Investigating the Geothermal Signature of the Kaimai Tunnel, New Zealand

Abstract

The Kaimai Tunnel passes through the Kaimai Ranges in the North Island, which mark the boundary between the Waikato and the Bay of Plenty Regions. The existence of the hot springs in the tunnel has been known for some time, but these springs have not been sampled or studied before. The objectives of this study is to sample the springs and determine the natural setting of the Kaimai tunnel springs and assess the type of geothermal system.
Six water samples from seepages in the tunnel have been analyzed for the water chemistry, and the results used to classify the water source, characteristic and geothermometry. In addition, the Cl-B-HCO3 diagram applied in this method can distinguish the water source from different aquifers. Results indicate that the springs have the same shallow groundwater source. The water is shown to be immature water, that has not reached equilibrium. There is no indication that the springs come directly from a deep reservoir.
The springs in Kaimai Tunnel are interpreted not to be related to geothermal activity, their slightly elevated temperatures are related to the natural temperature gradient inside the tunnel.