Northeastern Illinois: General Information

              ISWS - Center for Groundwater Science - Northeastern Illinois
Center for Groundwater Science Illinois State Water Survey
Address / Phone Information
Northeastern
Illinois
General Information
Map of counties and cities
in the Chicago Region
As early as the 1860s, wells were being drilled into what was to become
the most heavily developed aquifer system of the region, the deep
bedrock Cambrian-Ordovician aquifers. Despite the proximity of Lake
Michigan, the presence of this regional aquifer system beneath the
whole of northeastern Illinois contributed greatly to the industrial and
population expansion of the area. Wells reaching this important aquifer
system are typically 800 to 1,500 feet deep. Shallower wells tap and use
overlying formations that are not so widespread.
See: The
Future of
Water
Availability
& Use in
the
Chicago
Region
County-
Level
Forecasts
of Water
Use in
Illinois:
2005-
2025 (pdf
~8.9mb)
As the industry and population grew in
the Chicago region, withdrawals
exceeded the region’s 65 million gallon
per day (mgd) estimated sustained yield
for the Cambrian-Ordovician aquifer
system. By 1979, pumpage from this
deep bedrock aquifer in the eight-county
area in northeastern Illinois reached an
all-time high of 182.9 mgd, nearly triple
the estimated sustained yield of the
aquifer system. By 1980, continued
heavy pumpage had caused the
potentiometric level of the deep bedrock
aquifers at Chicago to decline more than
850 feet. Until Lake Michigan water
became available to the collar counties in
the early 1980s, pumpage in excess of
the sustained yield had occurred every
year since the late 1950s. Withdrawals
from the deep bedrock aquifers are
currently very near the estimated
sustainable yield. As a result of Lake Michigan diversions and consequent reductions in withdrawals from
the deep bedrock, recovery of water levels has been observed in some areas. However, continued heavy
pumpage persists in the Joliet area corresponds with the deepest groundwater levels.
Groundwater Quality As a general rule, the water in the deep bedrock aquifers tends to be more
mineralized than shallow aquifers, but it varies from location to location. The potential for contamination by
vertical migration of chemicals from the land surface is very low; however, other contaminant pathways,
such as abandoned wells, can pose a threat to the groundwater quality in the deep bedrock. The Cambrian-
Ordovician is also known to contain high concentrations of naturally occurring barium and radium.
Because of increases in water demand due to rapid growth in the region,
http://www.sws.uiuc.edu/gws/neillinois.asp (1 of 3)5/25/2007 2:23:55 PM