A multi-well tracer test for characterizing the preferential flow of the shallow aquifers in the Tatun Volcanic Area

A multi-well tracer test was conducted in a volcanic area where is mainly composed of sedimentary rocks units and tuff breccia with attitude of the N46E, 18S. in Northern Taiwan. The distance between the injection well #14 and monitoring wells #-2 and #6 are 236 and 682 m, respectively.

A Bimodal breakthrough curve was received from both wells indicating the existence of more than one channel in the system. Surprisingly, the first peak arrives simultaneously at both wells with almost a 3 times difference in distance. A much fast flow between Well #14 and #6 was found. 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. With the moment analysis, the difference in communication between the injection well and the two monitoring wells can be depicted by 50% of the flow circulation coming from 25% and 30% storage capacity for Well #2 and Well #6, respectively implying that groundwater flows through more fractures between Well #14 and 6.  An obvious tailing breakthrough curve of Well #6 also reflects more fractures than that of Well #2.