PARK SANITATION 



S55 



The raw sewage may be disposed of, if it is not possible to discharge 

 it into a community sewer system, by dilution or by treatment in a septic 

 tank. The effluent from the septic tank may be disposed of by dilution, 

 subsurface irrigation, or by filtration with subsequent disposal by dilution 

 or broad irrigation. 



Disposal by dilution. In disposal by dilution the raw sewage is dis- 

 charged directly into a body of water sufficiently large so to dilute the 

 sewage that no harmful results are produced. If a body of water such as 

 a lake, bay or stream is available, disposal by dilution is often feasible, 

 provided it can be accomplished without polluting any source of drinking 

 water or infringing upon riparian rights of adjacent landowners. Care 

 must also be taken to avoid contaminating bathing beaches, and if the 

 sewage is discharged into tidewater, possible injury to shellfish must like- 

 wise be considered. The winds, currents and tide will often carry sewage 

 for comparatively long distances from the point of disposal. 



Where a small stream is to be utilized for diluting the sewage, it must 

 be determined that the minimum flow of water in the stream is sufficient 

 to produce a satisfactory dilution. The stream should have a minimum 

 flow of 0.75 to one cubic foot per second for each one hundred persons, and 

 the flow must be constant and even, or malodorous deposits will occur along 

 the banks and the bottom of the stream. The sewer should extend out from 

 the shore to a point where the depth of the water and the distance from the 

 shore is sufficient to permit of ample dispersion of the sewage. Whenever 



PLATE No. 332 



PLAN AND SECTION OF A SiMALL SEPTIC TANK 

 SHOWING DOSING TANK AND AUTOMATIC SIPHON 



The effluent is disposed of by trench filtration. (United States Public Health Service, Crohurst.) 



