Which layer has a minimum thickness of 200 mm in a Type A dispersal bed?

Which layer has a minimum thickness of 200 mm in a Type A dispersal bed?

• A. The sand layer
• B. The stone layer
• C. Both layers
• D. Neither layer

Answer: (B)

In a Type A dispersal bed, the bottom layer is a coarse stone or gravel that provides drainage and structural support for the bed. That stone layer must be thick enough to allow proper water movement and to keep fines from clogging the system, which is why a minimum thickness of 200 mm is specified. The sand layer above it serves mainly to help distribute the effluent more evenly and provide filtration, but the 200 mm minimum requirement in this scenario applies to the stone layer.

In a Type A dispersal bed, the bottom layer is a coarse stone or gravel that provides drainage and structural support for the bed. That stone layer must be thick enough to allow proper water movement and to keep fines from clogging the system, which is why a minimum thickness of 200 mm is specified. The sand layer above it serves mainly to help distribute the effluent more evenly and provide filtration, but the 200 mm minimum requirement in this scenario applies to the stone layer.