In hydraulic containment-type underground storage caverns for liquefied petroleum gas (LPG) or crude oil, sufficient hydraulic potential around the storage caverns must be maintained to seal in the stored material effectively (called "water-sealing function"). At the Japanese national LPG stockpiling site in Kurashiki, a water curtain system that includes tunnels and injection boreholes was installed above the storage cavern; the system injects water to keep hydraulic potential around the storage cavern. To restrain the decrease in the water supply due to clogging, groundwater quality monitoring and water flow performance tests were conducted during the site's construction. Based on the tests and monitoring results, a water quality control method for injection water was formulated to maintain the water supply. With this control method, the water supply was maintained satisfactorily.

Japan has three underground petroleum stockpiling bases, located at Kuji, Kikuma, and Ichiki Kushikino, containing a total of 5 million m³ of crude oil. The underground rock caverns where the crude oil is stored were constructed from solid bedrock; and the crude oil is maintained in storage via a system of natural groundwater and artificial water sealing. The storage facilities have been operating for 30 years and during this time the three bases have been suffered strong shaking due to large earthquakes; with monitoring and appropriate action, stable operations have been maintained. In this technical report, we present examples of earthquakes experienced by the three underground petroleum stockpiling bases and their hydraulic effects.

Nitrate-nitrogen contamination of groundwater in Shimabara Peninsula continues to be a serious problem. In 2006, Nagasaki Prefecture established the Shimabara Peninsula Nitrogen Load Reduction Plan, and measures have been taken. In this study, we conducted a factor decomposition analysis of the nitrogen load potential using the open data attached to the plan and the data published by the local government and examined what factors have been changing the potential. The changes in nitrogen supply from agriculture, livestock industry, and household life were decomposed into (1) nitrogen intensity factors, (2) structural change factors, and (3) scale factors, and the effects of each factor were quantitatively investigated. Consequently, it was found that the total of the three sectors during FY2013-2019 showed a slight improvement trend, and this was due to the structural change factor in the livestock industry and the cropped area factor in agriculture. Thus, the slight decrease in nitrogen supply during this period is mainly due to the conversion to smaller nitrogen-supplying animals in the livestock industry and the decrease in cropped area in agriculture.

Although the regional land surface displacement data observed by Interferometric Synthetic Aperture Radar is expected to contribute to the effective calibration of land subsidence models, the land subsidence models cannot always reproduce the observed data or the inversion analysis possibly estimate a wrong parameter set because the observed data often contains the displacement components caused by unknown processes such as tectonic movement which are not considered in the land subsidence model. This study proposes the minimization of the entropy in terms of the total rotational energy of the residual between the calculated displacement and the observed displacement instead of minimizing the residual itself in the inversion analysis. A preliminary numerical experiment has shown that the proposed method successfully separates the regional displacement components caused by unknown processes and finds the optimal parameter set for the land subsidence model.