Investigating what's underground is complicated and missing something can be life or death, literally. You need to follow a considered process to ensure safety for you and all your crew.
Most utility locators agree that the best way to locate underground utilities is using PAS128 or a similar methodology. A methodology like this helps you to identify risks and further drill into those risks as you get closer to your proposed work.
As a rough guide the process for locating underground utilities can be broken down into the following steps:
Step 1: Plan search
When starting a new project, be it a new retaining wall or a multi stage highway upgrade it's important to find as much plan information as you can.
This information is usually held by Network Utility Operators and can be provided in the form of as-built drawings or digital GIS records.
UtilityFinder helps you with your plan search by providing you with a fully interactive map of the known digital utility info in your area. We can usually get 3 waters, comms, power and gas. But this depends on the region and what information has been supplied to us by NUOs or users.
Once you've started your plan search with UtilityFinder, you'll need to look deeper into each asset owners data. You must contact each Network Utility Operator in your area, who will provide the most up to date information they have (sometimes there's commercially sensitive utilities they can't share) and also indicate if you need a standover or specialised locate by one of their staff.
Contacting Network Utility Owners when digging is a legal requirement in New Zealand so make sure you do this.
Other mechanisms exist which help fulfill your obligations to NUOs, such as Before you dig. It's important to note, only some Network Utility Operators pay to be members of Before you dig so make sure you still contact the NUOs in your area who aren't on their list.
UtilityFinders asset owner map will help you to identify who you need to contact.
Step 2: Site reconnaissance
Once you have your plan information (both your digital UtilityFinder map and any plans supplied by the utilities) and all the known NUOs, it's time to get out on site.
You'll need to start looking for any visible signs of underground utilities. This can be in the form of things like manhole covers, valves, surface scarring or any other signs of utilities like nearby connections to buildings or properties.
If you're still in the design phase of your project, the best time to do your site reconnaissance is when you're doing your geotechnical investigation. This way you can do your utility detection at the same time.
Step 3: Non-invasive detection
Once you have your plan information and have done your site reconnaissance, it's time to start attempting to detect the utilities themselves.
Detecting utilities is reasonably technical and requires specialised equipment so it's recommended to hire a professional to do this part for you.
Some network utility operators will supply you with their own locators, but it's always best to hire an independent locator who can provide you with an unbiased report.
Utility locators use detection methods like electromagnetic locators (EML), ground penetrating radar as well as physically accessing surface features like manholes and underground access point during their investigation.
A professional locator will be able to provide you with a report that you can use to plan your work and they will mark out the utilities on the ground.
Encourage your locator to survey their detections and document their findings digitally. This will help in the future especially if you're still in the design phase.
Step 4: Invasive detection
Sometimes even after you have done your non-invasive detection, there'll still be ambiguity and in a lot of cases it's a good idea to do invasive detection to confirm the location of the utilities. Especially if you are planning to dig directly above or across them.
Invasive detection could be as simple as just potholing, which is where you hand dig a small hole to confirm the location of the utility.
Or as sophisticated as Hydro excavation which is often used to confirm the location of the utilities and is a non-destructive way to do this for a large area.
It's important to remember that you'll probably need to get the utility owners permission before doing invasive detection work.
Step 5: Documentation
Once you have completed all your detection work, make sure you document what you've found. This can be in the form of a report or a map that you can use to plan your work.
This documentation is important as it can be used to show that you have taken all reasonable steps to locate the utilities and that you have done your due diligence. This could be vital if there is a dispute later on.
You should also supply this documentation to any other parties working on the project, as more often than not they'll probably think they need to do a similar exercise despite it just being done.
Conclusion
Locating underground utilities is a messy process that requires careful planning and execution. This is just a high level intro into the process and there are many other aspects that you need to consider when working around underground utilities.
Remember that your crews safety is the most important thing when it comes to working around underground utilities, so always take the time to plan your work and ensure that you have taken all necessary precautions.
If you are unsure about anything, it's always best to consult with an independent utility locator who can help you to understand the risks and the best way to mitigate them.