigation scenario,the water level in the 26730045 and 26730042 monitoring wells increased significantly by 0.35–0.46 m/year.Simulated groundwater heads were used to determine the area's vulnerability to soil salinization.Irrigation areas are prone to long-term extremely high vulnerability,and underground drainage ditches are used to manage predicted soil salinization vulnerability.(6)Proposed the drainage design scheme of the future irrigation area.In the long run,the Subsurface Drainage Designs(SSDD)performed in the following order SSDD-III > SSDDI > SSDD-II for protection of extremely vulnerable areas in 2030.Under irrigated,SSDD-I,SSDD-II and SSD-III management scenarios,low salinization vulnerability zones were25.18%,51.16%,31.31% and 56.15% highlighting the role and advantages of subsurface drainage ditches in the prevention and control of soil salinization.The main innovations of the paper are as follows:(1)The spatio-temporal variation characteristics and change laws of groundwater quality in upper Pleistocene(Q3)phreatic aquifer,lower Pleistocene(Q1)confined aquifer and Neogene(N)confined aquifer and soil salinization were fully revealed;(2)The GIS weighted superposition technology is used to evaluate and partition the health risk of drinking water in multi-layer groundwater quality in the zone,and the F and As point source management zones(SPMZ)are divided,which is conducive to the rational development and utilization of groundwater resources and scientific management.(3)A numerical simulation model of groundwater system was constructed,the groundwater level and the critical groundwater level of soil salinization under the development conditions of the Hadashan Water Control and Irrigation Project(HWCIP)irrigation area were simulated and predicted,the area distribution of soil salinization under various management scenarios was quantified,and the prevention and control of soil salinization was proposed Groundwater drainage design scheme.