What material should cover the top of the absorption field gravel in septic systems?

In septic systems, the top of the absorption field gravel should be covered with a permeable material. This covering is essential for protecting the gravel while allowing water vapor and gases to escape, which facilitates the treatment and final absorption of effluent into the surrounding soil. A permeable layer helps maintain the necessary conditions for the operation of the septic system by providing sufficient aeration and ensuring that the underlying gravel can continue to function effectively in dispersing wastewater.

Using a permeable material prevents the compaction and clogging that can occur with non-permeable options, enabling the system to work efficiently. It ensures that the biological processes needed to treat the wastewater happen effectively, as the effluent must contact the soil for proper filtration and treatment.

In contrast, materials like concrete or plastic would not allow for the necessary exchange of gases and would impede the system's ability to treat wastewater effectively. Sand, while often used within the system, does not serve the same purpose as a protective cover, and may compact over time, potentially reducing the system's functionality. Thus, permeable material serves as the optimal choice to ensure both protection and effective operation of the absorption field.