Percolation | Polishing Filters
Trench Percolation Area
This system uses a series of trenches placed in the soil to distribute the treatment tank's effluent. Each trench has the following components:
Soil Overlay- Membrane
- layer of clean broken stone to secure pipe
- Distribution pipe
- Clean broken distribution stone
The pipe in each trench is connected to a single distribution box. This box evenly distributes wastewater between each trench.
Trench Kits
Gravity fed Kits are available and include:
- Distribution pipes
- Distribution box with accessories
- Geotextile cover
- Installation manual
Sizing
Trench design differs depending on the the method of wastewater treatment (EPA, 2009). The following tables states the trench length requirements as described in the EPA Code of Practice:
| Minimum Percolation Trench Length Required with Secondary Treatment Input | ||||||||
| P-T Values | Percolation Trench Discharge | Trench Length Required per no. of People (m) | ||||||
| 4 | 5 | 6 | 7 | 8 | 10 | 12 | ||
| 3-21 | ≤50 | 24 | 30 | 36 | 42 | 48 | 60 | 72 |
| 21-40 | ≤25 | 48 | 60 | 72 | 84 | 96 | 120 | 144 |
| 41-50 | ≤25 | 48 | 60 | 72 | 84 | 96 | 120 | 144 |
| 51-75 | ≤16 | 75 | 94 | 113 | 131 | 150 | 188 | 225 |
| 10m Maximum Trench Length (EPA, CoP, 2009) | ||||||||
| Minimum Percolation Trench Length Required with Septic Tank Input | |
| Number of People | Minimum Length of Trench Reqired (m) |
| 4 | 72 |
| 5 | 90 |
| 6 | 108 |
| 7 | 126 |
| 8 | 144 |
| 10 | 180 |
| 12 | 216 |
| 18m Maximum Trench Length (EPA, CoP, 2009) | |
Molloy Precast recommend that a gravity system and hence a trench system is not installed for trench lengths greater than 100m for secondary treatment systems. This is due to the difficulties in constructing the system to the correct levels and hence failure of the bed. In these circumstances we recommend a below ground or raised pressurised pad is constructed. Trench systems for septic tanks require extra care during construction due to tthe longer trench length lengths required.
Further Information
For further information do not hesitate to contact our design team. We would also strongly recommend a visit to our interactive training and display faciltiy where you can see exactly how a trench system is constructed and operates.
