Abstract
Groundwater seepage from a tunnel has been alkaline since it was excavated. Leaching experiments with boring core samples around the tunnel and analysis of the groundwater seepage and surrounding river water were conducted to understand the cause of alkaline water and neutralization processes. In addition, geochemical processes were evaluated by using PHREEQE.
The analytical, experimental and calculation results showed that the alkaline groundwater was primarily caused by the dissolution of calcite contained in the shale and sandstone distributed around the tunnel, and that mixing of the alkaline groundwater with the river water had an insignificant effect on the pH reduction during the dry season. The geochemical calculation suggests that the dissolution of atmospheric carbon dioxide effectively reduces the pH of alkaline seepage from the tunnel. This indicates that the effect of alkaline water can be mitigated by utilizing natural processes. However, it is necessary to quantify the dissolution of atmospheric carbon dioxide into the alkaline seepage.
