EPA ANNOUNCES SECOND EXPLANATION OF DIFFERENCES
Peoples Natural Gas Superfund Site, Dubuque, Iowa
The U.S. Environmental Protection Agency (EPA) Region 7 announces the second Explanation of Significant Differences to the Record of Decision for the Peoples Natural Gas, Dubuque, Iowa.
SECOND EXPLANATION OF SIGNIFICANT DIFFERENCES
MidAmerican Energy Company, who is conducting the remediation of this site, submitted a request to the Iowa Department of Natural Resources (IDNR) for support to modify the ground water remediation levels for benzene from the negligible risk level of 1 microgram per liter (µg/l) to the federal maximum contaminant level of 5 µg/l and the health advisory level (HAL) for naphthalene at the time of the ROD of 20 µg/l to the current HAL of 100 µg/l.
The IDNR sent a letter to the Environmental Protection Agency expressing their support for the requested change. These remediation levels for benzene and naphthalene are considered safe levels for public drinking water supplies. The EPA determined that the modifications to the ground water remediation levels are protective and consistent with federal applicable or relevant and appropriate requirements.
The site is the location of a former coal gasification plant which manufactured gas from approximately the 1930s to 1954. Production ceased when natural gas was introduced to the community. Waste products, such as coal tar, were generated and disposed at the site during plant operation. The coal tar contained several hazardous substances that contaminated the soil and ground water at the site. Volatile organic compounds, such as benzene, and polycyclic aromatic hydrocarbons (PAHs), were present in the soil and ground water at levels that could harm people if they were to come into contact with them.
The site occupies approximately five acres and is located between East 11th Street and Kerper Boulevard, approximately one-fourth mile east of downtown Dubuque in an industrial area near the Mississippi River. The city of Dubuque owns the eastern portion of the site and operates a public works garage on the property. Highway 61 was constructed on the western portion of the site after contaminated soil was removed and treated off site.
Following the completion of a remedial investigation and feasibility study, and an opportunity for public comment on the proposed remedy for the site, the EPA presented the selected remedy in a Record of Decision (ROD). The selected remedy included the following actions:
- excavation and treatment of contaminated soil and coal tar;
- extraction and treatment of contaminated ground water in the silty sand and alluvial aquifers; and
- in-situ bioremediation of contaminated soil and ground water;
During the design of the ground water extraction and treatment system, it was determined that extracting water from the alluvial aquifer would result in contamination being pulled down from the more heavily contaminated silty sand aquifer. The remedy was modified, through the first Explanation of Significant Differences, to provide for monitoring, rather than extraction, of ground water from the alluvial aquifer.
In December 1992, a Consent Decree was finalized with Midwest Gas (currently known as MidAmerican Energy Company), Enron Corporation, the city of Dubuque, and the Iowa Department of Transportation. They agreed to design and perform the site cleanup.
MidAmerican Energy has conducted the work at the site. Excavation and treatment of contaminated soil and coal tar was completed in 1998. Extraction and treatment of ground water began in 1996. The system was shut down in 2003 due to problems with the operation of the system. Studies are underway to determine the best approach for dealing with the contaminated ground water.
The in-situ bioremediation system operated from October 2000 through October 2002. Periodic monitoring of ground water in the silty sand and alluvial aquifers continues.
Detailed site information is available at the following locations:
EPA Records Center
901 N. 5th Street
Kansas City, Kansas
Carnegie-Stout Public Library
11th and Bluff
If you have questions or need more information on the Peoples Natural Gas Superfund site or this Explanation of Significant Differences, please contact:
Community Involvement Coordinator
U.S. EPA Region 7
901 North 5th Street
Kansas City, KS 66101
Toll Free: (800) 223-0425