Suffolk County Government Crest

Suffolk County Stormwater Management Program

Edward P. Romaine, County Executive

Department of Public Works

Department of Economic Development and Planning

What is a Septic System?

All raw sewage from your house sewer line (the main plumbing line in your home that all wastewater feeds into) must undergo treatment before it can be discharged back into the ground. This includes all toilet, bathroom, kitchen and laundry wastes. Your septic system provides the much needed treatment of waste through a series of physical, chemical and biological processes. A septic system consists of usually four components: the house sewer line, the septic tank, the (optional) distribution system, and the soil absorption system

The House Sewer Line:

All of the water that gets flushed down the drain from toilets, showers, bathtubs, washing machines, and sinks, to name a few, travels through plumbing lines that run throughout your household. Most of these lines discharge downward, using gravity, towards the lowest point in your home, which is typically your basement. In some cases however, the direction of flow may be aided by electric pumps. Every plumbing line will end up connecting to a master pipe that is typically bigger in diameter than the rest, and will run straight out through your home's foundation to the outside of the house. This larger diameter pipe is typically called the house sewer line or main discharge line. It's job is to convey all of your home's wastewater directly to a receiving structure, such as a city sewer line in towns with sewer districts. In this case however, the house sewer line connects directly to the septic tank, which is buried directly in line with the house sewer at a minimum of 7 to 10 feet away from the foundation of your home. Many house sewer lines also have what is known as an exhaust stack that runs vertically from the main line and ends sticking out of your roof. This is to allow for any excess gas to vent out of your system.

The Septic Tank:

The septic tank itself is a large, water-tight chamber, with its interior components comprised of an inlet pipe, multiple baffles (or sanitary tees), and an outlet pipe. Newer tanks are also equipped with gas baffles by the inlet and outlet pipes that are designed to prevent the harmful gases that are produced in the system from escaping back up the house sewer line or into the absorption system. The chamber itself is constructed of durable materials that are able to withstand being subjected to excessive corrosion, decay, frost damage or cracking. The chamber is designed to promote the growth of bacteria that aid in the biological decomposition of sewage. The interior components of the septic tank are designed to allow for the proper separation of solids from the wastewater and for the retention of “scum” and “sludge” that build up due to the biological processes. *Proper maintenance for the septic tank relies on the removal of the scum and sludge buildup every few years in order to maintain the system's effectiveness and also to prolong the life of the system.

The Scum Layer – is the thin, and almost foamy top layer, which contains organic and inorganic floatables, toxic gaseous elements from the bio-degradation processes and other low density waste that enters the tank.

The Wastewater Layer – is the wide, liquid middle layer, which contains a large portion of dissolved solids, and is composed of mainly the wastewater and tiny particulate matter that has undergone or is still undergoing some degree of bio-degradation. 

The Sludge Layer – is the very bottom layer of the tank, which contains the densest waste that consists of mostly non-degradable inorganic materials and the newest organic solids that are just beginning to undergo bio-degradation.

     Where is my Septic Tank located?

Your septic tank is located on your property and is usually in line with the direction of your house sewer line. Parking lots, driveways, or other impermeable or load bearing structures should never be built on top of your septic system, unless the systems are specially designed and reinforced to carry those loads. Other objects, such as trees and swimming pools, should also not be constructed near a septic system because of the risk of interference with system operations that they may impose. Your system should have been installed with the NYS minimum horizontal and vertical setback distances kept in mind. These minimum setback distances are required by NYS law and are vital to the safety of nearby water bodies and the water table below ground. The location of your septic system should be noted on plans or sketches of your property, and copies of those plans should be retained by the homeowner for future inspection and maintenance purposes. Sometimes, the location of your system can be identified by two visual access openings above the inlet and outlet baffles, although it is possible that you may have a manhole cover in place of one of the visual access openings. These openings should always be able to be easily located and accessible by licensed maintenance professionals. If you are experiencing trouble locating your system, a licensed system specialist should be able to assist you.

So, to summarize, the wastewater from your home drains into the house sewer line and enters the septic tank, where solids, or sludge, and floatable materials, or scum, are separated from the liquid component, called effluent, which then travels out of the septic tank and to an absorption system. So, let's now look at What is an Absorption System?