It was the first time that single well injection and withdrawal(SWIW) tracer tests were conducted in a low temperature Enhanced Geothermal System (EGS) well in Taiwan in an attempt to identify the tracers that can react well within the fractures of metamorphic rocks. Various tracers including Naphthalene Disulfonates, Safranin O, and Amino Family were first tested in the laboratory and then in the field. In the laboratory, 2,6-nds was found to behave conservatively on slate samples taken from the Yilan geothermal field, whereas Amino G and Amino C were found to adsorb reversibly (R-f = 1.39 and 1.10) at 90 degrees C and could serve as suitable tracers. Three types of breakthrough curves were found, suggesting a significant and extensive in situ groundwater flow exists at a depth of 1500 m.
