General installation guidance

Consideration should however be given to the water table level when carrying out deep excavations. In general it is advisable to limit the overall depth of the installation to 2.5m (Four layers of cells). Where the water table is particularly high it may be necessary to cap the installation with concrete to prevent floatation.

The storage tank is formed in the same way as for the attenuation system, the only difference being that one cell is omitted from the centre of each layer to form the riser well. When the tank cells have been assembled to the required height the impermeable membrane can be sealed, leaving a 'flapped' cutout over the riser well.

At this stage the central riser can be partially assembled into the well before commencing construction of the infiltration layers over the storage tank. The Waterloc cell connectors are not used at the interface between the storage and infiltration cells. Once the infiltration cells are in place and the riser has been assembled to the inlet chamber, the geotextile material can be formed around the whole construction and the excavation backfilled to within approximately 150mm of the top of the inlet chamber.