What is the minimum pressure head required on a shallow buried trench system?

• A. 200 mm
• B. 400 mm
• C. 600 mm
• D. 800 mm

Answer: (C)

In a shallow buried trench, you need enough driving pressure to push effluent through all the distribution outlets along the length of the trench, overcoming losses in the pipe and the surrounding fill. That driving pressure is expressed as a pressure head, the vertical column of water the system can sustain. The minimum head required to ensure even distribution and prevent underloading at the far end is 600 mm. If the head is lower, flow tends to concentrate near the inlet and the far portions of the trench don’t receive adequate effluent, reducing performance. The other options fall short of this required drive (200 mm and 400 mm) or exceed the minimum without necessity (800 mm), which is why 600 mm is the correct minimum.