27th June 2014
Met Geo Environmental prides itself on being able to offer utility mapping services to a high standard, and over the past 18 months has been contributing towards the development of a new comprehensive specification for utility mapping which is set to become the new benchmark for quality utility surveys in the U.K. What is it, and what do you need to know about it? Read on to find out…….
The new specification is called PAS 128 – Specification for Underground Utility Detection, Verification, and Location, and is launched on the 30th June, 2014 at the headquarters of its main sponsor, the Institution of Civil Engineers. The aim is that the introduction of this new standardised approach will help to increase market confidence in the definition and delivery of utility mapping services; act as a driver for improving professionalism in the industry; and result in a reduction in the delays, disruptions, and injury arising from the use of poor quality and inaccurate utility information. These are aims that Met Geo Environmental is excited to support and endorse.
PAS 128 has been developed after industry recognition that a standardised approach was needed in the UK. Up until now, there has been no recognised benchmark for utility mapping, other than The Survey Association Guidance document, the Essential Guide to Utility Surveys, which although aimed mainly as guidance for Clients specifying a survey, was also adopted by some utility mapping practitioners. This guidance document recognised a hierarchical approach to utility mapping, from a simple survey using just electromagnetic location (cat-and-genny techniques) to a comprehensive survey using multiple techniques and office-processed ground penetrating radar.
The new specification builds upon the foundations laid by the TSA document, but also looks abroad at similar standards introduced in America, Canada and Australia, and tries to combine the best of each. The new specification has been developed in close consultation with industry. The steering group included representatives from professional institutions such as The Institution of Civil Engineers, The Geological Society and the Chartered Institution of Civil Engineering Surveyors; trade associations such as The Survey Association, the Utility Mapping Association, and the National Joint Utilities Group, quasi-governmental organisations such as Ordnance Survey and Transport for London; with academic support from the University of Birmingham and additional support from other co-opted members. A public consultation on the second draft resulted in over 700 comments returning, which makes it one of the most commented upon documents in the history of the British Standards Institute. Met Geo Environmental has taken an active interest in the development of the standard through its membership and committee positions with EuroGPR and the Utility Mapping Association, and represented The Survey Association at the final Steering Group meeting at which the final draft of the document was agreed.
How does PAS128 work?
The new specification takes a hierarchical approach to the survey methods used to undertake desktop utility record searches, detection, verification and location of utilities. It starts with a project consultation, which allows the survey practitioner to develop an appropriate methodology for each area of the site or stage of the project. This allows different levels of survey to be specified at differing stages of construction projects, or on different parts of the same site, in line with the requirements and complexity of any individual project.
There are four survey categories identified, which represent the increasing amounts of effort required to obtain a greater level of detail and confidence in the final data provided. The four categories are as follows:
Survey Category D – Desktop Utility Records Search (Collation of existing records)
Survey Category C – Site Reconnaissance (Existing records supported and constrained by site inspection)
Survey Category B – Detection (where utilities are detected and located by non-intrusive geophysical methods)
Survey Category A – Verification (where utilities are observed at an inspection chamber, or exposed through excavation)
The specification makes the collation of records (Category D) a pre-requisite for any of the other surveys, however categories A-C can be carried out independently of one another. The specification also defines a planning process for each project, and requires a method statement, programme of works, risk assessment, and safety plan submitting for every project. The method statement should be submitted at tender stage, allowing clients to accurately assess different tenders to ensure that a like-for-like comparison is being made when costs are being evaluated.
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. It is up to the survey practitioner to assign different segments of utilities that have been located with the correct confidence level. A utility that has been located but whose depth cannot be ascertained would be awarded a QL-B3, whereas a utility that has been located by multiple techniques and has a well-defined position and depth would be awarded a QL-B1. The specification also distinguishes between methodologies where GPR data is checked in the field and those where data is bought back to the office for interpretation using specialist software. A suffix (P) is assigned to Quality Levels where post processing of data has been used to improve the confidence of the data.
The end result will be a survey drawing showing colour-coded utilities, as is currently standard, but each utility segment will have a defined level of confidence, from levels QL-D through to QL-A, allowing the final user to have an accurate understanding of which data is most reliable and where further investigations might be required. This drawing should also be accompanied by a report that details the methodologies used and draws attention to any key findings or warnings associated with data reliability.
Raising standards in Utility Mapping
The new PAS128 document attempts to raise standards of utility detection by specifying that a minimum of two geophysical methodologies must be used in all PAS128 compliant detection surveys, and the location of all survey results should be conducted using proper electronic surveying techniques.
It is well established in geophysical circles that two complementary techniques should generally be used to constrain interpretations – now this principle has been applied to utility mapping surveys – which are a form of geophysical investigation, only exploring the extreme near surface (PAS128 only applies to utilities within the first 3 metres). Met Geo Environmental welcomes this – our utility mapping personnel have been using GPR to complement electromagnetic location techniques for over fifteen years, and are well aware of the benefits it can offer. Of course, there will still be situations where the use of GPR is not possible, either because of unsuitable ground conditions (e.g. heavy clay soils, over reinforced concrete) or restricted access (dense vegetation, yards covered with obstructions), but the PAS allows alternative geophysical techniques to be used to constrain the information. Met Geo Environmental’s degree qualified geophysicists are specialised in a number of techniques over and above GPR, and can recognise when using alternative techniques might prove worthwhile. If this is not possible, the PAS enshrines the fact that the utility location has not been confirmed by multiple techniques by specifying that it cannot achieve the highest quality levels.
The specification also sets out minimum requirements for how the results of the survey are located onto base mapping. PAS128 recommends the use of a recent topographical survey as a base-plan, with the results of any utility mapping survey located using standard surveying methodologies such as using electronic total stations or RTK GNSS. This should mean that the final utility survey drawings are as accurate as possible, but does also place a requirement on Clients specifying PAS128 to be able to provide up-to-date, reliable topographic information. Met Geo Environmental have utility surveyors who are also practised in topographical surveying, and a large land survey department, so if topographic detail is required it can be quickly procured, thus reducing any project delays.
The End Result
It is hoped that the introduction of the new specification will lead to fairer competition, make it easier to evaluate competing tenders, provide a consistent level of service and raise survey standards. As a consequence of doing so PAS128 should reduce construction costs, improve risk management, and health and safety on projects. The increased level of information should also be able to be incorporated into BIM models more easily, to provide a holistic site overview.
The authors of PAS128 recognise that in order to deliver the expected increases in accuracy and certainty around utility mapping results, there is likely to be a consequent increase in the effort, cost and timescale required to deliver those results. However, it is thought that this slight increase in fees at the outset of a project will benefit the project and result in an overall reduction in costs, delays, and safety incidents when viewing the project as a whole.
Independent research carried out by the Federal Highway Agency in the USA (based on the similar US specification ASCE38-02) shows that there is added value to construction projects that employ this type of specification, with costs outlaid for utility mapping leading to an overall return on investment of $4.67 benefit for every $1 spent. This mostly comes about from a decrease in costly delays occurring mid-construction brought about from a reliance on inaccurate information.
Met Geo Environmental therefore looks forward to the introduction of PAS128, and is prepared to start offering PAS128 compliant surveys from the date of launch. Met Geo Environmental has been offering comprehensive GPR and EML surveys to detect utilities (both with and without post-processing) for over 15 years, and combined with our in-house topographical survey expertise is in the perfect position to be able to offer a comprehensive in-house service without reliance on sub-contracting any services, save for excavation works. Our experienced personnel will be able to consult with you from the outset of any project, helping you to determine the exact level of information required at each stage of the project. We will ensure you have the appropriate information readily available where and when you need it, and in a form that you can understand. Call our offices at any time if you would like to discuss the new PAS128 specification in more detail and see how it can benefit your project work-flow.