Ground‐Water Studies— Chicagoland Deep Tunnel System

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Abstract
The Deep Tunnel System planned by the Metropolitan Sanitary District of Greater Chicago will provide flood and pollution control for the combined sewer areas of the Chicago region. Elements of the Deep Tunnel System that are of main concern to the ground‐water resources of the area are the conveyance tunnels and the mined storage reservoir which will convey and store polluted storm‐water overflows. The Silurian and the Cambrian‐Ordovician aquifers, in units of which these elements will be located, will be protected from any deleterious effects of the System by ensuring that a positive hydraulic head, causing an inward flow, is continuously maintained around the tunnels and the mined reservoir. In the Cambrian‐Ordovician aquifer, this necessitates1 that ground‐water levels are maintained by artificial recharge. Extensive ground‐water studies were conducted to (1) demonstrate the feasibility of aquifer protection by recharge, (2) determine the needed amounts of recharge water, and (3) estimate the seepage of ground water into the tunnels and mined res.ervoir. The studies included field investigations, analog computer analyses and office evaluation of the collected data and analog results. The results indicate that (1) the proposed aquifer protection is feasible, (2) the recharge requirements will vary from 1.4 mgd in 1976 to 6.0 mgd in 2010, (3) seepage into the tunnels will be small, in amounts that can be easily controlled.

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