Study On Apparent Background Values Of Minor Components And Trace Elements In Shallow Groundwater Of Liujiang Basin

Apparent Background Values of groundwater means groundwater in the natural state which is formed by the superposition of normal human activities affect the content,range,proportional relationship of groundwater chemical components.It reflects the groundwater hydrochemistry elements process and characteristics of the evolution and development under the condition of on the natural state and normal human activities.Taken the shallow groundwater in Liujiang basin as the research object,the factor analysis is adopted to establish the relationship between minor components and major components,combined hydrochemistry analysis and mathematical statistics method to identify outliers.According to different detection rate of trace elements take the different mathematical statistics methods to identify outliers.Finally using the cumulative frequency curve calculate shallow groundwater apparent background value of minor components and trace elements in Liujiang basin,building apparent background value system of minor components and trace elements.Thesis mainly made the following conclusions:(1)Using factor analysis method to establish the relationship between minor components and major elements.From the angle of hydrochemistry analysis of major components to identify the outliers of minor components not only can explain abnormal hydrochemistry of minor components,can also identify outliers which cannot be identified by mathematical statistics.Hydrochemistry analysis of major components make up for the shortcomings in the mathematical statistics method to identify the outliers of minor components and is very important to reasonable identify the outliers of minor components.(2)After major component analysis preliminary eliminate outliers of monor components,from minor components statistical characteristic use I2σ method combined with probability method to identify outliers.This method not only can grasp the overall statistical characteristics of data,but also avoid the subjective error to identify threshold.Compared with mathematical statistics method,combined hydrochemistry analysis and mathematical statistics method is more stable and reliable to caculate apparent Background Values of groundwater and can be complementary advantages and disadvantages of the method.Compared with a focus on water chemical analysis method of HCA,combined major component analysis and mathematical statistics method use wider and can apply to all minor components.(3)For trace elements detection rate less than 25% use either the 95 percentile or detection limit as background value threshold.Trace elements detection rate at 25% ～75% use the KM method to estimate mean and standard deviation of the overall data,then take double standard deviation criterion to identify outliers.Compared with ROS model,the method apply wider and be more objectivity.(4)The minimum samples is estimated by statistical methods and selects total soluble solids and nitrate as comprehensive index and pollution index of groundwater sample estimation.Four subregions are satisfied the minimum sample of apparent background value.For the estimation results of censored data of minor components and trace elements indicate that the data detection rate is more than 75% using simple-substitution methods,detection rate is between 25% ～ 75% using the KM methods,detection rate is more than 75% directly using 95 percentile of data.The estimation methods are simple and ensureing the accuracy of the results.