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Hydrogeology and groundwater quality at monitoring wells installed for the Tunnel and Reservoir Plan System and nearby water-supply wells, Cook County, Illinois, 1995–2013

Scientific Investigations Report 2015-5186

Prepared in cooperation with the Metropolitan Water Reclamation District of Greater Chicago
By:
https://doi.org/10.3133/sir20155186

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Abstract

Groundwater-quality data collected from 1995 through 2013 from 106 monitoring wells open to the base of the Silurian aquifer surrounding the Tunnel and Reservoir Plan (TARP) System in Cook County, Illinois, were analyzed by the U.S. Geological Survey, in cooperation with the Metropolitan Water Reclamation District of Greater Chicago, to assess the efficacy of the monitoring network and the effects of water movement from the tunnel system to the surrounding aquifer. Groundwater from the Silurian aquifer typically drains to the tunnel system so that analyte concentrations in most of the samples from most of the monitoring wells primarily reflect the concentration of the analyte in the nearby Silurian aquifer. Water quality in the Silurian aquifer is spatially variable because of a variety of natural and non-TARP anthropogenic processes. Therefore, the trends in analyte values at a given well from 1995 through 2013 are primarily a reflection of the spatial variation in the value of the analyte in groundwater within that part of the Silurian aquifer draining to the tunnels. Intermittent drainage of combined sewer flow from the tunnel system to the Silurian aquifer when flow in the tunnel systemis greater than 80 million gallons per day may affect water quality in some nearby monitoring wells. Intermittent drainage of combined sewer flow from the tunnel system to the Silurian aquifer appears to affect the values of electrical conductivity, hardness, sulfate, chloride, dissolved organic carbon, ammonia, and fecal coliform in samples from many wells but typically during less than 5 percent of the sampling events. Drainage of combined sewer flow into the aquifer is most prevalent in the downstream parts of the tunnel systems because of the hydraulic pressures elevated above background values and long residence time of combined sewer flow in those areas. Elevated values of the analytes emplaced during intermittent migration of combined sewer flow into the Silurian aquifer decrease through time as water from the aquifer drains back into the tunnels in response to typical hydraulic conditions. Of the analytes sampled, fecal coliform provides the clearest indication of the location and timing of combined sewer flow into the Silurian aquifer surrounding the tunnel system.

Suggested Citation

Kay, R.T., 2016, Hydrogeology and groundwater quality at monitoring wells installed for the Tunnel and Reservoir Plan System and nearby water-supply wells, Cook County, Illinois, 1995–2013 (ver 1.1, May 2016): U.S. Geological Survey Scientific Investigations Report 2015–5186, 347 p., http://dx.doi.org/10.3133/sir20155186.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Methods of Study
  • Hydrogeology in the Vicinity of the Tunnel and Reservoir Plan System
  • Water Quality in Tunnel and Reservoir Plan System Monitoring Wells
  • Coliform Bacteria and Escherichia coli Data from Water-Supply Wells in the Vicinity of the Tunnel and Reservoir Plan System
  • Implications for Future Monitoring
  • Summary and Conclusions 
  • Acknowledgments
  • References Cited

Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Hydrogeology and groundwater quality at monitoring wells installed for the Tunnel and Reservoir Plan System and nearby water-supply wells, Cook County, Illinois, 1995–2013
Series title:
Scientific Investigations Report
Series number:
2015-5186
DOI:
10.3133/sir20155186
Edition:
Version 1.0: Originally posted April 4, 2016; Version 1.1: May 16, 2016
Year Published:
2016
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Illinois Water Science Center
Description:
vi, 347 p.
Time Range Start:
1995-01-01
Country:
United States
State:
Illinois
County:
Cook County
Online Only (Y/N):
Y
Additional Online Files (Y/N):
Y