Installation and Construction Practices
Installation and Construction Practices (Domain 5) tests the field execution that determines whether the design works: excavation and dewatering, bedding and backfill, tank anchorage, piping slope and support, and the tightness and continuity tests that must pass before backfill and again after repairs. The exam favors sequencing and acceptance-criteria questions.
Excavation and tank setting
- Shore or slope the excavation and keep water out of the hole; a tank set into a flooded hole is a buoyancy and bedding problem waiting to happen.
- Bedding is at least 12 in of pea gravel or sand, level and compacted, with no rock or debris against the shell. Backfill goes in evenly around the tank in lifts, never dropped from one side.
- Anchor before dewatering stops and keep the anchor system in place until backfill and paving loads are in service.
- Document the hole, bedding and tank before backfill; most jurisdictions make this a hold point.
Piping
- Suction piping slopes back to the tank at about 1% (1/8 in per ft) with a check valve at the tank.
- Pressure piping slopes back to the sump or tank so it drains and water cannot sit in a low trap.
- Respect FRP bend radii, support spacing and transition fittings; sump boots are installed to the manufacturer's detail and left testable.
- Seal every penetration and keep testable sumps accessible.
Testing and documentation
- Tank and piping tightness tests before backfill and after any repair; test pressure per manufacturer and PEI RP100, commonly 1.5× design pressure held at least an hour with no drop.
- Test the interstitial space separately, verify bonding continuity, and retain as-builts, test records and photographs.
Worked example
A 40 ft suction run must drain to the tank. At 1% slope, drop = 0.01 × 40 = 0.4 ft = 4.8 in. The far end is set 4.8 in higher than the tank entry, and the check valve is at the tank so the line stays full and the slope is not fighting a trap.
Traps
- Sloping pressure piping away from the sump and creating a water trap.
- Backfilling before the tightness test or the inspector's hold-point sign-off.
- Pressure-testing FRP above the manufacturer's limit.
- Leaving an empty tank unanchored while the water table rises.