On-Site Wastewater Treatment Systems
How often do you stop and consider what happens to the wastewater you produce in your home? The dishwasher, garbage disposal, clothes washer, toilets, shower, and bath are all household facilities that produce dirty water that must be disposed of. Millions of suburban and rural homes in the United States use on-site systems to dispose of wastes, and 85 percent of all on-site systems are the septic system. In Pueblo County alone, there are over 12,000 septic systems in use.
The majority of inspections made in this program are during the construction or remodeling of a system. We must inspect and approve the systems during certain phases of construction to insure that they comply with pertinent codes and regulations. Since the system contractors or property owners usually have heavy machinery and personnel onsite to resume construction of the system, it is important that we have sufficient manpower to promptly respond to requests for inspections. Delays in acquiring inspections can cost contractors or property owners hundreds of dollars. Therefore, to responsibly serve the citizens of Pueblo County, we place a high priority on promptly answering requests for inspections.
Your septic tank is an effective and inexpensive system if properly designed, installed, and maintained. As the homeowner, you can ensure the long life and proper operation of your septic system through periodic maintenance. This will save you headaches and money in the long run.
A septic system consists of two main parts - a septic tank and a leachfield.
The septic tank is a watertight box, typically holding 1000 to 1500 gallons, usually made of concrete, plastic or fiberglass, with an inlet and outlet pipe. Wastewater flows from the home to the septic tank through the sewer pipe. The septic tank holds the raw wastewater for a short period of time (a minimum of 30 hours is required) during which it undergoes two processes: separation and biological digestion. The function of the tank is as follows. The raw wastewater flows from the house into the tank through the inlet baffle and is deposited in the tank. The inlet baffle acts to slow down the incoming liquid so it does not cause turbulent mixing of the waste already in the tank. The quiet conditions in the tank allow heavy solids to settle to the bottom. The lighter solids and liquids, including grease and oils, which are lighter than water rise to the surface and form a floating mat, referred to as “scum”. In the tank a family of bacteria that live without oxygen called “anaerobic bacteria”, use the waste as food and digest most of the scum and settled solids.
The anaerobic digestion (decomposition) of these solids produces a foul smelling gas, and the digestive process is termed septic; hence, the name “septic tank”. The gas escapes back through the main sewer line and is vented through a pipe that extends up through the roof of your house. Most of the solids convert into liquid and gas during decomposition. The solids that do not decompose will remain at the bottom of the septic tank as an inactive mass called “sludge”.
The heavy solids decompose into gas or sink to the tank’s bottom to form sludge. The lighter solids and oily liquids float to the top to form the scum layer. In the middle zone of the tank remains a layer of liquid. In a single cell tank, this liquid drains out to the absorption field through the outlet baffle. In a dual cell tank, this liquid flows from the first cell into the second cell through a pipe or hole that connects the two cells. While the liquid is in the second cell, additional separation and bacteriological digestion occur. From the second cell, the liquid drains out to the absorption field through the outlet baffle.
The outlet baffle and center partition in a dual cell tank serves to prevent the scum and solids from being carried out into the absorption field. Solids and scum that are not liquefied remain stored in the tank. Regardless of how efficient the digestive process may be, sludge will accumulate in the bottom of the tank and eventually will have to be removed mechanically and hauled away. If the sludge and scum are not removed, they will accumulate until they eventually overflow into the absorption field. This can ruin the absorption field system.
The biological decomposition process in a septic tank does not purify wastewater; it treats it to some degree, but largely serves as a primary treatment storage vessel. Although the outflow from a septic tank to the absorption field looks clear, it can contain many disease-producing bacteria. Final treatment of the sewage and the destruction of disease causing organisms occur in the soil.
The absorption field (leach field) is the most important part of the onsite sewage disposal system. The absorption field is where the actual “disposal” of the liquid occurs. There are a large variety of absorption field designs.
Typically, an absorption field consists of a series of sewage distribution lines placed in trenches topped with soil.
One is a conventional design using perforated pipe buried in a gravel filled trench and backfilled with topsoil. The second is a newer design using plastic leaching chambers instead of gravel to hold the liquid effluent until it is filtered through and absorbed by the surrounding soils. There are many variations and different types of absorption fields in use today.
The soil in the absorption field absorbs and filters the partially treated liquid sewage. Other bacteria that live in the soil attack the liquid. After additional bacteriological action and filtering in the soil, the once liquid sewage is basically water that returns to natural underground water, is evaporated to some extent or taken up by plants. The disposal area must be large enough to absorb the liquid effluent discharged to it. If the area provided is too small, liquid sewage will ooze to the surface or back up into the house through the sewer, eventually discharging into the house at the lowest plumbing fixture. This can become a nuisance and a health hazard to you and the entire community.
Contact Information 719-583-4307