Suffolk County Government Crest

Suffolk County Stormwater Management Program

Edward P. Romaine, County Executive

Department of Public Works

Department of Economic Development and Planning

Even the most well designed and installed septic systems will eventually fail without proper maintenance and inspections. When failures occur, repairs must be done immediately to prevent any potential health hazards from occurring due to untreated sewage leaching into the surrounding soil. The cost of repairs necessary to fix a failed system far exceeds the cost of years of maintenance, and may even surpass the cost of initial installation. Most systems should be inspected at least once each year and cleaned at least every 2 to 3 years, regardless of flow rates. If the system is not cleaned periodically, the buildup of scum and sludge may eventually flow through the outlet pipe and reach the subsurface treatment system. This will lead to raw, untreated sewage contaminating the soil on your property. Solids entering an absorption system can lead to rapid clogging of pipes or perforations and will eventually cause premature failure of the system, which, depending on the severity, could very possibly lead to an extremely costly full system replacement. 

maintenance chart

This chart can help you decide when it is a good time to pump your septic tank.

Homeowner’s Question: What determines the size of the septic system that I have or will need?

Answer: There are many factors that determine the size of your septic system. The most important is your household’s DSF, or daily sewage flow. Other factors that can affect the size of your septic system include individual user habits, plumbing fixture flow volumes, and leaking faucets, among a few others.

Daily Sewage Flow

Your daily sewage flow is the quantitative discharge rate of raw sewage that is produced by your household over the course of 24 hours. Your household’s daily sewage flow is one of the most important and one of the most dynamic of all factors that are considered in the final design of your household’s sewage treatment system. Many variables are taken into account when your treatment system is designed so that it may be able to properly accept and treat your uniquely determined daily sewage flow. The number of occupants and the number of bedrooms in the household are the two most important factors that determine the minimum required size of your septic system. Typical flow rates are based on 55 to 75 gallons per day per person or 110 to 150 gallons per day, per bedroom. Systems are designed to accommodate two people per bedroom in a typical household.

Individual User Habits

The amount of water an individual uses on a daily basis directly affects the amount of water that is processed by your sewage treatment system at a 1:1 ratio. This means for every gallon of water that flows into your system, the same amount of wastewater flows out of your system. For example, that one family member (that we all seem to have) who enjoys taking their daily 30 minute shower will not only use all the hot water, but will also discharge an average of 150 gallons of water during that 30 minute shower. Those 150 gallons equate to double the recommended daily flow rate for that single person. When large quantities of water are used in a short period of time (typically discharge rates exceeding 5 gallons per minute), you should limit any further input into the system for a short period of time to allow the system to catch up. If ample downtime for your system to catch up is not allowed to occur, this type of use will eventually lead to a system overload, which most likely will cause problems in the future due to solids being washed out of the tank and into the absorption system.

Flow volume of Plumbing Fixtures

Prior to 1980, toilets used approximately 5 gallons per flush (gpf), faucets and showerheads used 5 gallons per minute (gpm), and the sewage treatment system was based upon a design flow of 150 gallons per day (gpd) per bedroom or 75 gpd per person. Since then, NYS environmental conservation laws have been passed requiring all installations of sink and lavatory faucets, showerheads, urinals, and toilets manufactured after 1980 to meet specific water-saving performance standards. After 1991, toilet flow rates were reduced to use no more than 1.6 gpf. Some companies, such as American Standard ©, have designed their products to perform above that standard a flow rate of 1.0 gpf. Also since 1991, many individual systems for dwellings constructed may be based upon a design flow of as little as 110 gpd per bedroom, or 55 gpd per person.

*Although the total volumetric load of wastewater from household fixtures to the treatment system has been drastically reduced since 1979, the actual biological load to the system has remained the same. For this reason, the design parameters for septic tank sizes have remained the same.