Region 5 Superfund (SF)

U.S. EPA REGION 5
WINNEBAGO COUNTY
WINNEBAGO COUNTY

Congressional District # 16

EVERGREEN MANOR GROUND WATER CONTAMINATION

EPA ID# ILD984836734
Last Updated: December, 2006

Site Description

The Evergreen Manor site is a narrow, two-mile long area of low level groundwater contamination in Winnebago County, Illinois, just north of Roscoe, Illinois. Contamination was discovered in 1990 when a mortgage company required a homeowner to sample their well, and found elevated levels of volatile organic compounds (VOCs). Between 1990 and 1994 the Illinois Department of Public Health and the Illinois Environmental Protection Agency (IEPA) sampled 267 residential wells, 203 of which had contaminated water, with 108 homes having water contaminated above drinking water standards. Between 1993 and 1995 IEPA sampled more residential wells and installed 24 monitoring wells. The results linked the groundwater contamination to industrial sources located near the intersection of Route 251 and Rockton Road, and indicated that the contamination extended southwest from the industrial area, under a mile of open farmland and about 300 homes in the Evergreen Manor subdivision before discharging to the Rock River.

In 2000, U.S. EPA began a federally-funded remedial investigation and feasibility study (RI/FS) to evaluate the remaining groundwater contamination at the site and develop cleanup options. The RI/FS found that the groundwater contamination is attenuating naturally and will attain cleanup standards by 2015. There may be as many as 73 private wells still in use in areas within or adjacent to the groundwater contamination. However, based on groundwater sampling from 1990 to 2002, U.S. EPA expects that the private wells are not contaminated or have levels of contamination below drinking water standards.

Site Responsibility

This site is being addressed through federal, state, and potentially responsible party (PRP) actions.

Threats and Contaminants

The primary contaminants found in groundwater at the site are trichloroethene (TCE) and tetrachloroethene (PCE), but low levels of other VOCs were also detected. U.S. EPA did not detect any VOCs in any of the surface water samples that it collected from the Rock River, and the surface water does not pose any current risks to human health or the environment. Low levels of some VOCs were detected in sediment samples collected within or just downstream of the approximate groundwater discharge zone into the Rock River. However, U.S. EPA does not expect the chemicals found in these sediments to pose a risk to human health or the environment.

Cleanup Progress

In 1998, U.S. EPA completed an engineering evaluation/cost analysis to evaluate options to address the contaminated drinking water supplies. In March 1999, U.S. EPA issued an action memorandum for a non-time critical removal action (NTCRA) to connect 281 residences with contaminated and threatened well supplies to the North Park public water supply. In May 1999, three potentially responsible parties (PRPs), Waste Management, Regal-Beloit, and Ecolab signed an Administrative Order on Consent (AOC) to conduct the NTCRA. U.S. EPA completed the public water hookup in 1999 and 2000. The private wells at the homes that were connected to the North Park water supply were permanently sealed.

A Record of Decision (ROD) was issued in September 2003. The remedy selected in the ROD calls for local groundwater use controls and Monitored Natural Attenuation (MNA), with contingency actions to be implemented should groundwater monitoring warrant them. The natural attenuation of chlorinated solvents is a well studied process through which dilution, dispersion, and biological degradation act to neutralize the contaminants. EPA is conservatively estimating that within 12 years contaminant levels will be below drinking water standards.

EPA signed an Administrative Order on Consent (AOC) with Ecolab and Waste Management of Illinois on September 29, 2004 to perform a Remedial Design (RD). The statement of work for the RD required the respondents to conduct studies that would provide the information necessary for the design and implementation of the Remedial Action (RA). This information included the current extent of the contaminant plume and an evaluation of the potential for vapor intrusion.

EPA authorized a phased approach to determining the need to perform vapor intrusion monitoring because of the uncertainty that surrounded the remaining contaminant concentrations and the horizontal and vertical extent of the groundwater contamination within the plume. This was especially true for groundwater near the vadose zone within the residential area that could pose the greatest risk to residents through vapor intrusion. Additional uncertainties existed because EPA’s vapor intrusion investigation was a one-time sampling event at only four homes in the area, where sample size, property and construction-specific factors, and seasonal variations were not considered. Given the degree of uncertainty, EPA deemed it appropriate that the respondents be given an opportunity to demonstrate whether a complete vapor intrusion pathway was present.

The respondents submitted a Remedial Design Work Plan on May 26, 2005, which EPA approved on June 7, 2005. The respondents conducted the RD investigations and a Remedial Design Report was submitted to EPA on February 13, 2006. The investigation re-sampled 24 existing monitoring wells and completed three vertical aquifer profiles through the center of the inferred plume. Sample results from the monitoring wells indicated no contamination exceeding the remedial standards set forth in the ROD. Volatile organic compounds were also detected in the vertical aquifer profile groundwater screening samples, but none of the detected concentrations exceeded the MCL. The Remedial Design Report thus concluded that a definable groundwater contamination plume no longer exists and that the vapor intrusion pathway is incomplete. EPA concurred with these findings on May 24, 2006, and will not require the respondents to develop a vapor intrusion monitoring program.

As required by the Remedial Design Work Plan, the respondents developed a Monitored Natural Attenuation Plan for the site, which has yet to be formally approved by EPA. Because all monitoring points that still have detectable groundwater contamination are below remedial standards, the remedy is essentially complete. The BIOSCREEN model employed in developing the ROD predicted that under appropriate conditions the contaminant levels could be below remedial standards in as little as 1.5 to 3 years, so these observations were not unanticipated. 

Because the ROD remains in effect, the provisions for the implementation of contingency actions will protect human health and the environment should monitoring indicate that conditions are deteriorating.

Contacts

Remedial Project Manager, U.S. EPA
william ryan (ryan.williamj@epa.gov)
(312) 353-4374

Community Involvement Coordinator, U.S. EPA
janet pope
(312) 353-0628

Aliases

EVERGREEN MANOR GW CONTAMINATION PLUME
EVERGREEN MANOR GROUNDWATER CONTAMINATIO

 

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