Approved Backfill Calculator

The use of proper backfill is critical to long term underground storage tank performance. Only approved backfill is allowed when installing fiberglass storage tanks and the backfill must meet ASTM C-33 Fine Aggregate requirements for deleterious substances and soundness. To verify that your backfill material meets our specifications, use the Approved Backfill Calculator. Material like limestone, sandstone, crushed concrete, seashells or shale should not be used as backfill, because it may break down over time.

To begin: Select the backfill material you wish to verify. Then enter the required data from your provider's sieve analysis.


Select your backfill material to continue.

Pea gravel should be clean, naturally rounded aggregate with particle sizes no larger than ¾” (19mm) with no more than 5% passing a #8 sieve(2.36mm). Dry density must be a minimum of 95 pounds per cubic foot.

(Note: if the sieve analysis includes a #4 sieve but not a #8 sieve, enter the amount passing figure in the #8 sieve area. The minimum requirement is still no more than 5% passing.)

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Crushed stone or gravel should be washed, with angular particle sizes no larger than ½” (12.5mm) with no more than 5% passing a #8 sieve (2.36mm). Dry density must be a minimum of 95 pounds per cubic foot.

(Note: if the sieve analysis includes a #4 sieve but not a #8 sieve, enter the amount passing figure in the #8 sieve area. The minimum requirement is still no more than 5% passing.)

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The pea gravel information you have provided meets the CSI specification for approved backfill and should be suitable for use when installing our fiberglass products. This tool is used to confirm that the backfill material meets our specification and is not intended to replace a sieve analysis from a backfill provider. A sieve analysis is still required and must be attached to the Tank Installation Checklist to complete a proper installation. If you would like a confirmation email sent to you for your records, submit your email address and a project name below.

Based on your information, the pea gravel you are attempting to use does NOT meet CSI specification.

Contact your backfill supplier.

Please fill out both fields.

Thank You

An email has been sent to you based on the information you supplied.