Soil Porosity

Prior to installating a septic tank you will need to carry out a porosity test. This is to determine ground conditions as required by building regulations part H2.

• Excavate a hole 300mm square by 300mm deep below the proposed invert level of the land drain

• Fill hole with water to a depth of 300mm and allow to drain away over night

• Refill to a depth of 300mm and note the time taken to drain away completely

• Repeat this exercise two more times and calculate the average time

• By reference to the table the length of drain run required for various capacity tanks may be established

The above is based on 500mm trench width, 2.0m apart. For lengths above 100mm it is acceptable to use 1.0m wide trench and halve the length.