The production and desalting of saline waters stored in a deep artesian aquifer, the Mount Simon Sandstone in northeastern Illinois, to aid in meeting projected water deficits for the Chicago region, are being considered. Because of the characteristics of the predicted Mount Simon water quality it would be necessary to dispose of large quantities of desalting-plant waste brine. Evaluation of brine disposal methods led to selection of disposal by injection through wells open to the lower Mount Simon aquifer. As feedwater for desalting plants would be withdrawn from the upper Mount Simon aquifer, injection-well fields were designed to eliminate contamination of feedwater and to keep injection pressures within acceptable limits. Wells capable of injecting 1 million gal/day ( gd) were designed. Injection costs were 12.5-19% of the total cost of producing water. Injection costs ranged from 17 cents per 1,000 gal for injection of brine from a 1-mgd reverse osmosis plant to 58 cents per 1,000 gal for brine from a 5-mgd distillation plant. The effect of brine injection may have a harmful effect on the quality of water withdrawn from existing wells open to the aquifers above the Mount Simon.

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