Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, School of Environmental studies, China University of Geosciences, Wuhan, 430074, Hubei, People's Republic of China.
Ground Water. 2023 Jul-Aug;61(4):532-543. doi: 10.1111/gwat.13269. Epub 2022 Oct 27.
As a special single-well test with dual-screened configuration, dipole flow test with a tracer (DFTT) has been an efficient tool for aquifer parameter interpretation. The tool is excellent for characterizing the vertical distribution of hydraulic conductivity, dispersivity and in situ reaction rate in aquifers. It is noteworthy that the effects of skin and ambient groundwater flow (AGF) on the solute transport, which have been widely investigated in terms of conventional tracer tests, have not been comprehensively studied with respect to DFTT. Meanwhile, it is important to elucidate the potentials of DFTT in identifying the primary skin properties as well as the methods to avoid the AGF effects on DFTT. Consequently, we developed a mathematical model for DFTT accounting for skin and AGF. The results show that a negative skin acts as a preferential pathway for tracer transport and the AGF effects on breakthrough curves (BTCs) can be easily mistaken for reaction. Through extensive mathematical model-based experiments, the BTCs calculated from the DFTT models with skin effects were categorized into four types, each of which is able to imply a specific kind of skin. Additionally, a new dimensionless parameter , composed of injection/extraction rate, hydraulic conductivity, hydraulic gradient of AGF and screen parameters, was defined to quantitatively indicate the AGF effects on the overestimation degree of the in situ first-order reaction, implying that one can adjust the field parameters of DFTT to keep less than 3.7% to achieve an overestimation error of reaction rate below 50%.
作为一种具有双屏蔽配置的特殊单井测试，偶极流测试带示踪剂（DFTT）一直是含水层参数解释的有效工具。该工具非常适合描述含水层中水力传导率、弥散度和原地反应速率的垂直分布。值得注意的是，在传统示踪剂测试中广泛研究了表皮和环境地下水流动（AGF）对溶质运移的影响，但尚未针对 DFTT 进行全面研究。同时，阐明 DFTT 识别主要表皮特性的潜力以及避免 AGF 对 DFTT 影响的方法也很重要。因此，我们开发了一个考虑表皮和 AGF 的 DFTT 数学模型。结果表明，负表皮作用于示踪剂运移的优势路径，并且 AGF 对突破曲线（BTC）的影响很容易被误认为是反应。通过广泛的基于数学模型的实验，从考虑表皮效应的 DFTT 模型计算出的 BTC 被分为四种类型，每种类型都能够暗示一种特定的表皮。此外，定义了一个新的无量纲参数 ，它由注入/提取速率、水力传导率、AGF 的水力梯度和屏蔽参数组成，用于定量表示 AGF 对原地一级反应高估程度的影响，这意味着可以调整 DFTT 的现场参数，使 小于 3.7%，以实现反应速率的高估误差低于 50%。
