PAS128 Surveys

A PAS128 survey is an underground utility survey carried out and reported to PAS 128, the British Standards Institution specification for underground utility detection, verification and location. What sets it apart from a standard utility survey is that every service on the drawing is given a quality level, so the people designing and digging know how far they can rely on each line.

Subvision Surveys has more than 3 decades of experience locating buried services. Our PAS128 surveys are carried out by surveyors qualified to NVQ Level 3 or 5 QCF, the level the 2022 revision of the specification sets out for survey practitioners, using electromagnetic location and ground penetrating radar together.

PAS 128 splits utility surveys into four types. Most projects use more than one, building up from the records to on-site detection and, where it’s needed, exposing the services themselves.

• Type D, desktop utility records search: collecting and reviewing the records of every utility company with apparatus in the area, without visiting site. We provide this as a desktop utility search pack, and it’s the starting point for every other survey type.
• Type C, site reconnaissance: a walkover to match the records to what can be seen on site, such as covers, chambers, street furniture, marker posts and reinstatement scars. It shows where the records look wrong or incomplete before detection work begins.
• Type B, detection: locating services on site with geophysical methods, normally electromagnetic location and ground penetrating radar together. This is what most people mean when they ask for a PAS128 survey, and it’s the bulk of the work on most sites.
• Type A, verification: exposing services, usually in trial holes or by vacuum excavation, to confirm their position, depth, type and size. It’s typically used at critical points such as crossings, new connections, or where piles and foundations come close to a service.

Each service on a PAS128 drawing carries a quality level that reflects how it was found:

• QL-D: taken from the records only. Useful for early planning, but not something to dig to.
• QL-C: records matched to features that can be seen on site.
• QL-B: detected on site. QL-B is split into sub-levels, from QL-B1 to QL-B4, depending on how confidently the service was detected and whether its depth could be measured.
• QL-A: exposed and verified, the most reliable position you can have.

The value of the quality levels is that a designer can see straight away which lines are firm and which need more work. If a new drainage run crosses a gas main shown only at QL-D, that’s a clear signal to upgrade that section to QL-B or QL-A before the design is fixed, rather than finding out when the excavator reaches it.

We start by agreeing the survey type and quality level with you or your principal contractor, along with the survey area and any critical zones. The 2022 revision puts more weight on this stage, because the effort a detection survey needs depends on factors such as site size, utility density and ground conditions.

The records search and site reconnaissance come next. On site, our surveyors use RD8000 and CAT4 electromagnetic locators with a Genny to trace cables and metallic pipes, and the IDS Detector Duo GPR to pick up plastic pipes, clay drains, empty ducts and anything else that won’t carry a signal. Using two methods together is what allows services to be recorded at the higher QL-B sub-levels.

All raw GPR data is kept, as PAS 128:2022 requires, and where post-processing is needed it’s carried out by trained staff. Services are marked on the ground, picked up with GPS or a total station, and drawn in AutoCAD with their quality level attached.

• An AutoCAD drawing in DWG and PDF, with every service colour-coded by type and labelled with its quality level
• Depths where measured, and a note wherever a service could be traced but not depthed
• A survey report setting out the survey type, the methods used, the areas covered and any limitations
• Paint marking on site where needed, so the groundworks team has the information as soon as we leave
• Areas that couldn’t be surveyed clearly shown, so they aren’t mistaken for being clear of services

The specification was revised in 2022, replacing the 2014 version. The main changes clients notice are:

• guidance on the training and qualifications of survey practitioners, with NVQ Level 3 or 5 as the benchmark
• clearer guidance on the effort a detection survey needs, including the use of two geophysical methods and coverage of the full site
• a requirement to record all raw data, with post-processing carried out only by suitably trained operatives
• a new specification for buried utility detection and avoidance, used to support permits to break ground
• new guidance on the accuracy of each detection method

If your project specification still refers to PAS 128:2014, we can talk you through what the update means for your survey before you instruct it.

Not every job needs the full specification. A homeowner digging a soakaway or a contractor replacing a fence line may be well served by a CAT survey or standard underground utility mapping. PAS 128 earns its cost on larger developments, highways and infrastructure work, and wherever a client or Tier 1 contractor has written it into the specification, because the quality levels give the design team and the contractor a shared, documented basis for decisions about risk.

Our utility mapping survey cost guide explains what affects the price of each option.

We carry out PAS128 surveys for Tier 1 contractors, developers, engineers and planners, and our team has worked on major projects including Wembley Stadium. We’re SSIP and ISO accredited, with SafeContractor, CHAS and Constructionline certification, and we’re Essex-based, working nationwide with a team of over 25 surveying professionals.

Because we also carry out topographical surveys and CCTV drainage surveys, the utility survey can be tied into the same site control and issued alongside the rest of your survey information.

Call us on 0333 920 9427 or use the form. Send us the site address, a red-line plan, the survey type or quality level in your specification if there is one, and a note of the work planned. We’ll confirm the right scope and come back to you with a quote.