Stormwater & soakwells · Perth northern and eastern corridor
Perth soakwells, sized to the storm and to the water table.
Stormwater and soakwell replacement from Yanchep to Forrestfield, out of Wangara. We dig the hole the storm needs, not the hole that fits the quote.
Licensed plumbing contractor since 2009 — 1,900-odd soakwells in Perth sand. Installed to AS/NZS 3500.3; we lodge the drainage detail with your council.
Section A–A · through the soakwell run
True scale · fixed 0–7 m axisThe section drawing needs JavaScript. The numbers beside it don’t: 220 m² of roof on a 1-in-20-year storm needs 3,300 L held on site — three 1200 × 1200 soakwells, $4,000 installed, on Bassendean sand with the winter water table 3.2 m down. Ring us on (08) 9000 0401 and we’ll do the arithmetic for your block.
Catchment area
220 m²Roof plan area plus any paving that drains to it. 60–400 m², in 20 m² steps.
Design storm
15 mmMost Perth councils design residential blocks to a 1-in-20-year storm and commercial lots to 1-in-100. We take the intensity from the Bureau’s IFD grid for your address; if your council nominates a different one, we design to theirs.
What drains to it
100%The runoff coefficient. A roof sheds all of it; compacted gravel keeps a little.
Ground & water table
3.2 mDepth to the winter (maximum) groundwater level, from DWER’s mapping of the Perth superficial aquifer. We keep 500 mm of dry sand under every base.
Soakwell size
1200 × 1200Capacity is πr²h floored to the whole 10 litres — the number the unit actually holds, not the one on the invoice.
Machine access
+$0Nobody hand-digs a 1200. With no machine access the 900 is the biggest hole we’ll quote you.
Reinstatement
+$0Whatever is over the lid has to come off and go back on. 300 mm of cover goes back either way.
Downpipe connections
490 mm PVC, run to 6 m, glued and bedded. $145 each.
What that costs
A soakwell in clay is a bucket with a lid. This block wants a piped connection to the council drain, or a detention tank and a pump, and both of those are a different trade’s job as much as ours. We’d rather tell you than dig you a hole that stays full until October.
How the number is made
One millimetre of rain on one square metre is one litre. So the volume you have to hold is area × storm depth × runoff, and the count is that volume divided by what one unit actually holds, rounded up.
We take no infiltration credit during the storm. The soakwells are sized to hold the whole event and soak away after it — which is the conservative assumption, and the one your council’s checker will make too.
A wet block doesn’t cost more to dig. The water table changes what we’re allowed to put in the ground, not what putting it there costs.
Prices
Six line items. That’s the whole price list.
Supplied and installed, GST included, on a normal suburban block with excavator access. Everything above is built out of these six numbers — nothing on this page comes from anywhere else.
Soakwell, 1200 × 1200
Precast to AS 4058, 1,350 L held. Excavation, aggregate surround, lid, 300 mm cover and backfill.
$980each, installedSoakwell, 900 × 900
570 L held. The biggest hole we’ll dig by hand, and the size that fits down most side accesses.
$620each, installedSoakwell replacement
Collapsed 1970s unit dug out, carted, and a new one bedded in clean aggregate in the same hole.
from $1,650per job — our minimum chargeDownpipe or pit connection
90 mm PVC to 6 m, glued, bedded and graded. Priced per connection, not per metre.
$145eachSite set-up & spoil
Set-out, service locate, spoil removal and compaction. One charge per job however many holes.
$480per jobHard-surface reinstatement
Paving lifted and relaid, or concrete saw-cut and patched, over each soakwell we open up.
+$180 / +$340per soakwell — paving / concreteLicensing, insurance and standards
- Operating since 2009 out of Wangara — two crews, one excavator, one mini-ex.
- Installed to AS/NZS 3500.3 by a licensed plumbing contractor, PL0000 (placeholder).
- Precast units to AS 4058, delivered from a Perth yard, batch-stamped.
- $20m public liability and workers’ compensation, certificates on request.
- We lodge the drainage detail with your council and hand you a copy.
- ABN 00 000 000 401 (placeholder pattern — this is a demonstration page).
What people say
Three jobs, in their words.
Sandline is a fictional business, so these are written as demonstration copy — the kind of specific, unglamorous review a real drainage customer leaves.
“Two winters of sandbagging the garage door. They came out, found the old wells were full of root and collapsed on one side, and put in three new 1200s off the two front downpipes. First storm after was that 40-minute one in June and the driveway just… didn’t.”Peter M.Wangara · three 1200s and a downpipe re-route
“I’d priced 1200s from three places. Sandline were the only ones who asked what suburb, looked up the winter groundwater, and told me my block wouldn’t take anything deeper than a 600. More holes, same money, and it actually drains.”Aleisha T.Bayswater · owner-builder, 1.4 m water table
“They turned up, dug a test hole, hit clay at 900, and told me a soakwell would be money down a drain that doesn’t drain. Didn’t charge me. Gave me two names for a piped connection. That’s who I’ll ring when we do the extension.”The Okonkwo familyForrestfield · quoted, then talked out of it
Where we work
The coastal plain, and where it stops being sand.
We work the sand. East of the transition the ground turns clay and a soakwell stops being the answer — we still come and look, we just usually tell you to spend the money somewhere else.
Get a price
Send us the block. We’ll send back the section.
Four fields and we can usually price it off the roof plan and the address. If the water table looks tight we come out and dig a test hole before we quote — that visit is free and it is the only way to be sure.
Send this and we’d call you back within one business day, usually before lunch. If it’s water in the house right now, ring the mobile instead — (08) 9000 0401.
Thanks — that’s with us.
We’d call you back within one business day to confirm the ground and book a look. Nothing is sent anywhere from this demonstration page — the details below stayed in your browser.
- Name
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- Suburb
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- On the section
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This is a demonstration build, so there is no back end and no email. On the real site this posts to the office and lands in the job board.
What we’d want to know
Your suburb. It gives us the soil and the winter groundwater level off DWER’s mapping before we’ve driven anywhere.
Roof area. Off the site plan if you have it. If not, we’ll measure it — it takes ten minutes and it is the only input that changes the volume.
What’s over the top. Lawn, pavers or concrete decides the reinstatement line, and it is usually the difference between two quotes that look identical.
Whether a machine can get in. A 900 mm side gate means a mini-ex instead of the excavator; no machine at all caps the hole at a 900, because nobody hand-digs a 1200. It changes the rate, not the volume — what turns three holes into twenty-one is the water table, not the gate.
Questions we get
Six things people ask before they ring.
Why does the council want the water kept on my block?
Because Perth’s street drainage was never built to take everybody’s roof. The NCC Volume Three (Plumbing Code) Part B1 and AS/NZS 3500.3 require stormwater from a roof to be disposed of properly, and in most Perth local governments “properly” means on site — into soakwells sized for a nominated design storm, not into the kerb.
Which storm is nominated is the council’s call. Residential blocks are usually a 1-in-20-year, 15-minute event; commercial and larger lots are usually 1-in-100. We take the intensity from the Bureau of Meteorology’s IFD grid for the address and design to whatever your council asks for.
How do you work out how many I need?
Arithmetic you can check. One millimetre of rain on one square metre is one litre, so:
220 m² × 15 mm × 100% = 3,300 L to hold
3,300 L ÷ 1,350 L per 1200 × 1200 = 2.44 → 3 soakwells
The 1,350 L is πr²h floored to the whole 10 litres — a 1200 × 1200 unit computes to 1,357 L, and we call it 1,350. We round the count up, never down, and we take no infiltration credit during the storm: the wells are sized to hold the whole event and soak away afterwards.
What has the water table got to do with a soakwell?
Everything. A soakwell works by losing water sideways and down into dry sand. If its base is sitting in the winter groundwater, there is nowhere for the water to go and the unit is a tank.
So we keep 500 mm of dry sand under every base, and there’s 300 mm of cover over the lid. A 1200 × 1200 therefore needs 1,200 + 300 + 500 = 2,000 mm of ground above the winter water table. On the coastal flats around Bayswater that level sits about 1.4 m down — so the 1200 is out, the 900 (which needs 1,700 mm) is out, and the 600 fits with nothing to spare, because 600 + 300 + 500 is exactly 1,400 mm. That is why some blocks get twenty-one small holes instead of three big ones.
What happens if my block is clay?
We tell you not to do it. A soakwell in clay is a bucket with a lid: it fills in the first storm and it is still full in October. On the clay-over-sand country around Forrestfield and Maddington the honest answer is a piped connection to the council drain, or a detention tank with a pump — and both of those are as much another trade’s job as ours.
The section above refuses to price it, on purpose. We’d rather lose the quote than dig you a hole that doesn’t work.
How do I know my old soakwells have collapsed?
The tell is water where it never used to be: a garage that takes an inch in a summer downpour, a soft dip in the lawn near a downpipe, or a downpipe that gurgles and backs up out of the top of the pit.
Most 1970s and 80s Perth soakwells were thin unreinforced precast or, worse, cement-rendered brick. Thirty-odd wet seasons of sand pressure and root ingress crack the wall, sand washes in through the crack, and the well silts up from the bottom. From above it looks fine. We dig one out, cart it, and put a new unit in the same hole where we can.
What don’t you do?
We’re not a civil contractor. We don’t build detention basins, we don’t design or install pumped systems, we don’t do subdivision drainage, and we don’t do the road-reserve connection into a council main — that needs the council’s own approval and a contractor set up for it.
What we will do is tell you which of those you actually need, and give you two names who do it. That call is free and it is the reason about one enquiry in six leaves without a quote.
This is a demonstration build by Sapience Analytics. Want one pointed at your customers?
Sandline isn’t a real business — the page is. Every figure on it is computed live from a pricing model written down before a line of code, including the state most trade sites would never build: the one where the honest answer is that you shouldn’t buy anything. That’s exactly how we’d build yours.