The sand in the mound of a "mound system" primarily serves what purpose?

In a mound system, the sand primarily serves as a constructed containment vessel. This means that the sand forms a crucial part of the system designed to hold and filter wastewater as it percolates through the material. The mound configuration elevates the drain field above the native soil, providing adequate drainage and allowing for treatment of effluent by natural processes in the sand and surrounding environment.

The specific properties of the sand, such as its texture and permeability, facilitate the movement of water while also assisting in the removal of contaminants through physical, chemical, and biological processes. By absorbing and treating the effluent, the sand ultimately helps to protect groundwater resources and ensures effective sewage management.

While the mound system does have elements of treatment and disposal, the primary role of the sand is tied to its function as a containment vessel, making it essential for the overall effectiveness and safety of the system.