Stream Pollution 29 



grows the practice increases, and probably also more rapidly than 

 the growth of the city would indicate. The reality and the serious- 

 ness of this practice has been recognized frankly, for instance by 

 the three sanitary experts in their report to the Chicago Real Estate 

 Board,* who say (p. 210) "A large part of the difficulty met in 

 disposing of Chicago's sewage has been caused by trade wastes 

 which have too freely been admitted to the sewers and open water- 

 ways. It is not reasonable that excessive burdens of cost and incon- 

 venience should be placed upon the public by manufacturing estab- 

 lishments in this manner." 



Furthermore one cannot doubt that the difficulty is increasing as 

 manufacturing plants become more numerous and trade wastes more 

 varied and abundant. In the course of the brief examination I 

 made in certain regions of New York State during the sum- 

 mer of 1918, positive evidence was obtained that domestic 

 sewage systems were carrying into public waterways recognizable 

 trade wastes of various character and very considerable amount. 

 It is important to emphasize this feature because it constitutes an 

 indirect though very real contribution to the pollution of the streams, 

 which may easily escape observation when the volume of these trade 

 wastes at any point is combined with a larger volume of domestic 

 sewage. As indicated in the comment of the Board of Sanitary 

 Experts at Chicago, quoted above, this material interferes, and 

 often seriously, with the process of self -purification which the 

 stream has to undergo. From the biological view point its effects 

 are apparent and even at times striking in the changes wrought in 

 the aquatic fauna and flora. Aquatic life is wiped out and appar- 

 ently does not reestablish itself readily, as It does when an excessive 

 volume of domestic sewage is reduced. Deposits of a resistant 

 character are laid down on the bed of the stream and deep-seated 

 changes seem to have been brought about that make the region 

 unsuitable for normal organisms and that endure unmodified by 

 natural influences. Unless the unwarranted mixing of industrial 

 and domestic wastes is checked, I am convinced that far-reaching 

 and serious modifications will be produced in our water courses, 

 which can be readjusted only with difficulty and after a long period 

 of time. 



* A report to the Chicago Real Estate Board on the Disposal of the Sew- 

 age and Protection of the Water Supply of Chicago, Illinois, by Messrs. 

 George A. Soper, John D. Watson and Arthur J. Martin. 1915. 



