Which component in a filter bed has a minimum thickness of 30 cm?

Which component in a filter bed has a minimum thickness of 30 cm?

• A. Filter sand
• B. Stone and pipe
• C. Topsoil
• D. None of the above

Answer: (B)

In a filter bed, the underdrainage pathway that carries effluent away is built around a layer of stone (gravel) with the distribution pipes running through or just above it. This stone-and-pipe assembly needs a substantial thickness to do its job: it provides enough pore space for the wastewater to spread laterally, prevents clogging by fines, and gives solid support so the pipes don’t sag or get crushed. Requiring a minimum thickness of about 30 cm ensures there’s enough media for effective drainage and reliable collection by the perforated pipe, which is essential for the system to function properly. The sand layer above serves as filtration, and topsoil covers the bed, but their roles and typical minimum thicknesses differ from the drainage layer.

In a filter bed, the underdrainage pathway that carries effluent away is built around a layer of stone (gravel) with the distribution pipes running through or just above it. This stone-and-pipe assembly needs a substantial thickness to do its job: it provides enough pore space for the wastewater to spread laterally, prevents clogging by fines, and gives solid support so the pipes don’t sag or get crushed. Requiring a minimum thickness of about 30 cm ensures there’s enough media for effective drainage and reliable collection by the perforated pipe, which is essential for the system to function properly. The sand layer above serves as filtration, and topsoil covers the bed, but their roles and typical minimum thicknesses differ from the drainage layer.