Use of Smoke Testing in the Establishment of Cave to
Surface
Connections
Being involved in our municipal utility
district, I've had a chance to see several technologies used in the maintenance
and repair of our water and sewer system here in Spring, Texas (outside
Houston). One of the technologies we use
in the maintenance and repair of our sewers is smoke testing. We place
non-toxic smoke in our sewer systems to periodically check for connections with
the surface. Over time, the Houston area
soils shift, and crack open, occasionally cracking a sewer pipe and will allow
storm water to enter into the sewer system. This is not a good thing, as the
cost of treating the sewer effluent is based on volume, and if storm water
enters the system, our cost to treat the effluent rises as this artificial
source of water enters the system. Smoke
testing is an efficient and cost effective way of finding those connections
between the sewer and the surface. Smoke
can rise out of cracks that originate in pipes that are buried up to 30 feet
deep.
The idea occurred to me that I could use
these canisters to help locate surface connections with cave passageways too
small to enter. So, I purchased several small canisters and went to Steve
Wilson’s farm in Virginia to try out the smoke testing idea. Steve has a small, 75' long cave, which is
an enlarged joint. He thought it might
go through the hillside, but he could never find the opening on the other
side...so off we went...luckily air was blowing into the cave, so the smoke
would readily enter the cave. I sent off
the canisters while Steve looked for the smoke at the surface....after a couple
of minutes, smoke came out of a small "rabbit hole" about 50' away
from the end of the known cave...this was no major discovery, but it did
indicate that the technique had merit.
Several tips:
Don't try and test a whole cave
system. While the smoke is non-toxic, it
can be irritating. Pick out a lead in a
cave- one passage- to start with.
Only do on days when air is entering the
cave. You'll be wasting your money if the smoke is blown out of the known
entrance.
Estimate the volume of smoke you need. You
do need to have an idea of the volume to fill the void you are
investigating. The canisters are sized
to produce a certain volume of smoke (i.e., 10,000 cu. ft, 100,000 cu. ft,
etc.). It is best to put in too much rather than not enough, so error on the
side of putting in plenty of smoke.
Once you have purchased the canister(s),
use them: they degrade quickly with moisture and become unusable in 1-2 years.
Have plenty of people at the surface that
can look for the smoke. Smoke will
appear in places you don't expect, so be prepared.
Don't do after a rain. The soil needs to be dry to allow the smoke
to rise through soil cracks.
Fall and winter is best, when some of the
leaves have fallen enough to allow for better visibility of the smoke.
Don't do on a foggy or windy day or you
may never see anything or get confused at what you are seeing.
Have survey markers available for your
spotters, so they can mark the location of the smoke.
Most local utility districts have
operators who can supply you contacts or sources for the smoke canisters.
Let me and others know if you have success
or failure using this technique.
Good Hunting!
Morris Hall
Example of
Smoke Test in Sewer 