Ontario · Site evidence · 2026
Septic test holes: the two hours of digging your whole permit rests on
Every number in your septic design traces back to what you find in two or three holes in your yard. Dig them right, log them right, and the rest of the paperwork is arithmetic. Dig them wrong and everything built on them is wrong.
What a test hole is: a pit dug in the footprint of the future bed — typically 1.5 m deep or to refusal — that lets you (and the inspector) see the soil layers, find the water table or bedrock, and take the sample that sets your percolation time. Most authorities want it left OPEN for inspection.
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Homeowner’s Guide44 pp.
Costs, permits, contractor vetting, and the owner-builder path — updated for the 2026 Building Code.
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1 Something’s wrong2 What it costs3 The permit4 Who designs it5 The paperwork6 Approval
The part nobody tells you
Designers charge $800–$2,000 just for the paperwork in these quotes.
Ontario law lets you do that part yourself, on your own property. OntarioSepticDesigner.ca turns your answers into the same 26-page package the township clerk sees every day — calculations, drawings, forms, all of it.
What the holes have to tell you
✓Soil layers — what each layer is (topsoil, sand, silt, clay) and where it starts and stops, measured from grade
✓Depth to water — seepage or standing water, and mottling (rust-coloured staining that marks the seasonal high)
✓Depth to bedrock or hardpan — if the machine refuses, that depth is your limiting layer
✓The percolation soil — the layer the bed will actually sit in, which is where your T-time sample comes from
How to dig them
Two or three holes spread across the proposed bed area — not one, because soil changes across a lot faster than people expect. A mini-excavator digs each in minutes; by hand with a post-hole auger is legal but brutal below a metre. Go to about 1.5 m, or until you hit water or rock. Fence or cover the open holes — they are a real hazard for kids and pets, and you may be keeping them open for a week or more until inspection.
The one call to make first
Phone your permit authority before you dig and ask two questions: do they want to witness the holes open, and do they accept an owner’s log or require a soils report on difficult ground. Five minutes on the phone saves re-digging.
The log: what to write down
For each hole, record the date, the location (tie it to two fixed points so it lands on your site plan accurately), and every layer with top and bottom depths. Note the exact depth of any water, seepage, or mottling — mottling counts as the seasonal high water table even if the hole is dry today. Photograph each hole with a tape measure visible. That photo has settled more than one disagreement with a reviewer.
| Depth | What you found | What it means |
|---|---|---|
| 0–25 cm | Topsoil | Stripped before construction |
| 25–90 cm | Brown fine sand | The percolation layer — T-time sample from here |
| 90–120 cm | Grey silt, mottled | Seasonal high water at 90 cm — the limiting layer |
| 120 cm+ | Wet grey clay | Confirms it — bed likely comes up as a raised bed |
A real log from a real lot near Barrie — and the reason that owner built a raised bed instead of losing a season arguing with the reviewer.
The $18,950 line that never appears on a quote
A real worked example: 3-bedroom bungalow, conventional bed. Tank supplied and set, pipe, stone, fabric, one day of machine and labour, permit allowance — $13,049 with HST. The same job quoted at $32,000. The gap is design fees, markup, and labour you may not need to buy.
Two minutes on the free checker shows the numbers your own lot generates — daily flow, tank size, risk level — before anyone quotes you.
What happens to these numbers
The percolation layer sets your T-time, which sizes the bed and drives most of the cost. The water or mottling depth becomes the limiting-layer line on your cross-section. The hole locations go on the site plan. When you enter the log into the Permit Package Builder, all of that flows through automatically — and the checker flags a limiting layer too shallow for a conventional bed before you order a single truck of stone.
Test-hole questions, answered straight
How deep does a septic test hole need to be?
To about 1.5 m, or to refusal on rock, or until you are clearly below the future bed bottom plus the required clearance. Deeper never hurts the evidence.
How many test holes do I need?
Two or three across the bed footprint is the practical standard. One hole is a sample of one — some authorities will not accept it.
Do I have to leave them open?
Most authorities want to see them open at the site inspection. Ask before you dig, and plan to fence them.
What is mottling?
Rust-orange staining in a soil layer — the fingerprint of a water table that rises seasonally. Reviewers treat the top of mottling as the high-water mark no matter how dry the hole is in August.
Can I dig test holes myself?
Yes. On your own property, digging and logging your own holes is normal owner-builder work. Difficult ground (fill, shallow rock, high water everywhere) is when a soils professional earns their fee.
Turn two holes into a complete design
Enter your test-hole log and the builder produces the T-time worksheet, the bed sizing, the cross-section and the site plan — every number consistent. $99.99.