Hydrogeochemical environment of aquifer groundwater in Shanghai and potential hazards to underground infrastructures

The Quaternary deposit in the Shanghai region is composed of a layered multi-aquifer-aquitard system (MAAS). The MAAS was formed mainly during the warm geological era over 2.6 million years ago. There is one artesian aquifer and five confined aquifer layers (AqI to AqV) in the MAAS with a very high groundwater pressure head. The groundwater in the aquifers of Shanghai is composed of both fresh and saline water due to it originating in different environmental conditions. AqI is the uppermost shallow confined aquifer, and it contains highly mineralised formation water with a wide variety of naturally occurring inorganic compounds. AqII and AqIII have slightly lower salinity and different hydrochemicals from those in AqI. The deeper aquifers, AqIV and AqV, have much lower levels of hydrochemicals. With the urbanisation of the Shanghai region, a large amount of underground infrastructure has been constructed in the shallow aquifers (AqI and AqII). As a result, the hydrochemicals in the groundwater present a potential hazard to this infrastructure. This paper reviews the hydrogeochemical compositions of aquifers in Shanghai and then discusses possible hazards to infrastructure construction within aquifers. In addition, this paper assesses the hydrogeochemical environment of the groundwater and the possibility of such environment-induced hazards arising in Shanghai.