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Effluent from the unit should be discharged to a percolation area subject to satisfactory results from site suitability assessment and in accordance with local authority conditions.
Illustrated to the left are typical layouts and cross-sections of the two main types of percolation constructlon |
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The treated waste water discharges, by pump or by gravity, into a network of perforated pipes laid in stone filled trenches.
The objective is to spread the effluent as evenly as possible over the required land area, thus minimising the possibility of the ground becoming over-saturated. |
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The percolation area or pipe lenght will vary due to “T” values (Min. 45m) but will be laid to the design shown to the left (assuming 300mm to 350mm wide trenches).
For pumped discharges (usually where the percolation is higher than the treatment plant) the perforated pipe is 50mm diameter.
For gravity discharges the perforated pipe is 100mm diameter. |
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Trenches are generally 300-400mm wide with the pipes laid on 250mm of clean 15-25mm stone and covered with a polythene or geo-textile soil barrier to avoid silting.
Layout of the trenches will be determined by site topography; the overall fall of the pipes should be not more than 1 in 200,
The pipes should be at least 1 metre above the highest water table level or fissured rock strata. |