雙井循環流場追蹤劑試驗常被用來推估現地含水層縱向延散係數，其基本假設為觀測井的濃度穿透曲線不受側向延散影響，可是在實際狀況下當溶質進入雙井循環流場後會同時受到縱向及側向延散的影響，進而兩者同時影響觀測井觀測的濃度穿透曲線，因此縱向延散係數應該無法唯一決定。本研究的目的探討側向延散作用對雙井循環示?劑試驗濃度穿透曲線之影響，並觀察在何種情況下可忽略側向延散度，唯一決定延散係數。研究中使用FEMWATER模擬雙井循環流場示?劑溶質傳輸，探討不同井距與縱、側向延散度對濃度穿透曲線的影響，為求準確，利用流線跟勢能線建立網格，其優勢為可降低數值延散上的誤差，讓結果較為精準。其結果顯示各濃度穿透曲線的峰值與峰值之間明顯間距，說明側向延散對濃度穿透曲線有相當顯著的影響，縱向延散不可為一決定。 Dipole flow tracer test have been proposed as an in situ method to determine the longitudinal dispersivity. The embedding assumption is that the breakthrough curve is not affected by transverse dispersion. However the tracer must undergo longitudinal dispersion and transverse dispersion process before it enters the extraction well, thus transverse dispersion certainly influences the BTCs in extraction well. The purpose of this study is to investigate how the transverse dispersion affects the BTCs during a dipole flow tracer test and examine the applicable condition of a dipole flow tracer test in determining the longitudinal dispersivity. In order to promote the accuracy of simulation streamline and equipotential line based grids and in this study FEMWATER is used to simulate the solute transport in a dipole flow fields, and to investigate how the breakthrough curves for different well spacing and transverse dispersivity on BTCs under different well spacing and longitudinal - transverse dispersion coefficient. Simulation results demonstrate that the transverse dispersion exerts significant effects on the BTCs in the extraction well in a large longitudinal dispersivity. The selection of operational parameters including distance, well spacing distances into well has significant influme on the applying condition of a dipole flow tracer test for determining the longitudinal dispersivity. It suggests that longitudinal dispersivity cannot be solely determined by analysis of the BTCs, simply because the BTCs are simultaneously affected by both the longitudinal and transverse dispersions. One should note that the a dipole flow tracer test can only be applied to evaluate the longitudinal dispersivity in an aquifer with a small longitudinal dispersivity.
