Factors affecting the leaching of nitrogen species from diatomaceous mudstone

Igarashi, Toshifumi*; Ueda, Takahiro*; Hokora, Hideyuki*; Jo, Mayumi*; Kudo, Hajime

Horonobe Underground Research Center, located in northern Hokkaido, Japan, has been excavating shafts and drifts of an underground research facility to establish general techniques for the assessment of deep geological environment. In this site, the groundwater seepage from the shafts and drifts as well as leachate from the excavated rock storage site contain high concentrations of total nitrogen. Ammonium-nitrogen (NH-N), the major nitrogen species in the seepage and leachate, has been removed by a nearby treatment facility. However, NH-N is easily oxidized to nitrite-nitrogen (NO-N) and nitrate-nitrogen (NO-N) by nitrification in the excavated rock storage site, which makes the removal process employed on site less effective. Therefore, column experiments that simulated the infiltration of rainwater through the storage site were carried out to understand the leaching and nitrification of nitrogen species and the factors affecting the phenomena. The results showed that the nitrification was inhibited when the rock layer was almost saturated, and that this process was temperature dependent. These indicate that nitrification can be mitigated by controlling hydrological conditions like water saturation.