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  • Emma Chetwynd Jarvis

What is a PAS128 survey and what are the different types?

PAS128 is the current specification for underground utility detection, verification and location. It is a publicly available specification issued by the British Standards Institute. The PAS128 standard requires accurate, quality information to be recorded to a consistent standard with regards to the location of underground utilities.

PAS128 allows a buyer to specify the type of survey they would like and the methodology by which it should be performed. Not only this, but it provides description of the deliverables which should be produced.


WHO USES PAS128?


PAS128 is used by engineers, construction contractors, project managers and utility owners as well as surveyors, geophysicists and subsurface utility engineers, all responsible for recording and using information about underground utilities.


DIFFERENT PAS SURVEY TYPES


When specifying a PAS128 complaint underground utility survey, there are different levels of detail required. The selection criteria ensure the data collected meets the on-site requirements of the specific project. The four different survey types are each assigned a letter from D to A with A being the highest quality and most detailed.


The PAS128 survey types are:


Category type D: Desktop survey


The underground utilities are plotted based on only recorded data. This is done by identifying known utility owners within the specified survey area and contacting them to request a copy of their asset information. The information is then collated onto one drawing. Results from a desktop search are described as the lowest quality level.


Category type C: Site reconnaissance


Underground utility are plotted based only on record data, but with on-site investigation to identify the physical features above ground which support the information provided by the desktop survey. An onsite reconnaissance increases the quality level of the survey as there is some confidence that a utility is present. Services identified this way can have their quality improved from D to C.


Category type B: Detection


Utilities detected by geophysical methods to get an exact horizontal and vertical position. They are carried out to one of four levels of accuracy with each requiring a different survey type. The results obtained using geophysical techniques should be recorded and compiled with the data from the records search and onsite reconnaissance. As geophysical techniques are used the technique can be labelled as quality level B.


Category type A: Verification


Utilities are verified and positioned by the eye, using physical identification. This could include visual inspection, vacuum excavation or hand dug trial pitting. Any service verified in this way can be awarded the highest level of confidence, so it is quality level A.


To learn more about the different levels of PAS surveys or to speak to one of our professionals, contact us today at emma@rocksurveying.co.uk or call 01905 456 384.