Tracer test for evaluating the shallow groundwater flow in a volcanic area, Taiwan

A tracer test, involving conservative and reactive, was conducted in a volcanic area in Northern Taiwan to evaluate shallow groundwater characteristics. The distance between injection Well #14 and monitoring Wells #2 and #6 are 236 and 682 m, respectively.  A breakthrough curve was received from both wells for conservative tracer, 2,6NDS, while the reactive one was obtained only at Well#6 indicating the existence of heterogeneity in groundwater and fracture distribution in the region.  A much fast flow between Well#14 and #6 was found as the first peak arrives at the same time with a 3 times difference in distance.  This result matches the local orientation of the formation and may show strong geology control groundwater flow of the region resulting in a preferential flow. However, a chaser influence was identified by an irregularity of breakthrough curves for both wells.