Three-dimensional Geological Mapping Program Initiated for the Lake Calumet Region, South Chicago
The Illinois State Geological Survey has initiated a project to map the three-dimensional (3-D) geology of the Lake Calumet Quadrangle in south Chicago. This urban geology project will be part of the Central Great Lakes Geologic Mapping Coalition (CGLGMC) mapping effort in northeastern Illinois. Mapping will (1) delineate deposits that lie between land surface and the uppermost bedrock, (2) determine the nature of the shallow Silurian bedrock, including its thickness and degree of fracturing, (3) evaluate the deeper bedrock units, and (4) ascertain the exchange of groundwater between glacial aquifers and the underlying bedrock aquifer. The most important aspect of this project will be the 3-D mapping of all materials in the study area and then ascertaining their engineering properties and potential for transmitting contaminants.
Beginning in the late 1800s, the Lake Calumet region was transformed from an area of sand dunes and low-lying marshes to one of heavy industry, residential development, and numerous dumping grounds for industrial and municipal waste. In 1893, for example, the Army Corps of Engineers reported that a milling company located at mouth of the Calumet River deposited so much slag and dredge that the area around it grew at a rate of four acres per year.
Land degradation continued into the 1980s as steel mills closed, creating numerous brownfields, and there were further plans to continue filling in most of the lake to provide land for private developers. About that time, though, environmental groups began to promote conservation and cleanup. The most significant strides began in 1996, with attempts to establish Calumet Ecological Park. In 2001, a new Calumet Initiative was announced that advocated the restoration and enhancement of open spaces while revitalizing economic opportunities.
The current land use of the quadrangle is a myriad of public parks, ecological restoration areas, industrial holdings, waste disposal and contaminated sites, infrastructure development, and residential and commercial establishments, all on top of filled and natural land. It is within this context that geological mapping will reveal "what lies beneath." Once the geology is mapped in detailed 3-D view, contaminated problem areas will be delineated, engineering properties of fill and natural materials will be identified to assist in construction designs and avoid hazards, and large-scale groundwater flow models will be developed, which may assist in pump and treat decontamination processes. This information could lead to the implementation by decision makers of cost-effective plans with future lower liabilities for economic development, environmental protection, and remediation and redevelopment.
The mapping of the Lake Calumet Quadrangle will first involve the careful review of existing geologic maps and other data in the study area. The focus will mainly be on compiling subsurface data from thousands of existing water-well logs on file at the ISGS as well as logs from engineering borings for foundations, highways, bridges, utilities, and remediation activities. Then exploratory drilling and geophysical activities will be conducted to better understand the depth, thickness, distribution, character, and continuity of subsurface natural and fill deposits. All data (including old maps) will be put into electronic formats and entered into the ISGS Geographic Information Systems (GIS) database. The ISGS then will construct various 3-D views of the geology. Maps will be made showing the (1) distribution, elevation, and thickness of the various natural glacial, postglacial, and artificial-fill deposits in the study area; (2) topography of the bedrock surface; and (3) bedrock lithologies. Once these maps are completed, interpretive maps for aquifer sensitivity and engineering conditions and other maps can be developed.
The mapping of the Lake Calumet Quadrangle will be a multi-year effort with partial funding by the CGLGMC, but most funding coming from State of Illinois appropriations to the ISGS. Additional federal and state dollars would enhance data collection and significantly reduce the time required to complete the mapping effort.