After several years of negotiation with the Local Authority Planners the water treatment works on the site of the slow sand filter beds in Hornsey was recently completed by Costain. Clark Smith Partnership was entrusted with the Civil and Structural design of this new major facility which ensures production of 50 mega litres of water per day for the local area.

The need for the project was particularly demonstrated during drought conditions when the source water quality was poor due to algae and the back up supply from ground water was found to be contaminated with bromate.

Due to planning requirements the plant is generally below ground level and was contorted to fit the process into two of the original slow sand filter beds alongside the reservoir and New River aquaduct. This created a number of design and construction challenges for the design team (CSP, Enpure and Thames Water Utilities Ltd) and the Contractor (Costain) to overcome. The treatment processes include dissolved air flotation, rapid gravity filtration, chemical dosing for ph and coagulation, catalytic GAC contactors (for the removal of bromate), aeration and disinfection; the majority of which are contained within reinforced concrete tanks below ground level with clad steel structures over.

Updated February 2010

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