ICC Underground Storage Tank (UST) Installation and Retrofitting Certification Practice Exam

The use of pea gravel and crushed rock as standard backfill materials for a fiberglass tank is based on their physical properties which provide adequate support and drainage. Pea gravel is well-rounded and facilitates excellent drainage around the tank, reducing the risk of water pooling, which could lead to corrosion or other structural integrity issues. Crushed rock, particularly when angular, provides stability and prevents movement of the tank during settling or changes in soil conditions. This combination allows the tank to be securely anchored while still allowing excess water to drain away, which is crucial for the longevity and safety of fiberglass tanks.

Other options, while they include pea gravel, either lack the drainage capabilities or structural support necessary for proper installation. Using dirt could lead to compaction issues over time, while incorporating sawdust could introduce organic material that can decompose, potentially compromising the surrounding structure of the tank. Thus, pea gravel and crushed rock are the preferred materials for effective and safe backfilling around fiberglass USTs.