Septic System Basics

Over 25 percent of Minnesota households use on-site sewage treatment systems, commonly referred to as septic systems, to treat their wastewater. Proper treatment of sewage recycles water back into the natural environments with reduced health risks to humans and animals and prevents surface and groundwater contamination. 

The design and installation of a septic system is controlled by local and states rules through a permit process.  The design takes into consideration all specific site characteristics including the type of soil, size of house, and sewage generating fixtures and appliances.  All systems must be designed, installed, inspected, and maintained by licensed professionals. 

The complete septic system is made up of three primary components:

• Plumbing: sewage collection
• Septic tank: primary treatment
• Soil treatment area: final treatment and dispersal.

Step 1:  Wastewater from the sewer pipes in the house enters the first compartment of the watertight concrete, polyethylene, or fiberglass tank. 

Step 2: As new water enters the tank; it displaces the water that is already here.  As it fills most of the tank, anaerobic bacteria start to break down the waste material, sludge falls to the bottom and a layer of scum floats to the top. 

Step 3: When the effluent water flows into the second tank, the filter and baffle help prevent scum from entering. The outlet baffle is arguably the most important part of a septic system.  It protects the drain field from getting clogged with solids and failing the system.

Step 4: Bacteria continues to break down existing waste in the second section of the tank.  

Step 5: Wastewater continues through the outlet baffle and into the leaching drain field.  Perforations in the drain field pipe allow effluent to seep safely into the surrounding gravel while the sludge and scum remain in the tank.

Step 6: The water flows into the soil while gravel allows oxygen to reach the bacteria and complete the decomposition of any waste material.  Gravel around the pipes allows water to flow into soil and oxygen to reach bacteria.

Step 7:  Treated water seeps down into the groundwater and aquifer, renewing the vital resource of drinking water. 

In the picture, you can see three layers.    In the middle is a fairly clear water layer.  This body of water contains bacteria and chemicals like nitrogen and phosphorous that act as fertilizers but is largely free of solids. 

The water is slowly absorbed and filtered by the ground in the drain field.  The size of the drain field is determined by local building codes and the number of bedrooms in the home.  If placed in hard ground or clay, a larger field or the use of fill is required to get the drain field to function properly. 

A septic system is normally powered by gravity.  Water flows down from the house to the tank, and down from the tank to the drain field.  It is a completely passive system.  In situations with poor drainage, it is sometimes necessary to construct a mound or shallow absorption drain fields with electrical lift pumps driving the wastewater up into the field. 

Whichever kind of septic system you have in your home, routine pumping and cleaning is required to keep the system functioning normally.  We recommend having your tank pumped and cleaned every two to three years to ensure proper function and long life.  Please feel free to call our office at (218)739-4320 if you have further questions on septic system basics.