Soil perc tests may also be performed in order to evaluate soils when a septic system is believed to have failed,
and when repair or septic field replacement are being considered.
Specifications for Digging Holes for Soil Percolation Tests for Septic System Design and Approval
How to Dig a Soil Test Pit
Soil Perc Test Hole Depth: A typical soil perc test hole like the one shown at the top of this page or pit is dug at least 4 1/2 ft. deep and usually five feet (5') deep.
On occasions a 6' hole is used if the approving health or building department septic inspector or engineer so requires.
The dept of the test hole for a seepage pit (as opposed to an absorption bed or drainfield trench) must extend to at least mid-depth and to full depth of the proposed bottom depth of the seepage pit, and must include at leats one test hole dug to three feet below the proposed bottom of the seepage pit.
Soil Perc Test Hole Width: a typical soil test pit is two feet wide. It may be larger depending on the excavator's skill and on local soil conditions.
Perc Test Shape: The bottom of the pit should be level and about 2 ft. x 4 ft. in size. This is important to permit accurate measurement of the soil pecolation rate.
At least one side of the soil test pit should be sloped so that if someone falls into the pit they can easily exit.
Some soil test pit specifications describe a stair-stepped side to the test pit to permit a person to climb out should they fall into the hole
In ouir opinion, except in areas of very stable soils, a backhoe operator digging the "perc test hole" is usually going to dig a sloped side (to permit inspection or escape) not a stairwell. And no test pit I [DF] have ever seen is anywhere as precisely excavated as those in our sketches, adapted from Oregon's DEQ recommendations.
But the bottom of the test hole should be at the required depth and should be as flat as possible in order to permit measurement of the rate at which water poured into the space percolates into the ground below.
Soil Perc Test Excavated Dirt Placement: soil that has been excavated to dig a test pit must be kept back at least two feet from the edge of the test pit.
Perc Test and Water or Rock: If the excavator encounters water or bedrock before reaching the five or six foot test pit depth, the excavation will normally stop at that depth regardless.
Soil Perc Test SAFETY:
In dry soils, for safety and ease of access (to be able to climb in and out of the hole, one side
of the hole must be sloped to permit someone to easily enter and leave the pit. The other side(s) of
the hole are roughly vertical.
In wet soils, for safety and ease of access in and out of the hole, one side of the pit must be dug
stair-stepped with each step no greater than 2 ft. in height.
Soil Percolation Test SAFETY: Earth which has been removed to create the hole must be piled at least 2' away from the hole edges, again
[DF opinion]: SAFETY: engineers or workers should not enter a soil test pit (nor any other excavation) while working
Re-fill the test holes after testing has been completed.
Where to Dig the Soil Test Pit for Septic Systems
Usually two percolation-rate test holes are dug, 50' to 100' apart in order to evaluate the proposed septic leachfield area.
Evidence of the seasonal high water table is noted (possibly based on changes in soil color at various depths).
For safety, septic soil drainfield perc test holes must be re-filled after the test is complete. If the hole must be left open
and unattended during the test it should be barricaded to prevent anyone from falling in. Here are some
hints from Callum County, Washington:
Dig the perc test hole downhill from the house site if possible.
Stay away from swales and drainage ways, and areas that are seasonally wet.
Keep 100 feet away from all wells and surface water, including irrigation ditches.
Septic systems cannot be located on slopes in excess of 45% (24 degrees).
It is helpful if property boundaries and the proposed house site are marked ahead of time.
Number of Soil Test Pits Required
The number of soil test pits required to obtain an approved septic system installation may be as few as one, and depends on
Local health or building department rules, including possibly other types of soil tests in place of percolatin tests when the actual test is observed by a health department offical who is on-site.
Local soil conditions
What variations in soil profiling are discovered when the first test hole is dug, spaced to prove that the whole area planned for the septic soakaway field is actually suitable.
The depth at which seasonal high ground water is found and the type of water table (perched, apparent, or artesian).
Size, shape, and type of septic absorption bed or leachfield being installed
The use of seepage pits (as opposed to drainfield trenches) that require additional test holes at full depth, half-depth and three feet below full depth of the pit bottom. (NYS A-75 cited below).
Often where I have visited building sites and have observed multiple test pit excavations that's because the excavator moved the test pit location until she found one that gave acceptable results. That's where the absorption bed should be located.
Here is a typical specification, from New York State's Appendix 75-A:
(2) If a subsurface treatment unit such as an absorption field is planned, at least four feet of useable soil
shall be available over impermeable deposits (i.e., clay or bedrock). Highest groundwater level shall be at
least two feet below the proposed trench bottom.
Where systems are to be installed above drinking water
aquifers, a greater separation distance to bedrock may be required by the local health department having
jurisdiction. At least one test hole at least six feet deep shall be dug within or immediately adjacent to the
proposed leaching area to insure that uniform soil and site conditions prevail.
If observations reveal
differing soil profiles, additional holes shall be dug and tested. These additional holes shall be spaced to
indicate whether there is a sufficient area of useable soil to install the system. Treatment systems shall be
designed to reflect the most severe conditions encountered.
If the percolation tests results are
inconsistent with field determined soil conditions, additional percolation tests must be conducted and the
more restrictive tests must be the factor used for the system design.
What is the Soil Test Pit Showing and How Does the Percolation Test Impact Septic System Design?
How much water is needed to perform a soil perc test?
Enough clean water, typically several 5 gallon pails, is poured into the soil percolatoin test pit hole to provide 1-2 feet of depth of water in the actual test pit (a 2' x 4' flat bottomed hole).
1 cubic foot = 7.5 U.S. gallons
Since the standard test pit hole is 2' deep x 2' wide x 2' across, that's 8 cubic feet.
8 cu.ft. x 7.5 U.S. gallons = 60 gallons of water to fill the hole.
I have never seen a soil test performed in which the test engineer poured 12 5-gallon joint compound buckets of water into the hole. But certainly you need enough water in the hole to permit a reliable measurement of the percolation rate.
In many jurisdictions and where there is less supervision, a smaller test pit is what's usually dug, perhaps half the bottom area as the standard given above. And typically a single 5-gallon bucket of water is poured into the hole.
How is the Soil Percolation Rate Measured?
Water is poured into the standard test pit.
The depth of water in the pit is measured using a tape measure or a calibrated rod or stick and that depth is recorded.
Depending on the rate at which water is absorbed into the soil, subsequent measurements of water depth are made at intervals ranging from a few minutes (very sandy, fast-absorbing soil) to several hours (slow perc rate soils) to overnight (terrible perc-rate soils).
At each subsequent perc test water level measurement the tester notes the elapsed time and the number of inches of water remaining in the pit.
Using a standard percolation test pit hole size of 2' x 2' bottom area, we have (24 x 24) 576 square inches of area to absorb water - allowing a somewhat standardized report of the soil's percolation rate.
A minimum usable perc test hole area accepted by some authorities (PERC TEST STANDARDS) is about 230 square inches (a bit less than half of the area given above).
Soil perc test procedures: pouring water, making observations, reporting results, are described in detail at SEPTIC SOIL & PERC TESTS - topic home.
Percolation rate examples:
Percolation rates are given in minutes per inch of water in the test pit.
Watch out: The stated or observed "soil percolation rate" only makes sense if the test pit bottom is flat, the sides of the test pit hole are relatively vertical, and if both the area of the test pit bottom in inches and the volume of water poured into the hole are known.
If 1 gallon of water is poured into this smaller tet pit hole (1" x 1" x 231") and if the water is absorbed in 2 minutes, the soil percolation rate, given in minutes per inch of water, is 2 minutes.
If 5 gallons of water (one full joint compound bucket) is poured into this smaller test pit and if it takes a full day (24 hours) for the water to absorb into the ground, that's a soil percolation rate of 288 minutes.
Soil percolation or perc tests are used to determine the ability of a soil
to transmit wastewater effluent through the soil profile.
The soil percolation rate is the amount of time water takes
to move through soil, measured in minutes per inch. Finer textured soils have slower percolation rates; it takes longer
for water to drain from a test hole. These soil types need larger drainfields than soils with faster percolation rates,
such as sandy soils, to handle a given amount of wastewater.
Soils with very slow percolation rates may not be suitable
for drainfields. In Nebraska [and other jurisdictions], if soils perc at a rate slower than 60 minutes per inch, consider installing a lagoon
system if the lot is at least 3 acres.
Otherwise, an engineer must design a specialized [alternative
design] septic system.
Soils with very fast
percolation rates, less than 5 minutes per inch, must be modified by adding a loamy sand liner to the drainfield,
so that proper treatment can occur. [adapted from Univ. of Nebraska, Lincoln Extension, Institute of Agricultural & Natural Resources, "Residential Onsite Wastewater
Treatment: Site Evaluation]
Soil Percolation Test Pit Design Specification Guidelines
PERC TEST STANDARDS - gives both calculation methods and typical required percolation rates for acceptible areas for septic system installations
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
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.
Continue reading at
PERC TEST STANDARDS - how to calculate and find acceptable percolatin rates for septic system soils, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
requirement to fill in a "perk hole"
(Apr 24, 2014) S justiss said:
if the perk hole is not filled in, can a neighboring occupant demand the developer do that?
S you are asking a legal question that I can't answer - it's one to take to an attorney. But gee whiz - seems to me that the attorney's consult fee will be more than the cost to fill in a perc test hole.
I agree that remaining holes in a property can be a safety hazard and might also interfere with proper drainage. Fill it in.
Question: Perc test hole specifications for Maine
8 June 2015 Anonymous said:
What are the standards for a Percolation test in Biddeford Maine?
The State of Maine abandoned the traditional percolation test in 1974 and replaced it with a system of site evaluation to determine suitability for subsurface wastewater disposal. These evaluations are performed by individuals licensed by the Department of Human Services.
Because of the diminishing number of sites with “suitable soils” and the belief that other site characteristics should be taken into consideration the Department developed the New System Variance procedure. This procedure assigns points to various site and system design characteristics and sets a minimum passing score of 50 points, with 65 points required for properties in Shoreland Zoning areas, and 75 points for lots in proposed subdivisions. Properties not meeting the requirement of original soil over limiting factor are judged by this system.
Numerical Classification System To Determine Overall Site Suitability For Subsurface Wastewater Disposal, October, 1987
found at www.maine.gov/dhhs/mecdc/environmental-health/plumb/documents/numerical-classification.rtf - 2011-11-10
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Soil Test Pit Preparation, 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, 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
Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
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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