What type of backfill material should be used?

The correct choice for backfill material is free-flowing. This type of material is essential in ensuring proper drainage and compaction around underground structures, such as underground storage tanks (USTs). Free-flowing materials allow water to move easily through the soil, reducing the risk of water accumulation that can lead to hydrostatic pressure or other issues affecting the integrity of the installation.

When backfilling around USTs, it is crucial to select materials that do not compress or settle significantly over time, which can compromise the tank's stability. Free-flowing materials typically include sand or gravel, which provide excellent drainage properties and stability. These characteristics help maintain the structural integrity of the installation and extend the lifespan of the UST by preventing water-related damage.

In contrast, stagnate, A-Morph-is, and egregious do not represent suitable backfill materials. Stagnate implies a lack of flow, which is not conducive to proper drainage. A-Morph-is does not pertain to any recognized geological or construction term, and egregious suggests something that is fundamentally wrong or inappropriate, which would not be applicable to safe and effective installation practices. Therefore, free-flowing backfill is the best choice for UST installations to ensure long-term performance