A mine site in care and maintenance for several years had an onsite tank farm comprising four 2 million litre tanks containing 98% sulphuric acid.
Over time, a slight weep of acid from a tank’s nozzle flange leaked about 250 L of sulphuric acid into the concrete secondary containment bund. The bund sump dissolved, leaking acid into the underlying soil. The soil reacted with the acid and expanded, with an increase in the ground level of up to 500 mm, severely damaging parts of the bund and its walls, and the pipework foundations.
The bund wall was repaired, and damaged areas of the bund floor sealed with limestone. The pipework between tanks was interconnected to allow acid to be diverted between tanks in an emergency. The frequency of facility inspections was increased.
However, hidden damage to the storage tank was revealed about 11 months later when the tank floor apparently split from the wall and there were leaks from the structure’s ring beam. About 3,000 L of sulphuric acid was released in the second spill and contained in the bund. The spill was neutralised using limestone, and the reaction product (gypsum) removed and disposed of.