Introduction to Subsurface Utility Engineering:
Why should I incorporate SUE into my project?
Subsurface Utility Engineering (SUE) is an engineering practice that makes it possible to more accurately establish the location of buried utilities within a project area. This provides a foundation for decision-making around construction design, allowing a designer to make important decisions related to utility coordination, utility accommodation and utility relocation at the outset.
Simply put, Subsurface Utility Engineering cuts project risk and eliminates surprises at later stages of a project. It also saves money. The Ontario Sewer and Watermain Contractors Association recently commissioned the University of Toronto to investigate the practice of using SUE on large infrastructure projects in Ontario. The study chose nine case studies and determined that the average rate of return for each dollar spent on SUE services was $3.41.
Not all SUE programs are created equal and there are key considerations involved to ensure that risk is effectively managed and a return on investment is realized. To help you achieve success on your next project, we’ve rounded up these considerations:
What exactly comprises a SUE program?
SUE is based on the CI/ASCE 38-02 Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data, which provides a framework for evaluating the integrity of data based on four Quality Levels:
Quality Level D (QL-D): Information derived from existing records or oral recollections.
Quality Level C (QL-C): Information obtained by surveying and plotting visible above-ground utility features and using professional judgment to correlate this information with QL-D information.
Quality Level B (QL-B): The application of surface geophysical methods to determine the existence and horizontal position of subsurface utilities within a project’s limits. Non-destructive technologies including Ground Penetrating Radar (GPR) and Electromagnetic (EM) tools can be leveraged at this stage to accurately detect conductive and non-conductive underground assets.
Quality Level A (QL-A): Also known as daylighting, QL-A provides the precise horizontal and vertical location of utilities along with type, size, condition and material, obtained by actual exposure, usually through vacuum excavation.
Do I need to apply all four Quality Levels?
Where a topographic survey exists that was recently completed by an engineer or Ontario Land Surveyor (OLS), QL-C can typically be considered complete as surface utility data is captured for the topographic survey. Topographic surveys and base plans should always be supplied to the SUE service provider at the project kick off meeting.
What is most important is that Quality Levels be carried out in their prescribed order – QL-D, QL-C, QL-B, QL-A. This is the most effective strategy for minimizing risk and avoiding rework. Data gleaned from QL-D and QL-C investigations is integrated, providing an opportunity to identify anomalies and gain the insights required to facilitate a targeted, informed QL-B investigation.
QL-D and QL-C should be applied to the entire project area including areas not expected to be affected by future construction, (e.g., temporary staging areas) whereas QL-B can be targeted to the impacted area. QL-A investigations are required when depth data or precise horizontal location must be obtained to achieve project goals. QL-A should also be considered when the results of a QL-B investigation appear to be conflicting with existing utility records in key project areas.
It is imperative that Quality Levels be carried out in their prescribed order as an effective strategy for minimizing risk and avoiding rework. Data gleaned from QL-D and QL-C investigations is integrated, providing an opportunity to identify anomalies and gain the insights required to facilitate a targeted, informed QL-B investigation.
How do I customize a SUE program for my specific requirements?
The SUE scope of work can vary greatly from project to project, and there are some key considerations for defining the scope of work. Ask these questions at the outset, and you’ll be able to tailor a SUE program to your project-specific requirements.
- What are the potential project risks associated with utility location information? Will utilities be involved directly or indirectly with the project?
- What level of utility information should be obtained to adequately manage risks such as project cost overruns, construction and design delays, stakeholder impact, etc.?
- At a project level, is there evidence to suggest the presence of buried objects or subsurface infrastructure?
- Do the existing records contain inconsistencies? Is there evidence of additional utilities or buried structures not on record?
- If utilities are not in the exact location as shown on the records, what risk might this pose on the project?
- Will the project involve excavation and if so, what is the depth?
- Is information on the vertical position (depth) of subsurface utilities or buried structures required to minimize risk or will information on the horizontal position suffice?
- Is the project high risk for utility conflicts with existing or future utilities? e.g., new bridge construction or bridge widenings where footings are placed; projects involving daylighted utilities that will clearly conflict and require rework; excavation projects, particularly tunnel/grade separations where there is a conflict.
What should I think about in terms of schedule?
There are several factors that can affect the SUE schedule which should be considered in relation to your project’s overall timeline. Examples of these factors include:
- Requesting data acquisition activities that reside outside the scope of SUE which may result in project delays. For example, chamber investigations may require traffic control, night work, special permits and on-duty police scheduling and fees.
- Other activities occurring on the project site, for example, topographical surveying, geotechnical or environmental assessments. Be sure to assess subcontractor project schedules for potential site access conflicts.
- The location of the SUE investigation. If the investigation occurs within a rail or congested vehicle corridor, traffic control and closures may be required. If however, the investigation is related to a boulevard or private construction land, there will be far fewer time constraints.
- The time required to review QL-B data, and then schedule test pits. Determining the necessity, quantity and location of test pits usually occurs after reviewing the completed QL-B investigation and subsequent CAD utility drawing.
What technology should be applied?
The CI/ASCE 38-02 Standard stipulates that “appropriate geophysical methods” be leveraged to carry out the Quality Level B aspect of a SUE program. As this is a generic statement, there is room for interpretation. The geophysical method that is primarily leveraged to carry out the Quality Level B aspect of a SUE program is Electromagnetic (EM) Induction – otherwise known as pipe and cable locating. This technique is extremely effective at locating utilities comprised of electrically conductive material or those that contain an intact tracer wire.
When data collected at the QL-D and QL-C stages of a SUE program reveals a likeliness that non-conductive utilities reside on the project site, such as concrete or plastic pipes, buried trunk sewers, etc. other methods can be leveraged to supplement the SUE scope of work. Keep in mind, the use of “SUE” or “Subsurface Utility Engineering” in estimates and project scopes refers to “appropriate geophysical methods”. Be certain to ask for alternate methods if required, such as CCTV Sewer Inspection, Sonding for Concrete Sewers, or Confined Space Entry (CSE), to name a few. Costs associated with these additional methods should be weighed against risk of not obtaining the information.
Be certain to ask for alternate methods if required, such as CCTV Sewer Inspection, Sonding for Concrete Sewers, or Confined Space Entry (CSE), to name a few. Costs associated with these additional methods should be weighed against risk of not obtaining the information.
What accuracy should be expected in a Subsurface Utility Engineering Program?
Instruments employed to locate utilities have industry recommended tolerances. For Electromagnetic Induction, the recommended tolerance is a 1.0m variance laterally in opposing directions from the centre of the detected location. This is based on an ideal situation where there is one toneable utility within the site. Ground Penetrating Radar (GPR) accuracy generally ranges between 200 mm – 500 mm. Equipment manufacturers do not make guarantees on vertical accuracy. Quality level A offers the most accurate and precise utility locating through actual utility exposure.
What deliverables should be anticipated?
SUE deliverable formats can vary greatly based on project specifications. Municipalities, for example, each have their own CAD standards related to utility marking colour codes, line types and annotations. CAD drawings are submitted through the municipality’s quality checker: a software tool that scans the submitted drawings to ensure they comply with the requirements of these standards.
Considerations for deliverables will include: whether data is to be reflected on separate layers or a single layer, labelling conventions, CAD software format (MicroStation or AutoCAD), digital submissions vs. hard copy, colour conventions, etc. The SUE report format may also vary based on whether the Project Manager desires photographs of test pits, test pit sketches, field sketches of utility locations, etc. When it comes to SUE deliverables, there’s a lot of room for customization to meet the unique needs of the project. Having said that, deliverables should always be overseen and stamped by a Professional Engineer.
When it comes to SUE deliverables, there’s a lot of room for customization to meet the unique needs of the project. Having said that, deliverables should always be overseen and stamped by a Professional Engineer.
What should I look for in a Subsurface Utility Engineering service provider?
Hiring a Subsurface Utility Engineering (SUE) service provider involves a significant transfer of risk. As such, it’s imperative to select an organization with the right qualifications and experience. Look for a service provider with highly experienced Subsurface Technicians, a qualified CAD department and the ability to offer seamless project coordination.
The right certifications. SUE service providers must have a Certificate of Authorization from the Association of Professional Engineers of Ontario (PEO). As SUE involves geophysical activities, it is recommended, but not mandatory, that the service provider also have a Certificate of Authorization from the Association of Professional Geoscientists of Ontario (APGO). A Professional Engineer is required to approve, sign and seal SUE deliverables and a Professional Geoscientist oversees geophysical activities that comprise the SUE scope, for example, the application of Ground Penetrating Radar (GPR) and subsequent analysis of GPR data.
Relevant experience. SUE service providers should have experience locating all utility types required within the impacted area and also have verifiable experience completing projects of similar size and scope. Expertise in a range of technologies is required – Electromagnetic Induction, Ground Penetrating Radar (GPR), sonding, surveying, Global Positioning Systems (GPS), Geographic Information Systems (GIS), etc. Certifications to look out for include Damage Prevention Technician (DPT) certification, and relevant safety certifications including First Aid, WHMIS, Confined Space Entry (CSE), Confined Space Rescue, and Working at Heights, to name a few.
Advanced experience with Ground Penetrating Radar and related technologies. Where non-conductive utilities and features are believed to be within the project area, such as plastic, fiber optic, cable TV lines, water and concrete sewer lines, foundations, ducts and chambers, expertise in the application of Ground Penetrating Radar is key. GPR data can yield a cross section of subsurface utilities and can also be depicted three dimensionally, providing data on the actual depth of utilities.
The ability to innovate when challenges arise. As SUE projects vary greatly in size and scope, unique and unexpected challenges can arise. Many variables can affect the ability to collect data such as broken tracer wires, soil conductivity, or the presence of water that makes it difficult to achieve a signal. It’s important to partner with a service provider that has experienced these challenges before and can innovate to overcome.
multiVIEW has been carrying out Subsurface Utility Engineering (SUE) investigations for more than 30 years, since before it was a recognized practice in Ontario. We can meet all of your SUE needs, and customize our services to project-specific requirements. To learn more about Subsurface Utility Engineering, read our latest Subsurface Utility Engineering White Paper or visit us online.