Stormwater Retention and Infiltration Chambers: An Alternative to Retention Ponds

This article looks at retention and infiltration chambers, an alternative to retention ponds used as stormwater management facilities. Find out what they are, how they are used, their advantages and limitations, and how to maintain them properly.

What is a retention or infiltration chamber?

Retention chambers temporarily hold runoff before releasing it to an outlet. Infiltration chambers, for their part, recharge the water table by allowing water to infiltrate into the soil. Retention and infiltration chambers are buried, creating underground basins that hold stormwater and runoff until it infiltrates into the soil or is released to an outlet.

How retention and infiltration chambers are built

Both retention chambers and infiltration chambers are made of corrugated plastic domes manufactured from durable materials that are, in some cases, recycled and recyclable.

Retention and infiltration chambers have an open bottom that allows stormwater or runoff to infiltrate into the soil. The plastic domes are placed on a layer of backfill stone with a porosity of about 40%. The same type of stone is used to cover them. If needed, several layers of domes can even be stacked on top of each other.

Installing a pretreatment device upstream of the chambers is recommended to capture sediment, floating debris, oils and grease. This minimizes the transport of these pollutants into the retention or infiltration chamber and helps preserve groundwater quality.

The system may also include a distributor, a header, flow regulators, inspection manholes and bypass manholes.

Retention and infiltration chambers typically have a service life of about fifty years.

Typical uses of retention and infiltration chambers

Retention and infiltration chambers are particularly useful in urban areas, where impervious surfaces such as building roofs, streets and parking lots prevent stormwater from naturally infiltrating into the soil. Some experts say that in urban areas, runoff can reach up to 55% of precipitation volume, while in natural environments it is limited to 10%.

Retention and infiltration chambers allow stormwater to be managed on the property where there is not enough space for other types of stormwater management facilities.

Like many stormwater management facilities (retention ponds, vegetated swales, constructed wetlands, etc.), retention and infiltration chambers work in parallel with the storm sewer system.

They help reduce downstream flooding caused by the increase in runoff from impervious surfaces, improve cities’ resilience to climate change and improve the quality of water discharged to the environment.

They are found in residential and commercial developments, in some industrial areas and under sports fields. They are particularly well suited to small spaces, but they can also be used to hold large volumes of water, for example under a shopping centre parking lot.

Advantages of retention and infiltration chambers

Compared with retention ponds, retention and infiltration chambers make better use of the land, have low maintenance costs and raise few aesthetic concerns.

In addition to recharging the water table, infiltration methods are reportedly more effective than conventional systems at removing fine sediment, nutrients, metals, bacteria and organic substances.

By reducing runoff volume, retention and infiltration chambers help minimize downstream overloading and protect watercourses from erosion. Thanks to their compact footprint, they can be used where space is limited.

They also have no thermal impact and pose no safety concerns.

Disadvantages and limitations of retention and infiltration chambers

On the other hand, retention and infiltration chambers are less effective than other types of facilities for quantity control, and the composition of the native soil can be a constraint. They depend on the depth of the water table, and the risk of groundwater contamination must be assessed.

A pretreatment device should be considered for commercial or industrial sites likely to release significant amounts of sediment or pollutants, such as service stations, highway rest areas, mechanical repair shops, auto parts recycling centres, petrochemical plants, oil refineries and used oil recycling plants.

Inspection and maintenance program for retention and infiltration chambers

To be fully effective, the system must be maintained regularly. The inspection and maintenance program is generally easy to implement.

Inspections and maintenance can generally be carried out entirely from the surface, through an observation well or an access riser. No confined space entry is required.

Inspection frequency should reflect the amount of sediment received. Inspections twice a year are generally recommended. They consist of using a flashlight and a measuring rod to check the depth of sediment accumulated in the pretreatment system.

When sediment exceeds a certain depth, it is removed to prevent it from being resuspended. This cleanout is simple and is done with a septic tank vacuum truck.

The collected material is treated and disposed of in the same way as material from conventional catch basins, in accordance with applicable local regulations.

Meeting the challenge of on-site stormwater management with infiltration and retention chambers

Stormwater management is a real challenge for municipalities. Infiltration chambers are a particularly attractive solution for underground retention and infiltration of stormwater in small spaces. They are an effective way to preserve land value and protect water resources.

To learn more about other types of stormwater management facilities, read Nine Types of Stormwater Management Facilities Used in Quebec, or consult our engineers specializing in drainage and stormwater management.

Retention chambers and infiltration chambers are made of open-bottom plastic arches buried underground.

Retention chambers

Retention chambers temporarily store stormwater and runoff before releasing it to an outlet.

Infiltration chambers

In addition to temporarily storing stormwater and runoff, infiltration chambers recharge the local water table through infiltration into the soil.

References

• Technical data sheet – CULTEC® stormwater retention chambers
• Technical data sheet – HydroStor™ retention basin
• Technical data sheet – StormTech underground stormwater management system
• Stormwater management – Quebec’s Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs