贵州岩溶区浅层地下水氯化物及硫酸盐环境背景值

以贵州抗旱打井找水项目2007-2015年采集的3 699件浅层地下水化学样品分析数据为依据，在分析区域地质背景和水文地质条件的基础上，对研究区地下水化学数据进行聚类分析及水文地质单元划分，运用箱型图和迭代标准差法剔除异常值，并判断各水文地质区水化学数据的分布类型，最后取剔除异常值后数据的95百分位数作为环境背景值上限阀值.研究结果表明:贵州岩溶区浅层地下水属中偏碱性，水中阳离子以Ca2+、Mg2+为主，阴离子以HCO₃-和SO₄2-为主，地下水类型主要为HCO₃-Ca·Mg和HCO₃-Ca型，区内地下水中离子的主要来源为岩石矿物的风化水解；地下水SO₄2-和Cl-分布类型以正态分布为主，对数正态分布次之，偏态分布最少，三叠系中统关岭组膏岩层及二叠系含煤地层中地下水的SO₄2-环境背景值阀值为68.71~164.32 mg/L，其他区域背景值阀值为19.42~39.05 mg/L；Cl-背景值阀值为3.45~6.65 mg/L，区域变化较小. 

Analysis of Environmental Background Values of Chloride and Sulfate in Shallow Groundwater in Karst Area of Guizhou

This study focuses on the environmental background values in shallow groundwater in karst area of Guizhou. Firstly, the study area is divided into different groundwater environmental units according to the analysis data of 3 699 shallow groundwater chemical samples collected for the Guizhou Drought-Resistant Well-Drilling and Water Prospecting Project from 2007 to 2015, and the analysis of the geological background and hydrogeological conditions. Then, the box plot and the iteration standard deviation method are used to eliminate the abnormal values, and determine the distribution type of water chemical data in each hydrogeological area. Finally the 95th percentile of the data is taken as the upper threshhold of the environmental background values after deleting the outliers. The results show that the shallow groundwater in Guizhou karst area is neutral alkaline water, the cations are mainly Ca2+, Mg2+, the anions are mainly HCO₃- and SO₄2- and the groundwater types are mainly HCO₃-Ca·Mg type and HCO₃-Ca type. The main sources of ions in groundwater are weathering and hydrolysis of rocks and minerals. The distribution types of SO₄2- and Cl- ions in groundwater are mainly normal distribution, followed by lognormal distribution and least skewed distribution. The environmental background threshold values of the SO₄2- ion of the Middle Triassic Guanling Formation and the Permian coal-bearing strata are 68.71-164.32 mg/L, while those of other areas are 19.42-39.05 mg/L. The threshold background values of Cl- ion range from 3.45 to 6.65 mg/L, and the regional variations are small.