Change in groundwater pH by infiltration of meteoric water into shallow part of marine deposits

Ishii, Eiichi   ; Hama, Katsuhiro ; Kunimaru, Takanori; Sato, Haruo

In order to research water-rock interaction contributing to pH of groundwater in Neogene marine deposits in Horonobe area, northern Hokkaido, Japan, petrological and hydro-geochemical characteristics were investigated. As a result of the investigation, the following were shown. Leaching of Na from rocks occurs at infiltration zone of meteoric water of shallow part of the deposits, and the leaching is caused mainly by cation exchange reaction between Na in smectite and H in groundwater. The pH of groundwater in the shallow part is controlled mainly by the above cation exchange reaction. The pH increases when meteoric water infiltrates into the rocks, and decreases when saline water re-fills the rocks.