Proprietary Stormwater Filters and MUSIC-link: Getting Accepted

The stormwater report says the site meets the council’s pollutant reduction targets. The council’s engineer opens the MUSIC file, sees a proprietary filter node with removal rates that would embarrass a wetland, and sends back an RFI asking where the numbers came from. Three weeks gone. I see this constantly, and it’s almost always avoidable. Here’s how the assessment actually works and how to get through it first time.

What a proprietary filter is, and why councils are wary

“Proprietary” just means a manufactured, branded device rather than a designed-in-place measure like a bioretention basin or a swale. In the tertiary treatment space (the fine sediment and nutrient end of the train) the ones you’ll meet in Sydney are cartridge filters and compact biofilters. Ocean Protect’s StormFilter is an underground vault of media-filled cartridges that stormwater siphons through, with the media exchanged every one to five years depending on load. Their Filterra is a high-flow biofiltration unit doing the job of a raingarden in a much smaller box. Atlan sells the AtlanFilter and AtlanBasin in the same territory. There are others.

These devices are legitimately useful. On a tight commercial site there is often no room for a bioretention basin of the size MUSIC wants, and a filter vault under the car park is the only thing that gets the nutrient numbers. The reason councils are wary isn’t the products. It’s the history: a lot of underground devices went in during the 2000s with removal rates from a brochure, were never maintained, and performed nowhere near the model. Stormwater Australia says as much in its explanation of why SQIDEP exists. Councils are now protecting themselves against a repeat.

What SQIDEP verification actually means

SQIDEP is the Stormwater Quality Improvement Device Evaluation Protocol, run by Stormwater Australia. A supplier who wants their device verified has it field tested under the protocol, the results are assessed by an independent evaluators panel, and if it passes, the device gets a certificate stating the removal efficiencies that the evidence supports. Verified devices have to re-register each year.

Three things follow from that.

First, a SQIDEP certificate is the strongest evidence you can attach to a treatment node. It’s not a brochure. Second, the certified numbers are often lower than the marketing numbers, because they’re what the field data supports. Third, a certificate covers a device at a stated treatment flow rate and configuration. If you size the unit smaller than the tested configuration relative to its catchment, the certificate doesn’t cover you.

Not every council requires SQIDEP. But the direction of travel is clear, and Atlan, Ocean Protect and others now publish their verified products and certificates. If a supplier can’t show you one, ask what evidence they do have and be ready for the council to discount it.

What MUSIC-link checks, and what it doesn’t

MUSIC (currently MUSICX from eWater) is the modelling tool nearly every Sydney council uses to assess water quality. MUSIC-link is a module inside it that holds a council’s own modelling rules. When you set up a model you select the assessing authority, which loads their rainfall template and their allowable ranges for the parameters. When you run MUSIC-link it produces a report showing, parameter by parameter, whether your model sits inside the council’s allowable range, and whether the targets are met. That report can be exported and submitted with the DA.

What it checks, in practice:

• The rainfall and evapotranspiration template.
• Source node parameters: imperviousness, pollutant generation, rainfall-runoff settings within the council’s ranges.
• Treatment node parameters: for bioretention, filter media depth and area, extended detention, saturated zone and so on; for generic treatment nodes, the transfer functions and flow rates.
• Whether the modelled reductions meet the council’s targets.

What it doesn’t check: whether the proprietary device’s node is honest. A generic treatment node with a made-up transfer function will pass MUSIC-link if the parameters are within range. That’s why the assessing engineer still opens the file, looks at the node, and asks for the evidence. MUSIC-link gets you past the first screen. The certificate and the report get you past the engineer.

The targets, and how they vary

Most Sydney councils set percentage reductions against an untreated baseline for gross pollutants, total suspended solids, total phosphorus and total nitrogen. A common set in NSW is in the region of 90% gross pollutants, 85% suspended solids, 65% phosphorus and 45% nitrogen, but councils differ, some set flow targets too, and growth-area councils and catchment-specific policies can be tougher. Don’t quote a number from memory. Read the LGA’s current DCP or WSUD guideline. Blacktown, for instance, publishes a WSUD developer handbook and standard drawings on its stormwater and WSUD pages and expects a MUSIC model for any site where water quality applies.

Nitrogen is the one that decides your design. Primary devices barely touch it. Cartridge filters and biofilters do, which is why they turn up on sites without room for a basin.

Getting it accepted: the process that works

1. Read the council’s modelling rules before you open MUSIC. Some councils only accept specific node types for proprietary devices; some publish their own parameter sets; some cap the reduction they’ll credit to any single proprietary device.
2. Talk to the supplier early and ask for three things: the SQIDEP certificate (or their best evidence), the MUSIC node or parameters they recommend for this council, and the treatable flow rate for the unit they’re proposing. Then check that unit against the flow it’ll actually receive.
3. Build the train, not just the filter. Primary treatment upstream (pit inserts, a GPT or a separator) so the filter isn’t blinded by litter. Then the tertiary device. Show the sequence on the plan and in the model in the same order.
4. Run MUSIC-link, fix anything out of range, and export the report. Where a parameter is legitimately outside the council’s range, write the justification in the report rather than hoping nobody notices.
5. Attach the evidence. Certificate, supplier sizing letter, MUSIC-link report, and the node parameters in a table. Assessment officers can’t approve what they can’t see.
6. Write the maintenance plan. Inspection frequency, cartridge or media replacement interval, who does it, and how it’s funded. For a strata scheme, note it’s going into the by-laws. Councils have been burned; this is the paragraph that reassures them.
7. Make the drawings match the model. Same device, same size, same catchment. If the model has a 30 cartridge vault and the drawing has 20, expect a question.

Questions I’d ask any supplier

• Is this specific configuration SQIDEP verified, and at what flow rate?
• What’s the head loss through the unit, and what’s the depth to invert? On flat Sydney sites this decides whether the device can go where you want it.
• What’s the realistic maintenance interval for a site like mine, and what does a full media change cost today?
• Who does the maintenance in Sydney, and can the owner buy the cartridges or media from anyone else?
• Which councils have accepted this node recently, and can you share the parameters they accepted?

If a supplier can answer all five without hesitation, they’ve done this before. If they can’t, budget for the RFI.

We’re independent on this. We don’t sell filters and we’ve put every major brand through councils across Sydney. Sometimes the answer is a proprietary vault; sometimes the honest answer is a smaller building footprint and a real raingarden. If you want the MUSIC model built to the council’s rules and the treatment train designed so it survives its first assessment and its tenth year of operation, that’s the job. Get in touch before the architect’s fixed the car park levels and there’s still room to put the device where it works.