When using different backfill materials, what is recommended to separate them?

The recommended choice for separating different backfill materials is a fabric filter. Utilizing a fabric filter provides several advantages: it allows for the drainage of water while preventing the mixing of different soil types or materials. This separation is crucial because different materials may have varying permeability, compaction characteristics, and can affect the stability and integrity of the underground storage tank (UST) system.

A fabric filter specially designed for use in backfill applications can maintain the effectiveness of drainage and prevent clogging, which is important for the long-term performance of the UST. Furthermore, fabric filters are typically lightweight, easy to install, and cost-effective, making them a practical choice in UST installations.

In contrast, other options like plastic lining may not allow for adequate drainage and could trap water, leading to potential issues like hydrostatic pressure or corrosion. Concrete barriers would be cumbersome and not suited for typical backfill needs, while metal sheets could rust or corrode over time, compromising the effectiveness of the separation between materials. Thus, the fabric filter stands out as the appropriate solution for this application.