Case Study: Correcting Old Waterline Mark Out by 40 ft.

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Trinity Subsurface was contracted for the private utility location of a 30” waterline. The client has established Planned Borings 101 and 102 on their construction site. The waterline was mapped on an old print, illustrating too close a proximity to the boring locations.

The owner of the waterline was not confident in its location due to the data’s unreliability. Before the arrival of Trinity Subsurface, the township placed flag markers where they “thought” the line was. This was based on the print alone. The client employed a forward-thinking team who understood the planned borings were too close to the potential waterline. To eliminate the risk of hitting an unconfirmed line Trinity Subsurface was called.

project blueprints to inform technicians on worksite

The site scope included several challenges for the Trinity Subsurface field employees to overcome. The land was underdeveloped and heavily overgrown. Therefore, equipment like our ground penetrating radar cart cannot be leveraged. Field employees must become experts in several utility locating methods, to tailor their strategy to a range of locations. In addition, the waterline was predicted to be more than 20 feet deep. This installation procedure occurs, oftentimes, to accommodate the topography of the area.

The Trinity Subsurface field employees began scanning to confirm the line’s location. They were unable to locate anything in or around the new marker locations. Next, the field employees expanded their scope. They went further afield using inductive scans and passive scans.  A small signal wasfound on passive scans. This led the field employees to a concrete structure obscured by overgrowth. Here, they directly connected to the surface feature.

connect to metallic utility features for a passive scan

The key to a successful underground utility locate is finding utilities with a direct connection. When the field employees apply a known and controlled signal to a utility, this is known as active locating. To isolate the target utility from other utilities, active locating is leveraged. Thus, the field employees were able to trace a line approximately 300 feet. This was at a depth of 27 feet and to the south of the proposed waterline flag marking. The found line and the township diverged as much as 40 feet. Neither the concrete manhole nor the older marker were found or designated by the township.

mark out utility lines to avoid accidental strikes during boring

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