Analysis Of Chemical Characteristics And Evaluation Of Groundwater Quality In Yantai City

The chemical characteristics of groundwater is an important part of hydrogeochemical research.The study of groundwater chemical composition and its types,temporal and spatial distribution and evolution is very important to understand the characteristics of regional groundwater environment.In this paper,diving in Yantai City is taken as the research object.Based on the monitoring results of water quality,the chemical characteristics and water quality of groundwater in the study area are analyzed and evaluated by using statistical method,single index evaluation method,fuzzy comprehensive evaluation method and improved Nemero comprehensive index method.The main results are as follows:（1）The main cations in groundwater are Ca²⁺,and the main anions are Cl^-and HCO₃^-,p H with an average value of 7 to 8,and the groundwater environment is weakly alkaline.In the study area,the alkaline earth metal ions of most water samples are larger than the alkali metal ions in the dry season,the carbonate hardness of some water samples is more than 50%,and most of the water samples belong to strong acid.During the flood season,the alkaline earth metal ions of most water samples are larger than the alkali metal ions,the non-carbonate hardness of some water samples is more than 50%,and most of the water samples belong to strong acids.it is concluded that the chemical type of groundwater is Cl·HCO₃·SO₄-Ca·Mg in the northern coastal area,Cl·SO₄·HCO₃-Na·Mg in the southern coastal area,and SO₄·HCO₃-Ca·Na in the inland.The ion spatial distribution of TDS is consistent with that of Na⁺,Cl^-,Ca²⁺and Mg²⁺.（2）The correlation coefficients between Na⁺and Cl^-in dry season and high water season from 2017 to 2020 were 0.906,0.961,0.840,0.908 and 0.736,0.920,0.912,0.898,respectively.Secondly,the correlation coefficient between Mg²⁺and SO₄^2-was between 0.7 and 0.8,showing a significant correlation.Through Gibbs diagram and ion proportion analysis,it can be concluded that most of Na⁺comes from the dissolution of evaporite such as rock salt and mirabilite,and a small part comes from the dissolution of albite minerals;Cl^-mainly comes from seawater intrusion,and part of it comes from the dissolution of rock salt or other chlorides in sedimentary rocks;the main sources of Mg²⁺and Ca²⁺are the dissolution of carbonate minerals in groundwater,and partly from the dissolution of silicate minerals and evaporated rock salts.Positive cation exchange occurs in groundwater,and the ion source of groundwater in high water period is mainly affected by rock weathering and rainfall control,while in dry season,the ion source of groundwater is mainly affected by rock weathering.（3）Groundwater quality evaluation:the best result of single index evaluation method is that the type I water index of Na⁺,is more than 60%,followed by Mn²⁺,.The indexes with the proportion of class III water below 50%are Na⁺,Cl^-,NH₄-N,total iron,oxygen consumption and Mn²⁺.The total hardness,NO₃-N and manganese ions have a great impact on the groundwater quality of class IV water,the proportion of which is 35%.The proportion of typeⅠ～Ⅲwater,class IV water and class V water is 88%,9%and 3%,respectively.The fuzzy comprehensive evaluation method takes the total hardness,TDS,NO₃-N and Mn²⁺as the evaluation factors of groundwater quality,and the final result is that the number of type I water is 0;the number of type II water is 6,accounting for 30%of the total number of diving samples;the number of class III water is 5,accounting for 25%of the total number of diving samples;the number of class IV water is 4,and the number of class V water is 5,accounting for 45%of the total number of diving samples.The largest weight values of type IV and V water evaluation factors are NO₃-N and Mn²⁺,of which NO₃-N is the main influencing factor.（4）In the pollution evaluation,the single factor index evaluation method shows that some of the water samples are seriously polluted,of which 5%are unpolluted,40%are slightly polluted,40%are moderately polluted,and 15%are heavily polluted and heavily polluted water samples.The revised Nemero index method shows that a small part of the groundwater samples in Yantai city are seriously polluted,of which 25%are unpolluted,65%are mild pollution,5%are moderate pollution,and 5%are severe pollution and severe pollution.