WATEE SUPPLY AND SEWAGE DISPOSAL 161 



The modern and sanitary way to construct sewers is to 

 place them underground. There is usually a sewer in every 

 street, and every house should be connected with the sewer. 

 These smaller sewers unite into larger ones, which finally 

 discharge the sewage into a lake, river, or ocean. 



178. A problem in sewage disposal. Every city has its own 

 peculiar problems relative to water supply and sewage dis- 

 posal. In Chicago the problem was to find a place to empty 

 the sewage so that it could not flow into the lake. This was 

 very difficult to do, because the streams flow into the lake. The 

 problem was solved by reversing the current of the river, and by 

 means of a canal the water was made to flow into a branch of 

 the Illinois River. Although Chicago is in the basin of the St. 

 Lawrence River, at the present time its sewage flows into the 

 Gulf of Mexico. The way this was accomplished and the pecul- 

 iar geography which made it possible form an interesting story. 



179. The sanitary canal. The route which afforded an easy 

 passage for the Indians, the French, and the builders of the 

 Illinois and Michigan Canal and of wagon roads and railroads 

 has proved equally suitable for the route of the canal built to 

 carry away the sewage of Chicago. 



The building of this canal was possible because, as stated in 

 the preceding chapter, no part of the old portage was more 

 than 15 feet above the level of the water of the lake. The 

 current now flows from the lake into the mouth of the river 

 and up the South Branch, where it enters a new canal, known 

 as the sanitary or drainage canal. This canal is made wide 

 and deep to serve as a ship canal as well as for drainage. In 

 this way part of the water of Lake Michigan, the normal out- 

 let of which is through the St. Lawrence system, now flows 

 into the Gulf of Mexico and carries with it the sewage of 

 Chicago. It is known that in prehistoric times Lake Michigan 

 stood at a higher level, and its waters emptied into the Missis- 

 sippi system along the route now followed by the drainage 

 canal. Therefore the canal restores an ancient outlet. 



