Underground services: a practical checklist.
Why plans alone are not enough, what safe locating involves, and the information a contractor needs before excavation.
Why homeowners should care before work starts
Underground services may carry electricity, gas, water, wastewater, stormwater and communications. Damage can cause serious injury, flooding, contamination and loss of service. WorkSafe warns that plans and surface mark-outs may not show the exact position or depth.[1]
This guide helps an owner understand the questions a competent contractor should be asking. It does not replace the contractor's site-specific risk assessment, service-owner requirements or WorkSafe guidance.
Four questions to ask before digging
- Have current service plans and property information been gathered?
- How will services be located and their position verified on site?
- How will the digging method change close to a known or suspected service?
- How will the information be shared with operators, spotters and everyone working nearby?
1. The five-layer control model
| Layer | Purpose | Failure if omitted |
|---|---|---|
| 1 — Records | Identify service owners, likely routes, assets and constraints. | Unknown networks or stale information remain outside the plan. |
| 2 — Locate and mark | Translate documentary information into a visible site hypothesis. | Operators cannot relate plans to the work area. |
| 3 — Verify | Confirm position and depth using an approved exposure method. | A marked line is treated as certainty when field reality differs. |
| 4 — Control work | Select plant, tools, approach distances, spotters and exclusion zones. | The method does not respond to proximity or service consequence. |
| 5 — Monitor and update | Keep controls aligned as the excavation moves and new evidence appears. | Initial information becomes stale while conditions change. |
WorkSafe recommends liaising with all relevant service owners, keeping current plans on site, accurately tracing and marking services, checking depth and using detection equipment suited to the task.[1] It also notes that multiple service owners and unmapped services may be present.
2. Planning before ground disturbance
Define the excavation envelope
Show the intended plan area, depth, batter or support requirements, stockpile position, plant working radius, haul route and access. A service outside the trench line may still be affected by plant reach, ground loading, vibration or undermining.
Identify permits and owner controls
Service owners may specify minimum approach distances, exposure methods, competent-person requirements or written permits. WorkSafe guidance states that activity closer than published minimum approach distances requires documented permission or consent from the service owner and that the owner’s specific requirements must be checked.[1] Do not reproduce a generic distance table as the project authority; retain the current owner document.
Plan the response to uncertainty
The method should state what happens if the service cannot be found, appears at a different depth, is encased, conflicts with the design, or is damaged. Emergency contacts, shutdown actions, exclusion and reporting procedures must be available before excavation, not assembled after a strike.
3. Field controls around mobile plant and exposed services
Operators need a clear view of marked services, excavation limits and the spotter. Spotters must remain outside plant danger zones while maintaining effective communication. The team should brief swing radius, blind spots, overhead hazards, access/egress and changes in ground support. WorkSafe’s guidance on road and roadside work similarly requires utilities to be identified before ground is broken and the service owner’s preferred uncovering technique to be confirmed.[2]
As the excavation approaches a service, use the method accepted by the service owner. Physical verification may involve carefully controlled potholing or vacuum methods where suitable. Exposed services must be identified, supported and protected from plant, spoil and collapse. Never assume an unrecognised pipe or cable is redundant.
Excavation stability remains a separate hazard. WorkSafe emphasises daily inspection and reassessment after events that could affect stability, safe access, protection from falls and ground-support measures such as shoring, benching or battering where required.[1]
4. Make service information part of the workfront handover
A useful daily or shift handover records the active work zone, current service plans, verified locations and depths, exposed assets, permits, remaining uncertainty, no-go areas, changed methodology and emergency contacts. Mark-outs should be maintained when weather, traffic or earthworks make them unclear.
Clients and site controllers also hold relevant information. Existing as-builts, private services, irrigation, abandoned lines and site modifications must be disclosed. Pidgeon Contracting’s health and safety page sets out the expectation that known hazards and access conditions are shared before work starts.
References
- WorkSafe New Zealand — Excavation Safety Good Practice Guidelines, including utility-service planning and field controls.
- WorkSafe New Zealand — Working near utilities and services.
- WorkSafe New Zealand — Guide for Safety with Underground Services.
Checked 15 August 2026. Always use the current WorkSafe and service-owner requirements for the actual work.
Planning civil excavation?
Provide the site address, proposed depth and footprint, current service information, access constraints and design documents before scope or programme is confirmed.