|t. F. Jenkins 



Continuous 



Monitoring 



of Total Dissolved Gases, 



a Feasibility Study 



ABSTRACT 



A preliminary investigation was undertaken to determine if a 

 continuous analyzer could be configured to monitor dissolved 

 gases in natural waters. A three-component system was designed 

 consisting of a pumping system, a continuous stripper, and a 

 detector. Prototypes of the first two components were assembled 

 and evaluated under field conditions. Based upon these results, 

 it is possible to configure an unattended, near-continuous 

 monitor to measure total dissolved gas concentration in natural 

 waters. 



The symptoms of gas bubble disease were first 

 observed in fish by Gorham (1901) at Woods Hole, 

 Massachusetts. These symptoms include the forma- 

 tion of gas bubbles in the blood vessels, behind the 

 eyes, and in the fins. Death can be caused directly 

 by gas blockages within the circulatory system or 

 indirectly by blindness or infections that enter the 

 system through associated breaks in the skin. 



In a later paper, Marsh and Gorham (1905) 

 explored the cause of this disease and associated it 

 with supersaturated levels of dissolved gases in the 

 aquaria waters. Gas bubbles occurring in diseased 

 fish were found to contain primarily nitrogen. They 

 concluded that supersaturated levels of nitrogen 

 gas were primarily responsible for the development 

 of the aforementioned symptoms. Subsequent 

 research has generally substantiated their conclu- 

 sions. Under certain unusual circumstances, how- 

 ever, an extremely high level of oxygen (Plehn, 

 1924; Woodbury, 1941) is also capable of producing 

 these effects. It is the common view today that, 

 while nitrogen is undoubtedly the major contributor 

 to this problem, its effect will be felt only when both 

 it and the total gas concentration* are in 

 supersaturation. 



Recently the Environmental Protection Agency 

 has published its proposed water quality guidelines 

 (Vol. 1, 1973). The proposed maximum acceptable 

 value for dissolved gas pressure is 110% of existing 

 atmospheric pressure. While this value will be dis- 

 cussed and may be changed, EPA's concern in this 



area is clear. The Army Corps of Engineers' recent 

 water quality directive will require all districts to 

 maintain adequate surveillance on all pertinent 

 water quality parameters. This will undoubtedly 

 apply to dissolved gas levels in the Pacific North- 

 west where potential problems have already been 

 identified. 



The three state-of-the-art methods currently 

 used to measure dissolved gases are: the Van Slyke 

 method, gas chromatography using a Swinnerton 

 stripping chamber (Swinnerton, 1962), and the 

 saturometer. The Van Slyke method is a well-known 

 technique in which water samples are introduced, 

 the dissolved gases liberated by a combination of 

 chemical and physical means, and the pressure 

 change measured with a manometer. From the 

 combination of this pressure change and the known 

 volume of the system, a total dissolved gas concen- 

 tration can be calculated. Individual dissolved gases 

 can also be found by the addition of chemicals which 

 specifically remove individual components of the 

 released gas, thereby reducing the pressure. 



The gas chromatographic method involves the 

 use of a Swinnerton stripping chamber. A known 

 volume of water is injected into the chamber, a con- 

 tinuous supply of helium gas strips the dissolved 

 gases from the water, and the stripped gases are 

 directed onto a gas chromatographic column. The 

 column most frequently used is molecular sieve 5A, 

 which separates the individual components by molec- 

 ular size. Each component elutes individually from 

 the column and passes through a thermal conduc- 

 tivity detector whose output is recorded on a strip 

 chart recorder. The area under each peak on the 



Jenkins: Earth Sciences Branch, Research Division, Cold Regions 

 Research Engineering Laboratory, U.S. Army Corps of Engi- 

 neers, Hanover, New Hampshire. 



♦Because of the equilibrium solubility of atmospheric gases, 

 total gas concentration may be closely approximated by con- 

 sidering only nitrogen and oxygen. 



707 



