Genetic relation between Holocene transgression and chemical composition of the shallow groundwater in Hangzhou, China

Hangzhou, China, is a world-famous tourist city. With the increase of the urban population and the development of tourism, the requirement of the quantity and quality of groundwater is steadily increasing. Hangzhou region evolved from the ancient shallow sea gulf. According to the local chronicle (Compilation Commission on Hangzhou Chorography (CCHC) 2000), the subsurface water was not potable due to salinity content before Wu-Yue Period (before 476 BC). After the large-scale dykes and dams were built, the encroachment of seawater was kept within limit. The drainage river and ditch were extricated from the encroachment of the tide. Moreover, the West Lake was dredged several times and the fresh lake water was discharged into the rivers, which resulted in gradual desalination of the groundwater. Up to now, although the quality of the shallow groundwater has obviously been improved, the degree of mineralization, the salinity, and the contents of the iron and manganese are still high, so that the groundwater cannot be used directly as drinking water or industrial water. To understand why the quality of the shallow groundwater is poor, the chemical composition of the modern phreatic water has been determined, and the relationships between the sedimentary environment and geochemistry of the aquifers and the chemical components of groundwater have been studied by mathematical statistical methods and simulating experiments. Such a study is very important to exploit and protect the groundwater resources properly and efficiently.