Which of the following lengths meets the minimum distribution pipe length requirement in a shallow buried trench system?

• A. 15 metres
• B. 30 metres
• C. 45 metres
• D. 60 metres

Answer: (B)

The idea being tested is that a shallow buried trench must have a minimum amount of perforated distribution pipe to spread effluent across enough area for proper infiltration. This minimum ensures the wastewater isn’t concentrated in a short segment and that the soil receives the flow over a suitable length.

Among the options, you’re looking for the smallest length that still satisfies that minimum requirement. Shorter lengths won’t meet the distribution needs, while longer lengths do meet the minimum, but they’re not the minimal amount required. So the correct choice is the smallest length that meets the minimum distribution pipe length requirement.