Water Environmental Risk Assessment Of Typical Concentrated Drinking Water Sources In Taihu Lake Basin

Taihu Lake is located in the economically-developed region of the Yangtze River Delta and is one of China's five largest freshwater lakes.It is also one of the most important water supply resources in the middle and lower reaches of the Yangtze River.It is responsible for supplying drinking water to surrounding major cities and improving water quality in the downstream areas.There are many drinking water sources in the Taihu Lake basin,of which there are 33 in Jiangsu Province.This article selects 8 typical centralized drinking water sources(Water Source A to H,5 lake reservoir type drinking water sources and 3 river-type drinking)in the Taihu Lake Basin according to factors such as region,source type,and water source scale were used for water environmental risk assessment.This paper investigates and analyzes the changes in water quality and the basic environmental conditions of water sources in recent three years(2015-2017).It also uses the entropy-weighted comprehensive index method and the AHP composite index method to evaluate the water quality,the basic environmental conditions and potential risks in water sources and eventually leads to the following conclusions:(1)Entropy weight index method was used to evaluate the water quality of 27 indicators of 5 lake-type water sources and 24 indicators of 3 river-type water sources respectively.The assessment obtained the water quality health status and Water Quality Health Index(WQHI)of each water source which was poor(20.33),good(68.75),good(82.29),good(76.06),poor(17.94),poor(17.66),good(73.09),good(69.21).Among them,the health status of two water sources is poor(Level V),and the main risk factors are chromium(Cr),lead(Pb)and toxic and hazardous organics;The health status of one water source is healthier(Level IV)and the main risk factors mainly include regular lake pollutants,lead(Pb)and toxic and harmful organic matter;The health status of four water sources isnot bad(level II),and of one water source is in good health status(Level I).(2)The risk assessment of the basic environmental status of the eight water sources was conducted using the analytic hierarchy index(AHP)method,in which the target layer was based on the environmental status assessment(A),the constraint layer was the risk source(B1),and the environmental management status(B2),The elemental layer is 21 specific survey items(C1~C21)under the constrained layer.The assessment results show that the basic environmental status risk level and risk index(BRI)for each water source are: high risk(0.73)and low risk(0.12).Low-risk(0.04),low-risk(0.07),low-risk(0.08),low-risk(0.06),low-risk(0.14),and low-risk(0.09),suggesting that the basic environmental status of seven water sources from sources A to H islow-risk and of one water source is in a high-risk(level III)state.The high risk of the basic environmental status is mainly caused by the existence of a large number of sources of pollution risk.(3)A risk assessment system for water sources was constructed based on the water quality health status and basic environmental conditions,and water environmental risk(WR)assessments were conducted for 8 typical centralized drinking water sources.The assessment results showed that two water sources are in high-risk(Level V)status,one water source is in higher-risk(Level IV)status,and four water sources are in low-risk(Level II)status,with 1 water source is in a low-risk(Level I)state.Because of the basic environmental conditions of each water source,except that water source A is a high-risk(level III),others are low-risk(level I),and the quality of water in each water source is not the same,so the results of water environmental risk assessment are basically classified as water quality health status levels.