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APPENDIX C Primary BackT111 Kequirements I. The backfill material surrounding an underground storage tank 9. When using select rounded stones, the material is to be a mix (UST) is a critical part of a proper tank installation. This document of rounded particles, sizes between 0.094 inch [2.36 mm] and gives guidelines for choosing the primary backfill material to use 3/a inch [19 mm]. when installing ourfiberglass underground storage tanks. • The rounded stones must conform to the specifications 2. The Installation Manual specifies that select rounded stones of ASTM C 33, sizes 6, 67 or 7. • No more than 5 percent (by weight) of the backfill may pass through a or crushed stones are to be used as primary backfill material. #8 sieve. See Table C-1 for additional information about specifications. 3. Primary backfill material is to be clean, free-flowing, and free of • Generally, rounded stones that meet the gradation requirements dirt, sand, large rocks, roots, organic materials, debris, ice and snow. are larger than allowable crushed stones. 4. No backfill material shall be frozen or contain lumps of frozen material at any time during placement. S. Another important characteristic of good backfill material is hardness orstability when exposed to water or loads. Most materials have no problems meeting the hardness requirement. • Materials like soft limestone, sandstone, seashells or shale should not be used as backfill because they breakdown overtime. 6. Coarse aggregate is a technical term for the material (rounded stones and crushed stones) that meets our backfill size requirements. 7. ASTM International and the American Association of State Highway and Transportation Officials have specifications forstandard sizes of coarse aggregate. • Table C-1 gives the standard sizes of coarse aggregate that meet the backfill material specifications for rounded stones and crushed stones. It identifies standard sieve sizes used to grade aggregate material. For each aggregate size, the amount of material finer than each laboratory sieve (square openings) is given as a percentage of the total weight of the sample. • ASTM uses size numbers 6, 67, 7 and 8 to describe specific gradation profiles for materials that pass through a series of sieves. Do not confuse these gradation profiles with sieve sizes. • C2.3.1.The percentages give an indication of the particle size distribution or gradation within a given aggregate size. With aggregate size number 6 of rounded stones, for example, 20-55 percent of the sample (measured by weight) should pass through a'/z-inch sieve. And, with aggregate size number 7 of crushed stones, 0-15 percent of the sample (measured by weight) should pass through a No. 4 sieve. S. Some material suppliers may produce materials that meet our requirements but are not identified by a standard coarse aggregate size number.The suppliershould be able to provide a specification that identifies the size or gradation of the material. • If the material supplier is unable to supply a gradation report, an independent testing laboratory can perform a sieve analysis on a sample of the material according to the ASTM C 136 testing specifications. The test results can then be compared against the size requirements for rounded or crushed stones shown in Table C-1. 10. When using crushed stones, the material is to be a mix of angular particles, sizes between 0.094 inch [2.36 mm] and 1/2 inch [12.55 mm]. • The crushed stones must conform to the specifications of ASTM C 33, sizes 7 or 8. • No more than 5 percent (by weight) of the backfill may pass through a #8 sieve. See Table C-1 for additional information. W PERCENTAGE OF STONES PASSING THROUGH SIEVE BY SIEVE SIZE Rounded Stones ASTM C 33 Size # #6 Stone #67 Stone #7 Stone 1 inch [25 mm] 100% 100% --- 3/4 inch [19 mm] 90-100% 90-100% 100% 'h inch [12.5 mm] 20-55% --- 90-100% 3/e inch [9.5 mm] 0-15% 20-55% 40-70% No.4 [4.75 mm] 0-5% 0-10% 0-15% No. 8 [2.36 mm] --- 0-5% 0-5% Crushed Stone %_ ASTM C 33 Size # #7 Stone #8 Stone 1 inch [25 mm] --- --- 3/a inch [19 mm] 100% --- 1h inch [12.5 mm] 90-100% 100% 3/e inch [9.5 mm] 40-70% 85-100% No.4 [4.75 mm] 0-15% 10-30% No. 8 [2.36 mm] 0-5% 0-10% W