In a shallow buried trench system, the distribution pipe should be at least how long?

• A. 25 metres
• B. 30 metres
• C. 35 metres
• D. 45 metres

Answer: (B)

Uniform distribution of effluent along the trench is critical in a shallow buried trench system. The distribution pipe must be long enough to spread the wastewater across more outlets along the trench, so the flow doesn’t all concentrate near the inlet and overload the first portion of the bed. A minimum length of about 30 metres provides enough outlet points and travel along the line for the wastewater to be released progressively, promoting even loading of the gravel and the soil below. This helps prevent short-circuiting, reduces the risk of selective clogging at the start of the trench, and supports more reliable treatment by allowing the soil to absorb water more uniformly. Shorter runs can lead to uneven distribution and performance problems, while the specified length reflects a practical standard to achieve consistent results.