Which of the following best describes the construction material of infiltration basins?

Infiltration basins are designed to collect and manage stormwater runoff by allowing it to percolate through the soil and gravel layers. The primary function of these basins is to promote groundwater recharge while filtering pollutants from the stormwater. The use of natural soil and gravel is essential because these materials facilitate the movement of water through the ground while providing natural filtration processes that help improve water quality.

Natural soil and gravel create a permeable medium, which is vital for the basins' functionality. They allow for the natural infiltration of water, which is a key element in stormwater management practices. In contrast, impermeable materials such as concrete and asphalt do not allow for water movement and would defeat the purpose of an infiltration basin. Plastic liners, while they may prevent leachate from contaminating groundwater, are not conducive to infiltration and would also not provide the desired environmental benefits. Thus, the use of natural soil and gravel accurately captures the essence of what infiltration basins are constructed from and how they operate effectively in stormwater management systems.