Karst Groundwater CCl₄ Pollution Trend Prediction And Health Risk Assessment Of A City In Eastern China

Globally,groundwater pollution has become more and more severe due to the increasing impacts of human action.The world is dealing with the difficult challenge of how to clean up contaminated groundwater sites,control risks and ensure the safe use of groundwater.This research explores the attenuation law of CCl₄,predicts its changing trend,analyzes its health risks,assesses the economic potential of extraction-aeration treatment technology and suggests sustainable management remedial actions in view of the CCl₄ pollution in the Qiligou water source in Xuzhou.We draw the following key findings:1)The attenuation law of CCl₄ was analyzed using 20 years of long-term monitoring data.The results showed that CCl₄ polluted Xuzhou karst water sources from pesticide plants.In 2001,the highest concentration reached 3903.2mg/L,which exceeded the national drinking water standard of 2μg/L by 1954 times,and the polluted area reached 17.5km².After 20 years of natural attenuation and extraction treatment,the concentration of CCl₄ has decreased year by year.According to the data obtained in October 2020,the highest CCl₄ detected in the southern part of the water source is11.44μg/L,which is still higher than the drinking water hygiene standard limit.2)Predicted the trend of CCl₄ concentration in the Qiligou watershed of Xuzhou.According to the existing monitoring water level and solute data,the parameter inversion is completed by PEST and then the prediction is made according to the inversion calibrated model.The results showed that the overall concentration of carbon tetrachloride in groundwater showed a downward trend.In 2030,the concentration of carbon tetrachloride in the southern region as a whole fell below 10μg/L,and the concentration of carbon tetrachloride in the northern region was less than 2μg/L.3)The CCl₄ health risk assessment of the Qiligou water source was carried out.According to the risk calculation model,the carcinogenic health risk value of CCl₄ from2004 to 2020 is between 5.59E-03 and 3.24E-02,and the non-carcinogenic health risk value is between 8.00E+02 and 1.19E+02.The overall trend is declining year by year,but the cumulative health risk value is still always higher than the highest risk level.According to the evaluation of the predicted value of CCl₄ concentration from 2021 to2030,the carcinogenic health risk value of CCl₄ is between 3.40E-03 and 1.15E-03,and the non-carcinogenic health risk value is between 8.40E+01 and 2.35E+01.The risk value has decreased year by year until 2030.It is still greater than the maximum risk-level value.4)Introduce common groundwater pollution control technologies.Based on the demonstration project,the extraction-aeration technology is highlighted.The calculation verifies that when the gas-water ratio is 5.75,the treatment effect of groundwater carbon tetrachloride pollution in the demonstration project can meet the requirements of GB5749-2006.The economic cost of the demonstration project is analyzed and the economic feasibility of the technology is determined.Based on the results and data of the risk assessment,the follow-up sustainable management of carbon tetrachloride contaminated sites in the Qiligou water source still needs to maintain long-term monitoring and carry out sub-regional control at the same time.Different risk control measures are adopted for sites with different risk levels.Strengthen technological innovation and develop in-situ restoration technologies,especially permeable reaction wall technologies with zero-valent iron as the medium,to treat residual pollution in the deep part of the aquifer.