Stormwater harvesting scheme at school

Providing at-source surface treatment

Sustainable water management and water-sensitive urban design is best achieved by a combination of underground in-system measures and pre-system surface treatments. Together with its underground solutions, Rocla now has stormwater treatment products from enviss for at-source surface treatment applications.

The enviss Sentinel pits are suited for at-source treatment using the enviss filter media to pre-treat stormwater prior to entering the underground stormwater system or harvesting storage. They are designed similar to other WSUD natural treatments such as raingardens or biofiltration systems, and being a single pit solution they are easy to install and easy to maintain. The envissDT software tool will ensure a cost-effective and sustainable solution by iterating over a range of sizes and simulating the performance from historical rainfall data. By using the software, Rocla’s engineers will help users determine the amount of water captured by the filter, the percentage of pollutants removed and the 'music' modelling specifications of the surface filter system.

Syndal South Primary School, located in the suburbs of south-east Melbourne, was looking for a way to keep its playing fields green during summer and reduce potable water usage. A stormwater harvesting system using the enviss Sentinel surface treatment was installed and now saves one megalitre of potable water every year.

Before the system was completed in September 2008, the school was facing another hot summer with very little water to maintain its sports fields due to continuing dry weather and tough water restrictions. A stormwater harvesting system that would capture and treat stormwater using the enviss filter technology was the applied solution.

The harvesting system was modelled with the envissDT software using 10 years of rainfall data, and took into account the water demands for toilet flushing and irrigation of the sports fields. The model enabled the designers to choose the optimal tank and filter sizes to meet demand. As a result, a bank of 60 enviss Sentinel filter pits was designed to treat the run-off before it was stored in a 130,000 L underground storage system installed beneath an existing oval.

By using the surface filtration and appropriate storage, the school was able to capture rainfall run-off from asphalt play areas and car parks in addition to the rainwater from the buildings, giving an 80% increase in the catchment area. This means more water is collected from each storm and greater mains water savings are made. The surface treatment makes this possible by removing sediments, nutrients, heavy metals and pathogens from the stormwater prior to it entering the system, resulting in a high-quality source of water that is safe to be used in a number of non-drinking water applications.

Syndal South Primary School now saves one megalitre of mains water every year, with the harvesting system able to supply 69% of the annual toilet flushing and irrigation demands.

The advantages of the system include:

• A high pollutant removal performance that can be achieved in a very small footprint. This can be as little as 0.3% of the impervious catchment area in Melbourne, which is about seven times smaller than comparable technologies and up to 10 times smaller than other WSUD natural treatments.
• Designed to be modular cartridges in order to suit any site and conditions. Cartridges can be combined to create filter areas as small or large as required.
• Easily designed using the envissDT simulation software.
• Maintenance is predictable and requires no specialist knowledge or training to replace a filter cartridge.
• Based on passive filtration and requires no chemicals or external energy for ongoing use.
• Extensive testing by Monash University with peer-reviewed methods and results.