WATEE SUPPLY, PLUMBING, ETC., FOE COUNTEY HOMES. 41 



A better method of disposal is by subsurface distribution. In 

 this method the tile are placed in the ground in herringbone or 

 gridiron fashion, not deeper than 14 or 16 inches from the surface 

 of the soil to the top of the tile. Figure 32 shows ground plans of 

 such systems. In very porous or sandy soils 1 foot of 4-inch tile 

 per gallon of discharge per day is sufficient. In the heavier loam 

 soils 2 feet of 4-inch tile are necessary and sometimes more for every 

 gallon. A rough estimate should be made of the number of gallons 

 of sewage in each discharge from the tank and the number of dis- 

 charges per day. Not less than 35 feet of 4-inch tile per person 

 should be used in sandy or porous soil and not less than 60 feet per 

 person in very heavy loams. 



In average loams 300 to 400 |< /-^ - 



feet of tile are sufficient for a 

 family of six or eight. 



Aeration of heavy soils can 

 be brought about by the use 

 of coarse cinders or gravel laid 

 in 12-inch to 16-inch layers 

 in the bottom of the tile ditch 

 with the top about 12 inches 

 below the surface. The tile 

 are laid in these at the usual 

 depth. Figure 33 shows such 

 an arrangement. 



The disposal tile should have 

 a fall not to exceed 1 inch in 

 50 feet, else the water will 

 rush to the lower end and 

 water-log the soil there. The 

 tile are usually laid about J 

 inch apart and in rows about 

 15 feet apart. The latter dis- 

 tance, however, will vary with 

 the porosity of the soil. Where there is no subsurface drainage, artifi- 

 cial drainage should be provided by means of tile drains laid below 

 the sewage tile as shown in figure 34. In some cases an impervious 

 stratum underlying the filter earth is underlain by a stratum of sand. 

 Cases have been noted in which this impervious stratum has been 

 broken by dynamite at 15-foot to 20-foot intervals along the tile line, 

 thus providing natural drainage. 



DISPOSAL BY INTERMITTENT SAND FILTRATION . 



If subsurface disposal is not feasible, for instance when the soil is 

 compact and nearly impervious or is swampy and underdrainage is 

 difficult to obtain, disposal by intermittent sand filtration is necessary. 



Fig. 33. — Cross section of single tile sewage disposal 

 system, showing method of aerating heavy soils. 



