Heath Consultants Optical Methane Detector (OM) - Manual (Page 47)

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D. Gas Pressure
Low-pressure gas systems generally will vent much more
slowly and poorly than higher pressure systems. High
soil moisture content can minimize the point that a sur-
vey in low-pressure areas is not practical. In most in-
stances, this is of a temporary nature and the survey can
be continued by moving to a high-pressure area in the
system. It is important that the technician know in what
pressure areas he will be working.
E. Snow Cover
The effect of snow cover on gas venting conditions is
related to the length of time it has been on the ground,
its moisture content and temperature variations. Newly
fallen snow with low moisture content is loosely com-
pacted and tends not to inhibit venting. As moisture
content increases, greater compaction occurs, which
tends to restrict venting. If the snow has high moisture
content, or rain has occurred since it fell, followed by
subfreezing conditions, venting may be considerably re-
duced. Disturbing the surface of the snow with the probe
will often release gas trapped in the snow.
F. Frozen Soil
The moisture content of the soil at the time it freezes
has a considerable effect on the venting conditions of
frozen ground.
The higher the moisture content, the less porous the fro-
zen ground is. However, as the ground freezes, it tends
to develop a well-defined system of cracks that will al-
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