What governs your site. Project approvals, design documents, regulator requirements, SDS and manufacturer instructions, and engineering advice govern the site-specific approach. This guide is general information for planning and discussion. It does not set doses, discharge limits or compliance outcomes for any site.
What the dosing system is actually doing
An HES basin is a sediment basin that receives a chemical treatment so that fine particles that would stay suspended under gravity alone can aggregate and settle. Queensland Government material identifies HES basins among the evolving technologies covered by its procedural guidance for large construction sites [1][2].
The dosing station has one job: deliver the right amount of treatment chemical, at the right point, in a way that follows the flow entering the basin. Everything else in the system, including the tank, pump, controller and injection point, supports that job.
Settle the design basis before choosing hardware
The most common setup problems start upstream of the equipment. Before a station is specified, the team should be able to point to documents for the following items.
- The basin arrangement: volume, number of cells, inlet and outlet positions, and the intended flow path.
- The expected range of inflow, from base conditions through to storm events, and how inflow will be measured or estimated.
- The approval conditions and any release requirements that apply to the site, as set out in project approvals and regulator requirements [2].
- Who is responsible for operating the station, topping up chemical, and recording what was done.
- How the station will be powered, accessed and secured, and whether it will need to move as earthworks progress.
Matching the configuration to the site
Trailer-mounted stations suit sites that want a self-contained unit that can be relocated as works move. IBC-mounted stations suit compact set-ups where chemical is held in an IBC. Neither is better in general. The right answer depends on basin layout, access for deliveries, available footprint and how often the inlet position is likely to change.
Whichever format is used, check the following during scoping rather than at delivery.
- Chemical storage and bunding meet the SDS and manufacturer instructions for the product, including compatibility of wetted materials.
- The injection point is where turbulence is available to disperse the chemical, and is not downstream of the flow it is meant to treat.
- Dosing responds to inflow in a way the site team can verify, rather than running at a fixed rate regardless of flow.
- There is a practical way to see that the pump is delivering, such as a visible flow check, a calibration column, or logged output.
- Sampling points exist upstream of dosing, after mixing and at the basin outlet, so performance can be checked at more than one place.
Dispersion and mixing matter as much as dose
General coagulation guidance treats dose and dispersion as linked: a correct dose that is poorly mixed can perform worse than a slightly different dose that is dispersed well [5]. That guidance is written for drinking-water plants and is used here only for the underlying principle. Construction basins are a different setting, so treat it as background, not as a design standard.
In a basin, this usually comes down to the inlet. A chemical added to a slow, stratified flow will not disperse as intended. A chemical added where flow is already turbulent, with enough run before the water reaches still conditions, has a better chance of doing its work in the basin rather than after it.
Commissioning and early tuning
Commissioning is where the station is proven against the real inflow and real chemistry, not just switched on. A sensible sequence is to confirm hydraulics and delivery first, then confirm chemistry against jar testing on site water, then observe the basin response over several different flow conditions. The calibration and monitoring guide covers this in more detail.
Tune one variable at a time. If dose, pH and flow all change together, the team cannot tell which change produced the result. Record what was changed, the time, the conditions, and what was observed.
What automation can and cannot do
Flow-paced and feedback-assisted control can reduce manual effort and keep dosing consistent. It cannot correct a flawed process design [5]. If the chemistry is unsuited to the water, the inlet does not mix, or the basin short-circuits, automation will reproduce the problem faster and more consistently.
Pre-start dosing checklist
- Design basis documents and approval conditions are on hand and read by the operator.
- Basin inlet, outlet and baffling are built as designed and inspected.
- Chemical product, SDS and manufacturer instructions are confirmed for the actual product on site.
- Jar testing has been done on representative site water, and the result is recorded.
- Injection point and mixing zone are agreed with the design engineer.
- Dosing output has been checked against a measured delivery, not assumed.
- Sampling locations and schedule are set, with an owner for each.
- Triggers for recalibration and escalation are written down.
- Spill response and chemical handling arrangements are in place.
Decision points
- If: The inlet position will change as earthworks progress
- Favour a relocatable configuration and plan how calibration is repeated after each move.
- If: Inflow varies widely between base flow and storm events
- Ask how dosing follows flow, and how the team will confirm it did so across the range.
- If: Basin performance is poor despite apparent dosing
- Check hydraulics, mixing and chemistry before raising dose. Raising dose is not a fix for short-circuiting.
- If: Site water changes character after rain or a change of work front
- Re-run jar testing and review the dosing basis. See the site optimisation guide.
Limitations and caveats
- This guide does not give dose rates. Dose depends on site water, chemistry and basin arrangement and must be confirmed by testing and engineering advice.
- Meeting a release requirement is a site outcome that depends on design, construction, operation and conditions. Equipment alone does not guarantee it.
- Chemical handling, storage and disposal must follow the SDS, manufacturer instructions and applicable regulation.
- Project approvals, design documents, regulator requirements, SDS and manufacturer instructions, and engineering advice govern the site-specific approach. This guide is general information for planning and discussion. It does not set doses, discharge limits or compliance outcomes for any site.
Company-reported example
Company-reported example · Not independently verified
Landfill HES basin treatment — July 2026An anonymous account supplied by Critical Elixirs. Read the reported treatment results alongside the evidence limitations; supporting test and field records were not available for review.
Sources
- [1] Queensland Government, Erosion and sediment control on construction sites (Reviewed 2 July 2026)
States that large construction sites in Queensland are subject to legal requirements, and that the procedural guides cover evolving technologies such as HES basins.
- [2] Queensland Government, Procedural guide for releases to waters from land development and construction sites 2500m² and greater (PDF)
The Queensland procedural guide for water releases from larger sites. Read it directly for the requirements that apply to your project.
- [5] General technical reference, not Australian construction compliance guidanceIreland EPA, Optimisation of Chemical Coagulant Dosing at Water Treatment Works (2014)
Drinking-water guidance used here only for general coagulation principles: water chemistry, coagulant selection, dose and dispersion, and pH interact, and automation cannot correct a flawed process design. It is not Australian construction compliance guidance.
Talk to an engineer about your basin
Send location, basin arrangement, programme and approval conditions. Sampling and jar testing may be part of scoping.