What is the role of sand in a mound soil absorption system?

The role of sand in a mound soil absorption system is primarily to provide a medium for effluent filtration and aeration. This is crucial because sand has specific physical properties that allow it to effectively filter effluent as it percolates through. The larger particles of sand create voids that facilitate the movement of water, while also allowing air to be trapped within those spaces. This aeration is essential for promoting the growth of beneficial microorganisms that help break down organic material in the effluent, ensuring a cleaner discharge into the environment. The filtration process helps remove particulates and some pathogens, making the effluent safer as it enters the underlying soil layers. Therefore, the presence of sand enhances both the treatment efficiency and the overall performance of the mound system.