[HARRISON 4 vanderleck] ANALYSES OF OTTAWA RIVER WATER 17 



as undesirable for drinking purposes," then the water of the Ottawa 

 River at Ste. Anne's, at all seasons of the year, must be considered unfit 

 for potable purposes. On three occasions only was B. coli absent from 

 5 c.c, and in these instances, although not shown on the table of results, 

 we found the organism in 20 c.c. samples. 



Excrétai B. coli which we isolated continually from Ottawa River 

 water at Ste. Années can only to a certain extent originate from the 

 washings of land in cultivation or from accidental infection. 



In winter time, the river bctAveen Ottawa and Ste. Anne's is covered 

 with ice from 1 to 2 feet thiclc, for more than three months, and the 

 only possible source of infection is the sewage of those towns on its 

 banks which have a sewerage system, namely Ottawa (80,000), HuU 

 (15,000) and Hawkesbury (5,000), with a total population of 100,000. 

 As already mentioned the river above Ottawa is nearly free from B. coli, 

 but the three towns mentioned discharge daily into the river 100 gallons 

 of sewage per capita, which amounts to ten million gallons daily. 



This laj-ge quantity of sewage is diluted according to the amount 

 of water in the river at different times of the year, and in order to 

 differentiate this sewage infection from contamination from all other 

 sources, we must make a comparison of the amount of water discharged 

 during the different months of the year. 



In 1908 September and October were the months of very low water, 

 and therefore their discharge is taken as a standard of comparison. In 

 April four times as much water is discharged as in one of these " stan- 

 dard " months, whilst March has a discharge of twice of one of the 

 lowest months. In this way all the months are tabulated. 



This table is computed from 8 years' observations of the daily 

 discharge of the river at Besserer's Grove. See sketch "Daily 

 Discharge of the Ottawa River at Besserer's Grove." 



The value of the above factors i? that they give us the dilution of 

 the sewage infection for the various months. For example, in April 

 with factor 4 the sewage is diluted 4 times as much as in September or 

 October. 



The average number of B. coli per c.c. for the three winter months 

 is, respectively, 221/2, 16 and 5 — an average of 14 B. coli per c.c. for the 



Sec. IV., 1909. 2. 



