大同盆地地下水中砷的富集规律及成因探讨

大同盆地地下水中砷主要富集在黄水河与桑干河的河间洼地及洪积-冲湖积平原的交接洼地,盆地中心的山阴一带是砷的主要富集区。垂向上,富集在2 0～2 0 0m承压孔隙水中。其中,2 0～40m及10 0～15 0m是主要富集段。盆地周边广布的太古界变质岩及中生界煤系地层是砷的原生物源,盆地内富含有机质的湖相沉积物为次生富砷介质,水化学还原环境是砷由沉积物向地下水中溶解的主要因素。断裂凹陷、低洼地形及细粒的含水介质是形成砷富集的有利条件。

A discussion of the enrichment and formation of arsenic in groundwater in Datong Basin

Endemic arsenism in drinking water in the Datong Basin is a serious problem and is typical in China. In this paper, the arsenic enrichment is analyzed based on field investigations and sampling analyses. The cause of formation is also discussed according to the characteristics of geological environment. The results indicate that arsenic is concentrated in the bottomland between the Shangan River and the Huangshui River, as well as the downfold connecting the pluvial plain and the alluvial-laustrine plain. The Shanying district located at center of the Datong Basin is a key section of arsenic enrichment. In a vertical direction, the depth of arsenic enrichment ranges from 20 to 200 m, in which confined aquifers occur. In particular, arsenic is found to be rich at depths ranging from 20 to 40 m and from 100 to 150 m. The arsenic-rich metamorphic rocks and coal-bearing strata around the margin of the basin are the original arsenic sources. Lacustrine deposits with rich organic materials are the secondary media containing arsenic. The chemical deoxidizing condition is the key factor affecting the dissolution of arsenic from sediments to groundwater. The block-faulted depressions, low-lying landforms, and fine-grained water-bearing media are adequate for the formation of arsenic in groundwater.