A raised leaching bed is considered under which condition?

• A. When the high groundwater table is less than 900 mm from the ground surface
• B. When groundwater is deeper than 2 m everywhere
• C. When the soil is clay
• D. When there is a shallow water table under 50 cm

Answer: (A)

Raising the leaching bed is used when groundwater comes up close to the surface, so you need extra vertical separation between the effluent and groundwater. When the high groundwater table is within 0.9 meters of the ground surface, a conventional leach field would be too close to groundwater, risking insufficient treatment and potential contamination. Building a raised bed adds fill and elevates the leaching area above the shallow water, creating the necessary unsaturated zone for proper drainage and treatment. The 0.9-meter threshold is a common design guideline to ensure there’s enough separation. The other conditions describe different soil or water-table issues, but they don’t define the standard trigger for a raised bed in this context.