Be careful. In the tank removal industry they use dry ice to displace the
volatiles within the tank. We usually break about 20 lbs. of dry ice into
pieces small enough to place down the 2" fill pipe. After sniffing no
hydrocarbons with a tester (usually 10-24 hours) we would excavate and
either remove the tank, or wash in place and then remove.

Be very careful with all tanks. There have been many instances of purged
tanks, at scrap yards, exploding and killing people months and years after
purging. The product is imbedded on the walls of the tank and evaporates
for a long, long time. e.g. tanks that are properly cleaned and safe can
become dangerous by letting them sit for a long time.

If you fill the tank, a weak concrete slurry is typical. I don't remember
from my engineering days what the porosity is for sand, but, rest assured
that uniformly graded sand is probably 20% voids and can hold volatile
hydrocarbons making them dangerous.

Ivan Vegvary
"davefr" wrote in message
...
I buried a 500 gallon gas tank in the late '70's for farm use. I used
it for about 10 years and then pumped it dry.

Complete removal is impractical since a small shed is built on top of
it and I don't want to demolish the shed.

I'd really like to cut the top off and fill it with rock or dirt so
it's decommisioned once and for all.

I checked with the state DEQ office and they told me 500 gallon tanks
are unregulated. My only obligation is to report a spill but this
tank never leaked since I quit using it very early in it's life.

I'm not too fond of the idea of using a cutting torch. Even though
it's totally dry there could still be fumes and I don't want to get
dead. For the same reason, I really don't want to use an angle
grinder.

I'm thinking sawsall or pneumatic chisel.

Anyone know how underground tanks are decomisioned? I'd like to
remove a 5' X 2' portion of it's top.

Is there a safe way to make 100% sure the tank is vented such as
injecting an inert gas that's heavier then gasoline fumes to drive
them out?

Other suggestions?