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APPENDIX C Primary Backfill Requirements 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 0.094inch[2.36mm]and gives guidelines for choosing the primary backfill material to use 3/4 inch[19 mm]. when installing ourfiberglass underground storage tanks. • The rounded stones mustconform to the specifications 2.The Installation Manual specifies thatseled rounded stones of ASTM C 33,sizes 6,67 or7. 2.The stones are a Manual o be sped as primary that ry backoundedfill ertonial. • No morethan 5 percent(by weight)of the backfill may pass through a #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 largerthan allowable crushed stones. 4.No backfill material shall be frozen orcontain lumps of frozen 10.When using crushed stones,the material is to be a mix of angular material at anytime during placement. particles,sizes between 0.094 inch[2.36 mm]and 1h inch[12.55 mm]. S.Another important characteristic of good backfill material is hardness ' The crushed stones must conform to the specifications or stability when exposed to water or loads.Most materials have no problems • of more than meeting the hardness requirement. No more than 5 v erSe a Table weight)of the backfill may pass • Materials like soft limestone,sandstone,seashells or shale should througha#8sieve.SeeTableC-lforadditionalinformation. not be used as backfill because they breakdown overtime. 6.Coarse aggregate is a technical term for the material(rounded stones PERCENTAGE OF STONES PASSING and crushed stones)that meets our backfill size requirements. THROUGH SIEVE BY SIEVE SIZE 7.ASTM International and the American Association of State Highway and Transportation Officials have specifications forstandard sizes of Rounded coarse aggregate. Stones • 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 ASTM C 33 Size# #6 Stone #67 Stone #7 Stone aggregate material.For each aggregate size,the amount u of material finer than each laboratory sieve(square openings) 1inch[25mm] 100% 100% --- is given as a percentage of the total weight of the sample. 3/4 inch[19 mm] 90-100% 90-100% 100% • ASTM uses size numbers 6,67,7 and 8 to describe specific gradation profiles for materials that pass through a series 1hinch[12.5mm] 20-55% --- 90-100% of sieves.Do not confuse these gradation profiles with sieve sizes. 'A inch[9.5 mm] 0-15% 20-55% 40-70% • C2.3.1.The percentages give an indication of the particle size distribution orgradation within a given aggregate size. No.4[4.75mm] 0-5% 0-10% 0-15% With aggregate size number6 of rounded stones,for example, No.8[2.36mm] --- 0-5°% 0-5% 20-55 percent of the sample(measured by weight)should pass through a 1h-inch 5 a with aggregate size number 7 of crushed stones,0-115 percent of the sample(measured Crushed by weight)should pass through a No.4 sieve. Stone 8.Some material suppliers may produce materials that meet our 14 requirements butare not identified by a standard coarse aggregate ASTM C33Size# #7 Stone #8 Stone size number.The supplier should be able to provide a specification that identifies the size or gradation of the material. 1inch[25mm] --- --- • If the material supplier is unable to supplya gradation report, 3/4inch[19mm] 100% --- an independent testing laboratory can perform a sieve analysis on a sample of the material according to the ASTM C 136 testing 1h inch[12.5 mm] 90-100°% 100% specifications.The test results can then be compared against 3/e inch[9.5 mm] 40-70% 85-100°% the size requirements for rounded or crushed stones shown in Table C-1. No.4[4.75mm] 0-15% 10-30% No.8[2.36 mm] 0-5% APPENDIX 43