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年度	110	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	1,657,500元
執行期間	2021/1/1 至 2022/12/31
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，本計畫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，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。本年度針對場址內的第一含水層與第一滯水層進行試驗，試驗結果顯示，單井的加熱試驗配合解析解的流速推估，深度17~19公尺與37~40公尺為流速相對較快的區域，深度19~35公尺則為流速相對較低的區域，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0.5公尺。跨孔的熱示蹤劑試驗搭配熱傳輸解析解分析結果顯示，第一含水層之流向結果約為東北往西南向，流向在不同季節下變化不大，與文獻報告之大致流向相符，透過跨孔試驗，地下水流向可以明確地予以描繪。透過地下水熱-水耦合數值模式模擬與率定，，推估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，且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。透過自製研發的高精度纏繞光纖在現地試驗結果，纏繞方式在短距離內大量增加光纖量測點，大幅度提高溫度資料在空間上的解析度，由原來的25公分提升至1.05公分，高解析度資料詳細記錄了地層中細微的溫度變化，有助於解析微尺度的水文地質資訊。藉由自製研發之temperature vector DTS（TV-DTS）實驗室測試與熱傳輸解析解模擬結果，當流體具有顯著性的流動時，TV-DTS確實能應用於單井的地下水流向測定。本研究後續工作將著重於利用自製研發的「高精度纏繞光纖」及「TV-DTS」，進一步提升光纖溫度感測器在空間上之解析度，解析關鍵細部地質構造，並同時獲得單井的高解析度連續性地下水流向與流速。此外，第二年度亦將針對試驗模場之深部含水層，進行地下水流速與流向之測定，進而推算其水文地質資訊。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，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 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 17~19 m and 37~40 m while lower velocities located at the depths of 19~35 m. The permeable/impermeable zones can be clearly identified and the associated spatial resolution can reach to 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 obtained high resolution of temperature improved from 25 cm to 1.05 cm can be used for further analysis of the hydrogeological information in small scales. Based on the tests of temperature vector-DTS (TV-DTS) in the laboratory and the analytical solution, the results show that TV-DTS has the capability to detect the groundwater flow direction in a single well. The future work will focus on the optimization of high resolution of wrapped DTS design and the implementation of TV-DTS at the field to further accurately estimate groundwater flow velocities and directions by just using a single well. Furthermore, the field experiments will also be conducted in the deeper aquifer to estimate the velocities and directions to further obtain the hydrogeological information next year. 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.