How Much Soil Comes Out of a Septic or Treatment Plant Dig — and What Happens to It?
(And why you usually don’t need to pay extra to truck it away)
If you’re having a septic tank or wastewater treatment plant installed, you might be wondering — how much soil actually comes out of the ground during the dig, and what happens to all of it?
We get asked this a lot, especially by people building on rural or semi-rural blocks around Bass Coast and South Gippsland. The good news? In most cases, you won’t need to worry about extra soil removal costs — because with the right planning, we can usually rework and spread the soil on-site.
Let’s break it down.
A typical treatment plant hole might be around:
2.5m (L) x 2.5m (W) x 2.0m (D)
That equals 12.5 cubic metres of compacted soil being dug out.
But here’s the catch — soil “fluffs up” when it’s excavated. It expands in volume because it's no longer compacted. This is called bulking, and it can increase the volume by 1.6 to 3 times, depending on the type of soil and how dry it is.
So, using that example:
12.5m³ of soil dug out
Bulked volume = 20 to 37.5m³ of loose soil
That’s a decent pile of dirt — and that’s not including the extra spoil from pipe trenches, soakage trenches, irrigation areas, or stormwater drainage work that often happens during the same job.
So where does all the soil go?
That’s where experience comes in. Our crew is skilled at managing site levels and spreading out soil so it disappears neatly into the landscape. We’ll work with the natural fall of the land, create gentle grades, and lose the excess spoil in gardens, embankments or other low-lying areas — all without leaving big mounds or mess behind.
In most cases, we can zero out the dig completely. That means you won’t need a truck to cart it away, which can save a fair bit on your overall install costs.
Of course, removal is always an option
If your site is tight, fully landscaped, or you're after a very clean finish, we can organise off-site removal of excess spoil. It’s not a problem — but it’s an added cost, and most clients prefer to reuse what’s already there if we can.
Need a treatment plant installed without the headache?
We’re locals who know the land, the regulations, and how to make a big job feel seamless. We’ll handle the dig, the install, and the clean-up — and make sure the finished site looks just as good as it works.
Inverloch based plumbing company, servicing all aspects of plumbing and 24-hour emergency works in the Bass Coast and South Gippsland.
📞 - 0488 253 663
📧 - admin@alldoneplumbing.com.au
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