Why should the backfill be porous?

Why should the backfill be porous?

• A. To improve drainage around the bed
• B. To reduce soil strength
• C. To allow oxygen to diffuse down to the leaching bed
• D. To prevent nutrient leaching

Answer: (C)

The main idea is that the backfill around the leach bed must be porous to allow air to reach the bed. Oxygen diffusion down into the infiltrative trench keeps the soil in an aerobic state, which supports the aerobic microbes that treat the wastewater and keep the pores open for drainage. This aerobic activity helps prevent clogging and maintains proper functioning of the bed. While good drainage is a beneficial effect of porosity, the critical purpose is supplying oxygen to sustain those aerobic processes; porosity isn’t primarily about reducing soil strength or preventing nutrient leaching.

The main idea is that the backfill around the leach bed must be porous to allow air to reach the bed. Oxygen diffusion down into the infiltrative trench keeps the soil in an aerobic state, which supports the aerobic microbes that treat the wastewater and keep the pores open for drainage. This aerobic activity helps prevent clogging and maintains proper functioning of the bed. While good drainage is a beneficial effect of porosity, the critical purpose is supplying oxygen to sustain those aerobic processes; porosity isn’t primarily about reducing soil strength or preventing nutrient leaching.