New York State Septic System Design Regulations 75-A.6 Septic tank design specifications InspectAPedia® -
Design specifications for septic tanks
Questions & answers about septic tank design specifications & regulations
Septic tank design specifications:
Section 6 of the septic design regulations discusses the design specifications for septic tanks, including
septic tank size requirements, septic tank cover access, septic tank characteristics, steel septic tanks,
tanks for aerobic septic systems, and related details.
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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.
Also see SEPTIC CODES & REFERENCES and SEPTIC CONSULTANTS. Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved
to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at "References."
(1) Septic tank capacities shall be based upon the number of household bedrooms.
An expansion attic shall be considered as an additional bedroom.
Table 3 specifies the minimum septic tank capacities and minimum liquid surface
areas.
TABLE 3
MINIMUM SEPTIC TANK CAPACITIES
NUMBER OF MINIMUM TANK MINIMUM LIQUID
BEDROOMS CAPACITY (GALLONS) SURFACE AREA (SQ. FT.)
------------ ------------------- -----------------------
1, 2, 3 1,000 27
4 1,250 34
5 1,500 40
6 1,750 47
NOTE: Septic tank size requirements for more than six bedrooms shall be
calculated by adding 250 gallons and seven square feet of surface area
for each additional bedroom. A garbage grinder shall be considered
equivalent to an additional bedroom for determining tank size.
(2) Septic tank covers shall always be accessible. Where manholes are
more than 12 inches below final grade, an extension collar shall be
provided over each opening. Extension collars shall not be brought
flush with the ground surface unless the cover can be locked to prevent
tampering. Driveways or other facilities shall not be constructed above
septic tanks unless specially designed and reinforced to safely carry
the load imposed.
(b) Design and Installation of Septic Tanks
(1) General Requirements for Septic Tanks. The following
applies to all septic tanks regardless of material.
(i) A minimum liquid depth of 30 inches. The maximum depth for
determining the allowable design volume of a tank shall be 60 inches.
Deeper tanks provide extra sludge storage, but no credit shall be given
toward design volume.
(ii) The minimum distance between the inlet and outlet shall be six
feet. All tanks shall meet the minimum surface area requirement for the
specific design volume specified in Table 3. The effective length of
rectangular tanks should not be less than two nor greater than four
times the effective width.
(iii) Tanks must be watertight, constructed of durable material not
subject to corrosion, decay, frost damage, or cracking. After
installation, all septic tanks shall be able to support at least 300
pounds per square foot (psf).
(iv) Tanks with a liquid depth of 48 inches or more shall have a top
opening with a minimum of 20 inches in the shortest dimension to allow
entry into the tank. Tanks with a liquid depth less than 48 inches
shall have a top opening that is at least 12 inches in the shortest
dimension.
(v) Tanks shall have inlet and outlet baffles, sanitary tees or other
devices to prevent the passage of floating solids and to minimize
disturbance of settled sludge and floating scum by sewage entering and
leaving the tank. Outlet designs such as gas deflection baffles are
strongly recommended in all tanks. Inlet and outlet baffles shall
extend a minimum of 12 inches and 14 inches respectively, below the
liquid level in tanks with a liquid depth of less than 40 inches, and 16
and 18 inches respectively, in tanks with a liquid depth of 40 inches or
greater. The distance between the outlet baffle and the outlet shall
not exceed six inches. Baffles shall be constructed of a durable
material not subject to corrosion, decay or cracking.
(vi) There shall be a minimum of one inch clearance between the
underside of the top of the tank and the top of all baffles, partition
and/or tees to permit venting of tank gases. Multi-chamber and
multi-tank systems shall also be designed to permit the venting of tank
gases.
(vii) Tanks shall be placed on at least a three inch bed of sand or pea
gravel. This will provide for proper leveling and bearing. Additional
instructions provided by the manufacturer shall also be followed.
(viii) There shall be a minimum drop in elevation of two inches between
the inverts of the inlet and outlet pipes.
(ix) Garbage grinders. An additional 250 gallons of capacity and seven
square feet of surface area is required when a garbage grinder can
reasonably be expected at the time of construction or in the future. A
gas deflection baffle or other acceptable outlet modification, and a
dual compartment tank or two tanks in series must also be provided.
(2) Design Specifications for Multi-compartment septic tanks or tanks in series.
(i) Dual compartments are recommended for all tanks and shall be
required on all tanks with an interior length of ten feet or more.
(ii) The first compartment or tank (inlet side) shall account for 60 to 75% of the required total design volume. (iii) The baffle separating
the compartments shall extend from the bottom of the tank to at least
six inches above the invert of the outlet pipe.
(iv) Compartments shall be connected by a four inch vertical slot at
least 18 inches in width, a six inch elbow, or two 4-inch elbows located
at a distance below the liquid level equal to one-third the distance
between the invert of the outlet and the bottom of the tank. At least
one access manhole shall be provided into each compartment.
(v) Tanks in series should be connected by a single pipe with a minimum
diameter of four inches.
(vi) The volume and surface area for meeting the requirements of Table 3
shall be based upon the total volume and surface areas of all the tanks
and chambers.
(3) Design Specifications for Concrete septic tanks.
(i) Concrete shall have a minimum compressive
strength of 2,500 pounds per square inch (psi) at 28 days set; 3,000 psi
concrete is recommended as a minimum.
(ii) Wall thickness shall be a minimum of three inches unless the design
has been certified by a New York licensed professional engineer as
complying with all appropriate requirements for thin-wall construction.
All walls, bottom and top shall contain reinforcing to assure support
for 300 psi.
(iii) All joints shall be sealed such that the tank is watertight;
joints below the liquid level must be tested for water tightness prior to
backfilling.
(iv) The walls and floor of cast-in-place tanks shall be poured at the
same time (monolithic pour).
(4) Design Specifications for Fiberglass and Polyethylene Septic Tanks. These tanks must meet the
following additional requirements:
(i) These tanks shall not be installed in areas where the groundwater
level can rise to the level of the bottom of the septic tank.
(ii) Particular care must be taken during installation, bedding, and
backfilling of these units so as to prevent damage to tank walls. The
manufacturer's installation instructions shall be followed.
(iii) All tanks should be sold by the manufacturer completely assembled.
If, because of size, the tank is delivered to the site in sections, all
joints shall be sealed with watertight gaskets and shall be tested for
water tightness after installation, and prior to backfilling.
(5) Design Specifications for Steel Septic Tanks. Steel septic tanks must have a label indicating corrosion
protection complying with Underwriters Laboratories, Inc., Standard
UL-70 or equivalent.
(6) Design specifications for Aerobic Septic Units. A homeowner may choose to install an aerobic unit
instead of a septic tank under the following conditions:
(i) The unit shall have a label indicating compliance with the standards
for a Class I unit as described in the National Sanitation Foundation
(NSF) Standard 40 or equivalent.
(ii) The rated capacity of the unit shall be equal to or greater than
the design flow as determined from Table 1.
(iii) The absorption system that follows the unit shall be sized in the
exact same manner as it would for a septic tank.
(iv) Units which do not include as a standard feature a service contract
which provides for, as a minimum, semiannual inspections and annual
pumping for three years or more are prohibited.
(v) The surface discharge of aerobic unit effluent is strictly
prohibited.
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Questions & answers about septic tank design specifications & regulations
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389
(2006), Advanced Onsite Wastewater Systems Technologies.
Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going
for homeowners but is a text we recommend for professionals--DF.
AEROBIC SEPTIC SYSTEMS
Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
Design Manuals for Septic Systems
US EPA Onsite Wastewater Treatment Systems Manual [online copy, free] Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm Onsite wastewater treatment and disposal systems,
Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers.
U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental
Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959.
Onsite Wastewater Disposal Books
Onsite Wastewater Disposal, R. J. Perkins;
Quoting from Amazon: This practical book, co-published with the National Environmental Health Association,
describes the step-by-step procedures needed to avoid common pitfalls in septic system technology.
Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in
both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers,
consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. (DF volunteers to serve as indexer if Burks/Minnis re-publish this very useful volume.)
While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference
for both property owners and septic system designers. We refer to it often.
While Minnis says the best place to buy this book is at Amazon (our link at left), you can also see this book at Minnis' website at http://web page .pace.edu/MMinnisbook
Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf
Planting Over Septic System Component", Daniel Friedman (author/editor, InspectAPedia.com), The Innovator, Winter/Spring 2008, BCOSSA, British Columbia OnSite Sewage Association, 201-3542 Blansard St., Victoria BC V8X 1W3 Canada
Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF.
Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
Test Pit Preparation for Onsite Sewage Evaluations, State of Oregon Department of Environmental Quality, Portland OR, 800 452-4011. PDF document. We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. Readers should also see Soil Percolation Tests and for testing an existing septic system, also see Dye Tests
Grass is Always Greener Over the Septic Tank, Bombeck, Erma: $ 5.99; FAWCETT; MM;
This septic system classic whose title helps avoid intimidating readers new to septic systems, is available new or used at very low prices.
It's more entertainment than a serious "how to" book on septic systems design, maintenance, or repair. Not recommended -- DF.
US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers.
Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill. Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers: * Current construction, maintenance, and repair methods
* New International Private Sewage Disposal Code
* Up-to-date standards from the American Water Works Association
Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF.
Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
The NSFC Products List has an excellent list of design manuals/modules available from their website or by telephone 800-624-8301
Submissions welcome. send us a suggested document link or request an exchange of website links
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