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How to Measure Septic Tank Bottom Sludge Thickness Level
Significance of accumulated septic tank sludge for septic system operation & failure
- POST a QUESTION or COMMENT about the septic tank sludge layer: measurement, thickness, diagnostics, guidance for septic tank cleanout interval.
Septic tank bottom sludge:
This article explains how to measure the thickness of the layer of sludge on the bottom of a septic tank - a step in deciding if a septic tank needs to be pumped out and cleaned.Septic tank pumping pumping frequency guidance is provided in a table at our website (seelinks listed at the ARTICLE INDEX the bottom of this article .) When the septic tank is pumped, measurements of the scum layer and sludge layer tell you the condition of the system.
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How to Measure the Bottom Sludge Layer Thickness in the Septic Tank: measuring the thickness of the settled sludge layer
Septic tank scum layer thickness measurements
(HOW TO MEASURE SEPTIC SCUM LAYER)
and septic tank bottom sludge layer thickness measurements
(HOW TO MEASURE SEPTIC SLUDGE LAYER), made or at least roughly estimated by the septic pumping contractor at the
time that a septic tank is pumped, provide key information that permits the home owner to know
- Whether or not the septic tank is being pumped often enough
- Whether or not there is evidence that the septic fields have been damaged by having not pumped the tank soon enough.
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 are listed at "References."
At SEPTIC TANK LEVELS of SEWAGE we explain how to interpret the meaning of high or low sewage levels in the septic tank as well as thick or thin scum or sludge levels.
Readers of this document should be sure to review our table of septic tank pumping frequency.
The same pole can be used for this purpose by removing the flapper, or a separate pole can be constructed. To re-use the scum pole, just pull the hinge pin which will drop the flapper assembly, leaving half the hinge still bolted to the pole end for next use. A simple septic tank sludge measuring pole and towel shown at left (courtesy USDA).
- A towel, preferably a light color, is wrapped around the end of the pole and secured thoroughly. The towel does not need to be a big bulge at the end of the pole but rather should be screwed or taped so that it simply wraps around the pole for about three feet from the bottom of the pole up. (A sheet metal screw through the towel into the pole makes sure you won't leave the towel behind in the bottom of the septic tank.
- Probe the septic tank to the bottom, just behind (not through) the outlet baffle, and keep the probe there for a minute or longer.
- Pull the probe back up from the tank bottom and observe the total height of sludge marked on the towel.
- Compare the sludge height from the tank bottom with the distance from the outlet baffle to the tank bottom.
- Sludge within 12 in. of the baffle or Tee or septic tank sludge closet than 18 in. to the actual point of effluent outlet from the tank (the horizontal outlet pipe) means that the tank needs to be pumped.
Also see TUBE for MEASURING SCUM & SLUDGE for a tool that can make both scum and sludge thickness measurements with a single device.
For deep or hard to access or commercial septic tanks that may need close monitoring, see ELECTRIC MONITOR for SCUM & SLUDGE and also take a look at Other Measures Scum / Sludge.
Where to Measure Septic Tank Scum & Sludge Levels
Because of the typical sludge settlement pattern, & possibly also scum formation pattern, measure the septic tank sludge and scum layers near the septic tank outlet for a single-chamber septic tank, or at the outlet of the first chamber in a two or more chambered septic tank.
The USDA sketch (left) shows where sludge measurements are being made in a two-chamber septic tank. Make sure your septic tank access is over the outlet, not the inlet, when you are making these tests.
Here is a sketch of measuring the scum & sludge levels in a single-chamber septic tank.
When to Measure Septic Tank Scum & Sludge Levels
An optimum septic tank / soil absorption maintenance plan includes opening, inspecting, and measuring the sludge and scum levels annually. If your inspections never find baffle damage, evidence of tank flooding, tank leaks, tank backups, nor thick sludge or scum layers, you can try extending this interval to alternate years or longer.
What is the settled sludge layer in a septic tank
The sludge layer on the bottom of a septic tank includes various solids which are not dissolved in the septic effluent and which are dense enough to fall to the bottom of the tank.
The septic tank bottom sludge is comprised of "settleable solids" and that portion of "suspended solids" which will, given enough time, also settle out. These accumulate at the bottom of the septic tank until they are removed by a septic tank cleanout procedure.
Normally a septic tank should be pumped when the bottom layer of sludge is within 18 inches of the tank outlet.
Other measures of scum layer and sludge layer indicate when to pump the septic tank
The following example was provided to us by Effluent Services, Ltd., an experienced septic service company in New Zealand. In New Zealand septic tank sizes range from 2000-6000 liters (500 gallons to 1,500 gallons U.S.) with the average being 3100 liters (about 800 U.S. gallons and below the minimum septic tank size permitted in most U.S. jurisdictions).
"Generally at a two year interval for septic tank pumping service the average septic tank in these size ranges will have a 400 mm scum layer with about a 200 mm sludge layer. With an average depth of 1600 mm, the solids content is about 600 mm thereby reducing the settling time by nearly 40%.
Similar rules of thumb offered by USDA on how much sludge or scum mean the septic tank needs cleaning include:
- Pump the septic tank when the total depth of scum plus sludge layers equals one-third of the depth of the tank
or
- Pump the septic tank when the bottom of the septic tank outlet baffle has less than three inches of clearance from the bottom of the scum layer (this may vary depending on the length of your outlet baffle or tee)
or
- Pump the septic tank when the bottom of the outlet baffle is less than 6 inches from the top of the sludge layer found on the septic tank bottom
This is very sound reasoning. Homeowners should use the scum and sludge layers found when their septic tanks are pumped as a way to determine whether or not the tank is being pumped often enough. In areas where most septic tanks are on the comparatively "small' side, a two year regular pumping schedule is reasonable for light-usage. In our experience, a 500-gallon septic tank in a home with a family of four is going to need very frequent pumping if the drainfield, leach beds, or soakaway system is to be protected.
When to Pump the Septic Tank based on thickness of the septic tank sludge and scum layers
The following is an excerpt from What Scum Sludge Thickness = Pump Needed.
"Generally at a two year interval for septic tank pumping service the average septic tank in these size ranges will have a 400 mm scum layer with about a 200 mm sludge layer. With an average depth of 1600 mm, the solids content is about 600 mm thereby reducing the settling time by nearly 40%.
Don't wait too long before removing septic scum and sludge People who wait until their septic system stops working due to a clogged or over-filled (with sludge and scum) septic tank have waited too long. As the bottom sludge layer increases in thickness, and as the top septic scum layer increases as well, the remaining "net free area" or "effective septic tank volume" of effluent in the tank is reduced in volume.
When a septic tank is operating with a low volume of "net free area" of septic effluent, the system lacks adequate volume to provide adequate settlement time - time needed for sludge to settle to the tank bottom and scum to coagulate at the tank top. In this circumstance, although drains in the building seem to be just fine, the septic tank effluent is remaining in a constant state of stirred-agitation. In turn, that means that the system is pushing floating debris into the leach field or other absorption system.
Pushing grease, scum, and small solid debris out of the septic tank and into the leach field reduces the future life of that expensive component of a septic system.
Beginning at SEPTIC TANK PUMPING PROCEDURE are the Steps in Septic Tank Cleaning Procedure in the order that they should be performed
...
Continue reading at SEPTIC TANK BACK FLOODING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see these
Recommended Articles
- SEPTIC TANK PUMPING MISTAKES - when not to pump a septic tank & what else can we foul-up
- SEPTIC TANKS - home
- SEPTIC TANK INSPECTION PROCEDURE
- SEPTIC TANK LEVELS of SEWAGE
Suggested citation for this web page
HOW TO MEASURE SEPTIC SLUDGE LAYER 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.
- New York State Department of Health, APPENDIX 75-A WASTEWATER TREATMENT STANDARDS - INDIVIDUAL HOUSEHOLD SYSTEMS , [PDF] New York State Department of Health, 3 February 2010, retrieved 3/1/2010, original source: https://www.health.ny.gov/regulations/nycrr/title_10/part_75/appendix_75-a.htm
- SEPTIC TANK/SOIL-ABSORPTION SYSTEMS: HOW TO OPERATE & MAINTAIN [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.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor [Website: /www.house-whisperer.com ] is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-873-8534 or by Email: johncranor@verizon.net
- Thanks to Richard at Effluent Services, Ltd., Cambridge 3434 NZ for the suggestions regarding the significance of the septic tank floating scum layer and settled sludge layer. New Zealand readers can contact this septic system service company at 07 827 0436 or Waikato Wide: 0800 EFFLUENT.
- Thanks to reader Robert Shirley, Calgary, for discussing alternative ways to measure septic tank sludge, including the relatively low cost electronic system on the market from Worldstone Inc. (SepticWatch) - a system to monitor sludge and scum and grease levels in grease traps or septic tanks - 04/20/2010
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor [Website: /www.house-whisperer.com ] is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-873-8534 or by Email: johncranor@verizon.net
- Worldstone, http://www.worldstoneinc.com/ electronic monitors, including via internet, for grease traps, septic tanks, oil tanks - manufactured by F.O.G. Solutions,
1348 Delta Drive, Saginaw, MI 48638, 866 279-2824, 989-928-1806, Fax 480-247-4983. The Company also makes an oil tank level monitor.
"Worldstone Inc. is a Braintree Massachusetts based company that specializes in separation tank monitoring. Using established ultrasonic technologies, Worldstone’s GREASEwatch, SEPTICwatch and OILwatch monitors capture critical tank information and transfers data to city officials, end users or service providers creating a safer, cost effective solution to manual inspections. Data from monitors can help establish appropriate service intervals, and document maintenance for regulatory compliance. Alarm features can help detect abnormal conditions and prevent costly backups.
Worldstone monitors are currently assisting over 200 major restaurants, hospitals, prisons, casinos and city officials across the United States."
Septic Tank Monitoring:
"The SEPTICwatch monitor provides continuous monitoring of the sludge, scum, temperature and liquid levels [in a septic tank]. ... real-time information on actual changes as a percentage of permissible floating solids, bottom solids and total solids. It also provides the immediate status of the liquid level within the tank in inches. Using the monitor's programmable Control Unit, the tank's optimum level for pumping is set, so the tank can be pumped when it's actually needed. The [septic tank] monitor's Control Unit can also be programmed to warn of dangerously high solid levels and lower than normal/higher than normal liquid levels - emergency conditions that could indicate system failure."
Grease Trap Monitoring:
"...GREASEwatch monitor uses ultrasonic transducers and an embedded microprocessor to continuously monitor the sludge, scum, liquid levels and temperature in your grease trap. ... get real-time information on incremental changes in the levels of floating solids, bottom solids and total solids at the touch of a button. ... the immediate status of the liquid level in the trap in inches. The Control Unit can be programmed to indicate how full the tank should be before pumping, so there's no more guessing when it's time for service. The GREASEwatch monitor lets you plan a pumping level that meets your needs and protects your investment." - 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.)
- 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). 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. \
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)
- Eco John® Innovative Toilet Solutions, Global Inventive Industries, Fountain Valley CA, PDF, product brochure
- "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, 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, 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.
- 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.
- 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 System, 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.
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
CONTINUE READING or RECOMMENDED ARTICLES.
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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