PERC TEST STANDARDS - What are the soil percolation rate standards and other soil requirements for septic systems?
The Massachusetts Title 5 Septic Inspection criteria does a great job of defining a (at least possibly) what is required to assure a functional septic drainfield.
The text explains the role of the biomass below the absorption bed, sets soil depth requirements, and recognizes the importance of keeping the bottom of the working biomass area in well drained soil sufficiently above the seasonal high water table.
Example of soil requirements for a functional drainfield.
This version is particularly clearly written and is for residents of Ohio but the principles apply anywhere. Readers should also see our example of state-regulated soil percolation tests at the NEW YORK STATE SEPTIC SYSTEM DESIGN REGULATIONS 75-A.4 - Soil and site evaluation for septic system design page.
In Ohio, soil absorption systems can be used in areas where the percolation rate of the soil is between 3 and 60
minutes per inch (soil permeability between 1 and 20 inches per hour).
At least 4 feet of suitable soil is required
under the soil absorption system to provide adequate treatment of the septic tank effluent. To accommodate the
construction of the system and provide adequate soil cover to grade, a minimum of 5 1/2 to 6 1/2 feet of suitable soil is
needed above the limiting layer.
A limiting layer may be bedrock, an impervious soil layer (hardpan, fragipan) or a
seasonally high water table (gray soil or mottles). The soil absorption system must be at least 8 feet from any drain
line on the lot, 50 feet from a water supply, and 10 feet from the property line, right-of-ways and the house.
systems cannot be placed on the flood plain and are limited to areas with less than a 15 percent slope.
Reference: ohioline.osu.edu/aex-fact/0743.html Ohio State University Fact Sheet Septic Tank - Soil Absorption Systems
Our separate article by Lockwood includes a description
of the calculations to answer the question: How Big Should the Leach Field Be? our article SEPTIC DRAINFIELD SIZE includes a practical example using sample calculations as well as a table of soil percolation rate vs. the necessary
leach field size.
Question: California MPI soil perc rates vs. "Codes"
2016/11/24 Puzzled said:
Perc Rates for leach fields are commonly expressed in Minutes per Inch. The inspector said my perc rate of 2 MPI requires advanced treatment in California.
When I check the Plumbing Code it says perc rates should be between 0.83 gallons per sq.ft. per day and 5.0 gallons per sq. ft. per day.
We cannot directly relate soil percolation rate numbers to gallons per square foot per day without knowing the dimensions of the test hole that was dug.
I'm assuming your MPI number means "minutes per inch" of soaking of water out of a test hole into the ground.
1 U.S. gallon = 231 cubic inches.
So if I had a 231 square-inch FLAT bottomed perc test hole and I filled it with FIVE INCHES of water, I'd have 5 gallons in my soil percolation rate test hole.
Then according to the (presumably California) plumbing code you're citing, if all five inches soaked away into the soil over a day (24 hours) that'd meet the uppe end of the soil percolation rate test specification.
Just as a sanity check, if your local building inspector allowed a gallon per square foot per day perc rate septic field, then you would need something like 2000 square feet for a functional field + recovery field area in a new septic design. (Average daily wastewater production for the number of occupants or number of bedrooms x 2)
Theoretical Soil Perc Test Hole Dimensions, Soakaway Rate, & Percolation Rate in MPI or Minutes per Inch
Percolation Hole Water Area Dimensions
Water Test Volume
Water Absorption Time
Percolation Rate in MPI
(Minutes Per Inch of water)
1 x 1 x 231 inches
This is a 0.83 gallon per square foot per day Perc Test result
1 x 1 x 231 inches
This is a 1-gallon per square foot per day Perc Test result
5 x 1 x 231 inches
This is a 5 gallon pe square foot per day Perc Test Result
1 x 1 x 231 inches
This is a 2 MPI perc test result
IF the soil perc test hole specification is as described in this table and its notes.
This data has not been reviewed by a septic design engineer. I may have missed something. - Ed.
The column on perc hole water dimensions emphasizes that we're only discussing the shape of the water volume in the test hole in order to permit calculation of a soil percolation rate that is standardized. Without specifying the dimensions of a soil perc test hole, simply pouring water into an arbitrarily sized hole at an arbitrary depth gives only a very crude guess at the soil's ability to absorb effluent.
In the real world, digging a soil pecolation test hole with a backhoe does not produce a perfectly rectangular opening with a perfecly-flat bottom of un-disturbed soil.
The actual depth of the soil perc test hole (typically set at 5 feet but varying significantly by local code and procedure) has to reflect the anticipated depth of the soil soakbed trenches and must consider the soil properties below that point as well as the seasonal high water table level.
Useful constants for soil absorption rate calculations
144 square inches = 1 square foot
231 square inches = 1.6 square feet
231 cubic inches = 1 U.S. Gallon
1440 minutes = 1 day or 24 hours
A 231 square inch flat bottomed (theoretical) perc test hole that absorbs one gallon of water in 24 hours
Here is a typical standard percolation test hole specification when soil testing for leachlines:
Test holes shall be augered or excavated to within 13 inches of the actual test depth which
corresponds to the anticipated depth of the leachline or the bed trench bottom. Vary depths to
include testing of side wall if the disposal system will be more than three feet below the ground
In addition, perform one test in the least permeable soil stratum found during the deep
excavation if the soil type changes within 5 feet of the proposed trench bottom. - San Bernadino soil perc test specifications, cited below.
Effluent entering a soil absorption system may contain varying combinations and amounts of potential contaminants.
A vertical separation distance of 24 inches between the bottom of a soil absorption system and the seasonally high water table has been suggested as a minimum soil depth fdor proper treatment of effluent and protection of groundwater.
Depth to the wet season water table can be monitored with observation wells or can be estimated from soil morphological characteristics.
Caution is advised when evaluating artificial drainage as a method to improve performacne of on-site sewage disposal systems.
We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. The Oregon DEQ onsite water quality program can be contacted at 811 South Ave, Portland OR 97204, 800-452-4011 or Oregon DEQ website: http://www.oregon.gov/DEQ/
Oregon's State DEQ has some nice sketches of a soil test pit from which we excerpt in the article above. These
notes paraphrase and expand on the Oregon DEQ's text.
SOIL PERCOLATION TESTING MANUAL, [PDF] CNMI Division of Environmental Quality, Gualo Rai, Saipan provides an excellent English Language manual guide for soil percolation testing. Original source: www.deq.gov.mp/artdoc/Sec6art108ID255.pdf CNMI Division of Environmental Quality, PO Box 501304, Saipan, MP 96950
"SOIL PERCOLATION (PERC) TEST REPORT STANDARDS" Suitability Of Lots And Soils For
Use Of Leachlines Or Seepage Pits", [PDF], San Bernardino County
Division Of Environmental Health Services
385 North Arrowhead Avenue
San Bernardino, Ca 92415-0160
Telephone: (909) 387-4666
Fax Number: (909) 387-4323
retrieved 2016/11/24, original source: http://www.sbcounty.gov/uploads/dph/dehs/Depts/ EnvironmentalHealth/FormsPublications/ 550034_on_site_waste_water_disposal_system.pdf
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Soil Test Pit Preparation, [PDF] fact sheet, Oregon DEQ Department of Environmental Quality, original source www.deq.state.or.us/wq/pubs/factsheets/onsite/testpitprep.pdf The Oregon DEQ onsite water quality program can be contacted at 811 South Ave, Portland OR 97204, 800-452-4011 or see http://www.oregon.gov/DEQ/
Percolation Testing Manual, [PDF] CNMI Division of Environmental Quality, Gualo Rai, Saipan provides an excellent English Language manual guide for soil percolation testing. Original source: www.deq.gov.mp/artdoc/Sec6art108ID255.pdf CNMI Division of Environmental Quality, PO Box 501304, Saipan, MP 96950
Test Pit Preparation for Onsite Sewage Evaluations, [PDF] 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.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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). 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 I recommend for professionals--DF.
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. 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.
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
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.
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.
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