An accurate survey of surface features is an integral part of almost every construction project. These are features that can easily be seen with the naked eye. Why then are features that can't be seen ignored when they can cause cost overruns, delays, and safety concerns? With exception of picking up any valves and pedestals that give us only a rough idea as to their location, the position of utilities such as gas lines, telephone ducts, hydro cables, and watermains are usually ignored. Instead common practice is to rely on old maps and as-built drawings that may or may not reflect the true conditions that exist underground. It is time to start putting as much effort in the survey of these below ground features as goes into above ground features.

The Ontario Regional COmon Ground Alliance (ORCGA), has recognized Subsurface Utility Engineering, or as it is better known as SUE, as a solution to this problem. It takes the issues related to mapping underground infrastructure, and applies a defined engineering process to ensure that reliable subsurface utility information is gathered. ONe of the basic principles behind SUE is the inclusion of quality levels on underground infrastructure maps. The quality levels are clearly defined in the American Society of Civil Engineers ASCE Standard 38-02: Standard Guidelines for the Collection and Depiction of Existing Subsurface Utility Data. Using quality levels provides an understanding of how the data was collected, which leads to increased confidence of the information that is displayed.

Both records research (QL-D) and the survey of surface features (QL-C) are straightforward, and are typically deemed to be the general practice used today in Ontario. Collection of QL-B information during the design stage of a project is not a general practice in Ontario, although the benefits of collection this information can be enormous. SUE service providers typically utilize a combination of geophysical instruments including: pipe and cable locators, metal detectors, ground penetrating radar (GPR), acoustic emission, and other techniques currently available to gather this information. In critical locations quality level A data is collected using vacuum excavation techniques. Air based excavation units are preferred because they minimize disruption to the surrounding soil and allow the native material to be returned to the hole immediately following excavation thus eliminating the need for dumping and hauling in new fill.

The field data is then collected using a variety of techniques, most commonly by a traditional total station or GPS equipment depending on the accuracy required. The survey will collect all visible surface features (QL-C), paint marks which indicate the horizontal position of the utility below ground as found using the geophysical instruments (QL-B), and the precise location of the utilities within the test holes (QL-A). The data is then incorporated into a CADD drawing and can also be delivered in a GIS format for inclusion in the owners GIS database.

The depiction of this data in the final format is another area that sets a sue service provider apart from a contract locating firm or a vacuum excavation firm. In the same was that a licensed land surveyor is expected to seal and stand behind his/her surveys, the engineer responsible for the investigation will stamp and certify the utility information on the drawings. This step insures that the information has been properly reviewed and that the owner can have confidence in the data provided at the various quality levels. It also shows that the SUE provider is willing to accept liability for the information, which is a major commitment to the quality of their work.

SUE services are still in their infancy in Ontario, however they are gaining a great deal of acceptance as project owners begin to realize the benefits that can be gained. The ORCGA lists SUE as one form of utility surveying that meets its best practices outlined for Planning and Design. Lower contractor bids, reduced delays, reduced redesigns, reduced utility relocations and improved project safety are only a few of the many benefits that users are experiencing. SUE services are here to stay in Ontario so you are encouraged to learn more about how they could be utilized to save money on the projects you are working on.

Credits
Author(s)
Lawrence Arcand 

Publication(s)
The Ontario Land Surveyor
Summer 2004