U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2009–1212

Prepared in cooperation with the Metropolitan Water Reclamation District of Greater Chicago

Preliminary Assessment of the Potential for Inducing 

Stormwater Infiltration in Cook County, Illinois

Preliminary Assessment of the 

Potential for Inducing Stormwater 

Infiltration in Cook County, Illinois

By William S. Morrow and Jennifer B. Sharpe

Prepared in cooperation with the Metropolitan Water Reclamation District 

of Greater Chicago

Open-File Report 2009–1212

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Morrow, W.S., and Sharpe, J.B., 2009, Preliminary assessment of the potential for inducing stormwater infiltration in 

Cook County, Illinois: U.S. Geological Survey Open-File Report 2009–1212, 26 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Study Area..............................................................................................................................................2

Methodology...................................................................................................................................................4

Hydrogeologic Characteristics...........................................................................................................4

Unconsolidated Deposits ...........................................................................................................4

Bedrock .........................................................................................................................................7

Wetlands and Depth to Saturated Zone...................................................................................7

Distance from Streams .............................................................................................................11

Land Cover and Use Characteristics...............................................................................................11

Buildings with Basements........................................................................................................11

Sewer Systems/Drainage Tiles................................................................................................11

Supply Wells ...............................................................................................................................11

Dewatering Activities................................................................................................................14

Legacy Contamination ..............................................................................................................14

Superfund Sites, Resource Conservation and 

Recovery Act (RCRA) Facilities, and Brownfields .........................................14

Leaking Underground Storage Tanks ............................................................................14

Preliminary Assessment of Infiltration Potential....................................................................................18

Mapping Characteristics to Prioritize Areas for Assessment.....................................................18

Groundwater Flow to Lake Michigan ..............................................................................................24

Summary........................................................................................................................................................24

References Cited..........................................................................................................................................26

Figures

Figures 1–17. Maps showing:

1. Drainage basins and streams in Cook County, northeastern Illinois ..........................3

2. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface, in northeastern Illinois ..................................................5

3. Surficial geologic units overlying areas with permeable glacial 

deposits 20-feet thick or greater and within 50 feet of land surface, 

in northeastern Illinois ........................................................................................................6

4. Wetland areas located within areas of permeable glacial deposits 

20-feet thick or greater and within 50 feet of land surface, Cook County, 

northeastern Illinois ............................................................................................................8

5. Average depth to seasonally high water table from the 1994 State 

Soil Geographic Database (STATSGO), northeastern Illinois.......................................9

6. Areas where estimated depth to saturated zone is 4 feet or greater, 

northeastern Illinois ..........................................................................................................10
iv

Figures—Continued

7. Land holdings of the Metropolitan Water Reclamation District of 

Greater Chicago (MWRDGC) and Cook County Forest Preserve areas, 

Cook County, northeastern Illinois..................................................................................12

8. Land parcels containing structures with basements, Cook County, 

northeastern Illinois ..........................................................................................................13

9. Locations of quarries and sand-and-gravel pits in Cook County, 

northeastern Illinois ..........................................................................................................15

10. Locations of U.S. Environmental Protection Agency Superfund sites, 

Resource Conservation and Recovery Act (RCRA) facilities, and 

Brownfield sites, Cook County, northeastern Illinois...................................................16

11. Locations of U.S. Environmental Protection Agency leaking underground 

storage tanks (LUST) in Cook County, northeastern Illinois .......................................17

12. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface but with wetland areas removed, 

Cook County, northeastern Illinois..................................................................................19

13. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface after removal of wetland areas and 

legacy contamination areas (except LUST sites), Cook County, 

northeastern Illinois ..........................................................................................................20

14. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface after removal of wetland areas, legacy 

contamination areas (except LUST sites), and areas where depth to 

water table may be less than 4 feet, Cook County, northeastern Illinois .................21

15. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface and where the Wedron Formation 

and (or) Grayslake Peat are present, Cook County, northeastern Illinois................22

16. Land holdings of the Metropolitan Water Reclamation District of 

Greater Chicago (MWRDGC) and Cook County Forest Preserve located 

within areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface, Cook County, northeastern Illinois............................23

17. Areas with permeable glacial deposits 20-feet thick or greater and 

within 50 feet of land surface within the Lake Michigan surface 

watershed, Cook County, northeastern Illinois.............................................................25
v

Conversion Factors and Abbreviations

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) .3048 meter (m)

mile (mi) 1.609 kilometer (km)

meter (m) 3.281 foot (ft)

Area

acre 4,047 square meter (m2)

acre .004047 square kilometer (km2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) .003785 cubic meter (m3) 

cubic foot (ft3) .02832 cubic meter (m3) 

Flow rate

foot per second (ft/s) .3048 meter per second (m/s)

cubic foot per second (ft3/s) .02832 cubic meter per second (m3/s)
vi

Miscellaneous Abbreviations

Cal-Sag Calumet Sag

CERCLA Comprehensive Environmental Response, Contamination and Liability Act

GIS Geographic Information System

ICN Illinois Climate Network

ISGS Illinois State Geological Survey

ISWS Illinois State Water Survey

LUST Leaking Underground Storage Tank

MWRDGC Metropolitan Water Reclamation District of Greater Chicago

NED National Elevation Dataset

NPDES National Pollutant Discharge Elimination System

NRCS Natural Resource Conservation Service

NWI National Wetlands Inventory

NWIS National Water Information System

RCRA Resource Conservation and Recovery Act

SSURGO Soil Survey Geographic Database

STATSGO State Soil Survey Geographic Database

TARP Tunnel and Reservoir Project

USEPA U.S. Environmental Protection Agency
Preliminary Assessment of the Potential for Inducing 

Stormwater Infiltration in Cook County, Illinois 

By William S. Morrow and Jennifer B. Sharpe

Abstract

The Metropolitan Water Reclamation District of Greater 

Chicago is responsible for all of the regional stormwater 

management for Cook County in northeastern Illinois, one of 

the largest urban areas in the United States. Continuing urban 

expansion in this area has increased stormwater runoff and 

combined sewer overflows and likely decreased groundwater 

recharge. Passive induced-infiltration structures may help 

reduce stormflow problems and increase infiltration. These 

structures must be properly located to function effectively. 

Using hydrogeologic and land cover and use characteristics, 

maps of Cook County were developed indicating areas having 

the most potential for inducing stormwater infiltration. This 

assessment is preliminary because the scale of the mapping 

only gives a general indication of potential infiltration areas 

and is not suitable for site-specific investigations. In Cook 

County, 76,080 of 612,636 acres (12.4 percent) were determined to have the greatest potential for passive induced-infiltration-structure locations. Of these 76,080 acres, 8,650 are 

within the Lake Michigan surface watershed, with the remaining 67,430 acres within the Illinois River surface watershed. If 

all the annual rainfall on the 8,650 acres infiltrated and flowed 

to Lake Michigan, the resulting groundwater flux would be 

about 33 cubic feet per second (ft3/s).

Introduction 

Artificial or induced recharge is the addition of water, 

usually surplus surface water, to groundwater storage by 

other than natural means. Induced recharge historically has 

been used for increasing potable groundwater supply, diversion and infiltration of reclaimed wastewater, and diversion 

and infiltration of excess stormwater runoff, through passive 

(infiltration-basin style structures) and active (injection-well 

structures) methods. 

Continuing urban expansion has resulted in an increase 

in stormwater runoff and combined sewer overflow events 

as well as a likely decrease in groundwater recharge in Cook 

County, Illinois (Allen and Bejcek, 1979). One method of 

potentially reducing flooding, reducing the size and frequency 

of combined storm-sewer overflows, and partially restoring depleted groundwater in the area is to divert stormwater 

runoff to passive induced-infiltration structures, which could 

range from smaller rain-garden structures to full-size infiltration basins. This also could potentially increase groundwater 

recharge in the Illinois River and Lake Michigan watersheds 

(fig. 1).

The Metropolitan Water Reclamation District of Greater 

Chicago (MWRDGC) is responsible for stormwater management in Cook County. Presently (2009), the MWRDGC is 

drafting a Watershed Management Ordinance, which may 

include requirements for volume control as a component of 

site stormwater-detention regulations.

 One method by which a volume-control requirement 

could be met is through construction of passive inducedinfiltration structures. Many standards and recommendations 

for infiltration-basin design requirements have been developed 

throughout the Nation. In Illinois, the adjoining counties of 

McHenry and DuPage have regulations and guidance regarding infiltration-basin design that include assessing suitability 

of hydrogeologic and land cover and use characteristics.

The U.S. Geological Survey (USGS), in cooperation 

with the MWRDGC, conducted a preliminary examination 

of the general potential for the application of induced passive 

infiltration in Cook County by determining what areas under 

MWRDGC or Cook County jurisdiction were suitable for 

passive induced-infiltration structures, based on hydrogeologic 

and land cover and use characteristics. 
2 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Purpose and Scope

This report summarizes the process used to delineate 

areas within Cook County that have hydrogeologic and 

land cover characteristics generally considered favorable or 

limiting for passive induced infiltration. This assessment is 

preliminary because the scale of the mapping only gives a general indication of potential infiltration areas and is not suitable 

for site-specific investigations. Field confirmation of a) the 

hydrogeology including nature of subsurface deposits, wetland 

areas, stream interactions, and depth to saturation, b) the orientation of sewer systems and drainage tiles, c) other infrastructure such as buildings with basements, supply wells, dewatering activities, and d) the nature of legacy contamination would 

be components of a detailed assessment of site suitability. The 

report also contains a preliminary assessment of what portion of those potential areas may contribute groundwater flow 

toward Lake Michigan. 

Water-quality issues are not in the scope of this report, 

but will need to be addressed prior to construction of any 

passive induced-infiltration structure. However, the purpose 

of a passive induced-infiltration structure in Cook County 

would be for reducing stormwater runoff, and not to replenish an aquifer used for a drinking-water source, because 

Cook County primarily uses Lake Michigan for a drinkingwater source.

Study Area 

Cook County, Illinois, includes Chicago and 129 smaller 

municipalities and is one of the largest urban areas in the 

United States. The MWRDGC is responsible for wastewater treatment for approximately 91 percent of Cook County 

exclusive of smaller isolated land areas that do not discharge 

directly into MWRDGC facilities. There are seven operating water-reclamation plants including the Stickney Water 

Reclamation Plant, the second largest in the world (fig. 1). 

The MWRDGC is responsible for stormwater management for 

the entire 946 mi2 area of Cook County. 

Quaternary glacial and alluvial deposits cover most of 

Cook County, with thicknesses from zero to approaching 

300 ft in some areas (Leetaru and others, 2004). These unconsolidated deposits generally overlie Silurian bedrock. (Arnold 

and Friedel, 2000; Bretz, 1955; Willman and others, 1975).

Cook County lies in the Great Lakes physiographic 

section. Approximately half of Cook County is within the 

Chicago Lake Plain subsection; the other half is within the 

Wheaton Morainal Plain/Valparaiso Morainal subsection 

(Fenneman, 1938). Notable geomorphic features include the 

sand deposits of the Wilmette, Rosehill, and Graceland Spits 

on the north side of Cook County and the moraine remnant of 

Blue Island near the south side of Cook County. 

Five drainage basins are in Cook County: Chicago; Des 

Plaines; Little Calumet-Galien; Pike-Root; and Upper Fox. 

Major streams include the Calumet River, Chicago River, Des 

Plaines River, Little Calumet River, Poplar Creek, Salt Creek, 

Thorn Creek, Tinley Creek, and other smaller streams. Most 

surface water flows into the Calumet Sag (Cal-Sag) Channel and the Sanitary and Ship Canal and eventually into the 

Illinois River (fig. 1).

In 1900, the Main Channel of the Sanitary and Ship 

Canal was opened, reversing the flow of the Chicago River. 

This reversal diverted a substantial volume of stormwater runoff, sewage, and Lake Michigan water from the Lake Michigan Basin into the Illinois River Basin. By Supreme Court 

Order, the State of Illinois is allocated 3,200 ft3/s from Lake 

Michigan. The lake water makes up a small portion of the 

water in the Chicago Waterway system, which mainly consists 

of treatment-plant effluent and natural sources. The Chicago 

Sanitary and Ship Canal and the Cal-Sag Channel converge 

near Lemont, Ill., and eventually pass through hydroelectric 

generators at Lockport, Ill. The Canal merges with the Des 

Plaines River near Joliet, Ill. 

In 1985, the MWRDGC Tunnel and Reservoir Project 

(TARP) began operation. TARP is a system of underground 

tunnels and below-grade reservoirs designed to reduce 

combined sewage overflows into the Chicago area waterways by capturing the overflows and storing the water until 

the treatment plants have the capacity to treat and release the 

water into the waterways. The system currently (2009) has the 

capacity to temporarily store 2.3 billion gallons of combined 

sewage overflow. When completed, TARP will be capable 

of storing 17.5 billion gallons of combined sewage overflow 

(Jonathan Grabowy, MWRDGC, personal commun., 2009).
DU PAGE COUNTY

WILL COUNTY

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS

Base from U.S. Geological Survey 1:100,000-scale digital data.

Albers Equal-Area Conic Projection:

Standard parallels 45 and 33 , central meridian -89 . o o o

COOK COUNTY

WILL COUNTY

ILLINOIS

INDIANA

COOK COUNTY

DU PAGE COUNTY

KANE COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

McHENRY CO.

KANE CO.

Calumet R.

C ag

hic o River

Des Plaines v Ri er

Little Calume

e

t v Ri r

Poplar

Cr

Salt Creek

Tho r rn C

Tinley

Cr

Chicago Sanitary and Ship Canal

Lake

Michigan

Chicago

Drainage

Basin

(07120003)

Des Plaines

Drainage

Basin

(07120004)

Little

CalumetGalien

Drainage

Basin

(04040001)

Pike-Root

Drainage

Basin

(04040002)

Upper Fox

Drainage Basin

(07120006)

EXPLANATION

Drainage-basin boundary with drainage-basin name and 8-digit hydrologic unit code

Drainge divide between Lake Michigan to the east and the Illinois River to the west

Chicago

Lemont

Lockport

Joliet

Stickney

ILLINOIS

Area

shown

Cal-Sag Channel

Introduction 3

Figure 1. Drainage basins and streams in Cook County, northeastern Illinois. 
4 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Methodology

To identify areas potentially suitable for induced stormwater infiltration, hydrogeologic and land cover characteristics 

were evaluated. The primary considerations were hydrogeologic characteristics (especially porosity and permeability), 

depth from ground surface to an aquifer capable of transporting the water away from the area, and the thickness of the 

unsaturated zone (depth to water table) of the area. 

Previous mapping studies related to potential infiltration 

in the study area include Berg and Kempton (1984); statewide map of potential contamination of shallow aquifers from 

surface and near-surface disposal of waste (Berg and others, 

1984); stack-unit map of earth materials to depth of 15 m 

(Berg and Kempton, 1988); statewide map of potential for 

aquifer recharge (Keefer and Berg, 1990); aquifer-contamination potential map in the central U.S. (Soller and Berg, 1992); 

and model of recharge potential as affected by land use in the 

upper Illinois River Basin (Arnold and Friedel, 2000). Previous mapping studies of potential infiltration generally relied 

on arbitrarily weighted attributions to geology, soils, permeability, and depth to water table to develop maps indicating an 

indexed range of possible values with qualitative terms such as 

“low” and “high.” The previous mapping studies did not take 

into account locations of man-made structures when determining the potential for infiltration. For this report, the delineation 

of areas suitable for induced infiltration were determined using 

a dichotomous decision process, with determining factors for 

infiltration either being false (deleted from the mapping area) 

or true (remaining in the mapping area). 

Geographic Information System (GIS) geospatial data 

sets comprising hydrogeologic and land cover and use information for Cook County were compiled and used in this process. Geology considered favorable to infiltration was used to 

determine the initial potential infiltration area in Cook County. 

GIS spatial data sets for National Wetlands sites then were 

applied and unsuitable areas were removed to refine potential 

infiltration areas. The depth-to-saturated-zone data set was 

developed by kriging available water-table levels from wells 

and surface-water elevations. This depth-to-saturated-zone 

data set also was used to delete unsuitable areas and further 

refine potential infiltration areas. Land cover and use including 

infrastructure and legacy contamination was used to refine the 

potential infiltration area in Cook County. Characteristics that 

need to be considered on an individual-site basis, but are not 

easily defined in the county wide mapping (e.g., basements, 

sewer locations, and supply wells), are discussed.

Hydrogeologic Characteristics

Surficial geology is an initial consideration. Geomorphically, the surficial geology of Cook County is a heavily 

urbanized and altered landscape. In general, constructing 

suitable infiltration systems requires excavation of the initial 

contact layer between stormwater and the underlying permeable geologic units, either by creating a porous vegetated 

contact area or creating an initially highly porous contact area 

for the stormwater. Surficial materials in Cook County are 

typically not original, undisturbed soils. Therefore, original 

surficial geology was not considered as a determining factor 

in delineation. 

Unconsolidated Deposits

The unconsolidated deposits underlying an infiltration 

structure must be sufficiently permeable to be able to accept 

the stormwater and be able to transport water away from the 

basin area, with surface water preferably entirely drained 

within 72 hours (U.S. Environmental Protection Agency, 

1993). The data coverage from Riggs and others (1997), 

“Coarse Grained Materials within 50 feet of the Ground 

Surface in Illinois,” was used to initially delineate potential 

induced-infiltration areas. The Riggs and others (1997) map 

was developed from the Berg and Kempton (1988) stack-unit 

map data and adapted in this study to delineate permeable glacial deposits that have a thickness of 20 ft or greater (continuous or non-continuous) within 50 ft of land surface. In Cook 

County, the resulting area includes large sections along major 

streams and areas along the Lake Michigan shoreline. These 

areas of permeable glacial deposits, 20-ft thick or greater and 

within 50 ft of land surface, are shown in figure 2. 

The shallow glacial deposits indicated by the stack-unit 

map to have aquifer potential comprise the Equality Formation, Henry Formation, Cahokia Alluvium, Peoria and Roxana 

Loess, Wedron Formation, Grayslake Peat, and Parkland 

Sand. All of these areas are included for potential stormwaterinfiltration location, but it is noted that the Wedron Formation, 

listed as “silty or clayey” in the stack-unit description, and the 

Grayslake Peat, a result of filling of water bodies and wetland 

areas, likely have lower hydraulic conductivities than are 

desirable for induced infiltration (fig. 3). 
DU PAGE COUNTY

WILL COUNTY

Base from Stack-Unit Mapping of Geologic Materials in Illinois to a Depth of 15 Meters,

Illinois State Geological Survey, 1995.

EXPLANATION

Areas with permeable glacial deposits 20-feet thick or greater and

within 50 feet of land surface in northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

COOK COUNTY

WILL COUNTY

Methodology 5

Figure 2. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface, in northeastern Illinois.
EXPLANATION

Geologic Unit

Cahokia Alluvium

Equality Formation, Carmi Member

Equality Formation, Dolton Member

Grayslake Peat

Henry Formation

Parkland Sand

Peoria and Roxana Loess

Wedron Formation, silty and clayey diamictons

Base from Stack-Unit Mapping of Geologic Materials in Illinois to a Depth of 15 Meters,

Illinois State Geological Survey, 1995.

DU PAGE COUNTY

WILL COUNTY

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Thorn Cr

Poplar

Lake

Michigan

Cal-Sag Channel

COOK COUNTY

WILL COUNTY

6 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 3. Surficial geologic units overlying areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of 

land surface, in northeastern Illinois.
Methodology 7

Bedrock 

Bedrock that is fractured may develop preferential flow 

paths, which would not allow sufficient filtering and attenuation of contaminants to improve water quality and could lead 

to contamination of the groundwater system. Bedrock that is 

not fractured generally will impede infiltration. For purposes 

of this report, the presence or lack of unconsolidated deposits, 

interpreted from the mapping of underlying geology, is used to 

determine if near-surface bedrock is of concern. By designating the initial condition of permeable glacial-aquifer deposits 

being at least 20-ft thick, bedrock is thereby assumed to be at 

least 20 ft or more below ground surface.

Wetlands and Depth to Saturated Zone

The National Wetlands Inventory (NWI) designated 

wetland areas where water saturation determines soil development and the animal and plant communities, and the soil is 

at least periodically saturated. Categories in the NWI include 

bottom-land forest, deep marsh, deepwater lake, and shallow 

marsh/wet meadows. Regulatory restrictions and consistent 

saturation of land areas identified in the NWI eliminate these 

areas from consideration as potential induced-infiltration 

areas. These wetland areas were superimposed on the initial 

map produced based on underlying geology. The NWI areas 

located in areas of potential glacial-aquifer deposits 20-ft thick 

or greater are shown in figure 4.

The depth to the saturated zone (water table) is important for several reasons. A buffer [temporary storage] zone of 

unsaturated deposits is needed to allow possible mounding of 

groundwater from infiltration, as well as insuring that there is 

a filtration zone to remove sediment and some contaminants 

from stormwater before it enters the groundwater system. Siltation and clogging of the initial contact layer by sediment and 

other solids in stormwater and (or) biological growth above 

the water table will occur, and maintenance and cleaning of 

this layer will be necessary (U.S. Environmental Protection 

Agency, 2000). McHenry and DuPage County regulations 

recommend an unsaturated zone depth of greater than 3 to 

4 ft. The unsaturated zone thickness of 4 ft was chosen for the 

Cook County area to be consistent with these nearby counties. 

Estimating depth to water table in Cook County is 

complex. Water-table conditions vary seasonally by several 

feet, and some areas that have widely fluctuating water tables 

may not be suitable during certain times of the year, particularly areas near streams that may be affected by stream bank 

storage. Currently (2009), there are not enough water-table 

wells or water-table elevation data to accurately determine the 

water-table altitude for the Cook County area. The population 

in Cook County uses Lake Michigan as the primary source of 

drinking water, and this use expanded into portions of DuPage, 

Will, and Lake Counties in the latter part of the 20th century. 

As a result, few wells are available in the area for use in measuring the depth to water table. For example, water levels were 

published in Russell (1963) for Cook County only in bedrock 

wells; no wells in unconsolidated deposits were included. The 

Illinois State Water Survey (ISWS) monitors approximately 

35 shallow groundwater wells in the Illinois Climate Network 

(ICN) and Water and Atmospheric Resources Monitoring 

(WARM) Programs, but none of the wells are in Cook County. 

No wells were found in the online ISWS Private Well Database that were listed as being in an unconsolidated aquifer and 

having water-table conditions. The Natural Resource Conservation Service (NRCS) Soil Survey Geographic Database 

(SSURGO) project for Cook County, which will provide 

an estimate of depth to water for the Cook County area, is 

scheduled to be completed in 2011 (Robert McLeese, U.S. 

Department of Agriculture, personal commun., 2008; Dale 

Calsyn, U.S. Department of Agriculture, personal commun., 

2008) and currently (2009), water-level data are not available. 

These data, when published, may be useful in further refining 

areas for potential induced infiltration. The available NRCS 

State Soil Survey Geographic Database (STATSGO) data 

are not sufficiently detailed for site-specific application. The 

data are included here only to show that water-table levels are 

expected to be shallow and near surface throughout the study 

area, generally within 0 to 3 ft below ground surface. The data 

also indicate that the areas with the shallowest water-table 

depths are in southern Cook County, and the deeper watertable depths are near the Des Plaines River and the Chicago 

Sanitary and Ship Canal (fig. 5). 

The depth to saturated zone was estimated using stream 

and pond water-surface elevations, which are assumed to represent adjacent subsurface water-table conditions. The USGS 

National Water Information System (NWIS) well database 

includes 45 wells in Cook County constructed in glacial aquifers that may indicate water-table conditions. The Illinois State 

Geological Survey (ISGS) well database includes 115 highway 

and engineering borings including water-level measurements 

that indicate water-table conditions. All of these presumed 

water-table measurements were taken at different times during the year and thus may not be representative of average 

conditions. These groundwater data and elevation points for 

streams and ponds (determined from the 10-m National Elevation Dataset (NED)) were combined and interpolated using 

kriging methods to develop a continuous water-table surface. 

This water-table surface was then subtracted from land-surface 

elevation to provide an estimated depth-to-water zone (fig. 6). 
Wetlands from U.S. Fish and Wildlife Service National Wetlands Inventory (NWI), 1987.

EXPLANATION

National Wetlands Inventory inside deposits area

National Wetlands Inventory outside deposits area

Areas with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

C ag

hic o River

Des Plaines v Ri er

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

8 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 4. Wetland areas located within areas of permeable glacial deposits 20-feet thick or greater and within 50 feet of 

land surface, Cook County, northeastern Illinois.
Base from U.S. Department of Agriculture, 1994, State Soil Geographic Database (STATSGO);

Natural Resources Conservation Service, 1:250,000-scale digital data,

accessed April 11, 2008, at http://soils.usda.gov/survey/geography/statsgo/

EXPLANATION

Average Depth to Seasonally

High Water Table, in feet

Boundary of areas with permeable

glacial deposits 20-feet thick or

greater and within 50 feet of

land surface in northeastern

Illinois

0 to 1

1 to 2

2 to 3

3 to 4

4 to 5

5 to 6

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Lake

Michigan

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Methodology 9

Figure 5. Average depth to seasonally high water table from the 1994 State Soil Geographic Database (STATSGO), 

northeastern Illinois.
EXPLANATION

Depth to saturated zone equal to or greater than 4 feet

Boundary of areas with permeable glacial deposits 20-feet

thick or greater and within 50 feet of land surface in

northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Lake

Michigan

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

10 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 6. Areas where estimated depth to saturated zone is 4 feet or greater, northeastern Illinois.
Methodology 11

Distance from Streams

Areas surrounding streams may have fluctuating groundwater levels from changing river levels resulting in bank-storage effects. At potential passive induced-infiltration-structure 

locations near streams, stream stage and groundwater-level 

monitoring for temporal variation during storms to determine 

the range of water-level fluctuation and estimating peak elevations and durations would be a component of a detailed assessment of site suitability.

In some areas in close proximity to streams and consisting of high-permeability deposits, the residence time of infiltrated water could be short because of the short distance of the 

stream to the passive induced-infiltration structure. Rather than 

long-term groundwater storage resulting from construction of 

a passive induced-infiltration structure in these areas, a timedelayed release of filtered stormwater into the stream may better describe the flow pattern. Depending upon the length of the 

delay, this may produce the desired effects of reduced stormflow peaks and decreased combined sewer flows, but would 

not produce substantial long-term groundwater recharge. 

Water-quality improvements may not be substantial, but are 

expected to improve relative to direct stormwater runoff. 

Land Cover and Use Characteristics

Land use and cover, specifically anthropogenic, can 

affect the hydrologic characteristics of infiltration basins as 

well as the legal and political encumbrances associated with 

a particular land parcel. The land cover in Cook County is 

approximately 75 percent low- to high-density developed land. 

Medium- to high-density developed land (50 to 100 percent 

impervious cover) is approximately 39 percent. The remaining 25 percent is primarily forest (9 percent) and open space 

(9 percent) ( U.S. Department of Agriculture, 2007). Most 

of Cook County is urbanized and has a large proportion of 

impermeable area including roads, parking lots, and buildings. 

As a result, passive induced-infiltration structures likely will 

be on land without infrastructure and small because of space 

availability.

Cook County Forest Preserves are relatively large areas 

of open space land cover and , thus, are possible areas to consider in initial assessments of potential areas for infiltration. 

MWRDGC land holdings also are possible areas to consider 

for siting passive induced-infiltration structures. Cook County 

Forest Preserve areas and MWRDGC land holdings are designated in figure 7.

Buildings with Basements

Buildings with basements, as designated in the 2006 

Cook County Assessor data (digital data obtained through 

MWRDGC), are useful in evaluating location suitability 

for a passive induced-infiltration structure. It is reasonable 

to assume that if a building has a basement, the water table 

generally is deeper than 4 feet. Areas having residential or 

commercial buildings with basements can strengthen the 

indication that potential areas are suitable for passive inducedinfiltration structures or can indicate that further investigation 

of hydrologic conditions is needed. Conversely, if a passive 

induced-infiltration structure is constructed near buildings 

with basements, raised groundwater levels may cause leakage 

problems in these buildings or increase existing problems. The 

location of buildings with basements in relation to potential 

recharge areas is shown for informational purposes in figure 8. 

Sewer Systems/Drainage Tiles

 Areas suitable for stormwater infiltration preferably 

would have up-to-date mapped locations of sewer lines and 

(or) tunnels. Newer sewer lines are grouted and less prone to 

leakage; however, older sewer lines are prone to leakage, both 

into and out of the sewer pipes, and may have considerable 

interaction with the subsurface water adjacent to the sewer 

line. Extensive interaction among passive induced-infiltration 

structures and sewer lines may reduce the effectiveness of 

decreasing stormwater runoff. Sewer-line locations and 

depths would be too numerous and complex to plot on maps 

presented in this report; locating these features would be a 

component of a detailed assessment of site suitability.

Parts of Cook County still may have drainage tiles present from when the land was farmed. Any drain tiles found in 

the subsurface likely will be collapsed, clogged, or intercepted 

and terminated as a result of urban development. If drain tiles 

are found during infiltration-structure construction, further 

hydrologic investigation may be necessary to determine 

their status.

Supply Wells

Proximity of supply wells to induced infiltration areas 

is a concern. McHenry County regulations specify that 

infiltration-basin systems should be at least 200 ft from supply 

wells. Cook County uses Lake Michigan for a drinking-water 

source; however, there are water-supply wells in Cook County 

according to the Illinois State Geological Survey online well 

database, ILWATER, available at http://www.isgs.illinois.edu/

maps-data-pub/wwdb/launchims.shtml. Many of these wells 

likely are not being used or are for non-potable use. Verifying 

well location, depth to producing zone, and status relative to 

a possible passive induced-infiltration structure would be a 

component of a detailed assessment of site suitability.
Data courtesy of Metropolitan Water Reclamation District of Greater Chicago.

EXPLANATION

Metropolitan Water Reclamation District

of Greater Chicago (MWRDGC) land holdings

Cook County Forest Preserve

Areas with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Cr

12 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 7. Land holdings of the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) and Cook County Forest 

Preserve areas, Cook County, northeastern Illinois.
Parcel data from the Cook County Assessor's Office, 2006.

EXPLANATION

Land parcel containing structures with basements

Boundary of areas with permeable glacial deposits

20-feet thick or greater and within 50 feet of land

surface in northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Lake

Michigan

DU PAGE

WILL

COOK

DU PAGE

LAKE

COOK

COOK

WILL

Methodology 13

Figure 8. Land parcels containing structures with basements, Cook County, northeastern Illinois.
14 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Dewatering Activities

Active and inactive quarries that are located near passive 

induced-infiltration structures can have substantial effects on 

hydrology. Pumping to dewater quarries could draw water 

through near-surface deposits toward the quarry. Infiltrated 

stormwater drawn to the pump may require treatment before 

it is disposed if it does not meet National Pollutant Discharge 

Elimination System (NPDES) standards, because of the short 

residence time in the ground.

In abandoned or unused quarries where pumping has 

been discontinued, water has likely filled the quarry to a stable 

level. Groundwater levels surrounding the quarry will reflect 

the quarry water level. The area surrounding the quarry may 

have water-table levels that make the surrounding area unsuitable for stormwater infiltration.

Quarries are shown in figure 9. The major bedrock 

quarries are McCook, Thornton, and Lyons. Sand-and-gravel 

producing quarries (pits) are located in the northwest. Local 

investigations of operation status, water levels, and depth to 

bedrock would be a component of a detailed site assessment 

before a passive induced-infiltration structure was constructed.

Legacy Contamination

Areas with documented contamination were designated 

not suitable for passive induced-infiltration structures because 

of the risk of off-site transport of contamination. Leaking 

Underground Storage Tank (LUST) sites are exceptionally 

numerous and are point locations only whereas the other three 

other types of legacy contamination are areal data. As a result, 

LUST sites are described and mapped separately in the following discussion of methods. 

Superfund Sites, Resource Conservation and 

Recovery Act (RCRA) Facilities, and Brownfields

Superfund sites are abandoned areas where sufficient hazardous substance is present for the USEPA to declare the area 

as unusable until cleaned up to designated standards under the 

Comprehensive Environmental Response, Contamination and 

Liability Act (CERCLA). Superfund sites listed are not on the 

National Priority List. Resource Conservation and Recovery 

Act (RCRA) facilities are designated by the USEPA as active 

treatment, storage, or disposal sites that handle physical, 

chemical, and biological waste. Brownfield sites are former 

industrial- or commercial-land areas that have lower levels 

of contamination, allowing reuse of the land once cleanup or 

development restrictions are in place. Brownfield sites are 

listed as not suitable, but may be suitable in the appropriate 

setting, dependent upon the severity of contamination and surrounding land use.

These sites were located by using USEPA and IEPA 

databases. The address of the land owner in the databases was 

linked to the parcel of land at that address. Multiple parcels 

of land may be owned by one business; therefore, the acres of 

land determined not suitable may be substantially underestimated. Brownfield-site boundaries and acreage are not well 

defined (Illinois Environmental Protection Agency, 2009a); 

therefore, total acreage of Brownfield sites is likely underestimated. The resulting land area for Superfund sites, RCRA 

facilities, and Brownfield sites is shown in figure 10.

Leaking Underground Storage Tanks

Leaking Underground Storage Tank (LUST) sites are 

where tanks have previously leaked fuel or other toxic substances. While many of these sites may have been remediated 

to USEPA standards, continued cleanup and monitoring of 

many of these sites may be ongoing. Presently (2009), there 

are 6,079 LUST sites in Cook County (Illinois Environmental 

Protection Agency, 2009b) (fig. 11). LUST sites will have had 

previous groundwater investigations including information 

on water levels and direction of groundwater flow at the site. 

The 2009 data are for individual sites and were not available as a combined data set that could be used to determine 

groundwater geology and levels on a countywide basis. These 

groundwater investigations will be useful at a localized level 

in determining if hydrogeologic conditions are appropriate for 

a passive induced-infiltration structure to be located upgradient or at a sufficient distance away from the LUST site.
EXPLANATION

Areas

Quarry or sand-and-gravel pit

with permeable glacial deposits

20-feet thick or greater and within 50 feet of land

surface in northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Methodology 15

Figure 9. Locations of quarries and sand-and-gravel pits in Cook County, northeastern Illinois.
Data obtained from the U.S. Environmental Protection Agency Envirofacts Data Warehouse;

accessed February 2009, at http://www.epa.gov/enviro/.

EXPLANATION

Areas

Brownfield site

Superfund site

RCRA facility

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

!

!

!

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Thorn Cr

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

16 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 10. Locations of U.S. Environmental Protection Agency Superfund sites, Resource Conservation and Recovery Act (RCRA) 

facilities, and Brownfield sites, Cook County, northeastern Illinois
COOK COUNTY

WILL COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

DU PAGE COUNTY

EXPLANATION

Areas

Leaking underground storage tank (LUST) site

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Lake

Michigan

DU PAGE COUNTY

WILL COUNTY

Methodology 17

Figure 11. Locations of U.S. Environmental Protection Agency leaking underground storage tanks (LUST) in Cook County, 

northeastern Illinois.
18 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Preliminary Assessment 

of Infiltration Potential

Cook County is approximately 612,636 acres of mostly 

medium to high-density urban land. Results of overlaying and 

evaluating hydrogeologic and land cover and use characteristics for preliminary assessment of areas suitable for a passive 

induced-infiltration structure are presented herein as a series 

of maps. 

Mapping Characteristics to Prioritize Areas 

for Assessment

The initial consideration for determining potential areas 

for passive induced-infiltration structures is the underlying 

permeable geology. Glacial-aquifer deposits that are 20 ft or 

more in thickness, but not necessarily continuous, within the 

first 50 ft below land surface were delineated based on data 

from Riggs and others (1997). These initial areas comprise 

153,992 acres (approximately 25.1 percent of the county) 

and largely consist of land along the major streams in Cook 

County, along with areas bordering Lake Michigan and in 

southern Cook County (fig. 2).

The NWI areas within the above-delineated areas were 

removed from consideration. A total of 9,756 NWI acres were 

deleted, leaving 144,237 acres or approximately 23.5 percent 

of Cook County (fig. 12).

Superfund sites; Brownfield sites; and RCRA treatment, 

storage, and disposal facilities were then removed from the 

remaining potential area. There are 855 acres of RCRA facilities, 669 acres of Superfund sites, and 0.6 acres of Brownfield sites present for a total of 1,525 acres deleted, leaving 

142,712 acres or approximately 23.3 percent of Cook County. 

The Brownfield site acreage may have potential for induced 

infiltration (fig. 13). The Brownfield site acreage likely is 

substantially underestimated because of insufficient database 

input, contamination sites being assigned to the designated 

parcel of land at the site address, and possible database status 

as a CERCLA (Superfund) site. 

Areas that may have less than 4 ft of depth to the water 

table were removed from the remaining potential area. A total 

of 66,632 acres were removed in this step, leaving 76,080 

acres or approximately 12.4 percent of Cook County. These 

remaining areas have the greatest potential for induced infiltration in Cook County (fig. 14).

Of the 76,080 acres of land with potential for induced 

infiltration, 4,390 acres are located where the poorly permeable “silty or clayey” Wedron Formation or Grayslake Peat 

may be present in sufficient thickness to limit infiltration. Of 

these 4,390 acres, 3,289 acres include the Wedron Formation 

and 1,101 acres include the Grayslake Peat. Although these 

areas are listed as coarse deposits by Riggs and others (1997), 

site-specific confirmation of geologic units and thickness 

is needed in these areas to confirm sufficient permeability 

(fig. 15). 

Currently (2009), there are 9,825 acres of land held either 

by the MWRDGC (1,458 acres) or the Cook County Forest 

Preserve (8,367 acres) in potential infiltration areas. These 

areas are shown in figure 16.
EXPLANATION

Areas

Areas

with

wetland areas removed, in Cook County

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface,

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Preliminary Assessment of Infiltration Potential 19

Figure 12. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface but with wetland 

areas removed, Cook County, northeastern Illinois.
EXPLANATION

Areas

Areas with

with

wetland areas and legacy contamination areas

removed in Cook County

with permeable glacial deposits 20-feet thick or

greater and within 50 feet of land surface in

northeastern Illinois

permeable glacial deposits 20-feet thick or

greater and within 50 feet of land surface

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

20 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 13. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface after removal of 

wetland areas and legacy contamination areas (except LUST sites), Cook County, northeastern Illinois.
EXPLANATION

Areas

Areas

after

removal of wetland areas, legacy contamination

areas, and areas where depth to water table may

be less than 4 feet, in Cook County

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface,

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Preliminary Assessment of Infiltration Potential 21

Figure 14. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface after removal of 

wetland areas, legacy contamination areas (except LUST sites), and areas where depth to water table may be less than 4 feet, 

Cook County, northeastern Illinois.
EXPLANATION

Areas

Areas

where the Wedron Formation and (or) Grayslake

Peat are present and may have lower permeability

to limit infiltration, in Cook County

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface,

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

22 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Figure 15. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface and where the 

Wedron Formation and (or) Grayslake Peat are present, Cook County, northeastern Illinois.
Data courtesy of Metropolitan Water Reclamation District of Greater Chicago.

EXPLANATION

Metropolitan Water Reclamation District

of Greater Chicago (MWRDGC) land holdings

Cook County Forest Preserve

Areas with permeable glacial deposits 20-feet thick

or greater and within 50 feet of land surface in

northeastern Illinois

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Preliminary Assessment of Infiltration Potential 23

Figure 16. Land holdings of the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) and Cook County 

Forest Preserve located within areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface, 

Cook County, northeastern Illinois.
24 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Groundwater Flow to Lake Michigan

Of the 76,080 acres that have potential for infiltration 

of stormwater, 8,650 acres (11.4 percent) are within the Lake 

Michigan surface watershed (fig. 17), with the remaining 

67,430 acres within the Illinois River surface watershed. 

Within the Lake Michigan surface watershed, water naturally 

would flow overland to Lake Michigan; however, storm-sewer 

drains in the basin divert almost all the surface runoff away 

from Lake Michigan and into the Chicago Waterway system 

or treatment facilities discharging to the Illinois River Basin. 

If it is assumed that the groundwater level mimics topography, then the water infiltrated into the Lake Michigan surface 

watershed likely flows toward Lake Michigan. Without a 

network of water-table observation wells, it is not possible to 

precisely determine whether the groundwater divide coincides with the surface-drainage divide, or if the groundwater 

divide is affected by groundwater withdrawals or anthropogenic changes in surface topography and drainage that may 

alter which areas that may contribute groundwater flow to 

Lake Michigan.

These 8,650 acres are approximately 1.4 percent of the 

612,636 acres in Cook County. The total possible stormwater infiltration in these 8,650 acres that could pass through 

the subsurface to Lake Michigan would be approximately 

1,036,000,000 ft3, if all the yearly average rainfall (33 in.) that 

falls on this watershed area were collected, stored, and allowed 

to infiltrate. For comparative purposes, this is approximately 

equivalent to a flow of about 33 ft3/s throughout the year. 

The potential for an appreciable groundwater contribution to 

Lake Michigan from induced infiltration within the surfacewatershed area is small, about 1 percent, in comparison to the 

amount being withdrawn by Illinois (approximately 3,200 

ft3/s) from Lake Michigan. However, this amount may be 

appreciable in comparison to the additional potable water supply available to Illinois communities. Other factors affecting 

the actual groundwater flow to Lake Michigan would be the 

amount of land available for potential infiltration and the land 

area being drained to the passive induced-infiltration structure.

Summary 

Areas for potential induced infiltration of stormwater 

runoff in Cook County, Illinois, were delineated based on 

hydrogeologic and land cover and use characteristics. Coarsegrained deposits 20-feet thick or greater within 50 feet of land 

surface were initially delineated in Cook County for the base 

map; this also eliminated areas where bedrock was within 

20 feet of ground surface. Wetlands, as delineated in the 

National Wetlands Inventory, along with unsaturated deposits 

thinner than 4 feet estimated based on available groundwater 

levels, elevations of surface-water bodies, and land-surface 

topography, using Geographic Information System methods 

also were then eliminated from consideration. Superfund–

Resource Conservation and Recovery Act facilities and 

Brownfield locations also were removed from consideration. 

A total of 76,080 acres of the 612,636 acres of land in 

Cook County were determined to have the highest potential for induced stormwater infiltration. Most of these areas 

are along selected stream reaches, notably the Des Plaines 

River, Little Calumet River, Midlothian Creek, Salt Creek, 

Poplar Creek, Thorn Creek, Tinley Creek, the Sanitary and 

Ship Canal, and the Calumet Sag Channel. The proximity to 

streams is owing to the presence of alluvium and the associated, generally greater, hydraulic conductivity in those areas. 

There are 1,458 acres of MWRDGC holdings and 8,367 acres 

in the Cook County Forest Preserve. There also are substantial 

areas for potential induced infiltration bordering Lake Michigan and in southern Cook County.

Within the Lake Michigan surface-water drainage basin, 

8,650 acres of land potentially are suitable for induced stormwater infiltration. The amount of groundwater flow to Lake 

Michigan, if all rain falling on this area was infiltrated, would 

be about 33 cubic feet per second on a yearly average basis. 

However, a more thorough investigation of the groundwater 

divide and flow of shallow groundwater toward the Lake, 

including possible sewer-pipe complications near passive 

induced-infiltration structures and the Lake, may be needed 

to make a better determination of the potential contribution of 

enhanced infiltration to Lake Michigan.

General areas potentially suitable for induced stormwater 

infiltration have been delineated for the entire Cook County 

area. This assessment is preliminary because the scale of the 

mapping only gives a general indication of potential infiltration areas and is not suitable for site-specific investigations. 

Field confirmation of a) the hydrogeology including nature 

of subsurface deposits, wetland areas, stream interactions, 

and depth to saturation, b) the orientation of sewer systems 

and drainage tiles, c) other infrastructure such as buildings 

with basements, supply wells, dewatering activities, and d) 

the nature of legacy contamination would be components of a 

detailed assessment of site suitability. 
EXPLANATION

Areas

within the

Lake Michigan surface-water drainage area, in Cook

County

Boundary of Lake Michigan surface-water drainage area

Areas with

with permeable glacial deposits 20-feet thick or

greater and within 50 feet of land surface in

northeastern Illinois

permeable glacial deposits 20-feet thick or

greater and within 50 feet of land surface,

88°10' 88° 87°50' 87°40' 87°30'

42°10'

42°

41°50'

41°40'

41°30'

0 5 10 MILES

0 5 10 KILOMETERS ILLINOIS INDIANA

Calumet R.

Little Calume

e

t v Ri r

Cr

Salt Creek

Tinley

C ag

hic o River

Des Plaines v Ri er

Cr

Chicago Sanitary and Ship Canal

Tho r rn C

Poplar

Lake

Michigan

Cal-Sag Channel

DU PAGE COUNTY

WILL COUNTY

COOK COUNTY

DU PAGE COUNTY

LAKE COUNTY

COOK COUNTY

COOK COUNTY

WILL COUNTY

Preliminary Assessment of Infiltration Potential 25

Figure 17. Areas with permeable glacial deposits 20-feet thick or greater and within 50 feet of land surface within the 

Lake Michigan surface watershed, Cook County, northeastern Illinois.
26 Preliminary Assessment of the Potential for Inducing Stormwater Infiltration in Cook County, Illinois

Riggs, M.H., Nelson, D., and Abert, C.C., 1997, Coarsegrained materials within 50 feet of the ground surface in 

Illinois: Champaign, Ill., Illinois State Geological Survey 

Geographic Information System database GISDB_HYDRO.

IL_Shallow_Coarse_Materials_Py., accessed at http://www.

isgs.illinois.edu/nsdihome/browse/statewide/aq50b.gif

Russell, R.R., 1963, Ground-water levels in Illinois through 

1961: Urbana, Ill., Illinois State Water Survey, Department 

of Registration and Education, Report of Investigation 45, 

51 p.

Soller, D.R., and Berg, R.C., 1992, Using regional geologic 

information to assess relative aquifer contamination potential—An example from the central United States: U.S. Geological Survey Open-File Report 92–694, scale 1:1,000,000. 

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