Levels of Utility Survey

The following levels of utility survey are defined in the Essential Guide to Utility Surveys, issue 4 October 2011 by The Survey Association. The levels increase in complexity and thoroughness from a relatively simple reconnaissance survey to a comprehensive search with the greatest likelihood of detecting all the services within the survey area.

On 30 June 2014, PAS 128 was launched. PAS 128 offers standard benchmark guidelines for utility surveys. Although it is a voluntary standard, it is being adopted by the majority of reputable utility survey providers.

Level 1 utility survey

Desk top survey involving a search of existing utility records. This can be consolidated onto one plan in CAD and overlain onto base mapping as an option. Can be used to target more detailed fieldwork.

A Level 1 survey is typically used as a low cost assessment of site to demonstrate extent of services.

Level 2 utility survey

A visual ‘walk-over’ survey carried out as a site visit. This would normally be in addition to a Level 1 survey and act as a reconnaissance on large projects to advise on the letting of the main utility survey. The site visit would be much enhanced if the results of the Level 1 survey were to hand for the walk over survey.

A Level 2 survey is a reconnaissance survey, which will advise the client on the most appropriate way to fulfil the survey objectives. It is an advisory survey only so no on site mark up or CAD plans would be produced.

Level 3 utility survey

Electro-magnetic location survey in passive and active mode with located services being marked onto ground surface. Includes cover lifting to allow line threading / sonding. Recorded manhole survey can be added as an option. Advisable to have Levels 1 & 2 surveys carried out in addition.

A Level 3 survey is a lower cost site assessment mainly useful for locating cables, ferrous pipes, ducts and gravity drainage. It will not detect inaccessible non-metallic mains and services.
Level 4 utility survey

A Level 3 survey but with the addition of Ground Penetrating Radar (GPR) in stake out mode to supplement EML results. Advisable to have Levels 1 & 2 surveys carried out in addition. It is important to agree the spacing of GPR scan lines to ensure the density of the data is adequate for the survey requirements. The scan line spacing will also help determine the difference between buried rocks/debris and pipes. In complicated environments a close spacing is essential (1m or even 0.5m or less) whereas, in areas that contain just a few services that travel consistently along, say, a road, scans at 1m centres are normal. In open areas such as parks and playing fields orthogonal spacing can be increased to 5m.

A Level 4 survey offers increased likelihood of detecting non-ferrous pipes and ducts. Unless specified record plans of survey results may not be produced.
Level 5 utility survey

A Level 3 survey but with recorded close centred GPR over an agreed % of the whole site complete with off-site post data collection processing, analysis and interpretation. Line & depth marked onto digital site plans in CAD.

GPR to be maximum 0.5m centres orthogonally in busy urban situations down to 2m centres orthogonally in rural highways. In open spaces such as parks and playing fields orthogonal spacing can be increased to 5m but client to determine % coverage with GPR and where it is to be located.

A Level 5 survey offers a better understanding of complex areas due to GPR scanning at close centres of these areas, but is limited by lack of full GPR survey coverage.
Level 6 utility survey

A Level 3 survey but with the addition of recorded GPR survey over 100% of the site with off-site post data collection processing, analysis and interpretation. Line & depth marked onto digital site plans in CAD. Intrusive trial holes to verify results can be added as an option.

GPR to be maximum 0.5m centres orthogonally in busy urban situations down to 2m centres orthogonally in rural highways. In open spaces such as parks and playing fields orthogonal spacing can be increased to 5m. All with 100% area coverage.

A Level 6 survey offers the most comprehensive level of survey with the highest expectation of picking up all services and other underground obstructions. Intrusive investigation on selected targeted areas can be used to verify results.

The above information is based on extracts from: The Essential Guide to Utility Surveys (Detailed Guidance Notes for Specifying a Utility Survey), issue 4 October 2011 by The Survey Association. Although this document is still valid, on 30 June 2014, PAS 128 was launched. PAS 128 offers standard benchmark guidelines for utility surveys. Although it is a voluntary standard, it is being adopted by the majority of reputable utility survey providers.