Project - Stowupland, Suffolk - Attenuation Tank

November 2007 - The lining of a typical small attenuation tank on a new housing site.

The tank was 6m x 5.5m x 1.2m providing a gross volume of 39.6 cubic metres.  The attenuation blocks were all the same size at 1m x 0.5m x 0.4m high and were oriented 6 blocks x 11 blocks x 3 blocks high, ie 198 blocks @ 0.20 cubic metres each = 39.60 cubic metres.

Our company approached the project by factory prefabricating a 1.00mm polypropylene liner into a five sided open topped 'box' format.  There was also a 300g per square metre geotextile fabric which was factory prefabricated on the same basis.

The materials were taken to site and the installation sequence was as follows:

1. Placement of the geotextile layer.
2. Installation of the prefabricated 1.00mm liner
3. Placement of the 198 blocks.
4. Sealing the liner to pipe inflow / outflow stub end penetrations.  Sealing of the vent.
5. Placing of the prefabricated lid liner across the top of the tank and its extrusion welding to the previously installed liner.  This created a fully welded liner to encase all six sides of the tank area.
6. Completion of the installation of the remaining geotextile overlay to the outside of the tank.

Our time on site was 1 day for the whole of the work detailed above.  The Contractor on site then joined the pipework runs to the sealed stub ends as left by our company.  The area was then backfilled and the project completed.

End Client:  Orwell Housing Association

Materials Used:  Exceliner PP 1.00mm (polypropylene) / 3600N geotextile

Grounds Works Contractor:  D A B Associates

Civil Engineering Merchant:  Collier & Catchpole Ltd

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