Where should the entry point for the final outlet be located?

The final outlet entry point for an on-site sewage facility is ideally located 25-50% of the depth below the surface. This positioning helps ensure that effluent is adequately treated through the soil layers before it reaches the groundwater or surface water sources, providing improved filtration and reducing the risk of contamination.

By placing the outlet at this depth, it allows for a sufficient amount of soil to act as a natural filter, which is crucial for the remediation of pathogens and chemical pollutants present in the effluent. It also facilitates the separation of the effluent from surface water, thereby minimizing the chance of direct pollution to nearby water bodies.

Although the other options suggest alternative depths, they do not offer the same balance between adequate treatment and prevention of surface contamination. For instance, placing the entry point at the surface level does not provide any filtration and exposes the effluent directly to potential pollutants. Similarly, positioning it too deep may hinder the natural treatment process, as the effluent could not effectively interact with the aerobic bacteria needed for digestion and breakdown of waste materials.