PAS128 is divided into four survey types that you can specify when requesting a PAS128 Survey:

The different survey categories translate to different Quality Levels (QL), with QL-D being assigned to information with the lowest confidence, and QL-A being assigned to information that has the highest confidence.

In between there are a range of quality levels associated with defined horizontal and vertical accuracies. This diagram shows the confidences associated with the various levels.

Survey Type DDesktop Utility Records Search
What’s involved?

Process

- IDENTIFY OWNERS PRESENT

- COLLATE UTILITY INFORMATION

- REPORT FINDINGS

Result: QUALITY LEVEL D

Utility information taken from record data

Record information should be less than 90 days old

As-built plans and historic information should also be used where available

Least confidence (no depth information)

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Survey Type CSite Reconnaisance
What’s involved?

Process

- OBTAIN LEVEL D SURVEY

- VISIT SITE WITH DETAILED PLAN

- ANNOTATE PLAN WITH SITE NOTES

Result: QUALITY LEVEL C

Record information correlated to on-site features

A topographic survey will aid interpretation and drawing production

Low – Medium Confidence (no depth information)

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Survey Type BDetection Survey
What’s involved?

Process

- OBTAIN LEVEL D SURVEY

- AGREE DETECTION METHODOLOGY

- CARRY OUT SITE SURVEY

- LOCATE RESULTS USING SURVEY TECHNIQUES

- PRODUCE DRAWING & REPORT

Result: QUALITY LEVEL B

Utilities detected by geophysical techniques using a set methodology

A range of confidence levels can be assigned based on the success of techniques used

Post-processing of GPR data can increase confidence in results and provide an audit trail

Medium – High Confidence – (depths of utilities can be detected if techniques successful)

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Survey Type AVerification
What’s involved?

Process

- OBTAIN LEVEL D SURVEY (and C,B)

- AGREE LOCATIONS TO EXPOSE

- EXCAVATE

- RECORD FINDINGS

Result: QUALITY LEVEL A

Utilities verified by exposure in an inspection chamber or trial pit

Multiple trial pits/ test holes can prove expensive

Often used to confirm results of a Type B survey

Best Confidence (highly accurate positioning)

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PAS128 Table1-Quality Level of Survey Outputs (normative)

Table reference: Table derived from "PAS128:2014 Specification for underground utility detection, verification and location (2014) BSI Standards Limited [London]" Full Text Available Here

Widespread adoption of PAS128 will provide:

- Clarity on what is being done and the methodologies being used.

- Consistency in approach so it is easy to compare like with like.

- Classification of results and a measure of the confidence placed on them.

- A standard format for deliverables, like reports and drawings.

- Accountability for the work undertaken.

"Research carried out in the USA has shown that the expected Return on Investment for money spent on utility mapping surveys is better than 4:1. This study was based on work carried out involving the US utility mapping specification ASCE:38."