Johnson Richard L, Simon Michelle A
Oregon Health and Science University, Department of Environmental and Biomolecular Systems, 20000 NW Walker Road, Beaverton, OR 97006, USA.
J Contam Hydrol. 2007 Aug 15;93(1-4):188-202. doi: 10.1016/j.jconhyd.2007.02.003. Epub 2007 Mar 6.
Dual-screened groundwater circulation wells (GCWs) can be used to remove contaminant mass and to mix reagents in situ. GCWs are so named because they force water in a circular pattern between injection and extraction screens. The radial extent, flux and direction of the effective flow of this circulation cell are difficult to measure or predict. The objective of this study is to develop a robust protocol for assessing GCW performance. To accomplish this, groundwater flow patterns surrounding a GCW are assessed using a suite of tools and data, including: hydraulic head, in situ flow velocity, measured hydraulic conductivity data from core samples, chemical tracer tests, contaminant distribution data, and numerical flow and transport models. The hydraulic head data show patterns that are consistent with pumping on a dual-screened well, however, many of the observed changes are smaller than expected. In situ thermal perturbation flow sensors successfully measured horizontal flow, but vertical flow could not be determined with sufficient accuracy to be useful in mapping flow patterns. Two types of chemical tracer tests were utilized at the site and showed that much of the flow occurs within a few meters of the GCW. Flow patterns were also assessed based on changes in contaminant (trichloroethylene, TCE) concentrations over time. The TCE data clearly showed treated water moving away from the GCW at shallow and intermediate depths, but the circulation of that water back to the well, except very close to the well, was less clear. Detailed vertical and horizontal hydraulic conductivities were measured on 0.3 m-long sections from a continuous core from the GCW installation borehole. The measured vertical and horizontal hydraulic conductivity data were used to construct numerical flow and transport models, the results of which were compared to the head, velocity and concentration data. Taken together, the field data and modeling present a fairly consistent picture of flow and transport around the GCW. However, the time and expense associated with conducting all of those tests would be prohibitive for most sites. As a consequence, a sequential protocol for GCW characterization is presented here in which the number of tools used can be adjusted to meet the needs of individual sites. While not perfect, we believe that this approach represents the most efficient means for evaluating GCW performance.
双筛地下水循环井（GCW）可用于去除污染物总量并原位混合试剂。GCW之所以这样命名，是因为它们促使水在注入筛管和提取筛管之间以循环模式流动。这个循环单元有效水流的径向范围、通量和方向很难测量或预测。本研究的目的是制定一个可靠的方案来评估GCW的性能。为实现这一目标，使用一系列工具和数据评估GCW周围的地下水流型，包括：水头、原位流速、岩芯样本测得的水力传导率数据、化学示踪剂测试、污染物分布数据以及数值水流和运移模型。水头数据显示出与双筛井抽水一致的模式，然而，许多观测到的变化比预期的要小。原位热扰动流量传感器成功测量了水平水流，但垂直水流的测量精度不足以用于绘制流型图。该场地采用了两种化学示踪剂测试，结果表明大部分水流发生在GCW周围几米范围内。还根据污染物（三氯乙烯，TCE）浓度随时间的变化评估了流型。TCE数据清楚地表明，处理后的水在浅层和中间深度从GCW流出，但除了非常靠近井的地方，这些水回流到井中的情况不太清楚。从GCW安装钻孔的连续岩芯上截取0.3米长的岩芯段，测量其详细的垂直和水平水力传导率。测得的垂直和水平水力传导率数据用于构建数值水流和运移模型，并将其结果与水头、流速和浓度数据进行比较。综合来看，现场数据和模型对GCW周围的水流和运移情况呈现出相当一致的描述。然而，进行所有这些测试所需的时间和费用对大多数场地来说是令人望而却步的。因此，本文提出了一种GCW特性描述的顺序方案，其中使用的工具数量可以根据各个场地的需求进行调整。虽然并不完美，但我们认为这种方法是评估GCW性能的最有效手段。
