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F__11FCE1V17=79"D <br />JE�.i"1 111 U ii <br />ENVIRONMENTAL HEALTH <br />DEPARTMENT <br />Compact backfill <br />carefully over and <br />around the piping <br />�$. <br />system. When using <br />tamping equipment, r <br />take care to prevent <br />vibration from driv- <br />ing small stones into be tamped into <br />shaded areas. <br />the pipe wall. The <br />amount of compac- <br />tion and the type of <br />soil determines the soil modulus. For example, pea grav- <br />el has a typical modulus of 1,000 psi with no compaction, <br />while sand requires slight compaction (85% Proctor den- <br />sity) to achieve a modulus of 1,000 psi. Refer to ASTM <br />D3839 or AWWA C950 for further details. <br />Cover the pipe as soon as possible after successful test- <br />ing to eliminate the chance of damage to the pipe, float- <br />ing of the pipe due to flooding, or shifting of the line due <br />to caving in of the trench walls. If damage is suspected, <br />the lines should be retested. <br />Take care to remove frozen lumps from all backfill materi- <br />als before using. Frozen earth will eventually thaw, leav- <br />ing the pipe with insufficient support and voids around <br />the pipe. <br />In all cases, the pipe must be completely surrounded with <br />select backfill (sand, 1/8" to 3/4" pea gravel, or 1/8" to 1/2" <br />washed, crushed stone). There should not be any voids un- <br />der or around the pipe. Six inches (150 mm) of the fill must <br />be placed under the pipe as bedding material. Native backfill <br />materials should never be used. <br />One of the most common causes of damage is paving stakes <br />being driven through the product. Be careful that the stakes <br />are not driven along the path of the piping. <br />