86o 



PARKS 



(Plates 337 and 339), in which by the use of stop boards the sewage can be 

 diverted into either of the fields. An absorption field should be dosed not 

 more than three times in each twenty-four hours. 



In the subsurface irrigation method of disposal, care must be exercised 

 to prevent the contamination of water supplies through pollution of the 

 ground water. Overloading, with the subsequent clogging of the soil, 

 must be avoided, and a suitable soil must be available. A loam or sandy 

 soil or loam mixed with sand or gravel will be found to be the best type for 

 this purpose. A clay soil is useless and any attempt to utilize such soil 

 for an absorption field is sure to result in needless expense and trouble. 

 Not infrequently the nature of the soil, the proximity of water supplies, or 

 lack of space, will prohibit the use of this means of disposing of the effluent 

 from septic tanks. Under such circumstances other methods of disposal 

 must be adopted, and as a rule underground filtration trenches or an inter- 

 mittent sand filter will give satisfactory service. 



Underground filtration trenches. Where only clay or other non-absorbent 

 soil is available filtration trenches can often be used in lieu of an absorption 

 field (Plates 332 and 340). Filtration trenches are dug about three feet in 

 depth and at the bottom of each trench is placed a collecting drain of open 

 joint tile surrounded with broken rock ranging from one-half to one and 

 one-half inches in diameter. The trenches are filled with sand, gravel or 

 earth to within a foot of the surface, where another line of open joint tile 

 is placed, likewise surrounded by broken rock, which receives the effluent 

 from the siphon chamber. The upper tile lines are installed and function 

 in the same manner as the tile lines of an absorption field, except that the 

 effluent instead of being absorbed by the adjacent soil filters down through 

 the material in the trench into the collecting underdrains, through which 

 it may empty into ditches or may be connected with a main drain through 

 which the effluent is carried to a stream or other body of water to be dis- 

 posed of by dilution. Four-inch field tile is usually used for both the upper 





v - XPTIC TANK 

 WITH SIPHON 



PLATE No. 336 



SEWER DISPOSAL SYSTEM WITH SEPTIC TANK, SIPHON CHAMBER, 

 DIVERSION CHAMBER AND ABSORPTION FIELD 



(Pennsylvania Department of Health.) 



