Pretreatment Unit

Storm water pretreatment system for settling

The configuration of the different pretreatment models allows a minimum accumulation of 25 % of its volume in sediment.

The pretreatment unit, installed upstream of a retention basin, captures sediments, oils and floating debris to prevent their migration to the retention system, thus averting any risk of clogging the clean stone. As a result of Stokes’ law*, fine particles remain trapped in the pretreatment unit. It is used to control the quality of runoff water in urban areas. The pretreatment unit retains particles of 100 microns or more, from very fine to very coarse sand, and effectively removes total suspended solids (TSS).

Model shown: 900 mm (36 in) model, with 4 outlets of 300 mm (12 in)
* Stokes law defines the behaviour of settling solid particles in a fluid.
Pretreatment Unit

Technical Documents


Advantages and Benefits

  • Monolithic system without interior moving parts.
  • The pretreatment unique design prevents the dispersion of hydrocarbons and floating debris.
  • Is an economical solution for the upstream treatment of some types of pollutants and for removing sand particles.
  • The pretreatment unit is easy to maintain because it provides direct surface access to the sediment accumulated in the reservoir.
  • This system eliminates work in confined spaces.
  • Installed upstream of a system, it ensures its sustainability.
  • The pretreatment unit is made from durable, lightweight and corrosion-resistant high-density polyethylene (HDPE).
  • Provides excellent resistance to de-icing salts, abrasives, chemicals and vibration.
  • The pretreatment unit can be easily adapted to all types of pipe while maintaining network watertightness.
  • Is easy to install on site, as it is much lighter than traditional systems.
  • Withstands CL-625, H-25 and HS-25 loads.



1. When it rains, surface runoff carries suspended sediments, oils and floating debris. Collection systems direct water to a storm water sewer which channels it to a pretreatment unit.


2. When water carrying suspended pollutants enters the tank, its velocity is reduced to begin the settling process.


3. Suspended solids are deposited through settling at the bottom of the unit.


4. Because of its permanently submerged water intakes, the pretreatment unit ensures retention and accumulation of floating pollutants.


5. The pretreatment unit acts directly at the source to prevent pollutants dispersing through the whole storm water sewer network.


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More Information

Inspection and maintenance: inspection and maintenance are facilitated by one or two chimneys providing access to recover oils and sediments.

Pipe connections: our systems are custom designed with a range of entry diameters at various configuration angles. Fittings for inlets and outlets are available to facilitate connections.

Separation by settling: gravity is used to separate suspended solids and oils.

Retention capacity: the volume of contaminants retained by the pretreatment unit is related to the diameter and length of the unit.

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