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Fact Sheet 9a

Source Area 4 Remedial Investigation Results

Southeast Rockford Groundwater Contamination Superfund Project

February 2001

Rockford, Illinois

Background. Illinois Environmental Protection Agency (Illinois EPA) investigations beginning in 1991 identified Area 4 as one of four major sources of groundwater contamination in the Southeast Rockford Groundwater Contamination Superfund project. In 1996, to gather data in preparation for developing remedies for the four major sources, the Illinois EPA conducted more extensive environmental investigations in the four areas.

Summary of Source Area 4 investigation results. Illinois EPA investigations show that the main source of contamination in Area 4 appears to have been underground storage tanks located beneath the parking lot south of the building formerly occupied by Swebco. The primary contaminant is the industrial solvent 1,1,1-trichloroethane (TCA). TCA is in a class of chemicals called volatile organic compounds (VOCs). They are called volatile because they readily evaporate. They are called organic because they contain carbon. Results for specific media (soil, groundwater, etc.) are summarized below.

Surface Soil

Two Illinois EPA surface samples collected in 1993 showed small amounts of VOCs below levels of health concern. In 1996, the Illinois EPA collected five surface samples in Area 4. Only one VOC, 1,2-dichloropropane, at 1 and 2 parts per billion, was detected. This chemical is not commonly found in other parts of Area 4 and is not at a level of concern. A few surface soil samples showed levels of chemicals often connected with motor oil and asphalt. One such surface soil sample was located in the residential area east of Swebco. This contamination may not be connected with the Area 4 contamination, but it will be more thoroughly investigated during construction of the remedy for Area 4.

Subsurface Soil

Results of Illinois EPA soil borings in Area 4 showed an area of contaminated soil, approximately 50 by 75 feet, located beneath the parking lot of the former Swebco Manufacturing, Inc. Besides TCA, sample results also showed much lower levels of other VOCs as well as semi-volatiles such as naphthalene and compounds found in oil and asphalt. Soil borings encountered low permeability clay approximately 62 through 65 feet below ground surface where the boring was terminated. Soil borings showed no contaminated subsurface soil beyond the source area boundaries.

Non-Aqueous Phase Liquid (Free Product)

Contamination that is present in high enough concentrations that it no longer dissolves in water is called free product or non-aqueous phase liquid (NAPL). TCA is heavier than water, and normally, if it were in NAPL form, it would sink through the water until it reaches a non-permeable layer such as clay. In Area 4, however, a soil boring showed eight feet of NAPL with 510 parts per million TCA present at the water table between 27 and 35 feet below ground surface. The proposed cleanup objective for TCA is 9.118 parts per million. Since the TCA is on top of the water table, it is probably mixed with a lighter substance such as oil. NAPL is of special concern because it is concentrated and continually releases contaminants into the groundwater and into the air pockets in the soil above the groundwater. Sample results, thus far, have not found NAPL beneath the water table.


Sample results from monitoring wells installed around Area 4 show that contamination has moved into the groundwater (water beneath ground surface). One downgradient well had 1,000 parts per billion TCA. The United States Environmental Protection Agency (U.S.EPA) drinking water standard for TCA is 200 parts per billion. The same contaminants were also present in private wells in the area before they were abandoned and the properties connected to the Rockford Public Water Supply. People with homes connected to the Rockford Public Water Supply do not have to worry about contamination of their drinking water, because the Rockford Public Water Supply is regularly checked for potential contamination. Water that does not meet U.S. EPA drinking water standards is not distributed to the public. The contaminated groundwater from Area 4 is moving offsite to the northwest.

Soil Gas

Since VOCs evaporate (vaporize) readily, vapors from subsurface contamination can accumulate in the air pockets between soil particles beneath the surface of the soil. Air and vapors in the air pockets are called soil gas. Illinois EPA soil gas sample results in Area 4 indicate that vapors from the contamination have moved beneath the soil to the east and somewhat to the west. Results indicate high levels of TCA and lower levels of two other solvents. Some soil gas sample results also show low levels of compounds found in petroleum products. None of these vapors pose a direct threat to human health unless they seep into basements through cracks in the basement walls or unless excavation releases the vapors to the air.

In 1992, the Illinois EPA and the Illinois Department of Public Health (IDPH) tested basement air in a home bordering Area 4. The home had concentrations of VOCs above health-based guidelines. The home had an abandoned well pit in the basement which could have been the route taken by vapors from the soil to the house. IDPH recommended that the well pit be plugged, which the property owner did. In 1994, that home was resampled along with another basement adjacent to the site. IDPH stated that levels detected in 1994 were below levels of health concern. The source of contaminants could not be determined, because the detected chemicals are also found in common household products such as paint and glue.

The U.S. EPA and the Illinois EPA plan to repeat sampling of several homes near Area 4 during the design phase of the remedy-probably in 2001. These tests will make sure that VOC concentrations have not increased and will provide data for U.S. EPA to compare to guidelines they are currently using.

Next Steps.

The Illinois EPA and U. S. EPA have proposed a plan to remedy Area 4 as well as the other three major sources of contamination for this project. For more information on all the remedies studied for Area 4 and the Area 4 proposed plan see the enclosed feasibility study/proposed plan fact sheet. You may also obtain more information from sources listed below.

For More Information:

Contacts: For more information about the project including fact sheets on the remedial investigation results, feasibility studies and proposed plans for each of the four major source areas, you may contact the Illinois EPA staff listed below:

Tammy Mitchell

Community Relations Coord.

Illinois EPA

1021 N. Grand Ave. E.

Box 19276

Springfield, Illinois 62794-9276

Phone: (217) 524-2292
Thomas Williams

Project Manager

Illinois EPA

1021 N. Grand Ave. E.

Box 19276

Springfield, Illinois 62794-9276

Phone: (815) 223-1714

Repositories: Full reports for the project may be reviewed at the following locations.

Rock River Branch

Rockford Public Library

3128 S. 11 th Street

Rockford, IL 61109


(Call for hours)
Ken-Rock Community Center

3218 S. 11th Street

Rockford, IL 61109


(Call for hours)

Administrative record file: The administrative record file is located at the Illinois EPA headquarters in Springfield, Illinois. Call 217-782-9878 for an appointment. The administrative record file will also be located on microfiche at the Main Branch of the Rockford Public Library at 215 N. Wyman in Rockford.