Odor Monitoring and Mitigation at the Hennepin County Waste to Energy Facility

Hennepin Energy Recovery Center (HERC) is a waste to energy facility owned by Hennepin County and operated by Covanta Energy. HERC has been in operation since 1989. The facility burns 365,000 tons of residential and commercial solid waste per year and generates about 34 mega-watts of electricity that is sold to Xcel Energy. HERC is located on the north side of downtown Minneapolis in the Historic Warehouse District, a neighborhood that is changing from industrial to a more commercial/residential mix with loft conversions and construction of new condominiums. The Minnesota Twins baseball team is also siting a new stadium in the parking lot immediately southeast of the facility. The potential for odors from the tipping floor of the facility affecting the neighborhood has become more of a concern due to the changes in the neighborhood. In March 2004 the County began an odor study. This included developing baseline information on odors from HERC and from the surrounding community by conducting daily odor monitoring at select points on the facility property and throughout the community: • Determining how far odors from HERC migrate into the community. • Quantifying detected odors using a Nasal Ranger. • Determining the factors that contribute to these odors. • Developing a method of controlling these odors. • Continued monitoring to determine the impact of mitigation methods. Odors detected were characterized as garbage odors, garbage-related odors, and neighborhood odors. Baseline data showed that while garbage odors from HERC were mostly undetectable beyond the perimeter of the property, there was room for improvement in decreasing the presence and intensity of these odors. The tipping hall was designed to operate under negative pressure to control odors, however the entrance and exit doors were always open and a negative pressure could not be maintained.