HUMBOLDT, COLES COUNTY, ILLINOIS
In November 1988, IEPA collected 11 soil samples, 1 on-site monitoring well sample, 4 residential well samples, and 4 surface water samples. Acetone, cobalt, lead, magnesium, and nickel were present in the soil samples. Vinyl chloride, 1,2-dichloroethane (total), trichloroethene, and heavy metals were present in the on-site monitoring well. Bis(2-ethylhexyl)phthalate, carbon disulfide, and di-n-octylphthalate, heptachlor epoxide, 1,1,2-trichloroethane, and phenol were found in residential wells at that time. Low concentrations of heavy metals were also found in the residential wells. Surface water samples contained antimony, beryllium, chromium, silver, and vanadium .
The most recent samples collected by IEPA in December 1995 included 9 on-site soil samples, and 6 groundwater samples from nearby residential wells and the monitoring well (Figures 2 and 3). The samples were tested for volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), pesticides, and inorganic compounds. The maximum concentration of each contaminant was compared with appropriate environmental comparison values used to select contaminants for further evaluation for both carcinogenic and non-carcinogenic health endpoints. A detailed discussion of each comparison value used is found in Attachment 1.
The results of soil analysis indicated that VOC and SVOC concentrations did not exceed comparison values. Likewise, pesticides were not found at any concentrations above the comparison values. Arsenic was the only inorganic compound found at slightly elevated concentrations in the on-site soils (Table 1). Adults exposed to the level of arsenic in site soil would not be expected to experience adverse health effects. Because the site is in a remote location and is surrounded by a fence, children are not likely to access the site.
No VOCs, SVOCs, or pesticides were in the residential wells at levels that exceeded comparison values. The monitoring well sample (G102) contained elevated levels of vinyl chloride when compared to the Maximum Contaminant Level (MCL) for drinking water (Table 2). The U.S. Environmental Protection Agency (USEPA) has established MCLs that represent a contaminant concentration deemed protective of public health (considering the availability and economics of water treatment technology). Vinyl chloride is classified as a known human carcinogen and exposure to levels found in the monitoring well (G102) could pose a low to moderate increased risk of developing cancer if consumed over a long period. However, the water is not being consumed, and vinyl chloride has not migrated away from the site to residential wells. Because of the proximity of the site to the Kaskaskia River, groundwater may discharge directly into the river rather than into residential drinking water wells. No known surface water intakes are within 15 miles downstream of the site (4). The dilution factor of the river would reduce levels of any contaminants that might migrate downstream.
Manganese levels were detected above the MCL (Table 2) in four of the groundwater samples (G102, G202, G204, G205). However, according to calculated hazard index and dose estimations, no adverse health effects would be expected for residents consuming this water (3).
Lastly, two surface water samples were collected from the Kaskaskia River during the 1995 FSIP. Although cadmium was detected above background concentrations, its presence has not been attributed to the site and exposure is unlikely or minimal .