A 360 000 litre Ausdrain EnviroModule2 underground rainwater harvesting tank has recently been installed at the newly constructed Salvation Army care facility in Chapel Hill, Queensland.

The Ausdrain EnviroModule2 rainwater harvesting tank is an underground modular system comprised of high strength EnviroModules. The modules form a structural void in the ground that is surrounded in a durable waterproof membrane.

The tank had originally been designed as two pre-cast concrete tanks; however, difficult site access resulted in the search for an alternative system. As the tanks were to be located at the rear of the building, the concrete tanks could only be craned in from street level located above a high bank obstructed by trees and vegetation.

After careful consideration of the alternatives it was decided that the Ausdrain system would not only be the most practical choice for this project but also the most cost effective.

The underground rainwater tank measures 11.4m x 18.0m x 1.35m and consists of 4388 Ausdrain EnviroModules. A 1mm re-enforced polypropylene liner surrounds the outside of the tank and there are two precast pits at either end of the tank measuring 900mm x 900mm each.

The first pit is connected to a 375mm inlet pipe and has a removable maximesh screen over the inlet to the tank. The second pit houses a submersible pump that connects to a 50mm suction line and a 375mm overflow pipe connects to the street stormwater drainage.

The EnviroModules were delivered to site in flat pack form and a forklift was used to move them to the rear of the building. The water storage modules were then assembled in close proximity to the excavated pit. The tank was constructed in 3 days with all components of the tank installed by hand and avoiding the need for costly crane equipment.