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年度	111	專案性質	實驗性質
專案類別	模場試驗	研究主題	調查
申請機構	國立臺灣海洋大學	申請系所	地球科學研究所
專案主持人	邱永嘉	職等/職稱	副教授
專案中文名稱	加熱式光纖溫度感測器井下跨孔高解析度地下水流速與流向調查
中文關鍵字	地下水污染、熱示蹤劑、光纖溫度感測器、地下水流速、地下水流向
專案英文名稱	Estimation of Groundwater Flow Velocity and Direction by Cross-borehole Test with Heated Fiber-optic distributed Temperature Sensor
英文關鍵字	groundwater contamination, heat tracer, fiber-optic distributed temperature sensor, flow velocity, flow direction
執行金額	1,800,000元
執行期間	2022/3/28 至 2023/2/28
計畫中文摘要	傳統的水文地質調查方式，僅能針對大區域的環境進行試驗，在地下含水層極為複雜的情形下，由於現地資料空間解析度的不足，將導致水文地質狀況掌握不易，產生含水層透水區段及地下水流速、流向推估上的誤判。有鑑於此，本研究選定於苗栗縣頭份鎮的永貞宮地下水污染場址，以熱能為地下水流示蹤劑，搭配創新的分散式光纖溫度感測器（fiber-optic distributed temperature sensor, FO-DTS）量測方法，並以主動式加熱方式，搭配自製研發高解析度纏繞光纖及單井流向與流速測定儀（thermal vector DTS, TV-DTS），獲取空間與時間上的高解析度連續性量測資料，進行高精度的水文地質環境調查工作，判釋井下透水區段，並推估地下水流流向與流速。前一年度已針對場址內的淺部（第一含水層）進行試驗與分析，本年度將針對深部（第二含水層）進行試驗與分析，並將兩年度之整體成果彙整後進行綜合討論與分析。 單井流速分析結果顯示，深度17~19公尺、37~40公尺及42~52公尺為最為透水之地層；在深度23~28公尺則為最不透水區域；深度5~15公尺、19~35公尺及70~80 公尺周圍的地層相對較不透水。流速推估結果顯示，深度18~20公尺、35~40 公尺及40~52 公尺區間的較高流速分佈，最高流速達1.75-1.95 m/day；深度20~35公尺及53~90公尺區間則為低流速帶，最低流速為0.2-0.5 m/day，細微流速特徵（微小流速增加與降低）亦可清楚的顯示於分析結果中。將流速分佈比對文獻報告，其結果與地層岩性分佈一致，透水與不透水區段可清楚的於以判釋，流速在空間中垂直方向上的解析度高達0.25-0.5公尺。跨孔熱示蹤劑試驗分析結果顯示，在影響半徑範圍內的下游觀測井水溫，受到加熱井的影響有升溫現象。二維熱-水耦合數值模式模擬與率定顯示，第一含水層的水力傳導係數為2.5× 10−5 m/s、熱延散係數為 0.38m。根據參數敏感度分析結果得知，觀測井溫度變化受水平水力傳導係數影響較為顯著。高解析度纏繞光纖的現地試驗結果不僅與單井流速分析結果非常一致，同時提升解析度從原來的25cm至1.05cm，使得更細微的溫度變化均可被詳盡的描述。自製研發的TV-DTS經過實驗室的優化後成功的應用於現地環境，淺層含水層（深度8-10公尺）的地下水流向大致呈現由東北往西南方向流動，深層含水層（深度38-40公尺）的地下水流向則大致呈現由北往南方向流動，此結果與前人的調查結果十分吻合。 經由不同污染場址的試驗結果彙整之後，本研究團隊嘗試以主動式 DTS 調查技術，建立水文地質調查方法之標準作業流程，包括：光纖種類、光纖佈設方式、加熱時間、加熱功率、地質條件及限制、試驗流程及應用範圍等，提出參考建議。本研究計畫透過分散式光纖溫度感測器的量測優勢，可提供地下水污染場址一個高解析的井下水文地質調查方法，若能夠將此調查技術納入污染場址調查的關鍵技術之一，尤其是針對深層的含水層，更能夠發揮其技術優勢。冀望未來能對於土壤與地下水污染調查及整治帶來新的契機。
計畫英文摘要	When using conventional approaches to explore field hydrogeology, only a relatively large scale of data can be obtained. Due to the complexity of aquifers, the insufficient measured data in terms of space and time could cause the mis-interpretation of permeable zones and groundwater flow velocity and directions. This will lead to the challenge of comprehensively understanding hydrogeological conditions within the aquifers. In this study, the groundwater contaminated site located in Toufen city in Miaoli county is selected to demonstrate the fiber-optic distributed temperature sensor (FO-DTS) technique based on the heat tracer test. The field experiments of single-well heating tests and cross borehole heat tracer tests, accompanied with the self-developed high-resolution wrapped DTS and thermal vector DTS (TV-DTS, focus on the first aquifer and the first aquitard this year. The estimated for groundwater velocities based on the analytical solution of heating line source from the single-well heating test shows that the higher velocities located at the depths of 7-19 meters, 37-40 meters, and 42-52 meters, while lower velocities located at the depths of 18-20 meters, 35-40 meters, and 40-52 meters. The associated highest and lowest velocities were 1.75-1.95 and 0.2-0.5 m/day, respectively. The permeable/impermeable zones can be clearly identified and the associated spatial resolution can reach to 0.25 - 0.5 m. The cross-borehole heat tracer test with the numerical simulation shows that the hydraulic conductivity and the heat dispersivity is 2.5 × 10−5 m/s and 0.38 m, respectively. According to the sensitivity analysis, the temperature is more sensitive to the horizontal hydraulic conductivity. The results of wrapped DTS experiments shows that due to the observation points increasing, the resolution of temperature could be improved from 25 cm to 1.05 cm and the device can be used for further analysis of the hydrogeological information in small scales. After testing and optimizing TV-DTS in the laboratory, the results of field experiments show that TV-DTS has the capability to detect the groundwater flow direction and velocity simultaneously in a single well. The groundwater flow direction in the first aquifer (depth of 8-10 meters) is roughly from northeast to southwest, while the flow direction in the second aquifer (depth of 38-40 meters) is roughly from north to south, which is consistent with previous investigations. After comprehensive analysis of the results from different tested sites, the standard procedures and limintation of applying the active-DTS at the groundwater contaminated sites, including the fiber-optic cable selection, cable deployment, heating duration and power, geological conditions, and experimental procedures, were addressed. The results obtained in this study can provide an alternative to investigate hydrogeology in boreholes with the high-resolution. The application of this innovative technique will open a new window for the field investigation and provide a reference tool for the remediation strategy in groundwater contaminated sites.