What must extend at least one foot beyond the drainline horizontally in an ET system?

In an Evapotranspiration (ET) system, the component that must extend at least one foot beyond the drainline horizontally is related to the specific requirements for porous media. This extension is crucial to ensure that there is adequate space for the moisture from the wastewater to be effectively absorbed and evaporated into the environment. The porous media plays a critical role in the functioning of an ET system, as it allows for the necessary movement of water through the soil structure. When the media extends beyond the drainline, it helps facilitate proper treatment and prevents saturation around the drainline, which could lead to system failure or inadequate treatment.

By allowing this extension, the system maximizes its efficiency in dealing with excess water and helps in maintaining the balance necessary for the process of evapotranspiration to work effectively. This aspect ensures that the area around the drainfield remains adequately aerated and prevents waterlogging, which is vital for the health and efficacy of the on-site sewage facility.