A septic system is an onsite wastewater treatment system that processes and purifies household waste (effluent). The effluent consists of black water (toilet wastes) and grey water (kitchen sink, bathtub, and laundry wastes).
There are two main components to the septic system, the septic tank and the drain field. Primary treatment occurs in the tank where bacteria digest organic matter in the waste water. Secondary treatment occurs in the drain field where bacteria complete the digestion and purification of the effluent as it slowly infiltrates the soil.
The septic tank is a watertight underground treatment tank constructed of concrete, plastic. It is approximately eight feet long, four feet wide, and five feet deep. The tank is used to retain, store, and treat solids, as well as release effluent to the drain field. The tank size is determined by the number of bedrooms in the dwelling.
As waste water flows into the tank, the heavy solids settle to the bottom and become a sludge layer; while fats, oils, and greases float to the top forming a layer of scum. A zone of clear liquid between the layers of scum and sludge is called a clarified zone.
All three layers have billions of bacteria that live naturally in the tank and perform the first phase of treatment to break down the solids in the tank. During the process of breaking down solids, gases are produced. These gases are vented from the septic tank through the plumbing vent on the rooftop.
Partially treated effluent flows from the septic tank to the drain field. The effluent is naturally purified as it percolates down through the soil.
In order for the effluent to properly purify, the distance between the drain field bottom and the water table should be greater than 4 feet. The state of Colorado requires a minimum of Four feet from the bottom of the drain field and Three feet for pressure dosing systems.
Soil testing is the method used to determine if a site has suitable soil to support a private on-site wastewater treatment system, otherwise known as a septic system. The soil must be able to absorb all wastewater derived from ordinary living conditions such as toilets, sinks, dishwashers, laundry facilities, etc. Colorado law states that a certified soil tester (CST) must perform this test.
Previously called a perc test, water was actually poured into holes in the ground for the purpose of measuring just how far into the ground a certain amount of water would go in a certain amount of time, thus determining the percolation rate. This method will no longer be used in the state of Colorado after Jan 1 2016.
Today, a soil test or site and soil evaluation consists of digging a minimum of three pits with a backhoe. The soil tester will enter each pit to evaluate the soil by identifying each horizon in the soil profiles. He will determine the depth of horizons, the types of soil, the structure, and consistency of the soil, locate the boundaries of horizons, and detect the presence of root structure. The pits are typically dug 8′ deep or until a limiting factor in the soil is reached, for example water or redoximorfic features. Your septic system must be installed within the soil-tested area.
The results of the site and soil evaluation will determine the type, design, and size of the septic system. The completed soil test is filed with the county planning and zoning department.
Before purchasing a vacant property you should have a soil test completed to determine what type of system can be installed.