First Five-Year Review to Begin, Mason City Coal Gasification Plant Superfund Site, Mason City, Cerro Gordo County, Iowa
The U.S. Environmental Protection Agency conducts regular five-year reviews on Superfund sites where cleanups have been completed. These reviews are required by the Superfund law [42 U.S.C. Section 9621 (c)]. EPA Region 7 and the Iowa Department of Natural Resources have initiated the first five-year review of the Mason City Coal Gasification Plant site in Mason City, Cerro Gordo County, Iowa.
The site is located in central Mason City and is bounded on three sides by city streets: South Pennsylvania Avenue to the east, Fifth Street Southeast to the south, and South Delaware Avenue to the west. The northern edge of the site is bounded by Willow Creek. The majority of the site is owned by Alliant Energy Corporation (formerly Interstate Power Company), with the exception of a small portion of the site with a sewer line which is owned by the city. Alliant continues to operate a power substation and a small garage on the site.
Beginning in the early 1900s, the site was occupied by a manufactured gas plant which generated gas for lighting and heating purposes in the Mason City area. The plant was decommissioned and demolished after natural gas became available. Residues from the gas manufacturing process, commonly referred to as coal tar, were left on-site and resulted in soil and ground water contamination. In June 1984 the city began excavation on the site for the installation of a new sewer line. During this excavation, coal tar was discovered underground. Approximately 1,000 to 1,500 gallons of coal tar was mixed with sand and put in an above-ground waste pile on-site awaiting disposal.
The contaminants usually associated with manufactured gas production include a group of semivolatile compounds. These compounds are referred to as polynuclear aromatic hydrocarbons (PAHs). Other contaminants usually found at manufactured gas plant sites include benzene, ethylbenzene, xylene, and toluene. Some forms of cyanide, arsenic, phenolic compounds, and metals may also be found.
Interstate Power conducted investigations to determine the extent of soil and ground water contamination. They also looked into remedies to clean up the contamination. During the course of these investigations it was determined that to speed up the cleanup, the contaminated soil and the waste pile should be dug up and treated. The treated soil was put back into the excavated areas on the site. This work was completed in 1996 and eliminated the ongoing source of ground water contamination.
Following this cleanup action, EPA selected monitored natural attenuation of ground water with land use restrictions to address the remaining ground water contamination at the site. Natural attenuation relies on natural processes to clean up pollution in soil and ground water. The ground water contamination does not extend beyond the site boundary and the contaminated water is not being used by any one.
Under EPA guidance, Alliant and Kansas City Power & Light Company (another former operator of the gas plant) will monitor the site to make sure natural attenuation is working. They continue to sample the ground water at the site quarterly. Land use restrictions have been placed on the site to ensure water supply wells are not installed and the property is not used for residential development.
EPA and the Iowa Department of Natural Resources will study site information during this five-year review and inspect the site to determine if the remedy continues to protect human health and the environment. We encourage the community to tell us about site conditions or any concerns you may have.
A final report will be prepared at the end of the review and will be available at the site information repositories.
The site administrative record is available at the following locations during normal business hours:
EPA Records Center
901 N. Fifth St.
Kansas City, Kan.
Mason City Public Library
225 Second St. SE
Mason City, Iowa
Questions or requests for information can be submitted to:
Community Involvement Coordinator
EPA Region 7
901 N. Fifth St.
Kansas City, KS 66101
Toll free: (800) 223-0425