PERCOLATION AREA DESIGN NOTES
Also the following conditions should be followed when siting a percolation area.
1. Preferably they should be located to the rear of a housing development furthest away from road.
2. No part of the percolation area should be within 20 m of the nearest dwelling house
3. No part of the percolation area should be within 3 m of the boundary of the adjoining site.
4. No water mains or service pipes should be located within the percolation area
5. No access roads, driveways, or paved areas should be located within the percolation area.
6. No part of the percolation area should be within 10 m of the nearest road boundary, stream or ditch
Size of Percolation Area
The size or area of the percolation area is dependent on the results of the percolation tests carried out on the site of the percolation area. Refer to the standard test sheet for determining the 'T' value for the site. The 'T' value is the time in minutes for a 1" or 25mm drop in the water level in the test hole(s)
The relationship between the value of 'T' and the length of distribution piping required for the percolation area is as given in Table 2.
Note 'T' values less than 5 may indicate that the percolation rate is too fast possibly polluting the groundwater
'T' values greater than 30 may indicate that the percolation rate may be too slow and leading to ponding of the effluent at the site of the percolation area. Where this occurs a raised percolation area may be necessary. Recommendations for its construction are in appendix A attached.
Percolation Area Distribution pipes
o Pipe should preferably be 110mm diameter perforated smoothwall plastic drainage pipes with perforations of 8mm diameter at about 75mm centers along the pipe at about 4, 6 and 8 o'clock positions.
Note: Wavin Plastics supply these pipes
Percolation area Construction
- The pipe trenches shall be set out at 2 m centers
- The percolation pipes should be laid in trenches at least 450mm wide and bedded on 250mm depth of crushed stone (20 - 30 mm in size)
- Pipes should be laid to fall of 1 in 200 approx.
- Pipes should be interconnected at end of pipe runs
- Once the drainage pipes are in place they should be surrounded and covered to a depth of 150mm of crushed stone which should extend the full width of the trench
- Before the trenches are backfilled with the topsoil the crushed stone should be covered with peat fiber, geotextiles or similar permeable or durable materials. This is to prevent the stone being silted up with topsoil.
Maintenance of Percolation area
The percolation area should be inspected periodically and any signs of malfunctioning noted. This will show itself by obvious sings of blockage at distribution box, ponding, smell or pollution in the surrounding area. In this event contact our sales office. A reserve percolation area may have to be constructed.