Overview
An underground tank with a controlled outlet for sites where above-ground space is limited and excavation is possible.
Pro / Contractor€€€Large storageExcavation access needed
Materials
- Poly or concrete cistern (size per design)
- Inlet/outlet fittings + inspection riser
- Backfill (sand/gravel) and bedding
- Overflow to storm or soakaway
- Optional: pump and filter
Tools
- Excavator, shoring (as required)
- Compactor, levels
- Pipe saws, solvent cement (for PVC)
Safety & Risks
- Trench safety and shoring required for deep excavations.
- Confined space rules for tank entry.
- Call utility locate before digging.
Maintenance
- Inspect screens and first-flush devices quarterly.
- Pump out sediment as needed; test pump annually.
Permits / Notes
- Building permit and storm connection approval usually required.
- Check groundwater table and buoyancy calculations.
Steps
- Engineering design for volume, buoyancy, and loads.
- Excavate and prepare level bedding; set tank per manufacturer.
- Connect inlet, outlet, and overflow; add inspection riser.
- Backfill in lifts with compaction; protect pipes.
- Install pump/filter if using water for irrigation.
- Commission, leak check, and restore surface.