| 摘要: | 水文地質調查提供污染場址地下水流速、流向、流量資料及水文地質特性， 對後續的污染調查、監測及整治有莫大的裨益。傳統的水文地質特徵調查技術抽 水實驗(pumping test)因抽出水處置問題並不十分適用於污染場址，微水實驗(slug test)則因實驗方法限制不易求得完整的水文地質參數。相較之下，單井循環流實 驗方法較適合污染場址水文地質調查。雙極水流實驗(dipole flow test, DFT)為近 年發展的一種單井循環流實驗。DFT 在井中用氣囊將井篩段分為上、下兩段， 上井篩段用幫浦抽水而下井篩段釋出抽入水，在含水層中造成循環流場因而沒有 抽出水處置問題，而且理論上可用於推估水平方向水力傳導數、垂直方向水力傳 導數、及比儲水係數。但實作顯示DFT 在不同之水文地質情況下，均會在短時 間內達到穩態，不利於推估垂直方向的水力導數及比儲水係數。針對此缺點，本 研究發展定水頭循環流水力實驗(constant head circulation flow test, CHCFT)，在上 井篩段利用定水頭注水方法維持固定負水頭(洩降)，下井篩段利用定洩降抽水維 持固定正水頭，產生長期暫態循環流場，可同時推估水平方向水力傳導數、垂直 方向水力傳導數、及比儲水係數。然而，目前所能使用的定洩降抽水方法無法將 井中洩降固定於地表下8 至45 公尺間，使得CHCFT 的應用範圍隨著受到限制。 因此我們將CHCFT 中定洩降抽水部份，置換為容易執行且無洩降限制的定流率 抽水，成為另一個單井循環流實驗模式: 定流率-定洩降循環流水力實驗(constant rate – constant head circulation flow test, QHCFT)。由於QHCFT 上、下井篩段中各 自所維持的水力實驗狀態不同，因此可以產生長期暫態循環流場，可同時推估水 平方向水力傳導數、垂直方向水力傳導數、及比儲水係數。本研究同時發展 CHCFT 及QHCFT 於受壓及非受壓兩種含水層形態下考慮正薄壁效應的理論， 並利用標準曲線分析方法(type curve analysis)以假想值資料(hypothetical data)演 練參數推估過程，發現當實驗井周圍存在薄壁，但其忽略其影響直接進行參數推 估時，可能會得到過小的垂直方向水力傳導係數及比儲水係數。 Single-well tests are less expensive than multiple well tests in hydrogeologic investigation. Single-well tests also withdraw limited amount of water and hence are suitable for contamination sites. The dipole flow test (DFT) is a single-well circulation flow test (CFT), which generates a circulation flow field in the aquifer by pumping water in the upper well screen section using a constant flow rate +Q and discharging the pumped water through the lower well screen section in -Q. In theory, DFT is able to estimate the horizontal hydraulic conductivity (Kr), the vertical hydraulic conductivity (Kz), and the storage coefficient (S).However, field experiments of DFT under different hydorgeological conditions showed that DFTs reached steady state rapidly, unfavorable for the estimation of Kz and S. This study improves the design of DFT, and develops the constant head circulation flow test (CHCFT), which generates a circulation flow field in the aquifer by pumping water in the upper well screen section using a positive constant head and discharging water through the lower well screen section using a constant negative head (drawdown). This constant-head condition renders CHCFT to reach steady state after a long period time, during which Kr, Kz, and S can be determined without difficulty. However, current constant drawdown pumping techniques can not discharge water continuously with a constant water level between 8 to 45 meters below ground surface, and makes the application of CHCFT limited. Hence we replace the constant drawdown pumping in CHCFT with a constant rate pumping which has less limitation on the drawdown level and develop another CFT model: constant rate – constant head circulation flow test (QHCFT). Due to two different pumping techniques are applied in two different screen sections, QHSCT reaches steady state after a long period as CHCFT, and Kr, Kz, and S can be determined without difficulty. When developing CHCFT and QHSCT, both confined and unconfined condition with skin effect are considered, and the type curve analysis is tested with hypothetical data for the determination of skin factor (Sk), Kr, Kz, and S. It is found if skin exists but its effect is neglected will result in a false determination of Kz and S. |
