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Fact Sheet
October 2008
EPA Announces Explanation of Significant Differences, Mason City Coal Gasification Plant, Mason City, Iowa
INTRODUCTION
The U.S. Environmental Protection Agency Region 7 announces the issuance of an Explanation of Significant Differences (ESD) for the Mason City Coal Gasification Plant located in Mason City, Iowa. The ESD describes significant differences to the original remedy that was selected for the Mason City Site, as documented in the September 19, 2000, Record of Decision (ROD).
BACKGROUND
The Mason City Coal Gasification Plant was the location of a former manufactured gas plant in downtown Mason City that operated from 1900 to 1951. An electrical substation and a small storage building are all that remain on the site. During a 1984 sewer installation, oily sludge was discovered in subsurface soil at the site. The primary contaminants of concern are polynuclear aromatic hydrocarbons (PAHs). The PAHs include compounds associated with the production of manufactured gas.
The selected remedy for the Site was monitored natural attenuation of ground water with institutional controls. New information has been developed since the ROD for three of the contaminants in ground water. Two of these contaminants, naphthalene and 2-methylnaphthalene, are now being added to the list of contaminants in the ROD that have cleanup levels established for them. New information led to the decision to change the cleanup level to a lower value for a third contaminant, dibenz(a,h)anthracene. All of these modifications are described in detail in the ESD.
The environmental covenant, one of the institutional controls implemented as part of the remedy for this site, is being modified to provide additional restrictions on future buildings on the site, to ensure subsurface vapors do not pose a health threat to building occupants.
All of these modifications are the subject of this ESD.
FOR MORE INFORMATION
EPA encourages the public to review the ESD and other site-related documents part of the Administrative Record. The Administrative Record and other site-related documents are available during normal business hours at the following locations:
Mason City Public Library
225 2nd Street SE
Mason City, Iowa
EPA Region 7 Office
901 N. 5th Street
Kansas City, Kansas
For more information on the site, please contact:
Beckie Himes
Community Involvement Coordinator
Office of Public Affairs
U.S. EPA Region 7
901 N. 5th Street
Kansas City, Kansas 66101
Phone: 913-551-7253
Toll Free: 1-800-223-0425
himes.beckie@epa.gov
