Project Overview
DTE retained NTH to provide engineering services for the removal of two underground storage tanks (USTs) and their associated fuel dispensers, and replacement of the system with one dual-compartment aboveground storage tank (AST).
Facility constraints and security restrictions created additional challenges for design and construction. However, through close consultation with the owner and contractor, NTH was able to modify the design to successfully complete the design and installation to meet the facility’s stringent requirements.
Project Scope
As part of DTE’s corporate-wide effort to remove underground storage tanks (USTs) and replace them with aboveground storage tanks (ASTs), NTH was retained as the design engineer for replacement of fueling systems. NTH had developed a standard design template for replacing the USTs and fueling dispensers with ASTs at DTE service centers and power plants. While the standard design would always be modified to meet site-specific considerations, hydrogeologic conditions and security issues at the Fermi nuclear power plant presented additional challenges for design of the tank and dispenser system. Security challenges immediately became apparent during the initial conceptual planning. The aboveground tank had to be located further from the security barricade than the underground tank, which caused issues for traffic flow and grading. NTH’s civil engineers were able to calculate multiple traffic flow patterns and prepared a new grading plan that allowed all site vehicles to fuel at the new system.
Since the system had to be able to fuel vehicles both in the unsecured and secured area of the facility, fuel lines from the tank in the unsecured area had to extend beneath the extensive security fence and exclusion zone. While open cut trenching would typically be used, plant security personnel had reservations about temporarily dismantling the fence. NTH suggested directional boring, which would allow the security measures to remain in-place during installation. However, uncertainty about elevations of utilities located in the exclusion zone between the unsecured and secured zone presented a concern for this method of installation.
To evaluate if there might be utility conflicts with potential directional drilling, NTH deployed our subsurface utility engineering (SUE) expertise to carefully review historical utility drawings and conducted a geophysical investigation within and adjacent to the exclusion zone. Geophysical methods included ground penetrating radar (GPR) and electromagnetic utility line locating. Where potential utilities were located, NTH conducted targeted test pits performed using soft-dig air knife technique to verify the presence and depth of the utilities.
The geotechnical investigation NTH conducted prior to the design of the AST foundation also identified very shallow groundwater conditions at the site, which necessitated a specialized foundation system for the tank. NTH’s structural design engineers identified appropriate foundation options and, after consulting with our geotechnical engineers regarding soil bearing and hydrogeologic conditions, prepared a site-specific foundation design for the new tank. Through a collaborative approach, NTH’s multidisciplinary design engineering team was able to overcome these and other challenges at this unique property and deliver a design package that the contractor was able to successfully build.
