Case Record – Dealing with excess water on site.

Details:

Date: Location Main Contractor: Contract:

February 2003 Hatfield, Hertfordshire Carillion Building Design and build of academic building, student residences and sports facilities for the new De Haviland Campus at the University of Hertfordshire campus.

Issue

Prolonged rain across the country has meant many sites had to deal to deal with excess volumes of water. At the University of Hertfordshire project the residential and sports facilities are being constructed on a vast expanse of flat open land (approx. 300 acres) of which the project occupies approx 30 acres. It was necessary to make a deep excavation for the swimming pool and when excavating commenced it was seen that the groundwater was highly polluted with suspended solids.

There is a legal duty to obtain discharge consent prior to commencing certain pumping activities and to ensure compliance with the relevant conditions imposed by the authorities. Permission to discharge into the drainage system to the brook would not have been granted with the degree of contamination found.

Solution

A system was set up whereby the water is pumped up above the water table using a suction pump and the pumped through a series of settling tanks.

Firstly the water is pumped above the water table using a suction pump. It is then received at an open setting tank, where large suspended solids settle out. Here the clearer water falls free from the final tank and is absorbed through a purpose built 15m trench, which is lined with a Terram lining and filled with rejected stones. The water is pumped and filtered again (closed tank), by which stage it is perfectly clear and of adequate quality to discharge into the surface water system.

This shows how a simple practical solution can be found to aid environmental compliance on site.

Business Benefits:

• Avoid pollution
• Simple and cost effective solution.