Water & Wastewater Treatment

38 | september 2014 | WWt | www.wwtonline.co.uk In the know Getting to grips with water storage hotels, railways, health care, commu- nity and utilities' sectors. Cylindrical sectional water tanks (Fig 3) These are available in aluminium, galvanised and stainless steel and the range of materials offered provides cost-effective and project-specific op- tions for the potable, irrigation and fire protection sectors, amongst others. They are built using hydraulic jacks allowing the tanks to be erected within days by a small team. This process of being built 'from the top down' reduces health and safety risks by removing the requirement of working at height. Cylindrical tanks are generally sup- plied with a choice of a liner or mastic- based sealant. The most commonly specified option is the liner sealed design where the inside of the tank shell is lined with a synthetic EPDM, PVC or butyl rubber liner. Being a very flexible product in terms of size the tank can be built to greater heights using a smaller footprint if desired or can be of greater diameter and lesser height depending on space availability. Base supports (Fig 4) It is vital that the tank base support is properly designed and built. If this is not the case there is a very high risk of prod- uct failure. The base is usually prepared using one of the following options. Flat foundation: A flat concrete base has to be level and not varying more than 2mm per metre or 6mm per six metres when measured later- ally or diagonally. The design of the concrete slab is the responsibility of the contractor to ensure the correct ground bearing conditions are taken into account. Close centre beams: GRP sectional tanks can be supported by I-beams placed at 500mm centres on top of a concrete slab. This will enable level- ling to be carried out more easily. Pier walls: GRP and steel sectional tanks can be supported by concrete piers placed at 1000mm centres. This option is useful when self-draining of the tank is a requirement. Tank installation (Fig 5) Check that your installers are certified to carry out the work specified and that a full risk assessment report is provided before installation is approved. Technicians should be fully trained and carry relevant certification includ- ing Site Management Safety Training Scheme (SMSTS), Construction Plant Competence Scheme (CPCS), Construc- tion Skills Certification Scheme (CSCS), Client/Contractor National Safety Group (CCNSG), International Powered Access Federation (IPAF), Prefabri- cated Access Supply & Manufacture Association (PASMA) and Confined Space Trained (CITB). Inspection, maintenance and repair (Fig 6) As with any product it is important that water storage tanks are inspected and maintained regularly. Regular maintenance should include internal and external visual inspections and, where required, ultrasonic thickness measurement, internal ROV inspec- tion, cleansing and disinfection. Roof structures and supports should be inspected, fittings and fastenings checked, internal and external seals and seams should be checked for water-tightness. sponsored by Smart liquid lime www.neutralac.co.uk Figure 2: steel sectional tanks have unlimted storage capacity and are less likely to fracture during seismic activity than Grp Figure 3: Cylindrical sectional tanks offer great flexibility Figure 6: regular inspection is crucial Figure 5: A well-installed tank needs fully-trained technicians Figure 4: Tank bases are usually prepared as flat foundation (le ), close centre beams (centre), or pier walls (right)

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