Guidelines for Underground Electronic Utility Marker Technology74
Underground electronic utility markers incorporate unique frequencies and/or data transfer capabilities to identify an underground asset. In general, radio frequency identification (RFID) has been in use for a few decades and incorporates unique frequencies for each type of utility; this allows locators and operators to identify specific types of underground utilities. Data-transfer RFID allows users to write to and read information from the marker. Advantages of utility-specific frequency RFID markers include greater depth of detection, no need to read data to identify a utility type, and tradition of use. Advantages of data-transfer RFID markers include utility agnosticism (does not require different frequencies to communicate utility type) and ability to write and read specific underground utility information from the marker.
Underground electronic utility markers fall into two primary use case categories: point marking and path marking. Both device types generate an electromagnetic radio frequency to provide accurate location information. Point markers are installed along the vertical axis to identify the specific location of an underground facility feature, component, or utility type. Path markers are installed along the horizontal axis along a buried underground facility and provides a running line direction and location of an underground utility. Examples of point markers include: ultra-high frequency (UHF) RFID subsurface tags, high frequency (HF) subsurface markers, UHF RFID magnets, active UHF RFID subsurface tags, marker balls, disk markers, near surface markers, full range markers, mini markers, box markers, tap tee markers, duct markers, and RFID tags. Path markers include intrinsically locatable plastic pipe, UHF RFID tape and rope, and HF RFID tape and rope.
Facility owners/operators consider several factors associated with the installation, location, and data integration of electronic markers including the following.
Installation Factors
- Signal drift, burial depth, and power loss over time due to changing environmental conditions
- Signal loss that occurs with distance traveled
- Electronic markers’ operating specifications to maximize underground facility and marker lifetime
- Ease of integration with other systems
According to VDOT’s paper, Electronic RFID Marking and GPS Based Utility As-Built Mapping System, additional potential spacing protocols for electronic point maker placement for new construction are:
- Every 25 ft along the facility path
- At significant horizontal and vertical changes in direction
- At critical utility crossings, tees, and service connection
- On appurtenances that are important to the utility owner
Location Factors
The quality of the locating frequency may deteriorate if the underground utility marker is adjacent to a plurality of underground facilities with underground utility markers operating at a similar frequency. The following potentially applicable point marker locating frequencies, according to VDOT’s paper (Electronic RFID Marking and GPS Based Utility As-Built Mapping System), can be used to avoid signal interference and identify and locate a specific utility type. The verification frequency associated with the RFID tag can vary.
Commonly-Used Frequencies for Various Underground Electronic Utility Markers
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Underground Facility
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Point Frequencies
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Path Frequencies
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US UHF RFID
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Power
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169.8 kHz
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34.9kHz
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902-928 MHz
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Water
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145.7 kHz
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73.5kHz
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902-928 MHz
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Wastewater
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121.6 kHz
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41.4kHz
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902-928 MHz
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Telecommunication
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101.4 kHz
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48.8kHz
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902-928 MHz
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Gas
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83 kHz
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53.9kHz
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902-928 MHz
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Cable TV and Communications
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77 kHz
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48.8 kHz
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902-928 MHz
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General Purpose/Reclaimed Water
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66.35 kHz
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44.9 kHz
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902-928 MHz
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Data Integration Factors
Additional factors are related to the storage and labeling of data tagged to an underground utility marker via RFID technology, including:
- Information to be stored with the unique identifier
- Metadata template definition and creation to promote data collection consistency and underground utility marker operation across varying technology solutions
- Sample data elements to collect may include: asset type, asset material, asset class, asset owner, burial depth, latitude/longitude, EM manufacturer, and emergency contact information.
- Underground utility marker with RFID tagging integration into routine QLA investigations (subsurface utility engineering quality level) to label the location and burial distance of the exposed pipe