The Use of Sodium Bromide as the Tracer to Identify the Regional Groundwater Flow Path in the Tatun Volcano Group(TVG), Taiwan

Abstract:

In order to identify regional flow path, the inter-well natural-gradient tracer tests were conducted in the south and north of Cising Mountain, respectively. Tracer breakthrough curves observed from north and south indicate different transport mechanisms may be involved in regional groundwater flow. It took 286 hours for tracer to transport through 860m arriving at Well-17 in the south while 9 hours for tracer to flow through 690m to arrive at Well-30 in the north. Based on single fracture model and borehole geological properties a, we suggest that the groundwater transport is mainly controlled by the formation fractures in the south Cising Mountain with velocity of 0.083 cms while the groundwater in the north region is dominated to flow along the boundaries of different layers of lava flow with velocity of 2.12 cms. Integrated the hydrogen and oxygen isotope compositions with tracer tests, we concluded that the major groundwater recharge to the south Cising Mountain region comes from the Caigongkeng Mountain. On the other hand, the groundwater recharge for the north Cising Mountain region primary comes from the Eastern Cising Mountain with minor contribution from the Caigongkeng Mountain.