1916] KURAL ENGINEERING. 287 



continued until May 31, 1914. The investigation included a sanitary survey 

 of the Potomac River watershed and laboratory studies of the water, mud. 

 plankton, and shellfish. The sanitary survey included investigations as to the 

 number of persons on the watershed, the prevalence and distribution of typhoid 

 fever, the water supplies, sewage-disposal systems, and character and amounts 

 of trade wastes. 



It vi'as found " that at no point above Washington is the water of the 

 Potomac River safe for use as a public water supply without reasonable treat- 

 ment. ... At no time was the condition over and about the Washington sewer 

 outlet such as to constitute a nuisance. Even during the period of lowest 

 stream flow and highest temperature the river in the area of heaviest pollu- 

 tion . . . has at all times sufficient oxygen available for the sewage now dis- 

 charged into the river and enough to take care of the sewage which will 

 probably be added for several years to come. In addition to the dissolved 

 oxygen contained in the water of the river as it flows from the Great Falls, 

 the great areas of flats on each side of the river for many miles act as oxygen 

 generators. The amount of oxygen given off, depending in part upon the con- 

 dition of plant life, turbidity, and sunshine, is, therefore, greatest during the 

 summer when there is the most need for it. In addition to releasing enormous 

 volumes of oxygen these flats are breeding places for plankton forms, which 

 themselves materially assist by biological processes in the breaking down of 

 sewage and the consequent purification of the river. . . . Few intestinal organ- 

 isms from above reach Maryland Point, and these disappear in the stretch of 10 

 miles between that point and Popes Creek, at which section evidence of pollution 

 from the upper river has disappeared. 



" In an examination of oysters from all the beds in the whole river and its 

 tributaries, extending over an entire season, no dangerously polluted oysters 

 were found in the Potomac River proper. . . . Analysis of the results obtained 

 during the year in the examination of shellfish and of water taken from over 

 tlie oyster beds shows that the periods of highest Bacillus coli count in the two 

 were not coincident." . . . 



Tests of bacteriological methods are also reported in some detail. As a 

 result of these studies it is recommended that the lactose bile presumptive test 

 be not used, because of the unreliable results obtained therefrom ; and that 

 the use of lactose broth fermentation tubes, with confirmation on endo medium, 

 be adopted as a routine procedure in the examination of water and shellfish 

 for the determination of the presence of B. coli. 



Analyses of waters, J. C. Bbunnich {Ann. Rpt. Dept. Agr. and Stock 

 IQueensland}, 191/f-15, pp. 50-52). — Analyses of 65 samples of Queensland 

 waters are reported and discussed with reference to their use for domestic, 

 stock-watering, and irrigation purposes. 



Results of first year's experiments with small sewage treatment plants by 

 U. S. Public Health Service, L. C. Fbank (Engin. and Contract., ^5 (1916), No. 

 18, pp. 420-422). — The results of experiments with the Imhoflf tank and sand bed 

 combination for use on a small scale are reported, from which the following 

 conclusions are drawn : 



" It is possible by means of a five-hour mean detention period in a properly 

 designed Imhoff tank to remove from the raw sewage of small communities 98 

 per cent of the settleable solids without producing a nuisance. A mean deten- 

 tion period of six hours, based on the average daily flow, will not cause the 

 sewage to become septic or foul smelling if it is fresh when it enters the tank. 

 The accumulation of a disagreeable mass of grease and fecal matters in the first 

 compartment of the settling chamber may be prevented by the introduction of 

 a horizontal coarse mesh screen at the water level of this cliamber. The screen 



