[SEPTIC-TANK SYSTEMS]
Septic-tank systems, if installed and maintained properly, provide the most sanitary method of sewage disposal for farmhouses equipped with running water.
Ground water or rock close to the surface, lack of sufficient fall for the sewage to flow by gravity, and too small an absorption area for the effluent limit the satisfactory operation of a septic tank. When these conditions exist, special advice should be sought from a competent local sanitary authority. Adverse soil conditions can be overcome if sufficient fall and space are available.
The five essential parts ([fig. 1]) of a septic-tank system are (1) the house sewer; (2) the septic tank; (3) the effluent sewer; (4) the distribution box; and (5) the disposal field. In special cases a grease trap (see [fig. 11], [p. 19]) is added. To facilitate inspection and repairs it is good practice to keep in the house a chart showing the location of the tank and other parts of the system.
A septic tank does not necessarily purify the sewage, eliminate odor, or destroy all solid matter. Its purpose is to condition the sewage or domestic waste by bacterial action, so that it can be disposed of in a more satisfactory manner.
Figure 1.—A septic-tank system.
OPERATION OF A SEPTIC-TANK SYSTEM
In a septic-tank system the sewage flows by gravity from the farmhouse through the sewer into the tank, where it should remain at least 24 hours. While passing through the tank the solids are acted upon by anaerobic bacteria, which work only in the dark and where there is little air. The heavy particles settle to the bottom as sludge, the lighter particles float as scum, and the remainder passes out of the tank through the effluent sewer to the disposal field. The gas released in the process escapes through a vent provided either in the T to the house sewer or the effluent sewer.