Which of the following factors contributes to the overall absorption area size in a mound system?

In a mound system, the overall absorption area size is significantly influenced by the permeability of the soil. Specifically, soils that have slower permeability require a larger absorption area to ensure that wastewater is adequately treated without causing surface ponding or overloading the system.

When permeability is slow, water moves through the soil at a reduced rate, which means that it's essential to increase the surface area for absorption in order to allow for adequate infiltration and processing of wastewater. This larger area helps to distribute the effluent more evenly and prevents saturation of the soil in any one area, ultimately supporting proper filtration and biological treatment processes.

Factors such as a higher loading rate, faster permeable soils, or deeper installation depth do not necessarily contribute positively to the sizing requirements for absorption areas in the same manner. In fact, higher loading rates or faster permeable soils typically reduce the need for larger areas, as they can drain and treat effluent more efficiently. Therefore, slower permeability is the crucial factor that dictates the larger size of the absorption area in a mound system.