The new Publicly Available Standard from the British Standards Institute specifies the minimum that should be done in respect to underground utility detection, verification and location, and also provides guidance and pointers to best practice. It sets out 4 types of survey: Desktop Study (Type D), site reconnaissance (Type C), detection (Type B), and verification (Type A). The PAS supports both the practitioner and the client throughout the project cycle. At tender stage It is required for the practitioner to submit: a) The survey type(s) to be deployed, including the extent for each type b) For survey type B, detection methods to be deployed as specified in Table 2, including estimated extent for each method c) Comment on these survey type(s) and, for survey type B, detection methods, with regard for satisfying the client’s requirements d) Comments on the expected achievable quality level e) Names and experience of the project team f) How the survey area is to be managed to maximise the area available for survey and ensure the safe execution of the works The client should then be able to compare apples with apples when seeking multiple quotes. Following the work, the practitioner should submit a detailed report including: • detailed survey outcomes including how successful each detection methodology proved to be and a plan showing any areas where these detection methodologies were not successful • Utility segments identified with the quality level achieved • Recommendation for any further survey work required to meet the client’s requirements All recorded and processed data, site notes, metadata, and intermediate stage processing files shall be retained, and shall be available to the client on request It is recommended as best practice for all data to be recorded as evidence of detections and of work undertaken. This is required where post processing has been specified. This is optional for other detection surveys – unless the client chooses to make it a requirement. The practitioner needs to set out what they did and where, what the outcome was, i.e. what accuracy and confidence was achieved and what areas of uncertainty and risk remain. The practitioner should then stand by their deliverables. If used properly by the client, the practitioner can no longer hide behind the ‘black box’ of complex geophysical equipment to explain away why something was missed or inaccurate in their survey output. If adopted by the industry the PAS could enable: • Clear definition for a minimum standard of utility verification and location • More control to the client • More comeback for the client when issues arise • Fewer incidents related to service strikes • Fewer delays caused by unknown buried services Dr George Tuckwell www.safe-ground.co.uk

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PAS 128:2014 Specification for underground
utility detection, verification and location
What it requires and how to use it
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Dr George Tuckwell PhD FGS CGeol CSci
Director

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PAS128 – launched on 30th
June, 2014
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What is a PAS?
•A Publicly Available Specification (PAS) is a
sponsored fast-track standard
•Written by a drafting panel, supported by a steering
committee.
•After two years the PAS is reviewed and a decision
is made as to whether it should be taken forward to
become a formal British Standard
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Aims of this PAS
PAS128 aims to provide:
•Clarity in the service provided and
methods employed
•Consistency in the approach to data
capture
•Classification of the results and the
confidence that can be associated with
them
•Standardisation of the format of
deliverables
•Accountability for the work undertaken
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Specification of minimum requirements
vs best practice guidance
Specification:
The normative text set out the minimum that must be done.
Best practice:
The informative text provides guidance and also points to
best practice.
This allows a range of responses to any request from the
client, who needs to decide what specification they want, and
what contractual conditions they want to put in place
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Survey types
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ABCD
Type D
Desktop
utility
records
search
Type C
Site reconn-
aissance
Type B
Detection
survey
Type A
Verification

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Survey output - Quality Levels
Each segment of utility in the deliverables will be identified with a ‘Quality Level’
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QLD – Desk study
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a) Identify known utility owners within
the specified survey area
b) Request asset information from
identified utility owners
c) Collate all data on utility owners
and their assets

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QLC – Site reconnaissance
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On-site checks shall document
a) The presence, type and markings of utility-
related surface features
b) Measurements between known surface
features on the ground compared with
those depicted on the plan
c) Differences between the map/drawing or
digital features supplied and those extant
on the ground

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QLB – Detection surveys
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•Use geophysical techniques to detect and identify
utilities within the survey area
•The quality level (accuracy) achieved shall be
documented as QL-B1, QL-B2, QLB3 or QL-B4
•If post-processing has been used to improve the
confidence of the data, the quality level shall be
suffixed with the letter ‘P’

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Detection accuracy
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The positional
accuracies for QL-B1,
QL-B1P... etc. and how
these vary with depth

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QLA – exposure and verification
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Data shall be obtained through visual
inspection of the utility
a)at access points such as in a manhole or
inspection chamber; and/or
b)by its excavation and exposure

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Detection – levels of effort and return
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PAS 128 sets out guidance on the minimum effort required for
different situations.
For example, an urban area expected to be congested with multiple
surveys would be expected to require a more dense detection grid in
order to detect utility segments accurately.
It also makes clear that additional confidence and accuracy can be
obtained by post-processing the data;
that is taking the recorded geophysical data off site,
processing it in 3D volumes to enhance and isolate signals
from buried utilities, and transferring the results of that
analysis onto detailed CAD drawings.

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Detection – levels of effort and return
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Post-processing of data – when and why?
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Some subsurface environments are too complex
to detangle using real time signals on site

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Recording data and post-processing provides
more accurate interpretation
Survey grid baseline
DirectionofGPRsurveylines

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Post processed data can deliver detail not
possible from site mark out

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Comparing apples with apples at tender stage
It is required for the practitioner to submit:
a)The survey type(s) to be deployed, including the extent for each type
b)For survey type B, detection methods to be deployed as specified in
Table 2, including estimated extent for each method
c)Comment on these survey type(s) and, for survey type B, detection
methods, with regard for satisfying the client’s requirements
d)Comments on the expected achievable quality level
e) Names and experience of the project team
f)How the survey area is to be managed to maximise the area available
for survey and ensure the safe execution of the works
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Transparency of work done - Deliverables
A detailed report including:
detailed survey outcomes including how successful each
detection methodology proved to be and a plan showing any
areas where these detection methodologies were not
successful
Utility segments identified with the quality level achieved
Recommendation for any further survey work required to meet
the client’s requirements
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Transparency of work done - Deliverables
Retention of survey data/records:
All recorded and processed data, site notes, metadata, and
intermediate stage processing files shall be retained, and shall
be available to the client on request
It is recommended as best practice for all data to be recorded
as evidence of detections and of work undertaken
•This is required where post processing has been specified
•This is optional for other detection surveys –
unless the client chooses to make it a requirement
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Why were these missed?

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Accountability of results
In the deliverables the practitioner must state:
the quality level (level of accuracy) achieved for each
segment of utility identified; and
which detection techniques were used in all surveyed
areas of the site, including areas where no utilities have
been detected.
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Survey quality/accuracy and accountability

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Accountability of results
The client gets further protection if they specify:
all geophysical data to be recorded and retained
evidence provided of the detections achieved and
areas where detections were not possible as part of the
deliverables
Benefits:
Evidence is retained of the work done
Data can be reviewed at a later date in light of
subsequent findings or as part of a routine audit, either
by the practitioner, the client, or a third party
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Evidence of detection work done
Survey company A
claims that GPR
didn’t work
GPR data acquired by
survey company B

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Protection for the client
•The practitioner needs to set out:
• What they did and where
• What the outcome was, i.e.
• What accuracy and confidence was achieved
• What areas of uncertainty and risk remain
• What further could be done to reduce risk
•The practitioner should then stand by their product
•If used properly by the client, the practitioner can no longer hide behind
the ‘black box’ of complex geophysical equipment to explain away why
something was missed or inaccurate in their survey output.
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Take up
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If adopted by the industry the PAS
could enable:
•Clear definition for a minimum
standard of utility verification and
location
•More control to the client
•More comeback for the client
when issues arise
•Fewer incidents related to service
strikes
•Fewer delays caused by unknown
buried services

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George Tuckwell is the director responsible for geophysics within RSK, providing site
investigation, consulting and expert witness services.
Amongst others, he has advised National Grid, the Environment Agency and the
United Nations on the deployment of geophysical technologies. George is a past Vice
President of the Geological Society of London, is a Chartered Geologist and a
Chartered Scientist and is a member of the Editorial Board of the Journal of
Engineering Geology and Hydrogeology.
He provides expert witness services in cases relating to the use of geophysical
technologies, the interpretation of, and reliance placed on, the data acquired. This
includes cases of buried service detection, mapping and avoidance.