Completed November 2023. Arenco brought Perfect Contracting in to remove old underground storage tanks from a site near Medlow Bath Station in the Blue Mountains, then clean up the ground they had been sitting in. We took it from start to finish: digging the tanks out, pumping and purging them, removing all five, digging out and carting away the contaminated soil, holding the pit open for validation, then backfilling and compacting it so the site was ready for the next stage.
From the street it looked like a fenced, grassed yard. The old fill points poking through the grass were the only sign of what was underneath.
Services delivered
- Digging out around the tanks and their old pipework with an excavator
- Pumping out the tanks by vacuum truck and purging them
- Soil samples dug with the excavator while the pump out was going on
- Gas testing on every tank, and a clearance from an independent occupational hygienist before each one came out
- All five steel tanks lifted out, loaded and sent to a metal recycler
- Contaminated soil dug out and carted away in separate loads, with the pit taken back into the sandstone and the sides benched
- The excavation held open until validation sampling cleared it
- Backfilled with road base in 300 mm layers, each layer compacted, and the site prepared for compaction testing
The challenge
Nobody had reliable drawings of what was in the ground. The only way to know how many tanks there were, how they were connected and what state the soil was in was to dig carefully and let each stage decide the next.
The site sits in a small Blue Mountains town right beside the highway. Access was down a narrow lane past neighbouring buildings, so every truck movement was planned, traffic controllers were used where needed, and the crew and trucks travelled up from Sydney for each shift.
The job also had to run in order. The pump out and purge came first, then gas testing and clearance, then removal, then soil, then validation, then backfill. No stage started until the one before it was signed off.
How the job was done
The crew started by digging down around the tanks with a 14 tonne excavator until the tank tops and old pipework were exposed. A vacuum truck pumped out and purged the tanks, and soil samples were dug while it was on site.
An independent occupational hygienist then gas tested each tank and cleared it for removal. The tanks were lifted out one at a time, loaded straight into trucks and skips and sent to a metal recycler.
Once the tanks were out, the contaminated soil was dug out and carted off site in separate loads, and the excavation was taken back into the sandstone with benched sides. The pit stayed open behind barriers until validation sampling cleared it. After that, road base went back in 300 mm layers, each compacted with a plate on the excavator, and the finished pad was trimmed and prepared for compaction testing.
Soil and environmental controls
- Tanks pumped out and purged before any lifting, so nothing was left in them
- Gas testing and a hygienist clearance on every tank before it moved
- Contaminated soil loaded out separately from clean material
- Stockpiles covered and dampened, with erosion and sediment controls on the site boundary
- Spill kit kept on site the whole time
- Tank steel recycled through a metal recycler
- Excavation left open and barricaded until validation, not backfilled over soil that had not been cleared
Safety
Old storage tanks are a hazard until they have been emptied, purged and tested. No tank moved until it had been pumped out and gas tested, and a hygienist had cleared it for removal. The pit was barricaded the whole time, excavations deeper than 1.5 metres were benched or battered, and services were checked through Before You Dig Australia before any digging started.
Overhead wiring near the work area and a narrow access lane meant the excavator and truck movements were planned before each shift, and the site was left secure at the end of every day.
Lessons learned on this job
Every job teaches the crew something. These are the ones we took from Medlow Bath, and we use them on every tank job.
What worked
- Pump out, purge and gas test first, every time. Nothing was lifted until a hygienist had cleared it
- Keeping contaminated soil separate from clean material right from the first bucket, so the loads were straightforward
- Holding the pit open until validation cleared it, then backfilling in 300 mm layers with compaction on each layer, so the pad was ready for testing
What was difficult
- No reliable drawings, so the tank count and layout only became clear as the digging went on
- A Blue Mountains site worked from Sydney, with trucks running up and down the highway and a narrow lane past neighbours to get in and out
- A job that had to run in order, where each stage needed a sign off before the next could start, so the programme had to allow for waiting time
Tank removal across NSW
Old underground tanks turn up on station precincts, depots, service stations and industrial sites all over NSW, and often the drawings are missing. Perfect Contracting does underground tank removal, site remediation, demolition, civil works and early works from its Marrickville yard, with our own excavators, trucks and supervisors, including regional sites like the Blue Mountains. For another tank job, see our underground tank job at Lidcombe. Our sister company Perfect Concrete Care was also working for Arenco in the same town, doing coring and cutting at Medlow Bath Station.
The outcome
All five tanks out and recycled, the contaminated soil gone, the excavation validated, backfilled and compacted. The site was handed back as a level, compacted pad ready for the next stage of works, in October and November 2023.
See more Perfect Contracting projects or contact our estimating team.
Perfect Contracting acknowledges the Aboriginal and Torres Strait Islander people as Traditional Custodians of the country on which we live and work. We pay our respects to the Traditional Custodians and Elders past, present and future, and honour their connection to the land and ongoing contribution to society.