本研究結合示蹤劑實驗結果、地下水氫氧同位素分佈以及地下水水位變化建立大屯火山群淺層地下水傳輸模式。本研究自2012年7月起採集大屯火山群地區10口溫泉監測井之地下水樣本並分析其穩定氫氧同位素以及量測其地下水水位；另於七星山南麓及北麓兩地以溴化鈉(Sodium Bromide)作為示蹤劑各進行一次自然水力梯度雙井實驗。根據研究結果顯示，七星山北兩麓地區的地下水穩定氫氧同位素分布明顯重於七星山南麓，顯示兩地的水體來源不同。而由地下水水位變化幅度及趨勢也顯示兩地的水文行為有所不同。從示蹤劑實驗所獲得之穿透曲線(Breakthrough Curve)顯示七星山南北兩麓地區的淺層地下水傳輸由不同的機制所控制；七星山南麓地區的穿透曲線出現明顯的拖尾行為(tailing)，顯示地下水傳輸機制除了平流作用之外也包含了延散作用，而北麓地區的穿透曲線則呈現典型以平流作用為主要傳輸機制。根據地形及地質特性推測七星山南麓的地下水傳輸途徑以較為破碎的岩層中的裂隙為主，而七星山北麓地區的地下水則為不同期的熔岩流交界裂隙作為傳輸途徑。另外，將示蹤劑實驗結果與穩定氫氧同位素分布趨勢結合後，推測七星山南麓地下水體主要補注源為小觀音山，部分補注源為七星山。而七星山北麓地下水主要補注源則為七星山東側，部分補注源為七星山主峰及小觀音山。
The purpose of this study is to understand the shallow groundwater transport mechanism of the Tatun volcano group, by integrating tracer test, hydrogen and oxygen isotope composition of groundwater and groundwater level variations. This study started in July 2012. Two-well sodium bromide tracer tests carried out under the natural gradient in the south and north of Cising Mountain. The difference of hydrogen and oxygen isotope composition of groundwater between south of and north of Cising Mountain indicates that groundwater comes from different sources. The tracer breakthrough curves also indicate different transport mechanisms of groundwater dominated in the south of Cising Mountain, advection and mechanical dispersion, and advection in the north. Based on in-situ topography and geology properties, we suggest that advection and mechanical dispersion in the south Cising Mountain exist in the fracture of formation while advection to the north takes place in the boundaries of different layers of lava flow. Combination of the distribution of hydrogen and oxygen isotope composition in groundwater and tracer tests, we hypothesize that the major groundwater recharge source of the south Cising Mountain is the Caigongkeng Mountain with part of water from the Cising Mountain itself. The major groundwater recharge source of the north Cising Mountain is the Eastern Cising Mountain, and minor part from the Caigongkeng Mountain.
