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The Illinois Department of Public Health (IDPH), in cooperation with the Agency for Toxic Substances and Disease Registry (ATSDR), has determined from the available data that the DuPage County Landfill National Priorities List (NPL) site currently poses no apparent public health hazard since there is presently no exposure to contaminants at levels of health concern. The site could pose a health threat due to the potential for future exposure to groundwater; however, there is no evidence of an advancing contaminant plume. Historically, contaminants in the groundwater have generally been restricted to within 100 to 200 yards of the landfill. Although some low-level groundwater contamination has been detected in some downgradient private wells, the source of the contamination is uncertain. Present evidence does not indicate the landfill as the source. In the future, if erosion or other disturbance of the cap (e.g., construction) increases the infiltration of precipitation, this may lead to contamination of downgradient (west, southwest, and south) private and municipal wells.

Completed exposure pathways include dermal contact with and ingestion of contaminated sediments and surface water, as well as inhalation of volatile compounds and dust. The exposure to dust, sediments, and surface water is probably negligible. The amount of exposure to airborne volatile chemicals is uncertain, but is also probably negligible. Potential exposure pathways include the future ingestion of contaminated groundwater, dermal contact with and ingestion of polluted soil (exposure probably negligible), and consumption of contaminated plants (unlikely) and fish (possible future).

Recommendations include periodic monitoring of downgradient private wells, continued monitoring of on-site wells (especially those between the landfill and the downgradient private wells), regular landfill cap maintenance, institutional controls to prevent construction on the landfill, and further characterization of off-site geology and hydrogeology. health education to assist area residents in understanding their potential for exposure regarding the landfill site is recommended.


A. Site Description and History

The DuPage County Landfill covers 40 acres within the 1,235 acre Blackwell Forest Preserve, near Warrenville, Illinois, in Section 26, T39N, R8E. On February 7, 1990, the site was added to the National Priorities Listing (NPL) of the U.S. Environmental Protection Agency (USEPA).

The Blackwell Forest Preserve (Preserve) contains a campground, picnic areas, roads, streams, three lakes, trails (biking, cross-country skiing, hiking, horseback riding, and running), and the DuPage County Landfill. The hill formed by the landfill is used for tubing in the winter. In the past, Sand Pond was used for swimming. The site is bound by Spring Brook on the northwest and west, the West Branch of the DuPage River on the southwest, Butterfield Road (Route 56) on the southeast, and the center of Silver Lake on the east and northeast (Figures 1 and 2).

Originally, the site was an abandoned gravel pit. In 1960, it was purchased by the DuPage County Forest Preserve District (FPD), the current owner. They intended to use landfilling to reclaim the gravel pit for recreational use, which was a rather innovative idea at the time. Between 1960 and 1965, more than 1,100 additional acres were purchased to expand the Preserve to 1,235 acres. All of this was done because of concerns that (1) landfills in the area were rapidly reaching capacity, (2) expanding urbanization in the area would quickly consume many acres of land, and (3) undeveloped natural areas should be maintained. The FPD resumed gravel excavation in 1963 and continued through July 1969. This mining provided funds and fill material. At that time, it was decided to create an aboveground landfill rather than use the conventional trench method (Warzyn, Inc., 1994; Warzyn Engineering Inc., 1992; Booth and Vagt, 1986; Illinois Environmental Protection Agency (IEPA) files, 1989).

The Illinois State Geological Survey (ISGS), Illinois Sanitary Water Board, and Northeastern Illinois Planning Commission expressed the following concerns about using the site for a landfill: (1) seasonally elevated groundwater levels, (2) nearby populated areas, (3) the position of the landfill on the edge of the cones of depression of Warrenville public water supply wells, (4) extensive sand and gravel deposits, and (5) probable hydraulic connections between the proposed landfill and waters used for recreation (Warzyn, Inc., 1994; Warzyn Engineering, Inc., 1992; Warzyn Engineerinooth and Vagt, 1986). Despite these concerns, the landfill was designed and developed. The DuPage County Public Works Department (PWD) was contracted to construct the landfill under FPD supervision.

In October 1966, William Ross and Associates submitted preliminary design specifications, which recommended that the landfill cover 35 acres, have a 3:1 clay to refuse ratio, and have a honeycomb of 1 acre clay-lined cells, offset for stability (Booth and Vagt, 1986).

During construction and subsequent waste disposal activities, the FPD alleged that important deviations from the design occurred, and the landfill was not being operated properly (Booth and Vagt, 1986). Specifically, they alleged the PWD:

  1. instructed public works personnel to disregard FPD instructions and requests;
  2. failed to cover refuse at the end of each day;
  3. used insufficient fill between individual refuse cells;
  4. used sand and gravel for all cover material; and
  5. completely disregarded design specifications for at least several months in 1966, when open dumping was practiced.

Aside from these deviations, the PWD also (1) located a cell without a clay floor over a rubble-filled ditch which connected the southern end of Silver Lake with Spring Brook, (2) dumped refuse in an area northeast of the designated landfill, and (3) used a 1:1 ratio of natural fill to refuse. In 1968, the FPD dissociated itself from the project; however, in 1969, they were given responsibility for the construction of clay bottoms and side seals. The landfill was completed and closed in 1973. Its top is 846 feet in elevation (Booth and Vagt, 1986), and the boring for one gas vent showed that refuse exists about 10 feet below the summit (Lanham, 1990). The cover consists of 2 to 15 feet of sand and gravel, and (often very little) clay (Booth and Vagt, 1986). On the sides of the landfill, the cover does not meet current Illinois closure requirements (Lanham, 1990).

The landfill accepted general municipal and some industrial wastes from surrounding communities. There is no record of the disposal of hazardous materials, but some of the industrial wastes may have been hazardous. Materials known to be buried at the site include demolition, municipal, and scavenger waste, as well as grass clippings. It is believed that demolition and municipal waste comprised most of the fill material. Kroehler Manufacturing, Naperville, sent unknown quantities and types of waste to the landfill. Owens-Illinois, St. Charles, deposited waste from glass manufacturing at the site. It has been estimated that in 1968, 8,000 tons of dry sewage sludge from the Metropolitan Sanitary District of Greater Chicago and 1,095 to 1,460 tons of trash were placed in the landfill. It has also been estimated that a total of approximately 40,000 tons of dry sewage sludge and 5,500 to 7,300 tons of trash were placed in the site. In the 1970s, the news media suggested the DuPage County Landfill was a modern-day solution to the dual problems of solid waste disposal and the need for undeveloped natural areas in an urban setting (Warzyn, Inc., 1994; Warzyn Engineering, Inc., 1992; IEPA files, 1989).

The results of early (before 1980) groundwater monitoring around the landfill are not available in published documents. Leachate was reportedly first observed in a monitoring well in 1968, but the chemicals, their concentrations, and the date of sampling are unknown. In addition, it is uncertain when the wells were drilled or first sampled. Reportedly, additional monitoring wells were installed around the landfill in the 1970s. Early in 1980, brown leachate seeps were found around the waste area, which raised concerns about environmental contamination and led to a regular program of groundwater monitoring. As a precaution, Sand Pond, previously used for swimming, was closed to the public. Sampling at that time, however, did not show contamination.

To date, action taken at the site has included groundwater monitoring, installation of gas vents, leachate collection, periodic maintenance, and regrading of leachate seeps. To control leachate production and migration, the FPD has installed interceptor trenches and added clay soil cover to low areas on the landfill where water has ponded. Leachate seepage continued, however, in spite of these actions. Since 1987, about 30,000 gallons of leachate have been removed and incinerated at the Chemical Waste Management incinerator in Chicago. The Wheaton Sanitary District has received a permit from IEPA to accept an average of 5,000 gallons of leachate per week from the landfill. This leachate would be treated and discharged into Spring Brook about 2 miles upstream from the site. In early 1991, a 90-day trial period showed no deleterious effect on the biological treatment processes of the plant or the composition of the sludge. To date, the FPD has taken little leachate to the sewage plant; however, the present leachate collection system drains only two parts of the landfill. In negotiations with USEPA, the FPD agreed to expand the leachate collection system, which will probably increase the amount of leachate removed. The landfill cap has also experienced erosional problems (Heaton, 1995; Warzyn, Inc., 1994; Clavel, 1991; Booth et al, 1986; IEPA files, 1989).

On April 30, 1992, the Agency for Toxic Substances and Disease registry (ATSDR) released an Interim Preliminary Health Assessment for the site. On October 7, 1995, the Illinois Department of Public Health (IDPH) released a draft of the current document for agency comment. Both documents were prepared by IDPH through a cooperative agreement with ATSDR.

B. Site Visit

A site visit was conducted on April 17, 1989, by representatives of IDPH and USEPA. A locked gate and fence surrounding the summit of the hilltop restricts access to this part of the site, but the rest of the landfill is readily accessible. Aside from the access roads and parking lots, motor vehicles are not allowed on-site. Gas flares and vents installed on the hill have been caged to prevent contact and damage. The site is well-vegetated, and there are no obvious physical hazards. Monitoring wells are encased in metal and locked, and the Preserve is routinely patrolled by FPD police. The site conditions remained essentially unchanged during October 17, 1991, (IDPH and ATSDR personnel), May 23, 1993, December 29, 1994, January 10, 1996, and December 16, 1996, (IDPH personnel) follow-up site visits.

On December 29, 1994, odors were noted within 10 to 20 feet of some of the gas vents, including one near the summit and two along a paved path to the top of the hill. Some gas vents had signs saying "Caution Flammable Methane Gas." The lower slopes of the landfill, particularly on the northern and southern sides, have some trees, while the rest of the hill is covered by herbaceous vegetation. Pine Lake (formerly called Supply Lake) is closed to swimming (posted), but not fishing. Three people were fishing in Silver Lake.

On January 10, 1996, two people were ice fishing and a family of four (with small children) was ice skating on Silver Lake. A posted park brochure said Silver and Pine Lakes were open for fishing. Odors were noted near only one gas vent at the top of the landfill. On the paved trail to the top of the landfill, a sign indicated that odors were from landfill gas, and that in the future, methane gas may be used to heat a park office or other building. By December 16, 1996, a leachate collection system had been installed on the landfill. Most of the paved path to the summit of the hill had been covered with gravel. No one was observed on any of the park trails or fishing at any of the on-site lakes. Odors were noted near some gas vents.

C. Demographics, Land Use, and Natural Resource Use

In 1989, the FPD (1990) estimated that the preserve received about 105,000 visits, and in 1991, this number increased to around 264,562 (Warzyn, Inc., 1994). About 80 employees work part- or full-time in the preserve (Warzyn, Inc., 1994).

About 256 people live within 0.5 miles; 4,458 live within 1 mile; and, 13,153 live within 2 miles of the site (Warzyn, Inc., 1994). About 355 private wells are thought to be within 3 miles of the site, but more may exist. Many of these wells, however, are upgradient of the waste area. About 120 private wells are within 4,000 feet west, southwest, and south of the site and may be downgradient. A non-community public well at the Cenacle, a religious retreat, drew water from the shallow dolomite aquifer about 100 yards southwest (downgradient) of the site, but this building is now served by Warrenville municipal water. The closest private well is upgradient of the landfill. Private well locations near the site are shown in Figures 3a and 3b.

The City of Warrenville, revised 1990 census population 11,390 (U.S. Dept. of Commerce, Bureau of the Census, 1990), is immediately south of the site (Figure 1). It draws drinking water from the shallow bedrock aquifer via nine public water supply wells. Two to four of these wells are used at any given time to supply drinking water to the city. The closest one is about 0.6 miles downgradient of the landfill (Figure 4). At this time, some of the larger western suburban communities, including Wheaton and Naperville, are beginning to use Lake Michigan for their water source. In DuPage County, therefore, Lake Michigan water may eventually replace groundwater as the most widely used water source.

At this time, agricultural, recreational, and residential land use occurs around the site. In the future, more homes will likely be built because the population of the area has been growing rapidly. There are no known sensitive populations in the immediate area of the Preserve, and the nearest people live about 0.2 miles south and southwest of the site.

D. Health outcome data

The State of Illinois maintains databases for cancer and birth defects. These data are organized according to zip code and can be used to compare incidence rates of the site zip code to the state as a whole or a control group. Such a comparison is made if (1) exposure to chemicals is occurring at levels which may cause an adverse health effects, (2) the adverse health effect is recorded on one of the state databases, and (3) many people in a given zip code are exposed. A comparison is also made if the community is concerned that a disease rate is elevated and the three conditions above are satisfied.


During an October 17, 1991, USEPA public meeting, residents voiced their concerns about possible contamination of private and municipal wells. IDPH has also received calls from nearby residents concerning possible contamination of their water supply (private wells or Warrenville municipal).

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