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Primary Piping System Installation modulus of 1,000 psi with no compaction,while sand re- quires slight com- Proper construction of trenches is important. They should paction (85%®Proctor be wide and deep enough to accommodate the piping and density)to achieve a backfill material. See Table 5 for recommended minimum modulus of 1,000 psi. burial depths. Refer to ASTM D3839 or AWWA C950 for fur- 1. Typically,all piping should slope at least 1/8"(3 mm)per then details. foot toward the tank. Support pipe properly to prevent 4. Cover the pipe as soon Backfill nwst traps or sumps. as possible after suc- be taffwed Into 2. The piping should be separated by a distance of at least cessful testing to elimi- shaded areas. four to six inches(100 mm-150 mm). For double-wall nate the chance of dam- secondary containment piping installations,refer to Table age to the pipe,floating 12 on page 19 for proper distances. of the pipe due to flood- ing,or shifting of the line due to cave-ins. If dam- age is suspected, the I Table 5 lines should be retested. _ ! _ _ _ _ _ _ _ _ _ _ _I_ _ _ _ 5. Frozen earth will even- 4•(min.' tually thaw, leaving the YES NO +00 MMI Table pipe with insufficient I support and voids around the pipe. Take care to remove d bl frozen lumps from all backfill materials before backfilling. 1 1 Ts-{mtn.l t nm 1 1 Remember,in all cases,the pipe must be completely sur- rounded with select backfill(sand,1/8"to 3/4"pea gravel,or 118" s• to 1/2"washed crushed stone). Native backfill materials should 150 mm never be used. In all cases,there must never be voids(areas The pipe must be completely surrounded with select that do not contain backfill)under or around the pipe. Six inches backfill(sand,pea gravel or washed crushed stone). (150 mm)of the fill must be placed under the pipe as bedding material. 3. Compact backfill carefully over and around the piping sys- tem. When using tamping equipment,take care to pre- vent vibration from driving small stones into the pipe wall. The amount of compaction and the type of soil determines the soil modulus. For example,pea gravel has a typical TABLE 5.Recommended Minimum Burial Depths Based on Soil Modulus of 1,000 psi or Higher (Refer to ASTM D3839 or AWWA C950 for etho eory) Min.Amount of Sand,Pea Minimum Gravel or Washed Crushed Stone Pipe Size Burial Depth Above the Top of the Pipe (in.) (mm) Surface Condition (in.) (mm) (in.) (mm) 2 50 Unpaved 17 432 12 305 Paved,min.4"(100 mm)asphalt 12 305 8 203 Paved,min.4"(100 mm)concrete 9 229 5 127 3 75 Unpaved 20 508 14 356 Paved,min.4"(100 mm)asphalt 13 330 9 229 Paved,min.4"(100 mm)concrete 11 279 7 178 4 100 Unpaved 20 508 14 356 Paved,min.4"(100 mm)asphalt 14 356 10 254 Paved,min.4"(100 mm)concrete 11 279 7 178 6 150 Unpaved 36 914 14 356 Paved,min.4"(100 mm)asphalt 24 610 10 254 Paved,min.4"(100 mm)concrete 20 508 7 178 RED THREAD IIA Pipe & Fittings 6