Identification And Migration Mechanism Of Groundwater Pollutants In The Jilantai Salt Lake Basin In Northwest Arid Area

In recent years,the environmental pollution problem around the salt lake basin in Jilantai has received attention,and although some research results have been available,there is an obvious lack of research on the water quality in the key pollution areas,therefore,the Tugeligaole basin was selected for the study,and 132 groundwater samples were collected during the abundant water period（June-September）and the dry water period（October-May）from 2020 to 2022 to determine physicochemical indicators and to conduct field physical and hydrogeological tests;and mathematical statistics,Piper trilinear diagram,correlation analysis,factor analysis,Gibbs diagram and and ion ratio to identify the main controlling factors of groundwater quantity and quality evolution;and the single factor evaluation method,Nemero comprehensive pollution index method,health risk evaluation model and water quality index evaluation（WQI）are used to identify pollutants and evaluate the health of groundwater,and the migration change pattern of pollutants is predicted by coupled groundwater quantity and quality simulation model,which is important for the protection and development and utilization of groundwater resources in the Salt Lake Basin.The main results are as follows:（1）The groundwater is weakly alkaline and slightly saline;the main ion concentration is low during the abundant water period and high during the dry water period,and the spatial distribution is enriched from upstream to downstream,with Cr⁶⁺and As showing local point-like high value distribution.Groundwater chemical composition is controlled by evaporative concentration,geoenvironmental background factors,traffic discharge factors,human activity factors,primary geological factors and carbonate dissolution.The groundwater water chemistry type is mainly Cl-Na type.The groundwater evolution process is influenced by evaporative concentration,evaporite dissolution,and cation exchange.Evaporite mineral dissolution is the main source of Na⁺,Ca²⁺,SO₄^2-and Cl^-in groundwater.（2）The northwestern part of the basin is in a safe and clean state during the bountiful and dry periods,and the local area in the southeast reaches the range of the warning line,where light pollution occurs,and there is no moderate and heavy pollution.Health risk evaluation of As,F^-and Cr⁶⁺in groundwater in the basin found that oral ingestion was the main exposure pathway for groundwater health risks,with higher health risks for children than adults and higher risks during dry seasons than during wet seasons;Cr⁶⁺has the largest contribution to carcinogenic risk and is the pollutant of key concern in the shallow groundwater of the basin;F^-is not harmful to human health for the time being,but there is a potential risk.Cr⁶⁺is also a key factor affecting groundwater quality,and the risk of water quality pollution tends to migrate southward during the dry season relative to the wet season,with a higher area of pollution than during the wet season.（3）The groundwater numerical model was used to simulate the solute migration scenario of pollutant Cr⁶⁺.The results showed that the diffusion range of Cr⁶⁺pollution plume expanded with the increase of time.The horizontal diffusion distance of pollution plume in 15 years was 1491 m,and the vertical diffusion distance was 412 m.The pollution plume showed irregular oval diffusion in the northeast direction,and the concentration of pollution plume center decreased by 39%,but it still exceeded the Class III standard of’Groundwater Quality Standard’（GB/T 14848-2017）and maintained the trend of continuous diffusion.