Containment of Aggressive Chemicals at Water Treatment Plant

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 Engineeers 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 compatability charts).

The modular bund is quick and easy to install on the tarmac surface at Watchgate and as a modular
constrcution 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

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The bund with tank installed.

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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.