Kerr-McGee & Kress Creek Ecological Risk Assessment
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Kress Creek (KCK) and the Sewage Treatment Plant (STP) are two of four sites in and around West Chicago, Illinois, that have been contaminated by materials generated and stored on the Kerr-McGee Rare Earths Facility (REF). This report presents the results of the SERA conducted for these two sites in light of the objectives presented above; media data collected in 1993 through 1995, and 1999 through 2001 were used to conduct this analysis. Additionally, the RI Report for the Kress Creek and STP Sites, prepared by BBL (2004) was used for project background information.
Kress Creek/West Branch of DuPage River Site
The Kress Creek site (KCK), located in DuPage County, Illinois, includes about 1.5 miles of Kress Creek and 5.2 miles of the West Branch DuPage River (WBDR), and contains contaminated sediments, banks, and/or floodplain areas. The site became contaminated by past surface water runoff from the REF that discharged into the creek via a storm sewer outfall located south of Roosevelt Road (Route 38), just east of the Elgin, Joliet, and Eastern railroad tracks. The KCK Site includes the creek from the storm sewer outfall to the creek's confluence with the WBDR, and the WBDR from the confluence to the McDowell Dam. The study area originally ended at the Warrenville Dam, but later was expanded further downstream to the McDowell Dam.
Sewage Treatment Plant Site
The STP Site includes the West Chicago Sewage Treatment Plant (STP Upland), which is owned and operated by the City of West Chicago, and approximately 1.2 miles of the WBDR from the northern boundary of the STP property to the river's confluence with the creek (STP River). The STP upland became contaminated from the use of thorium mill tailings as fill material. Kerr-McGee and the City of West Chicago conducted voluntary cleanup actions at the STP Upland during the mid-1980s (prior to the site's listing on the National Priorities List). The STP River has areas with contaminated sediments, banks and/or floodplains and became contaminated by runoff and erosion from contaminated areas of the STP Upland.
These quantitative results should also be considered in the context of the qualitative characterization of habitat quality and the occurrence of other stressors within the study area. As noted above, high quality aquatic and riparian habitat is generally limited to the lower reaches of the study area. Additional stressors related to residential and commercial development within and in close proximity to the study area in the upper reaches may contribute to the relatively poor habitat quality in those areas and may be responsible for 6-the chemical constituents seen in media samples collected in Kress Creek. These locations generally coincide with the occurrence of both radionuclide and chemical COPCs at levels that significantly exceed ecologically-based benchmarks, indicating the potential for adverse effects. The combination of effects potentially associated with the COPCs and those associated with radiological stressors may further increase the possibilities of adverse impacts to ecological receptors in the upper reaches of the Kress Creek system and as a result, remedial activities should focus on the mitigation of these sediments. The proposed cleanup standard of 7.2 pCi/g for combined radium-226 and radium-228 is protective of biota when compared to the toxicological thresholds used here to calculate risk (e.g., BCGs for uranium and Ra-226 and Ra-228 are 2000 pCi/g (U-238); 100 pCi/g and 90 pCi/g, respectively).