Tanks A Lot: How to Decommission a Tank in Place
The Oregonian Monday, December 12, 1994
A lot of homeowners are scratching their heads about what to do about their
old underground heating oil tanks, expecially if they've switched to natural
gas. There are no laws that say you have to fill or remove an old residential
tank, unless you suspect it has leaked. Then the law says you should report
it to the Department of Environmental Quality for technical assistance with
an investigation or cleanup if one is required.
Still, some homeowners aren't taking any chances on having unanswered questions
about an underground tank botch a home sale or cause a future problem. they
are removing or decommissioning the abandoned tanks. Most people hire contractors
to follow these steps, and to document the process along the way with papers
and pictures to prove it's been done.
Decommissioning in place a 675-gallon underground tank might cost from $775
to $850; removing it might cost $1,000, estimates Barbara Reilly, owner of Residential
Tank Services.
Here are the recommended steps to decommission an old tank, from the DEQ:
1. Obtain the necessary permits.
2. Drain and flush all piping into the tank, being careful to avoid spilling.
3. Remove all liquid from the tank, even liquid requiring a hand pump to
remove. Remove any solids or sludge. Any material which cannot be recycled must
be disposed of in accordance with applicable federal and state laws.
4. Carefully dig down to the tank. If you decide to cut the tank, clear it
of all vapors first using dry ice or other approved safety procedures.
5. Remove the product lines, such as the gauge pipe, fill pipe and other
tank fixtures, up to the building foundation and cap.
6. Cap or remove any non-product lines, leaving the vent line open until
after the tank is purge of vapor during the inerting process.
7. Temporarily close off all other opening in the tank so that all vapors
can be vented through the vent line during the inerting process.
8. Fill the tank with a non-reactive solid material, such as
A. Concrete slurry mix: The preferred method. Add a wetting
agent to the mixed concrete to reduce separation of the water from the sand
and gravel.
B. Sand: Open the top of teh tank so that the tank can be filled
completely. Fill the tank to nearly full and wash sand into the tank with a
small amount of water puddled to cause the sand to flow to the tank ends. Avoid
using large amounts of water.
C. Sand and earth: Fill the tank with sand to nearly 80 percent
of its capacity and fill the remainder with a mixture of soil and water in a
free-flowing mud.
Fill the tank completely to prevent future collapse of the tank and any structure
above the tank. It may be necessary tocut the tank open to clean it and to ensure
that the fill material completely fills all areas of the tank.
9. Plug or cap all openings in the tank, including the vent line unless the
tank was opened when filling the tank with inert material.