Drainage Channel and Waterway; A History of the Effort to Secure an Effective and Harmless Method for the Disposal of the Sewage of the City of Chicag (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: CHAPTER III. CHICAGO'S WATER SUPPLY SYSTEM. Chicago obtained its first water supply from wells. These were dug in the sand which had been heaped up by the winds, or in the silt deposited by the receding waters of the lake. Acting as a great filter bed the sand might have kept the water free from pollution, had there not been an impermeable stratum of blue clay near the surface. In spite of serious contamination the wells were used for twenty years after Chicago was incorporated as a village, although they were not the only source of water supply. To understand how the wells became unh't for use, a reference to the geological structure of the region embracing Chicago is necessary. The underlying rock is Niagara limestone. Upon this rests the blue clay, whose average depth is about 100 feet. Lake Michigan formerly extended to the ridge already referred to as the watershed of the St. Lawrence and Mississippi basins. As the underlying rock comes to the surface at the ridge, so the clay stratum thins out at the rim. When the lake receded, sand banks, or dunes, were formed across the basin, which extended from the bluffs at Winnetka southward twenty or thirty miles. Between these ridges of sand there were formed inland lakes or ponds in which a luxurious vegetation sprang up. From the resulting decay came the vegetable mold which lies on the surface in some places within the city limits. It is upon this bed of sand and vegetable mold with blue clay beneath that the city of Chicago stands. At no place was the original level more than twelve feet above the lake. It was thecustom when Chicago was a village, as in small villages everywhere to-day, to dig both the well and the vault on the same lot. The wells were never more than twelve feet deep, and usually six. The seepage from t...