The SIM standard specifies that a professional locating contractor must utilize multiple locating technologies. These include ground penetrating radar (GPR) and electromagnetic pipe locators (EM). Utilizing multiple technologies while locating will capitalize on each tool’s strength – creating a redundant confirmation when designating subsurface elements.


The national standard for certification (ASNT SNT-TC-1A) states that a minimum of 8 hours of classroom training and 60 hours of practical application coaching is needed to be certified as NDT Level 1. The SIM Specification details much more than these requirements. To be SIM certified an operator must complete a minimum of 8 weeks of field mentoring and 2 weeks of classroom training.


When completing a professional locate on your jobsite, having the right training and the best tools is only part of the equation. SIM addresses a step-by-step approach to collecting subsurface data to ensure that the results are repeatable and accurate. SIM practitioners must follow a checklist that is designed to ensure optimal results for every situation encountered in the field.


According to the Common Ground Alliance (CGA), over the last 20 years improperly located or not located subsurface utilities have caused $1.7 billion in damages and resulted in 1,906 injuries with 421 fatalities.

The CGA represents a body of industry stakeholders that advocate for the 811/One Call utility funded public property locating service. Part of this advocacy is publishing the “Dirt Report”, an awareness document of the previous year’s utility strikes nationwide. Their efforts to mandate the use of the 811/One Call system has resulted in legislation across the US that requires calling the service before excavation.

Most – if not all – of these losses could have been avoided through a detailed site investigation using multiple technologies and highly trained personnel.

Outside of the free 811/One Call public property utility location service, there is a vibrant private property utility location market. Contractors that service this marketplace use specialized technologies like ground penetrating radar to image and mark-out underground utilities, as well as scan concrete for critical targets like structural steel embedments. These two locating services are widely used in the construction industry to increase site safety and limit damages to unknown utilities and structural elements.

However, the One Call service, while valuable, does not locate private utilities. It also does not provide depths on the subsurface utility lines it locates, which is why it is vital for general contractors and construction project managers to utilize a private locating service before breaking ground.

The issue then becomes one of thoroughness and accuracy because while the technology for underground utility locating is somewhat standardized, the way in which it is employed is not. The precision and attention to detail of the operator can and does make the difference between a clean locate and a costly and dangerous utility strike.

That is why the Subsurface Inspection Methodology (SIM) was developed: to provide greater education, advanced field training, a repeatable process that locates utilities and other subsurface infrastructure accurately.



The purpose of this paper is to quantify the components that form the SIM process. Universal adoption of the methods and applied technology strategies used during the typical subsurface investigation will yield higher quality results for the end client and lower hit rates for the contractor. The scope of this paper is limited to the private property underground utility location market and the location of critical embedments in concrete.

Subsurface Investigation Methodology, (SIM):

SIM, Subsurface Investigation Methodology is a guide to using the locating technologies of an electromagnetic receiver and ground penetrating radar combined with a proven training approach to achieve a very low investigation error rate. SIM does not involve the practice of geophysics, geology, land surveying or engineering.

SIM contains three primary elements, the human asset, technology asset and methods applied in the field. The best site results are accomplished when the experienced, trained field technician can utilize multiple technologies in a comparative analysis of results from each technology. Thus, a highly skilled technician can locate the same target using multiple technologies resulting in confirmation of findings and results.

SIM is detailed in the following sections:

The SIM Specification standard is the industry-leading, metrics-based guideline for the underground locating and concrete scanning industries.

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