Water & Wastewater Treatment

In the know Digging deeper: stormwater management Lightweight plastic cells form the main structure of the tank 40 |SEPTEMBER 2015 | WWT | www.wwtonline.co.uk as possible for ease of transport and handling, but strong enough to bear the load from above and comply with CIRIA C680 guidance. Most modular systems are now designed to incorporate lightweight plastic cells, which form the main structure of the tank. For infiltration, this is then surrounded by a strong outer geotextile covering. For attenuation applications, the plastic structure is covered with a waterproof membrane, with the geotextile layer still used as added protection for the membrane. For optimum performance and longevity it's always advisable to opt for polypropylene plastic cells (as these do not contain chlorine and are more easily recycled) and a high strength non-woven protective geotextile fleece (minimum 200g per m2). The attenuation membrane joints should be heat welded and made from a low-density polyethylene that is at least 1mm thick. Getting it right on site A well designed SuDS system not only delivers operational benefits, but it can also ease some of the logistical challenges facing projects, and even The systems can cope with heavy loads help reduce their carbon footprint. The development of stackable modular tank systems has been particularly revolutionary in terms of transport and storage – cutting costs and emissions and taking up minimal space. For example, one lorry transporting conventional modular tanks can typically carry around 90m3 of actual product, with the rest of the space taken up by air. The same lorry transporting a stackable system could carry around 400m 3 of product. This makes for fewer loads, takes lorries off the road and improves a project's environmental impact. At the construction stage, installer training is paramount. With such a breadth of new system improvements and techniques coming to market, those that don't stay up to date will undoubtedly see their installations suffer. Manufacturers have an important role to play in this, and groundworkers should make the most of the installation support on offer from their stormwater supplier. Some have a specialist installation team that can take full responsibility for the process, or help provide guidance, advice and even on-site supervision. Ongoing maintenance is another critical part of long-term system performance and efficiency – especially now there are products on the market that, if correctly maintained, will have an operational lifespan in excess of 50 years. Building in new features like integral Vario sha˜s helps make maintenance a more straightforward process. These sha˜s not only work as an inlet, filter and flow control system, they can also be placed anywhere in the tank to allow for complete system inspection. On the technological side, we are also now seeing the introduction of advanced camera solutions. Modular stormwater tanks with Vario sha˜s and in-built inspection channels provide easy access for camera technology, allowing for remote inspection with minimal hassle. These cameras can be used to periodically check the system for any silt or gravel build up – ensuring optimum performance for the lifetime of the system. Setting the standard for the future With so many external factors and developments impacting on the efficacy of stormwater solutions, it's important that there are clear guidelines in place to help specifiers and building owners get the best out of their systems. For this reason, at Graf UK we're calling for the introduction of a national standard that sets minimum requirements for the design, installation and maintenance of SuDS. Not only would this help ensure that systems continue to perform in line with expectations, it would also provide official recognition of the crucial role SuDS will play in helping UK buildings respond to changing stormwater patterns – now and well into the future. • Top five features of a successful SuDS install ● Planning ahead – incorporating system design into the planning application ● Accurate system sizing (including capacity of the tank itself and the flow controller) ● Opting for the right structure and materi- als (in compliance with CIRIA C680) ● Proper training, to ensure the installa- tion is carried out to the highest possible standards ● Regular, ongoing system inspection and maintenance

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