Septic System Design Flow Rate Specifications
Sewage flow rates & model regulations for septic designers

Sewage or wastewater flow rate assumptions & specifications for septic designers:

These model septic design regulations discuss sewage flow rates to be used in designing onsite wastewater treatment facilities for individual households.

This document uses the New York State wastewater treatment standard for individual household septic systems (Appendix 75-A) to provide an example of state regulated design and installation of both conventional tank and leach field septic systems and alternative septic system designs, including raised septic systems, septic mound systems, intermittent sand filter septic systems, and evaportion-transpiration septic systems.

Photo above: the wesite author (third from left) at Camp Virginia where the onsite waste disposal system consisted of a latrine fondly named Oklahoma. To go to the toilet we'd say "I'm going to Oklahoma".

Sewage Design Flow Rates & Regulations

Model source: New York State Septic Regulation Appendix 75-A.3 - Sewage flows - Effective Date: 12/01/90 or later and cited in detail atReferences or Citations . The page top photo of campers at Camp Virginia (1950's) appears in our detailed discussion of OUTHOUSES & LATRINES.

Definition of daily design flow of wastewater

The daily design flow is the volume of wastewater that should be assumed when determining the volume of wastewater that the sewage system (septic system or soakbed or drainfield or other treatment system) must be capable of handling. "Handling" means both adequate treatment and disposal without discharge of wastewater to the surface, to nearby waterways or to other unacceptable locations.

The following table gives septic system design flow rates that shall be assumed by septic system designers, giving flows in gallons of wastewater per day per bedroom in the home served by a private onsite wastewater disposal system, that is, a private septic system. Different septic design flow rates are assumed depending on the modernity and efficiency or water usage rate of the plumbing fixtures in the home. --DF

(a) Roof, footing, garage, cellar and surface water drainage must be excluded from the system. Water softener, water recharge and backwash wastes normally are not to be discharged to the system unless a separate subsurface discharge to an area 250 feet from wells or water courses is unavailable.

(b) Minimum design flows for various configurations of plumbing fixtures shall be as shown in Table 1.

Notes to theTable Above

This table is adapted from the New York State Department of Health regulations Appendix 75-A part 3 with additional text and comments to clarify the different categories of plumbing fixture water usage rates.

GPF = gallons per flush at the toilet. Note that for dual-flush toilets that use a smaller flush volume when only liquid waste is present may use still less water but the flow rate assumptions in the NYS table address the alternative, solid-waste larger flush volumes of these fixtures.

GPM = gallons per minute of water flow at the faucet or shower head

Other estimates of daily water usage can be found at WATER QUANTITY USAGE TABLES

Actual Septic or wastewater drainfield size (leach field size, soakbed size, soakaway bed size, absorption trench size) is given as drainfield trench lengths and dimensions in Table 4A, Septic Wastewater Effluent Input Flow Rate (Gallons per Day) found at SEPTIC DRAINFIELD SIZE

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Continue reading  at SEPTIC DRAINFIELD SIZE where we provide wastewater application rates and a detailed table of septic soakbed or leachfield or drainfield size as a function of soil percolation rate and wastewater volume flow in gallons per day, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• DICTIONARY of SEPTIC SYSTEM & WASTEWATER TERMS for a more complete dictionary of septic system and wastewater terminology
• HOT WATER QUANTITY DAILY USE
• HOT WATER PEAK DEMAND USE
• SEPTIC TANK SIZE for septic tank sizing guidelines & codes
• SEPTIC SYSTEM DESIGN ALTERNATIVES - home
• SEPTIC SYSTEM DESIGN BASICS - home
• SEPTIC & SEWAGE TREATMENT CODES & REFERENCES - home
• PLUMBING DRAIN FIXTURE UNITS DFUs - measure of the wastewater volume or loading of a drain waste or vent system
• U.S. SEPTIC AUTHORITIES & DESIGN SPECIFICATIONS - start of this series
• WATER QUANTITY USAGE TABLES

Suggested citation for this web page

SEWAGE FLOW & DESIGN FLOW ESTIMATES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC SYSTEMS

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Citations & References

In addition to any citations in the article above, a full list is available on request.