Mr. Tawney. Did you go into the matter of standard of purification of sewage or treatment of sewage, to what extent it should be purified?
Mr. Hubbell. In a general way only. Accepting the 500 B. coli standard, the indications are that approximately 90 to 95 per cent purification would be needed bacterially to our sewage to meet that standard. That, however, is a question for the future to determine. It is, in my opinion, a little doubtful as to just what percentage of bacterial removal would be required in order to produce that result, but from my studies I concluded that from 90 to 95 per cent would be required.
Mr. Mignault. And could be realized?
Mr. Hubbell. Yes; and could be realized; there is no question about that.
Mr. Powell. I gathered the impression from your report, by a hasty glance at it, that while you did not quarrel with the standard of 500 B. coli per 100 cubic centimeters you inclined rather to a more severe standard.
Mr. Hubbard. Well, that question is involved with the one of seasonal variation. I made quite extensive studies to determine the seasonal variations in the Detroit River independent of the data that was shown in the International Joint Commission’s first report. I found that for normal conditions in the Detroit River the number of B. coli present was, perhaps, two and a fourth times the average in the summer time, and about one-quarter of the average in the cold months, following approximately the temperature curve.
Mr. Tawney. To what condition do you attribute that increase in the summer? In your judgment, has navigation anything to do with it?
Mr. Hubbell. In my judgment, the navigation has very little to do with it, because the curve falls before navigation stops.
Mr. Powell. What is the crisis in the curve—in what month?
Mr. Hubbell. June, July, August, and September are the high months. The highest point of the curve which I determined for the entire river was in September, but for the waterworks’ intake it was in August.