Watchgate Water Treatment Plant near Kendal is United Utilities clean water treatment plant for Manchester’s water supply from Thirlmere and Windermere.On site a tank holding 12% sodium hypochlorite was contained by wooden bunding which would not have been effective in the event of a spill.
To meet best practice for chemical storage , an impermeable bund was required to provide containment. Although the tank was 58,000 litre capacity it was only filled to 30,000 litres so required a bund of 39,000 litres capacity. (110% of the liquid stored).
A bund of 14.14m x 4.12m x 0.91m (i.e. 53,000 litres capacity) was specified using modular 3 ft containment walls. This construction has a proven track record and exhaustive testing to withstand the pressures of liquid stored. (See Engineers testing on fluid retention and hydrostatic pressure report).The bund needed to be lined with an LLDPE liner compatible with up to 15% concentration of sodium chlorite stored. (See chemical compatibility charts).
The modular bund is quick and easy to install on the tarmac surface at Watchgate and as a modular construction can be easily relocated which is likely for this tank.
During installation records of the liner were kept and the welds of the liner were sample checked by site tensometer.
After installation, the bund was tested for impermeability by filling with 30,000 litres of water and checking the water level did not drop for three days.
The bund passed this impermeability test indicating no leakage.
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