862 



PARKS 



diameter. Above this layer is another layer of gravel from four to six inches 

 in depth and composed of stones one-fourth to three-fourths inch in diam- 

 eter, with the finer ones on top. Above the gravel is placed a bed of sand 



4 Vitrified Sewer 

 from TanK. 



/ 



'Space for 4 

 Jtop Boards' 



Y. 



PLATE No. 339 

 PLAN OF DIVERSION CHAMBER SHOWN IN PLATE NO. 337 



(Commission of Immigration and Housing of California.) 



from thirty to thirty-six inches in depth. The sand grains should have an 

 effective size of from 0.25 to 0.35 millimeter and a coefficient of uniformity 

 of from two to four. 



If a sandy soil is available, filters can be constructed by stripping away 

 the upper layer of debris, evacuating any rock, clay or loam pockets, and 

 placing the underdrains at a depth of from six to eight feet. Such a filter 

 should be divided into beds by earthen embankments, which can be made 

 of the strippings removed from the surface. 



Shallow, flat-bottomed wooden troughs are laid on the surface of the 



r f>ope,r 

 <nl orcrushia 

 to , 



Cross Section of- 



Fi It* v ~T*t *r h f J 



Filter Trench 



liii&l^^^ 



w:-;-* yy> ; ;.ti>vf;y.-;;>v>A.- u 



ttW^"KKfX4^3^ 45l 



W* ' i *WraWP ( 1f - : srad ? In J' 



PLATE No. 340 



SMALL SEPTIC TANK SHOWING METHOD OF USING 

 FILTER TRENCH AND VENTILATION SYSTEM 



(Wisconsin State Board of Health.) 



