Factors Affecting Leaching Behavior of Nitrification Products from Diatomaceous Mudstone by Column Experiments

Horonobe Underground Research Center， located in northern Hokkaido， Japan， has been excavating shafts of underground research laboratory for R&D of radioactive waste disposal. In this site， the groundwater seepage from the shafts and leachate from the waste rock storage site contain high concentrations of total nitrogen. Ammoniumnitrogen， the major chemical species of nitrogen in the seepage and leachate， has been treated by the effluent treatment facility. However， the ammonium-nitrogen is transformed to nitrite- and nitrate-nitrogen (nitrification products) by nitrification. As a result， the concentrations of total nitrogen increase to the effluent guideline due to nitrification. Therefore， column experiments were carried out to understand the phenomena and the factors affecting the leaching behavior of nitrification products. The result showed that the nitrification was inhibited when the column layer was almost saturated， and that the nitrification occurred near the surface of waste rocks， in particular， at 25℃. These results indicate that nitrification can be mitigated by controlling the hydrological conditions in the waste rock storage site.