スケール付着とローカルイベントの影響評価に基づく 温泉自動モニタリング装置の設計

The continuous monitoring of onsen (hot springs) is important for assessing the quality and sustainability of the onsen, and for evaluating the effects of geothermal energy developments on the onsen’s water supply. Due to the complexity of the data, automated monitoring once a week or less is insufficient to detect changes in the quality of the onsen due to natural variability or scaling in a pipeline, and other factors such as the weather and maintenance operations. In this study, the effects of scaling and other site-specific factors on the performance of the monitoring sensors were revealed by field experiments at the Obama and Kakkonda sites. The sensors considered in the experiment measured the flowrate, temperature, electric conductivity (EC) and fluid pressure. The sampling rate of each sensor was 1 measurement per second. The analysis of scale samples using X-Ray diffraction and energy dispersive X-ray spectroscopy revealed that the main components of the scales were aragonite at the Obama site and amorphous silica at the Kakkonda site. At both sites, the scaling reduced the accuracy of the observations of EC, although its effect was negligible for the other variables being monitored. The daily averages derived from the 1/sec observations were almost the same as those derived from the 1/hour observations. However, there were differences in the results for the daily observations when measured at noon and midnight. Site-specific maintenance operations correlated with pressure change, and fluid temperature decreased with increased precipitation. These results suggested that the onsen monitoring device can be constructed with the sensors used in this study, except for EC. In addition, a sampling rate of one measurement per hour, along with information about regional phenomena, are needed for the accurate evaluation of the onsen quality.