Subsurface Utility Engineering: Understanding Data Quality Levels

What is Subsurface Utility Engineering?

Subsurface Utility Engineering (SUE) is the investigation of underground utilities and structures.  There are four levels of data quality in SUE . These are typically designated with the letter A through D.  “A” is the most accurate data level and “D” is the least accurate.  

Subsurface Utility Engineering

What are the Different Quality Levels of Data?

Quality Level D

This level of data involves gathering data from historical records such as architectural drawings, “as-built” drawings, utility records, photos, survey records, and even interviews with persons familiar with the site to gain anecdotal information.  This data is usually limited and may not produce a complete picture of what is on site.  The source of some data may be unknown or questionable.  The completeness and accuracy of the data may be in doubt. Memory fades over time. Old prints may not show changes that have been made. “As-Builts” may not show the true route.  In any event, once the data is collected, it is compiled into a drawing that states the quality level.
Quality Level C

This level of data involves the process of surveying the visible utility features such as manholes, catch basins, valves, fire hydrants, and gas risers.  If they have already been surveyed, checking the surveyed locations for their accuracy.  This data is compiled with the Quality Level D data and both levels are labeled accordingly.  Quality Level C data could, and often will, conflict with the Quality Level D data and raise questions as to the locations of some underground utility lines.
Quality Level B

This level of data involves horizontally designating the underground utilities on the surface using paint or flags. For example, by markings provided through an 811 call or by contacting a private utility locating company like Trinity Subsurface.  Electromagnetic and ground-penetrating radar equipment, as well as other private utilities lactating techniques, are harnessed. The utilities are located with their location marked on the ground surface. While this data can be highly accurate, it is still an approximate location and typically does not provide depth information.  This data is added to the data collected from Quality Levels D and C.  The designated utilities are surveyed and added to the drawing, comprising the results of a Quality Level B investigation.

Underground Utility Locating Service 
Quality Level A

This level of data involves physically locating the actual utility – often by ‘potholing.’ It is typically the most accurate form of data.  Once the utility is potholed it is located horizontally and vertically by survey measurements. Potholing, or “daylighting”, utilities is also the only reliable way to confirm the size or existence of concrete encased duct banks. If inches count and vertical measurements are needed, Potholing is the most reliable way to obtain the data.

How can the Different Data Levels be Utilized?

The quality levels of SUE work to complement and build on each other.  They can be performed in phases or all at the same time.  When the drawing of the utility locations is completed it will designate to what quality level each utility line is shown. This will give the designers an idea of the quality of the information they are working with which, in turn, will tell them what confidence they can place in the related utility locations. 

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