Wheel and tyre wash systems for a compliant site exit

Almost nowhere by name, and that is the useful answer. What regulations set is an outcome — sediment must not be tracked onto the public road, and site water must not reach a drain or watercourse untreated — together with a plan that names the control you are relying on. A wheel wash is one control; a stabilised stone access, a rumble grid and a sweeper contract are others. The exception is your own paperwork: where a development consent, a licence or a contract names a wheel wash, it stops being a choice.

It depends which duty is breached, and there are usually three available at once: a road or highway offence for depositing material on a carriageway, a water-pollution offence if the runoff reaches a drain, and a breach of the conditions your site was approved under. In practice the first contact is a notice and the cost of cleaning the road — often recoverable from you by the road authority — and the expensive outcome is a stop-work order on a programme rather than the fine itself.

Sometimes — they sit at the same point on the site and guidance treats them as alternatives. The difference is measurable: the US Environmental Protection Agency puts sediment removal at less than 30% up to 60% for gravel pads and shaker racks, against 75% or more for a properly installed wheel washing rack. On a dry site with light traffic over a stabilised stone access, a grid is often enough. On sticky clay, in the wet, or where the road outside is a residential street, it generally is not — and a dry control has nothing to say about the undercarriage.

A single pass, without stopping, in under a minute — the vehicle drives through at a crawl and the jets run while the wheel turns. A 4 m bay clears around 50 vehicles an hour, which is why the sizing question is peak hour, not daily average: the queue that matters is the one at shift change. Bay length is the lever, because it is also how many times the tread turns under spray — 4 m turns it once, 8 m twice, 12 m three times.

Far less than hosing by hand, because the water is recirculated rather than consumed. Up to 90% of the wash water is recovered every cycle: it drops into a tank below the bay, the solids settle out in stages, an oil skimmer and coagulant dosing clean it up, and it goes round again. The system draws make-up water to replace what leaves on the vehicle and in the sludge. Containment is also what keeps the discharge question out of scope — nothing goes to the drain.

The plan that names the control, evidence that it was working on the day, and the sludge disposal record. Several jurisdictions ask for a wheel-wash log specifically, and dust-control regimes that inspect against a checklist treat "was it running" as a separate question from "do you have one". A control you cannot evidence is, for audit purposes, a control you do not have.

The regulator does not care which, only that the outcome holds for as long as the site does. Portable wins where the exit moves: no excavation, commissioned inside a workday, relocated across phases and onto the next project — and it can be hired rather than bought. Concrete earns its civil works where the gate outlives the programme: a quarry, a batching plant, a depot, a landfill or a long-life mine.

It settles out of the water in the tank under the bay and leaves as sludge. With a plain settling tank that is a scheduled job, usually done by plant already on site moving spoil. With a PCET scraper-conveyor dirt trap — the trailing C in the model code — a chain-and-flight mechanism lifts the solids out continuously into a chute, so nothing is shut down to clear it. Where the sludge goes is worth settling before anyone quotes: it is a waste stream with its own paperwork.