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Buyer's Guide to Septic Systems

The purpose of a home's septic system is to dispose of the water generated by the occupants in such a manner that the soils on the property can disperse it without causing an adverse effect on ground water and in turn on public health and the environment. To accomplish this a septic system consists of the following elements:

1. A sewer line that connects the home's plumbing to the septic tank;
2. A septic tank that allows for the settling of solids and provides the initial treatment of the septage. A properly functioning septic tank will reduce pollutant levels and produce an effluent of fairly uniform quality.
3. A distribution system that directs the flow of effluent from the septic tank to the leaching system in such a manner to insure full utilization of the system. Most systems are "gravity" systems, meaning the flow runs through piping and distribution boxes without the assistance of any mechanical device, such as a pump or siphon;
4. A leaching system, which disperses the sewage effluent into the surrounding natural soils. There are many types of leaching systems. The specific type utilized on a particular property is usually dependent on the soil conditions which exist on the site. Most residential installations utilize stone-filled leaching trenches, but galleries, pits and beds have historically been used.

For a leaching system to function properly it must:

1. Provide enough application area. The application area is the amount of surface area of soil within the leaching system where sewage effluent is applied (referred to as "wetted" area). The amount of application area needed for a given house depends on the characteristics of the soils on the property and the daily flows (in gallons) generated from the house.
2. Be surrounded by natural soil conditions which will be able to dissipate and disperse the discharge without becoming over saturated.
3. Provide enough capacity to store effluent during periods of unusually heavy use or when rainfall or subsurface flooding reduces the ability of the system to disperse the liquid. Note: Curtain drains or ground water interceptor drains are sometimes installed upgrade of the leaching system to minimize high ground water conditions.

It is important to realize that, once a system has been installed, only one of the above factors can be controlled by the homeowner. The homeowner can control how much water is actually being discharged to the system. Since each system has a set maximum capacity, it behooves the homeowner not to exceed that amount.

Home Water Requirements

Total use
(US Gallons)

 Source: USDA "Water Systems Handbook."

Septic Tank Capacity vs Usage

Average sewage flow                 Minimum Gallons

 gallons per day                  Effective Capacity(1)

        0-500                            900

        601-700                          1200

        801-900                          1500 

Source: Florida ASHI Seminar, Kissimmee, October 1993