Locating Sewers for Build-Over Asset Applications
Why sewer mains and property connections are the hardest assets to locate — and what has to be true on site to get a design-grade result on a single visit.
Prepared by Aidan Waszaj, Operations Manager · South-East Scanning Pty Ltd · August 2026 · Rev 1
A build-over asset referral turns on a small number of details: where the sewer main runs, where the property connection leaves it, where the connection point sits, how deep each is, and how far each is from a boundary. On a drawing those numbers look trivial. Obtaining them is the most access-dependent task in utility locating, and the one most likely to fail on the day.
Almost every dispute on a sewer job comes back to the same thing: the attendance was scoped as though the sewer were a cable. A gravity sewer is not a cable and cannot be traced like one. There is no signal on the pipe and nothing to connect to. Everything depends on whether we can physically get inside the line — and that depends on what the property has, and what has been built over it since.
This guide sets out what a gravity sewer offers a locator, what it does not, and what must be true on site before an attendance can produce a design-grade result. Used as intended, it lets a locate be scoped once, attended once, and reported once.
1 Four assets, and the words that separate them
Most of the confusion on these jobs begins with vocabulary. Urban Utilities defines the terms below, and a referral is assessed against them, so it pays to be precise.
| Term | What it means |
|---|---|
| Sewer main | The reticulation pipe owned and maintained by the asset owner. In established Brisbane suburbs it commonly runs through rear yards rather than the street. |
| Sewer service junction | The downstream end of a property connection, where that connection meets the main. It is a fitting on the main and is not visible from the surface. |
| Sewer property connection | All pipes and fittings between the junction on the main and the property service, up to and including the connection point. It is asset-owner infrastructure, even though it sits within the lot. |
| Sewer connection point | The upstream end of the property connection, where the private house drainage connects to it. This is the point a referral most often asks for, and the one most often impossible to reach. |
| Private sanitary drain | Everything upstream of the connection point. It belongs to the property owner, not the asset owner, and is not what the referral is asking about. |
| Maintenance structure | A chamber through which access can be gained to the infrastructure — in common speech, a maintenance hole. Access to the network is limited to these, and to any inspection openings on the property connection. |
A locate on the main does not give you the property connection, and a locate on the private drain does not give you the connection point. They are three separate exercises, each needing its own point of entry. Where a report shows a long private line running to the house and nothing else, the connection point has not been located — it has been assumed. An assessor will notice.
2 What a referral actually asks of a locate
Urban Utilities' Build-Over Asset Referral Guidelines set out what must be uploaded before an application is treated as properly referred. The items that bear directly on locating work are these:
- A pipe location report with a site plan showing the infrastructure within the site, and dimensions to that infrastructure from the property boundaries.
- Where retaining walls are involved, the reduced level at the top of the sewer main in Australian Height Datum at each retaining wall location.
- Photographs of every sewer maintenance cover located within the site.
- An architectural site plan showing the asset owner's infrastructure within or adjacent to the site — all maintenance structures and property connections — correctly represented spatially against the boundaries and the proposed works.
- Structural drawings demonstrating that suitable access will be provided and maintained to any sewer maintenance covers, and to the junction of any sewer property connections on the site.
- A clear statement that a report consisting only of general photographs of the infrastructure will not be accepted.
Beyond the lodgement checklist, information requests during assessment routinely add further conditions on the deliverable itself: that position was determined by a Quality Level B method rather than by survey, that the level of accuracy is stated, that both invert level and top of pipe are given, that side and front or rear boundary offsets are shown, and that location and depth details obtained solely from ground-penetrating radar are not accepted.
First, the deliverable must include offsets, levels, a stated tolerance, and a stated quality level. Marks on the ground and a set of photographs will not satisfy the requirement, however good the field work was.
Second, radar on its own cannot satisfy the requirement, whatever it finds. The asset must be traced. That is a documentation constraint sitting on top of a physical one, and both point the same way.
A note on Australian Height Datum
A locate gives depth below the surface at the point of measurement. A referral asks for levels in Australian Height Datum, tied to the boundaries and reflected on the architectural and structural drawings. Those are different things. We undertake the locate, mark the alignment, and provide depths, diameters, and offsets; a surveyor then picks up our marks and converts them to datum. On most build-over jobs the locator and surveyor both attend, and sequencing them the right way round — locator first — saves a second survey visit.
3 QL-B and QL-C: the distinction the whole job turns on
AS5488 classifies how a position was obtained, and therefore what it may be relied upon for. Two of the four levels matter here.
| Level | How it is derived | What it supports | What it requires on a gravity sewer |
|---|---|---|---|
| QL-C | Visible surface features correlated with asset-owner records. | Preliminary layout and scoping. No guaranteed positional tolerance. | Surface features visible on site. No entry into the pipe is needed. |
| QL-B | Geophysical location, with the asset detected and traced. | Design, and build-over or build-adjacent submissions. | A signal inside the pipe — which means an open, serviceable access point, or a tracer wire. |
Re-issuing the report does not change the level, nor does adding annotations to it. The evidence was either collected on the day, or it was not. If a dimension is going to an engineer or to a referral, access must be in place before the technician arrives. This is the single most useful thing to carry into a design meeting — and the reason we now ask, at quoting, what the locate is for.
4 Why we can't simply scan the sewer with radar
This is the question we're asked most often: "You have radar, so why can't you just find it?" The honest answer has five parts, and only the last is administrative.
- Depth and attenuation. Radar energy is absorbed by conductive ground, and Brisbane's reactive clay soils are about as unhelpful as it gets — frequently wet. A rear-yard main typically sits 1.5–3 m deep, a property connection usually shallower. Reaching those depths needs a low-frequency antenna, which trades resolution for penetration. In wet clay the useful signal is often gone well before the pipe.
- Contrast. Radar detects boundaries between materials of differing dielectric properties. A vitrified clay pipe, surrounded by damp clay and partly filled with water, contrasts poorly with its surroundings. The pipe is there; the radar simply has very little to reflect off.
- Detection is not identification. A response at 2.2 m could be the sewer — or a stormwater line, an old trench, a rock, a root mass, or a former service. Radar shows a signal response, not an object identity, and the deeper and weaker the response, the less distinguishable it is.
- A crossing is not an alignment. Even a strong, unambiguous response only tells you that something crosses a scan line at a point. It does not give the run of the pipe, the fall, the junction position, or the connection point — the things a referral asks for.
- The asset owner's position. Urban Utilities does not accept location and depth details obtained solely from ground-penetrating radar. Even where radar produces a good result, it cannot stand alone in the submission.
Radar is genuinely useful on these jobs when used as a corroborating method rather than the primary one. It resolves trench lines and disturbed ground that indicate a likely alignment; it picks up shallow private drainage that carries no signal; it confirms a pit is where it appears to be; and it supports and cross-checks an electromagnetic trace. What it cannot do is replace the trace. On a gravity sewer, the trace is the job.
5 How a gravity sewer is actually located
A gravity sewer is a non-conductive pipe carrying no signal. Electromagnetic locating — the workhorse of QL-B for power, comms, and metallic water — requires a conductor, and there is none here. The method is therefore to put a signal inside the pipe and follow it from the surface.
Traceable rodding
A traceable rod is a fibreglass rod with a copper conductor running through it, wound on a drum and fed into the pipe from an access point. A transmitter energises the conductor, and the technician follows the signal along the surface with a receiver, marking position and reading depth at intervals. A variant uses an inert rod with a sonde — a small self-contained transmitter — at the tip; the sonde is located as a point rather than a line, so the technician advances it in stages and marks each position.
Rodding is effective, but it has real limits. Realistic push distances are much shorter than the length on the drum. Every bend costs distance, silt and root mass resist the rod, and a rod that has been forced becomes a blockage of its own. A rodding attendance is a physical negotiation with the pipe, and it does not always win.
Sonde in a camera head, and CCTV
A CCTV crawler or push camera with a sonde in the head does everything a rod does and adds the thing a rod cannot give: sight. The footage shows where the junctions are, whether a connection exists at all, whether it enters at the invert or above it, and the condition of the line. Distances are read off the counter, and the camera is parked at the features that matter so the sonde can be located and marked from the surface.
Rodding needs an opening. A sonde needs an opening. CCTV needs an opening. A tracer wire is the only method that does not — and, as Section 9 explains, most of Brisbane does not have one. Everything in this guide reduces to a single question: is there a way into this pipe today, and can it be opened?
6 Upstream, downstream, and why direction decides the outcome
A gravity sewer is built to carry flow in one direction, and every fitting in it is shaped accordingly. That geometry, which is exactly what makes the network work, is what makes it awkward to trace.
Downstream is straightforward. Fed in at an inspection opening on the property connection and pushed with the fall, the rod sits in the invert, gravity and any flow assist it, and junctions present as swept entries in the direction of travel. The rod arrives at the main, and the run between the two is traced and marked.
Upstream is the difficult direction. Fed in at a maintenance hole and pushed against the grade, the rod meets every fitting the wrong way round. Junctions are swept downstream, so a rod pushed up the main runs straight past a property connection rather than turning into it, and there is no way to steer it. Where a connection enters above the invert — on a riser or a drop — the rod cannot climb into it at all. Benching, silt, root intrusion, and offset joints all add resistance, and the further upstream the rod goes, the less control the operator has over the tip's position.
Attending the maintenance hole will usually give you the sewer main. It usually won't give you the property connection or the connection point. Those require an opening on the property connection itself, or CCTV from an access point that reaches them, or physical exposure. If a referral needs the connection point, that needs to be scoped before the technician is booked — not discovered on the day.
7 Brisbane backyards, where access is the whole problem
Much of Brisbane's sewer reticulation was laid through rear yards rather than along the street — in some suburbs following the rear boundaries of an entire block. It was a sensible design when the land was open and the houses were new. Ninety years of decks, sheds, pergolas, pools, retaining walls, paving, garden beds, and mature trees later, it is the reason this work is hard.
What limits access, in the order we encounter it
- Structures that have been covered over. Maintenance holes and inspection openings disappear under mulch, turf, pavers, concrete, decking, planters, and stored material within a few years. A structure not visible at a design visit is very often still there — finding it is part of the attendance rather than a given.
- Lids that will not come off. Corroded lids, seized or missing bolts, cracked rims, lids tiled, rendered, or concreted in. We carry Gatic lifters, leverage tools, and hydraulic tools, and open the large majority of pits we attend — but we stop where further force would risk breaking the lid or rim. Rectification of a compromised lid is the asset owner's responsibility, and the return visit once it is serviceable is a separate attendance.
- Structures on the neighbouring property. On a rear-boundary sewer, the maintenance hole commonly sits on or across the boundary, sometimes wholly within the adjoining lot. Where it is the only viable entry point, attendance depends entirely on a neighbour with whom we have no relationship. That access must be arranged, in writing, before the job is booked.
- Properties with no inspection opening at all. Some houses have an inspection opening, shaft, or boundary trap riser near the connection point. Many older ones have nothing. Where the private drain runs fully buried to a connection point with no opening, there is no access to the property connection and no rod or camera can be introduced. This is not a shortcoming of the equipment or the technician — there is simply no door.
A build-over asset referral is required precisely because something has been built over or near the asset. The sites that need the referral are therefore the sites where access has most often already been compromised. It's worth saying plainly to a client at design stage: the deck that has to be assessed may well be sitting on the only access point we would have used to assess it.
8 When there's no access: CCTV and vacuum excavation
Two methods remain when the ordinary route is closed. Both cost more than a standard attendance, and both are frequently the cheapest thing a client does on the job, because they end the correspondence.
CCTV inspection
Where a single opening exists but the configuration between it and the point of interest is unknown, CCTV converts assumptions into measurements. It establishes whether a property connection exists at all and where it joins the main, provides distance along the pipe to the junction and to the connection point, indicates whether the connection enters at the invert or on a riser, and records condition, root intrusion, offsets, and previous repairs. With a sonde in the head, each of those features can be located and marked on the surface. Some approvals also require a condition inspection before and after construction, and the same footage serves that purpose. What CCTV does not do is create an entry point — it solves not knowing what is between here and there, not having nowhere to start.
Vacuum excavation
Non-destructive vacuum excavation physically exposes the pipe, allowing its position, depth, diameter, and material to be measured directly. It is the only route to QL-A, and there are situations in which nothing else will do: where there is no access point anywhere on the property connection; where a footing, pier, or pool shell must be set to a tight clearance and an estimate is not good enough; where the connection point must be proven rather than inferred; and where the asset owner has asked for exposure. It is slower and more expensive than any other method — plant, spoil handling, traffic management, reinstatement, care around a live asset — but that cost is worth weighing against the alternative, which is commonly a refused referral, a redesign, a second locate, and a delay measured in weeks.
Every excavation on site — including pool and pier excavations, and potholing itself — sits within this sequence. Locating supports PLAN and PREPARE, and it informs POTHOLE. It does not remove the obligation to pothole before mechanical excavation near a located asset.
9 Tracer wire — the thing that would solve this, and mostly isn't there
A tracer wire is an insulated conductor laid in the trench alongside a non-conductive pipe, terminated at an accessible point so a signal can be applied and the pipe traced from the surface without ever going inside it. Where one exists and is intact, it turns a difficult job into a simple one.
- Sewers laid in newer subdivisions — particularly PVC and PE mains in estates developed in recent decades — are frequently laid with tracer wire, and some are terminated at accessible points.
- The great majority of Brisbane's reticulation predates the practice. Vitrified clay and early PVC mains in established suburbs have no wiring and no way to accept a signal other than through an opening.
- Where a wire is present, it is only as good as its continuity and its termination. Broken wires, unterminated ends, and wires never connected at the pit are all common.
- A wire traces the wire, not the pipe. It is usually laid directly over the line, but where the trench was reworked, the two can separate.
The practical point for a designer: if the site is in an estate developed in the last twenty years or so, say so at the time of booking. It changes the method, sometimes the price, and sometimes the achievable quality level.
10 Getting a result on a single visit
Almost every second attendance we make on a sewer job was avoidable. The items below determine the outcome. Working through them before the booking is made is the difference between one visit and three.
- State at booking that the locate is for a build-over asset referral. This sets the required quality level and cannot be corrected after the fact. A locate scoped for layout is a different job to one scoped for a referral.
- Provide the BYDA response, the sewerage service diagram, and any property connection details held by the asset owner. Records are QL-D and won't be relied on for position, but they tell us where to look and what to expect.
- Provide the survey plan, the proposed footprint, and the proposed depth and footing type. The clearances that matter determine where the effort goes, and whether potholing is needed at a specific point.
- Walk the property and find every sewer structure, then photograph each one. Behind sheds, under decks and stairs, along fence lines, through garden beds. Photograph damaged, sealed, and built-over lids too — those are the ones that change the scope.
- Expose any covered lids, and arrange rectification of anything sealed or damaged, before the attendance. Rectification of a compromised lid sits with the asset owner, and arranging it takes time. Starting that after a failed attendance adds weeks.
- Confirm whether there is an inspection opening on the property connection. If there isn't, and the referral needs the connection point, expect CCTV or vacuum excavation — and price for it at the outset.
- Arrange access to the adjoining property, in writing, where a structure sits on or across the boundary. A verbal arrangement with a neighbour who isn't home on the day is not access.
- Confirm whether levels in Australian Height Datum are required, and engage the surveyor to pick up our marks. Sequence the locator first, then the surveyor. Reversing that order usually costs a second survey visit.
- Allow a contingency in the program and the budget for vacuum excavation. On a site with poor access it's a likely outcome, not an unlikely one, and a contingency is cheaper than a stalled referral.
- Book the locate before the design is fixed. Where the asset turns out not to be where the record placed it, an early locate is a design input. A late one is a redesign.
11 What can realistically be delivered, by site condition
This is the honest version of the conversation we would otherwise have at the end of an attendance.
| Condition on the day | What we can deliver | What that supports |
|---|---|---|
| Maintenance hole open and serviceable, and an inspection opening on the property connection open. | Main and property connection traced and marked, with depths, offsets, and a stated tolerance. QL-B. | A referral submission, subject to levels being tied to datum by a surveyor. |
| Maintenance hole open, no inspection opening on the property connection. | Main traced at QL-B. Junction position established by CCTV where the chamber allows. Connection point inferred at QL-C, or exposed at QL-A. | The main is design-grade. The connection point needs a further step before it is. |
| Maintenance hole sealed, damaged, or built over. | Surface features correlated with records. QL-C, and nothing beyond it. | Preliminary layout and scoping only. Not a referral submission. |
| Only viable access point is on the adjoining property, and access has not been arranged. | As above. QL-C. | Preliminary layout and scoping only. |
| Clearance critical at a specific footing, pier, or pool shell. | Vacuum excavation at that point, confirming position, depth, diameter, and material. QL-A at the point exposed. | The highest available confidence at that point. The line reverts to a lower level between potholes. |
| Estate sewer with a terminated and continuous tracer wire. | Trace from the surface without internal access. QL-B. | A referral submission, on the same terms as the first row. |
12 Limitations, and how to use this guide
This document provides general guidance on locating sewer infrastructure and the constraints that apply to it. It is not a utility location, a clearance to excavate, engineering advice, or advice on the approvability of any design. It does not substitute for a BYDA enquiry, for a utility location undertaken to the quality level appropriate to the intended use, or for the asset owner's own approval process.
Requirements described here reflect Urban Utilities' published guidance as at the date of this revision and are summarised rather than reproduced; the asset owner's current requirements govern, and other South-East Queensland asset owners apply their own. Verify the current requirement for your site before relying on any statement here. Where a design encroaches on an asset or its zone of influence, assessment against Queensland Development Code MP1.4 is a matter for a private building certifier, and the structural design a matter for an RPEQ engineer.
Let's talk about your site
We undertake utility location, ground-penetrating radar, concrete scanning, CCTV drainage inspection, and structural diagnostics across South-East Queensland, with reporting classified to AS5488. Send through the BYDA response, the survey plan, and the proposed design, and we'll advise the quality level each part of the job calls for — and what has to be true on site to achieve it. We'll review a site's BYDA response and photographs before a locate is booked, at no charge, where doing so is likely to avoid an unproductive attendance.
South-East Scanning Pty Ltd — Specialists in Utility Locating, GPR Concrete Scanning & Structural Diagnostics
1 Mitaro Rise, Pacific Pines QLD 4211 · info@southeastscanning.com.au · southeastscanning.com.au
Prepared by Aidan Waszaj, Operations Manager · aidan@southeastscanning.com.au
