GRW/Drainage/TBT-GRW-011

Attenuation Tank Installation

Groundworks & Earthworks › Drainage › Attenuation Tank Installation

All Categories/Groundworks & Earthworks/Drainage/Attenuation Tank Installation

Attenuation Tank Installation

Toolbox Talk Record

Ref: TBT-GRW-011  |  Issue: 1  |  Date: March 2026
PresenterProject
LocationDate

What?

  • Attenuation tanks store stormwater temporarily and release it slowly to prevent downstream flooding.
  • Systems include modular geocellular crates, precast concrete tanks, and large-diameter pipe storage.
  • Excavations for attenuation systems are often deep and wide, requiring full excavation support controls.
  • Geocellular crate systems are lightweight individually but require careful handling in windy conditions.
  • Precast concrete tank sections weigh several tonnes each and require crane lifts with approved plans.
  • Geomembrane wrapping must be installed without punctures to maintain the tank waterproof integrity.
  • Backfilling must follow the designer specification exactly to avoid crushing or displacing the tank system.
  • Working in deep excavations for tank installation creates confined space and collapse risks.
  • Temporary works design may be required for excavation support, dewatering, and traffic loading.
  • CDM 2015, LOLER 1998, and excavation safety requirements all apply to attenuation tank installation.

Why?

Excavation collapseDeep, wide excavations for attenuation tanks create significant collapse risk if sides are not properly supported.
Crush injuriesPrecast tank sections and heavy crate pallets cause fatal crush injuries if lifting and handling are not controlled.
System performanceIncorrect installation, punctured membranes, or poor backfilling can cause the system to fail and result in flooding.
Do Don't
  • Support or batter excavation sides before anyone enters the tank excavation.
  • Use a lift plan for placing precast sections or heavy crate pallets.
  • Inspect geomembrane wrapping for punctures before and during backfilling.
  • Follow the designer backfill specification for material type and compaction.
  • Secure lightweight geocellular crates against wind displacement during installation.
  • Dewater the excavation to keep the formation dry for tank placement.
  • Ensure safe access and egress is provided within the excavation at all times.
  • Check for buried services before excavating the tank formation area.
  • Obtain temporary works approval if traffic loads will cross the excavation.
  • Record installation details including membrane integrity checks for handover.
  • DON'T enter unsupported excavations for attenuation tank installation.
  • DON'T lift precast tank sections without an approved lift plan in place.
  • DON'T puncture the geomembrane with tools, boots, or sharp aggregate.
  • DON'T backfill with materials that differ from the designer specification.
  • DON'T place heavy plant or traffic loads over the tank without design approval.
  • DON'T leave lightweight crate systems unsecured in windy conditions on site.
  • DON'T compact backfill directly against geocellular crates without protection.
  • DON'T allow water to accumulate in the excavation during tank placement.
  • DON'T skip buried service checks before starting the excavation work.
  • DON'T deviate from the installation sequence in the method statement.

See also: Below Ground Drainage Installation | Excavation Safety Awareness
ebrora.com

RAMS Builder

Generate professional Risk Assessment and Method Statements in minutes. 10 document formats, site-specific content, instant Word download.

Learn More