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Metropolitan Water Reclamation District of Greater Chicago

Mainstream Tunnel System

  • Service Area: 220 square miles
  • Tunnels: 1.2 BG capacity, 40.5 miles
  • Reservoir: McCook Reservoir

TARP Overall

  • 17.5 billion gallons (BG) total capacity
  • 110 miles of tunnels, 2.3 BG capacity
  • Three reservoirs, 15.15 BG capacity
  • 352 square mile service area
  • 3.75 million people within service area
  • Over $180 million annual flood damage savings
  • 1.5 million structures protected from flooding
  • Phase 1 (Tunnels) completed 2006
  • Phase 2 (Reservoirs) to be completed 2029


TARP Fact Sheet

Schedule a Tour

Thursdays, 10 a.m.
2 hours
Link to Form

The Mainstream Pumping Station, located in Hodgkins, is one of three stations in the Tunnel and Reservoir Plan (TARP) system designed to capture combined sewer overflows from an area of 375 square miles, preventing backflows into Lake Michigan, mitigating waterway pollution caused by combined sewer overflows and providing an outlet for flood waters. The Mainstream Tunnel System consists of 40.5 miles of tunnels, 13 to 33 feet in diameter and 240 to 300 feet below ground. It extends from Wilmette, Illinois, in the north to McCook, Illinois, at its southern end. Sewage and stormwater entering the tunnels through drop shafts are carried to the Mainstream Pumping Station, where the flow is pumped to the MWRD's Stickney Water Reclamation Plant.


Mainstream Pumping Station pump room