A non-metallic pipe such as storm water and sewer pipes can be traced just like any other underground service, although there are some extra steps, we need to take to get an adequate level of accuracy ready for construction or planning and design works.
Storm water pipes are generally made of non-metallic materials. Depending on the size and the age of the pipe, they can be made up of:
- Reinforced concrete
- Pvc polyvinyl chloride
- VC vitrified clay
- Brick tunnels
- Precast Cement
Because storm water and sewer pipes are mainly constructed of non-conductive materials, we cannot use typical electromagnetic locating methods to pinpoint their location. Locating a non-metallic pipe requires:
- Access to a manhole or pit or rodding point
- Extra equipment on top of the usual electromagnetic locators
- Pipe to be clear of blockages
- Slightly more time to set up and pack up
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It’s not like an electrical cable where we can get a power signal through a traceable 50hz passive signal emitted by live cables just by waving the Electromagnetic (EM) receiver aka “the magic wand” over the service or by inducing a current into a copper water service.
The actual magic happens when the intent to locate a sewer pipe takes place.
Access to the Storm Water Pipe: What we do is pop up the sewer or storm water manhole lid and see where the pipes are running from the surface.
The easiest way to locate a storm water pipe
The easiest way to confirm the depth and location of a storm water pipe is to open up a storm grate or manhole and physically measure the pipe size and invert level. By measuring the actual dimensions and recording the information we can class this as a QL-A at this point. The actual dimensions and measurements have been verified and can be trusted with a high level of confidence.
Although the Quality A location level depths and pipe sized is localised to this one area, by stringing together multiple measurements gathered at a couple of pits and manholes, we can survey the data and get a quality information which maybe adequate enough to plan initial designs.
For further confirmation in accuracy of the pipe location, we would recommend electromagnetic locating and non-destructive digging.
Equipment needed to locate a non-metallic storm water or sewer pipe
The next step is to feed a flexible fibreglass rodder which either has a traceable wire integrated inside the rod, or a traceable sonde which transmits a set frequency attached to the end of the rodder into the pipe that you want to trace
Flexi-trace’s or flexi-rodders are needed more and more in this modern age of utilising the ease of installation and cost savings of using non-metallic materials to manufacture underground pipes and cables.
Flexi-rodders can come in many thicknesses depending on the application with thinner rods being suited to being pushed down tight and bend pipes where thicker diameter rods need to be rigid so the don’t bend through larger diameter pipe works.
In some cases, using a sonde maybe beneficial to the application needed to be located.
A sonde is a battery powered transmitting device that also comes in various sizes which can be attached to the end of a flexible rodder. A sonde emits a signal at a set frequency which is then able to be located with a typical Radiodetection locator receiver.
Sondes are very versatile because they do not require the need for a rodder with a trace wire built in, although this extra wire is an advantage, it’s not necessary as the sonde can be traced itself.
Luckily, Geoscope are well equipped for any situation when it comes to locating storm water and sewer pipes.
Rodding the pipe
To get a trace on the storm water or sewer pipe to be located, we need to feed enough of the push rodder/sonde through the pipe so we can trace it.
This means if our work area is 50m long and the storm water manhole is at the start of the project, we need to push our flexi-trace at least 50-60m inside the pipe to get a trace throughout the scope of the project.
Difficulties in feeding and locating traceable rodders could be manhole or pit is very deep or the pipe to be traced has debris or blockages.
If the pipe has any blockages in the lines such as tree roots, rocks and silt soils to even boulders and sadly rubbish, these will need to be cleared in order to get our lines through the pipe in order to be located.
One way we have these lines cleared is by using high pressure water with special nozzles called jetters to clear the blockages and sometimes even cutting tools when the roots are that tough.
Once the blockage has been cleared, we can continue on in the process of locating the storm water pipe.
Once we have a traceable rodder, sonde or transmitting device in the length of pipe, we can match the frequency to our receiver to pinpoint the location of where these devices are inside the pipe.
When locating the rodder in line mode, which is basically locating the wire inside the rodder, you will want to choose a frequency which is suited to the area depending on congestion of nearby utilities and the length of the target needing to be located. More on Frequency selection here.
Sondes will come in a variety shape and sizes too with varying frequencies although the typical frequency found are 512Hz or 33kHz
This in-turn will give us an indication of where the pipe is located in 3-dimensional position to a QL-B quality location level. Note, this does have some greater tolerance in accuracy compared to a level A location which means it needs to be potholed to confirm the depths and position. But with the modern equipment we use today, this type of location method gives us a pretty decent guide to work off as a starting point.
It’s not rocket science and it’s not overly hard to achieve a sewer pipe location. It comes down to process.
Following process is what gives us the best chance of success at locating underground services.
Geoscope are the professionals here so let the locating process flow. Sit back and concentrate on planning the design and excavation process and concentrate on how to protect these critical services at your site once they’ve been located.
What’s the best way to see if there are pipes in my storm water easement?
If you want to do some prior investigation to save time and see if there are storm water pipes running through your easement or boundary line, the best advice I’d give someone keen to save them a little bit of time and money on the locating side of things would be to take a walk around the block.
What we usually do before we take a site visit is check out google street view for signs of pits, grates and kerb inlet pits. By matching these up with existing records and council drawings (if available) we can get a greater picture in our head of what pipes should go where before even stepping foot out on site.
You can do this also, but because it’s usually your house we’re doing the investigation at, you can do this in person.
Spot any pits or grates in the area and work out the natural fall of the land. Most of the time, storm water pipes will work naturally with the land and you can find out where the pipes should be draining to.
How do I know if there is a storm water pipe in an Easment?
Sometimes, you may receive a council drawing indicating there is a storm water easment running through your property that you’re planning to work on. But how do you know if there is a pipe inside the easement and how do you go about finding it?
Whenever we’re engaged to locate a storm water pipe within a person’s property, there is usually a requirement from the engineer or the actual council from where the property is on to find certain details of the pipe in question. The typical things they need to know about the pipe are:
- The pipe diameter
- Pipe material
- Pipe invert level
- Pipe location / offset
- And possibly RL’s
To measure a storm water pipe diameter, we have to get access to the pipe somewhere upstream of the area of works and preferably downstream also to confirm the pipe diameters are the same size through out the run. This can be done by accessing the pit or grate in a nature strip, kerb or reserve.
Sometimes council plans will indicate a manhole inside the easement of a backyard, but these are can be commonly covered by garden beds, sheds or topsoil and lawns.
Once the pits are found and opened and pipe diameters recorded, we can also measure the invert level at the same time.
The invert level means the bottom. It’s the best place to measure as the water will flow along the bottom of the pipe (invert) and needs a certain grade/fall for it to flow in certain circumstances.
If an excavation crew was trenching nearby and needed to know how far they would be from the top of the pipe, we could also indicate the pipe obvert level, which means top of pipe.
By looking inside the pit and the pipes, we can quite easily determine if the pipe work is made of reinforced concrete or Pvc or certain material etc.
Once the pipe has been accessed, we can start to rod the pipe with a traceable rodder. Preferably ridding from the highest point heading down stream to allow our rodder to use gravity to work its way through the pipe.
If rodding upstream is the only method that is possible due to pit and property access restrictions, it can be achieved, albeit at a greater effort.
When we get the traceable rodder and sonde combo through the pipe, we then have a traceable line we can apply a signal to which can be located like tracing a copper water service.
What are some signs of storm water pipes are underground?
- Manhole lids
- Down pipes
- List types of pits and manholes
- Kerb outlet
- Head wall
- Gulley pit
- Side entrance pit