What is the permissible range of particle sizes when gravel is used for backfilled material?

The permissible range of particle sizes for gravel used as backfill material, which falls between 1/4 to 1 inch, is crucial for ensuring proper drainage and stability around underground storage tanks. This range is optimal because it allows for adequate void spaces for water drainage, thus preventing the buildup of hydrostatic pressure, which could lead to structural failure or tank floatation.

Gravel within this size range also provides sufficient support to the tank while allowing for easy compaction, which minimizes the risk of settling and ensures that the backfill offers good structural integrity. It's important for backfill material to be well-graded, allowing for both structural support and proper drainage to comply with environmental regulations.

In contrast, the other ranges provided do not meet the criteria necessary for effective backfilling. For example, particles smaller than 1/4 inch may not provide adequate drainage, leading to water retention and increased pressure. Larger particles, such as those in the range of 1 inch to 2 inches, may not fill the space effectively, leading to uneven support and potential instability. Therefore, the selected range of 1/4 to 1 inch is recognized as the most effective for this application.