WATEB SUPPLY, PLUMBING, ETC., FOE COUNTRY 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. 
\< ^ H 
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 ^^'iy/y.'\o^<f 
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 \ 
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. 
Fig. 33. — Cross section of single tile sewage disposal 
system, showing method, of aerating heavy soils. 
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. 
