How a septic system works
A traditional septic system has three main components: Septic tank: • A large concrete, fiberglass, heavy plastic or coated steel tank divided into two compartments, with access ports at  the top for inspection and service
• uses time and gravity to separate wastes into three layers: i) Heavy materials, which settle to the bottom here they are broken down into sludge by naturally occurring bacteria ii) Light soaps, greases, fats and similar materials, which rise to the top as a layer of scum, and iii) Liquids with some suspended solids • Whenever waste water from sinks, appliances and toilets comes out of the house into the first compartment, it pushes an equal amount of liquid from that first compartment into the second one -- which then forces the same amount of liquid out of the second chamber and into the pipes leading to the leaching bed. • If the tank is properly operated and pumped out regularly, only the liquid component leaves the tank as “effluent” i) The sludge should remain well below the outlets ii) Baffle walls or pipes stop the scum from going out into the bed iii) Some installations include filters at the outlet pipe (recommended) Distribution system: • A system of pipes leading from the septic tank to the leaching bed • may include a distribution chamber to direct waste water evenly to different parts of the leaching bed • Traditional systems use gravity, but some sites use pumps to move water uphill from the septic tank • Larger systems use pumps to distribute the waste water over the leaching bed area Septic tank Leaching bed • Typical bed is an arrangement of connected pipes with holes along the sides and bottom, surrounded by stone/gravel and properly draining soil or other filtering material • Liquid leaving the septic tank travels down the pipe, seeping through holes into the gravel and soil filtering materials • In the stone layer, oxygen-using bacteria break down “waste particles” • Below the stone, natural organisms form a "biomat" • In the soil filter - an extremely important component of the septic system - chemical, physical and bacteriological reactions remove remaining solids and bacteria before the fully treated water meets the underground water table • soil filtering materials must allow the waste water to drain aw ay slowly enough that contaminants are filtered out, but also quickly enough that the bed doesn’t fill up in most instances • Some waste water in the soil gets taken up by grass roots - nutrients are used and water is released through a process known as evapotranspiration
Types of Leaching Beds
Conventional
 • Most common type • used where the natural soils are suitable filter materials and the ground is well drained • leaching bed pipes are laid in stone-filled trenches below normal ground level Raised • Second most common type • Used where natural soils are not suitable filter materials, or the site has a high water table, or bedrock is close to the surface • Appropriate soil is brought in to the site to create a leaching bed that is high enough above the underground water table or bedrock • Pipes are laid in stone filled trenches in the imported soils • requires a large extra area of appropriate soils “downstream” from the bed (in the direction the waste water will flow as it seeps through the soil); called the “mantle”, this is an important part of the soil filter Filtered
 • used where a smaller bed area is required due to site conditions or lot size • Instead of trenches, the whole bed area is excavated and filled with a layer of “filter” sand which must meet specific requirements for grain size • A layer of stone is placed on top of the sand, and pipes are laid into it • Pipes can be laid closer together • can be installed in-ground, partially raised or fully raised • may also use a mantle. Groundwater table, bedrock or poorly draining soils Shallow Buried • used where a smaller bed area is required • can only be used with a “tertiary treatment” unit, which provides more treatment than a traditional septic tank • Filtered waste water is pumped under pressure through perforated pipes; it gets sprayed into specially designed pipe chambers, to spread the waste water evenly over the trenches • requires additional maintenance, plus annual inspection and testing Alternative Systems Other types of treatment units are available. Some are designed to take the place of traditional septic tanks. Some provide an additional treatment step between the septic tank and the leaching bed. They are designed to greatly reduce the need for large leaching beds. Some alternative systems use compressors or motors to bubble air through the waste water. Others use highly efficient filtering materials (peat moss and synthetic foam are the basis of two of the newer systems).Lots of individuals and companies are working on other improvements. A call to the local Building Department or the provincial Buildings Branch (416) 585-6666 can identify what systems can be accepted for use in Ontario. Or, you can check the Branch web site at www.obc.mmah.gov.on.ca If one of these alternative systems is used, the manufacturer must provide a complete description and instructions for operation, servicing and maintenance . Communal Systems |