National Water Research Institute, Environment Canada, Burlington, Ontario, Canada.
Ground Water. 2010 Nov-Dec;48(6):869-77. doi: 10.1111/j.1745-6584.2010.00703.x.
Measurement of dissolved gases in groundwater is becoming increasingly common and important. Many of these measurements involve monitoring or sampling within wells or from water pumped from wells. We used total dissolved gas pressure (TDGP) sensors placed in the screened section of various wells (4 to 72 m deep) to assess the dissolved gas conditions for open wells compared to the conditions when sealed (i.e., isolated from the atmosphere) with a hydraulic packer (one well) or when pumped. When the packer was installed (non-pumping conditions), TDGP rose from <1.7 to >3.1 atm (<172 to >314 kPa), with declines noted when the packer was removed or deflated. While pumping, TDGP measured in many of the wells rose to substantially higher levels, up to 4.0 atm (408 kPa) in one case. Thus, when groundwater is gas charged, the background aquifer TDGP, and likewise the dissolved gas concentrations, may be substantially higher than initially measured in open wells, indicating significant in-well degassing. This raises concerns about past and current methods of measuring the dissolved gases in groundwater. Additional procedures that may be required to obtain representative measurements from wells include (1) installing in-well hydraulic packers to seal the well, or (2) pumping to bring in fresh groundwater. However, observed transient decreased TDGPs during pumping, believed to result from gas bubble formation induced by drawdown in the well below a critical pressure (relative to TDGP), may disrupt the measurements made during or after pumping. Thus, monitoring TDGP while pumping gas-charged wells is recommended.
地下水溶解气体的测量正变得越来越普遍和重要。这些测量中有许多涉及到在井内进行监测或取样，或者从井中抽取的水样。我们使用放置在各种井（4 至 72 米深）筛管段的总溶解气体压力（TDGP）传感器，评估开井和密封（即与大气隔离，用液压封隔器密封一口井）或抽汲时的溶解气体状况。安装封隔器（非抽汲条件）时，TDGP 从<1.7 增至>3.1 大气压（<172 至>314 kPa），当封隔器被移除或放气时会出现下降。在抽汲时，许多井中的 TDGP 上升到更高的水平，在一个案例中达到了 4.0 大气压（408 kPa）。因此，当地下水充气时，背景含水层的 TDGP，以及溶解气体浓度，可能比开井初始测量时高得多，表明井内存在大量脱气。这就引起了对过去和当前地下水溶解气体测量方法的关注。为了从井中获得有代表性的测量结果，可能需要采取其他程序，包括（1）安装井内液压封隔器来密封井，或（2）抽汲以引入新鲜地下水。然而，在抽汲期间观察到的瞬态 TDGP 下降，据信是由于井内压力下降到临界压力（相对于 TDGP）以下导致气泡形成，这可能会干扰抽汲期间或之后进行的测量。因此，建议在抽汲充气井时监测 TDGP。
