长江下游沿岸(南通-上海段)第I承压水砷超标原因分析

Reasons of Exceeding As Content for No.I Confined Groundwater in Coastal Area of the Lower Course of Yangtze River (Nantong-Shanghai Section)

地下水中砷含量过高是由特定的环境水文地质条件和环境水化学条件所引起的。从长江下游沿岸（南通—上海段）第Ｉ承压含水层的沉积环境、环境水文地质条件出发，根据砷的水文地球化学性质，借鉴前人的试验资料，分析第Ｉ承压水中砷富集的影响因素及探讨砷超标的原因。

Environmental background value of As for No.1 confined water in coastal area of Nantong-Shanghai section is below 002mg/l. Exceeded As content in groundwater is caused by special environmental hydrogeological and hydrochemical conditions. At present, the reason is considered as secondary pollution from the Yangtze River. Because of change of redoxomorphic conditions, microAs is deposited and adsorbed by bed materials of the Yangtze River. Then, as influent seepage flow As is desorbed into No.1 confined water. Owing to the reduction condition(Eh<178mv), it is favourable for the congregation and migration of As into coastal area of the Yangtze River. The direction and speed of migration, controlled by movement and seepage velocity of No.1 confined water, are basically similar to runoff direction of groudwater.