Document Detail

In-well degassing issues for measurements of dissolved gases in groundwater.
MedLine Citation:
PMID:  20456503     Owner:  NLM     Status:  In-Data-Review    
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.
J W Roy; M C Ryan
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Ground water     Volume:  48     ISSN:  1745-6584     ISO Abbreviation:  Ground Water     Publication Date:    2010 Nov-Dec
Date Detail:
Created Date:  2010-11-05     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882886     Medline TA:  Ground Water     Country:  United States    
Other Details:
Languages:  eng     Pagination:  869-77     Citation Subset:  IM    
Copyright Information:
Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.
National Water Research Institute, Environment Canada, Burlington, Ontario, Canada.
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