Septic & On-Site Wastewater Installation SWMS

Septic and on-site wastewater installation covers the excavation, siting, assembly and commissioning of septic tanks, aerated wastewater treatment systems (AWTS), pump wells, absorption trenches, evapotranspiration beds and associated pipework on unsewered lots. The work combines deep trenching in variable ground, entry into partially-buried concrete or polyethylene tanks that meet the confined space definition, exposure to raw sewage and biological pathogens, and coordination around excavators, tip trucks and vacuum tankers. Ground collapse, engulfment, oxygen deficiency and hydrogen sulphide accumulation are foreseeable and have killed plumbers and drainers in NSW.

Under the Work Health and Safety Regulation 2025 (NSW), this activity is high risk construction work under section 291 — specifically paragraphs (f) confined space, (g) trench deeper than 1.5 m, (l) contaminated or flammable atmosphere and (o) powered mobile plant. Section 299 therefore requires a Safe Work Method Statement prepared before work commences, kept available for inspection, and complied with. Controls follow the hierarchy: eliminate entry where possible, engineer shoring and ventilation, then administer entry permits and atmospheric testing supported by PPE.

Hazards identified

12 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Eliminate confined space entry where possible: install tanks with above-ground risers, external inlet/outlet couplings and remote sampling ports so internal entry for connection or cleaning is not required.
2. 2Substitute in-situ concrete tank cutting with pre-cast tanks supplied with factory-formed penetrations to remove respirable crystalline silica generation on site.
3. 3Engineer trench stability in accordance with AS 2865-2009 Confined spaces and AS 2870 site classification: benching, battering to the angle of repose, or using proprietary trench shields/shoring for any excavation ≥1.5 m or where ground conditions warrant, with a competent person inspecting each shift.
4. 4Before Dial Before You Dig plans and locate all underground services, then hand-expose (potholing) within 500 mm of marked services; de-energise or make safe any services in the excavation zone before mechanical digging.
5. 5Establish confined space entry controls to AS 2865-2009: written entry permit, continuous atmospheric monitoring for O2 (19.5–23.5%), LEL (<5%), H2S (<10 ppm) and CO, mechanical ventilation, tripod and winch retrieval, and a dedicated standby person outside the space.
6. 6Segregate powered mobile plant from workers with exclusion zones, spotter, reversing alarms and a traffic management plan; no worker in the trench while the excavator bucket is over the opening (WHS Regulation 2025 s215).
7. 7Rig tank lifts using certified lifting equipment inspected to AS 2550.1 and AS 1418.1; use tag lines, verify the crane/excavator lift chart, and keep personnel clear of the swing radius until the tank is landed.
8. 8Wet-cut concrete penetrations, risers and lids using water suppression and on-tool extraction meeting the Code of Practice for Managing the risks of respirable crystalline silica from engineered stone and other silica-containing materials; provide P2 respiratory protection to AS/NZS 1715 and AS/NZS 1716.
9. 9All electrical work on AWTS panels, pumps and alarms performed by a licensed electrician, protected by 30 mA RCDs, tested and tagged to AS/NZS 3760, and installed to AS/NZS 3000 with IP-rated enclosures suited to the wet zone.
10. 10Provide biological PPE for sewage contact: chemical-resistant gloves, safety eyewear/face shield to AS/NZS 1337.1, coveralls, and gumboots to AS/NZS 2210.3; establish hand-wash and decontamination station on site, and confirm workers' tetanus and Hepatitis A vaccination status.
11. 11Barricade all open excavations and tank openings to AS 4687 with hard barriers or covers rated for foot and vehicle loads; never leave a tank uncovered at cessation of work.
12. 12All workers hold White Card (CPCCWHS1001); confined space entrants and standby persons hold RIIWHS202E; SWMS content is consulted with workers under WHS Act 2011 (NSW) s47–49 and reviewed under WHS Regulation 2025 s302 after any incident, change in the work, or at least annually.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

A two-person plumbing crew is installing a 3,500 L concrete septic tank and 30 m of absorption trench for a new dwelling on a 2-hectare block at Wilberforce in the Hawkesbury LGA. The excavator digs a 2.3 m deep tank pit in sandy loam that shows signs of collapse on the northern face. The SWMS requires the crew to batter the pit to 45°, install a trench shield in the 1.7 m disposal trench, and treat the tank interior as a confined space during inlet baffle fit-out. Before the plumber enters the tank to bed the inlet tee, a four-gas monitor is lowered, forced ventilation runs for 10 minutes, an entry permit is signed by the PCBU, and a standby person maintains voice contact with a tripod and retrieval harness rigged above the access. The excavator is locked out and swung clear during entry. Dial Before You Dig plans confirmed a Telstra conduit 4 m east of the pit, which was hand-exposed before mechanical excavation.

Related legislation

• Work Health and Safety Act 2011 (NSW)
• Work Health and Safety Regulation 2025 (NSW)
• Plumbing and Drainage Act 2011 (NSW)
• Local Government Act 1993 (NSW) — On-site Sewage Management approvals
• Protection of the Environment Operations Act 1997 (NSW)
• Public Health Regulation 2022 (NSW)

Frequently asked questions