The Septic System

The septic system is really a Wastewater Recycling System that utilizes the natural soil to treat the wastewater before returning it to the groundwater basin.

What happens when you flush the toilet?
Where does the wastewater go?
For those of you not connected to a municipal sewer, the solution lies in the septic tank.


A septic tank is typically the first component of a septic system.  A system can be as simple as a septic tank with a efficient filter screen and a drainfield or include any number of add-ons, such as an aeration tank, sand filter, pump/siphon chamber or sand mound.

No one should enter a septic or other treatment or holding tank for any reason without being in full compliance with OSHA standards for entering a confined space.  The atmosphere within the septic or other treatment of holding tank may contain lethal gases, and rescue of a person from the interior of the tank may be difficult or impossible.

A septic tank looks like the illustration above.  The size of the tank depends upon the number of bedrooms in teh house, not the number of people or plumbing fixtures.  The sized range from 750 gallons on up and may be configured as one or two septic tanks.  Having two septic tanks (or a two compartment septic tank) increases detention time of the waste water, which helps to further reduce the suspended solids that could flow into the drainfield.

The drainfield is the area where the liquid from the septic tank soaks into the ground.  The soil & micro-organisms remove viruses, bacteria, and most other contaminant's typically found in household wastewater.  The drainfield area may consist of one or more trenches, a rectangular bed or an above grade design like a mound (as discussed later).  One or more observation tubes are placed in the drainfield area to monitor the infiltrative surface.

When the effluent (the technical name for the treated liquid from the septic tank) has to be lifted uphill into a drainfield, another tank is installed after the septic tank.  This tank contains a pump with floating on and off switches to send the effluent into the drainfield at preset intervals.  This pump tank (also known as a pump chamber, dosing chamber or lift station) has a high water alarm float switch connected to an alarm to warn the user when the pump has failed to come on.

Since 1980, pump tanks have about a one-day's reserve capacity once the pump fails and the alarm sounds.  However, most septic system effluent pumps provide maintenance free service for many years.

The waste water entering the septic tank separates into 3 layers.
1:  Solid waste that settles to the bottom of the tank; (sludge)
2:  Grease, fat and floating solid materials which rise to the top of the tank; (scum)

3:  A partially clarified liquid zone; effluent.

The solid waste is food for anaerobic bacteria, which releases gas and liquid components.  The gas is dispersed through the plumbing system vents in the house and drainfield vents.  Solids do accumulate in the septic tank.  The tank must be serviced (pumped out) every 3 years or when ever the solid component of the tank exceeds 1/3 of the tank volume to reduce the chance of solid material flowing into the drainfield.

Grease and other floating solids are prevented from flowing out of the tank by a baffle, filter, or screen located on the inside of the tank at the outlet end.  Another baffle is placed on the inlet side of the septic tank.  This forces the incoming waste down into the tank, which prevents short-circuiting across the tank.  These baffles can deteriorate over time and must be checked at each tank servicing.  In theory, only liquid flows out of the septic tank and into the drainfield, thereby recycling the household waste water into the ground.  There are tank effluent filters available that can prevent larger suspended solids in the wastewater from getting out of the septic tank, which may clog pumps, distrubution pipes and soil.  These filters are commonly serviced with routine septic tank pumping.

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