Geochemical monitoring of hot springs surrounding the Matsunoyama binary power plant

Abstract

Binary power generation test using about 97 °C hot spring fluid is progressing at the Matsunoyama geopressured hot spring field in Niigata Prefecture characterized by about 9,000 mg/l Cl and high methane concentration. At Matsunoyama, the geochemical monitoring was carried out at Takanoyu#3 well used for the binary system and the surrounding hot spring wells from October 2010. The flow rate of Well-3 was almost constant in spite of the change of flow rate used for binary test of Takanoyu#3 well. The coefficients of variation of pH, EC, temperature and chemical concentrations were from 0.01 to 0.06 until February 2014. But the coefficients of variation of HCO3 concentration, Si concentration at Takanoyu#3 and Ca concentration at Well-3 were more than 0.1. The main reason of variation was the Nagano North Earthquake (2011) occurred at 12 March, 2011 near Matsunoyama hot spring field. At Well-3, the Ca concentration increased from 100 to 200 mg/l and the HCO3 concentration decreased from 320 to 240 mg/l at the time of this earthquake. At Well-1, Na and Cl concentrations were stable during 70 years.