But what filling material to use so that a decision could later be taken about their future?
They might later be put back in commission, taken out of the ground or simply left in the ground permanently out of use but safe.
The answer came from Gilbarco who arranged for Grouting Plus Solutions to fill the tanks with Bacel Hardfoam. This is a product relatively new to Australia, but widely used in the UK and Northern Europe for this purpose.
In eight hours all the tanks were filled. The Bacel was 'foamed' on-site mixing air, water and enviro-friendly Bacel amino-plastic resin. This white foam pours like shaving creme, so it can be pumped a long way for difficult access sites.
It was a quick and easy operation to connect to the fill pipes of the tanks and pump them full of foam while the air escaped up the vent pipes. The Bacel foam rapidly absorbs any residual hydrocarbons, making the tank safe.
After 24 hours the Bacel sets into a rigid foam, hence the name "Hardfoam".
Sometimes immediate removal of a tank from the ground would cause major disruption. Sometimes it is best not to make decisions about the future when a tank is first abandoned.
But, if a Bacel-filled tank is to be taken out of the ground at a future date, it's easy. The Bacel Hardfoam is so light that it makes only a very small weight difference.
And the Bacel-filled tank is safe to be cut up because residual hydrocarbons are absorbed into the Bacel.
If a tank remains in the ground, it will be permanently safe thanks to the Bacel fill.
Another option is to re-commission a tank. If that eventuates, it's no problem: the Bacel can be removed by simply dissolving it with steam.