LG Constructors, a Division of CH2M Hill


LG Constructors, a Division of CH2M Hill, contracted INNOVA to design, supply and install the acoustical treatment for the Xcel Energy 575 MW High Bridge Combined Cycle Project located along the Mississippi in St. Paul, Minnesota.


INNOVA developed an acoustical model for the site that considered sound reflection from the Mississippi waters, the river’s valley topography, and prevailing atmospheric conditions. INNOVA then designed the acoustical treatments to lower noise to the St. Paul City code and at the nearest residence located 800 feet away.


The noise ordinance for the City of St. Paul required the Project to limit nighttime noise emissions under normal operations to 50 dBA at the nearest residential receiver.

  • 50 dBA at 800 feet at the nearest residence.


The major noise sources inside the powerhouse included:

  • Two (2) Mitsubishi 501 combustion turbines
  • One (1) Mitsubishi TC2F steam turbine and generator
  • Two (2) Nooter Eriksen HRSG units


INNOVA utilized one of its proprietary wall and roof systems to reduce noise from the core powerhouse. INNOVA also designed, supplied and installed the building’s secondary structural steel, concrete masonry, brick facing, built-up roof, and acoustical windows, doors, and ventilation system.

  • Structural steel
  • HVAC
  • Electrical, doors
  • Partitions and ceilings
  • Two (2) overhead bridge cranes


The timeframe for the scope of work was shorter than typical for a project of this size. INNOVA rose to the challenge by allowing only eight weeks to design and start fabrication of the noise reduction components. The powerhouse building was completed fewer than nine months after receiving the noise-reduction contract from LG Constructors.


The acoustical treatment provided by INNOVA performed as predicted with the Project meeting the City of St. Paul noise limit. The High Bridge Project also received the first-ever Minnesota Star Award (MNSTAR) for the highest standard of worksite safety. The Project delivered 300,000 accident free man-hours, of which INNOVA accounted for one-third. Xcel Energy and LG Constructors were presented with this first-time award for new construction by Minnesota’s State Governor.