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Alliant Energy – Marshalltown Generating Station

Alliant Energy - Marshalltown Generating Station Site under Construction at Dusk

Marshalltown Generating Station is a 650 MW 2 x 1 combined cycle natural gas-fueled power plant owned by Interstate Power & Light (Alliant Energy). This plant consists of two Siemens 501F gas turbines (SGT6-5000F, 230 MW each), two Nooter Eriksen HRSG’s and one Siemens steam turbine (SST6-5000). Construction began in the fourth quarter of 2014 and went online the second quarter of 2016. This facility now includes a full building enclosure of the STG, CTG’s and HRSG’s to allow the owner better year-round equipment maintenance and winter cycling abilities.

Boldt served as the prime subcontractor for the project, performing concrete, steel erection, rigging and rigging engineering, and installation and alignment of centerline equipment. The concrete scope of work for this project was a complex process of forming, placing embedded items, and inserts requiring engineered forming systems. These installations included U-drains formed into the mass foundations which were poured monolithically, with pours up to 1,000 cubic yards of concrete. The steam turbine pedestals required precision placement of electrical conduits, steam, condensate, water and air piping inserts, in addition to the other embedded steel materials and anchor bolts. These installations were accomplished in a fast-paced environment requiring precision layout.


Alliant Energy

Marshalltown, Iowa


Boldt Role
  • Subcontractor
  • Self-perform Construction
Project Type
New Construction
Project Size
650 MW

Conventional Electric Power Plants

Project Highlights

  • Boldt served as a prime subcontractor for the project, self-performing a number of key trades.
  • The natural gas station provides clean energy for nearly 500,000 homes and businesses.