Geologists Help State and Federal Agencies Determine Origin of Sediment at the Ottawa, Illinois, Superfund Site

Analyzing a superfund site at Ottawa

Ottawa, Illinois, was previously the site for several facilities producing watch dials that glowed in the dark as a result of radioactive substances combined with the paint. The factories are gone now, but some manufacturing waste products remain, combined with other human-made and natural deposits and dumped at various localities in the Ottawa area. Consequently, a number of sites are under remediation. An Illinois State Geological Survey (ISGS) geologist met with geologists and engineers from the Illinois Emergency Management Agency, U.S. Environmental Protection Agency, and Weston Solutions, Inc. at one such Superfund remediation site in Ottawa to help them solve a geologic problem: the origin of the material. The contamination at this site is the result of fill material from numerous sources, including radium-bearing materials from the Radium Dial Co. or Luminous Processes, Inc. Excavations at site NPL-9A in downtown Ottawa revealed a black sandy, peaty layer that occurs between the underlying St. Peter Sandstone and the overlying definitive fill material. The black sandy material exhibits some radioactivity, but the overlying fill does not. The site geologists were unsure whether the material is a natural deposit or anthropogenic fill. Determination of the origin of the dark horizon will influence remediation decisions. If the material is a natural deposit or is composed of natural deposits, then its removal might not be necessary; being able to leave it in place would reduce remediation costs. A sample was collected and brought to the ISGS for analysis. Initial analysis indicated that the material is composed mostly of quartz sand grains (approximately 80% by volume). These very fine- to medium-sized, frosted, subrounded grains are very similar to the underlying St. Peter Sandstone. The radioactivity of the sample is only slightly higher than that of background samples, suggesting that the material may be non-anthropogenic. Possible origins include post-St. Peter, pre-Pennsylvanian deposition, post- Pennsylvanian deposition, or even prehistoric deposition.