Stormwater Installation

Stormwater and sanitary drainage are entirely separate systems: (1) STORMWATER carries rainwater from roofs, gutters, and paved areas. Pipes are typically larger (90-225mm) and shallower. Fall gradient typically 1:100. No treatment required. (2) SANITARY DRAINAGE carries wastewater from toilets, sinks, showers. Pipes typically smaller (40-100mm) and deeper. Requires ventilation and access pits. Both systems must be kept separate - connecting them causes cross-contamination and environmental pollution. AS/NZS 3500.3 covers stormwater specifically.

BYDA (1100) locates and marks all underground services before excavation: electrical (high voltage = electrocution hazard), gas (explosion risk), water mains, telecommunications, and wastewater. 20,000+ service strikes occur annually in Australia. Striking services causes: electrocution, gas explosion, water flooding, loss of utilities to neighbourhood, and massive liability claims. Calling 1100 is LEGALLY MANDATORY before any excavation. Service locators typically attend within 3-5 business days and mark services on ground with paint/flags. No excuse for striking services.

Stormwater pipes typically require 1:100 fall (1m drop per 100m length). Minimum 1:200 in some configurations, maximum 1:50 to prevent scour. Too shallow (< 1:100): water pools, mosquito breeding, sediment accumulation, blockages. Too steep (> 1:50): velocity erodes pipe internal surface, creates noise, risks pipe jumping at changes of direction. Use laser level or pipe laser to set correct gradient before laying pipes. Measure gradient at 10m intervals to confirm accuracy. Incorrect gradient is leading cause of stormwater system failure.

Yes. Licensed plumber required in all Australian jurisdictions. Most states (NSW, QLD, WA, SA, TAS, NT) offer specialist "Stormwater" or "Drainage" licence for workers performing only stormwater/drainage work (no sanitary plumbing). Victoria and ACT may require full plumbing licence. Check with your state's plumbing regulator: SafeWork NSW, WorkSafe VIC, QBCC (QLD), etc. Apprentices must work under direct supervision of licensed tradesperson. Working without licence is illegal and insurance claim may be denied.

Residential stormwater trenches typically 300-600mm deep (shallow). Commercial or council main connections can exceed 1.5m. For trenches DEEPER THAN 1.5 METRES: engineered shoring is MANDATORY. Options: (1) Sloping at 45-60 degrees (requires wide trench); (2) Adjustable aluminium/steel frames (most common); (3) Steel trench boxes. Shoring must be certified safe by competent person before worker entry. One cubic metre of soil weighs ~1,600kg - trench collapse is catastrophic. Previously disturbed soil (new build sites) is extra risk.

PVC solvent cement contains MEK and THF - toxic volatile organic compounds (workplace standard: MEK 150 ppm TWA). Hazards: (1) Vapours heavier than air - accumulate in trenches; (2) Vapours ignitable - no smoking/ignition sources; (3) Fumes cause dizziness, nausea, respiratory irritation. MANDATORY CONTROLS: (1) Perform cement joining in OPEN-AIR (never in trenches/pits); (2) Wear organic vapour respirator (Class A carbon cartridge) if any odour detected; (3) Do NOT use near enclosed spaces; (4) Check cement expiry (one-year shelf life); (5) Use per product instructions (do not exceed recommended amounts). If strong fumes detected - stop work, move to fresh air, ventilate area.

Hydrostatic testing is MANDATORY before backfill per AS/NZS 3500.3. Procedure: (1) Seal pipe ends with inflatable test plugs; (2) Fill system with water to 100kPa pressure (or per design); (3) Hold pressure for 10-15 minutes while monitoring with pressure gauge; (4) Acceptable: no visible leaks and pressure drop < 20kPa in 10 minutes. If test fails: leaking joint (typically solvent cement insufficiently cured). Do NOT backfill until test passes. Testing confirms system integrity before property damage occurs from leaks. Document test results on site for council approval.

Concrete cutting may be needed for pit openings or driveway/path modifications. SILICA HAZARD: Respirable crystalline silica (< 5 micrometres) is carcinogenic (IARC Group 1). Chronic exposure causes silicosis (lung fibrosis), lung cancer, COPD. Workplace exposure standard extremely low: 0.025 mg/m³. WET CUTTING MANDATORY SINCE SEPTEMBER 2024 (eliminates 99% of dust vs dry cutting). Procedure: Use wet-cut concrete saws with water recirculation system. P2 mask still recommended even for wet cutting. Best practice: HIRE LICENSED CONCRETE CUTTING CONTRACTOR to avoid any on-site exposure.

On-site detention (OSD) systems are required in many councils for commercial and higher-density residential properties. OSD temporarily stores stormwater during heavy rain, releasing it slowly into council mains to prevent flooding. System includes: (1) Underground detention tank (concrete, plastic); (2) Pump or gravity outlet with flow control restrictor; (3) Overflow to secondary outlet. OSD design per council specifications and site conditions. Typical storage capacity 5-50 cubic metres. Installation includes: tank excavation/placement, pump installation, control settings, and safety access covers. More complex than simple gravity drainage - consult council on requirements before design.

Deep pits (> 1.5m) present CONFINED SPACE HAZARDS: (1) Trench collapse risk - soil weight ~1,600kg/m³; (2) Atmospheric hazards - oxygen depletion, hydrogen sulfide gas (from decomposing organics) toxic at 10+ ppm; (3) Water accumulation - drowning risk; (4) Restricted access/egress. MANDATORY CONTROLS: (1) Competent person stability assessment; (2) Engineered shoring or sloping; (3) 4-gas atmospheric monitoring before entry (H₂S, O₂, CH₄, CO); (4) Forced ventilation; (5) Formal entry permit; (6) Standby person at surface trained in rescue; (7) Rescue harness and retrieval rope. Best practice: use PRECAST concrete pit chambers (avoids hand construction and pit entry entirely).

A "competent person" for trenching is someone with knowledge, experience, and authority to assess trench stability, identify hazards, and authorise safe working procedures. Role includes: (1) Daily pre-work trench inspection - assess soil type, cracks, water seepage; (2) Determine if shoring required (trenches > 1.5m ALWAYS require shoring); (3) Certify shoring is adequate before worker entry; (4) Monitor work and inspect shoring for movement; (5) Authorize worker entry/exit; (6) Respond to unexpected conditions (e.g., discovering underground obstruction or rock). Competent person must have training in soil classification, shoring requirements, and rescue procedures. Site supervisor, licensed plumber, or external consultant can fill this role - but must have documented competency.