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.

The largest contractor in the private utility location market is GPRS. In 2018, GPRS completed over 52,000 projects with an error rate of less than ½ of one percent. This success can be attributed to a comprehensive approach that includes an experience-driven training program, a strategy to obtain redundant results and methods of data collection applied in the field.

The approach GPRS uses is a specification detailing a subsurface investigation, step by step. Subsurface Investigation Methodology, or SIM, specifies the required training, technologies and methods in the field.


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:

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