How to Measure Septic Tank Floating Top Scum Layer Thickness

How to measure septic tank scum layer to determine when the septic tank needs cleaning
- How and Why to Measure Septic Tank Scum and Septic Sludge Level in the Septic Tank & guide to septic tank scum and sludge layers in deciding when to pump a septic tank
MEASURE SCUM & SLUDGE - separate article
HOW TO MEASURE SEPTIC SCUM LAYER
HOW TO MEASURE SEPTIC SLUDGE LAYER - separate article
TOOLS for MEASURING SCUM & SLUDGE - separate article, simple tube or Electronic septic tank scum and sludge level monitoring - also for grease traps
SEPTIC TANK PUMPING PROCEDURE - separate article
SEWAGE LEVELS in SEPTIC TANKS - separate article details normal & abnormal levels and what they mean.
Questions & Answers about how, when, where, & why to measure the scum layer thickness in a septic tank & what the thickness means about tank condition & the need for pumping.
References

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Septic tank floating scum layer thickness: this document explains the tool and the procedure for measuring the thickness of the floating scum layer in a septic tank as an aid in determining septic tank condition and whether or not the septic tank needs to be pumped and cleaned. We include descriptions of how to make septic sludge and scum measuring tools. Whether your system is a conventional septic tank and drain field, an above ground septic system, or even a holding tank, pumping and inspecting the septic tank is a critical septic tank maintenance and septic system maintenance chore.

How to Measure the Scum layer thickness in a septic tank: How to measure the thickness of the floating scum layer in a septic tank

This procedure is modeled after the procedure described in classes for obtaining a Massachusetts Title 5 Septic Inspectors License. However other states and authorities describe a similar procedure. Some septic contractors have built and bring to the pumpout job their versions of the equipment described below.

The septic tank scum layer probe shown at left (courtesy USDA and US FPS) is also illustrated in a photograph just below.

Page top septic tank sketch courtesy Carson Dunlop Associates. 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. Septic tank pumping pumping frequency guidance is provided in a table at our website (seelinks listed at Related Topics .) When the septic tank is pumped, measurements of the scum layer and sludge layer tell you the condition of the system. At SEWAGE LEVELS in SEPTIC TANKS 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.

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.

Watch out: Safety concerns when measuring septic tank scum and sludge levels: The procedure described below involves opening a septic tank and probing to determine the thickness of settled sludge in a septic tank and to measure the thickness of the floating scum layer in the tank. This procedure is dangerous, involving possible exposure to methane gas and possible risk of falling into a septic tank. The procedure should be performed by a qualified septic contractor. No one should open, inspect, or examine a septic tank while working alone.

Sanitary concerns when measuring septic tank scum and sludge levels: wear gloves when handling the septic probe and watch where you're swinging the pole around so as not to splash septage on your assistant (never work alone on septic systems). The equipment should be washed after use if it is to be retained for future use. Some septic contractors carry their poles in a long plastic-lined box which goes back on the truck.

How to Make the septic tank probe for measuring scum & sludge layer thickness

Photograph of a septic tank sludge and scum layer thickness measuring tool

The septic tank scum and sludge measurement tool shown here is one used by a septic contractor to probe the thickness of the scum and sludge layers. A 6x6" to 6x8" board is attached at the end of a (roughly) 8 ft. pole.

We recommend using 2" poly piping for this purpose as it's easy to wash off. A simple door hinge is bolted to the end of the pipe and to the flapper board.

While some pumpers let the board float to feel the points described below, I've seen others who used a board which was fixed at a 90-deg. angle to the pole. (See illustration above).

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

Septic tank sludge and scum measurement in a single chamber tank - USDA DUF

Open the septic tank access port. If the tank is a single compartment septic tank (USDA sketch at left) this inspection is preferably at the tank outlet end as that's the point where risk of discharge into the absorption system is critical. However some tanks provide a ready access port only at the inlet side - less desirable but you can look there too.

Watch out: if your tank is a two compartment type the solids, floating scum and settled sludge are accumulating at the inlet portion of the tank. Inspecting at the final septic tank outlet end will not discover sludge and scum early enough to prevent septic system damage. Such tanks may have a center inspection port which admits tank access at the outlet of the sludge/scum containing compartment. That's where to test in two-compartment septic tanks.
Insert the septic tank measureing tool: At the opened septic tank access port, probe with the flapper pole through the scum layer until you feel outlet baffle or sanitary tee. This means that the pole is turned so that the board will extend under and be able to feel the bottom of the baffle.
Mark the pole (chalk or pencil will work) to indicate that point. We line up the mark with something easy to reach such as the top of the access port which serves as a uniform reference point for the later measurements.
Now lift up the flapper pole to feel the resistance of the bottom of the floating scum layer.
Mark the pole again, using the same reference point as described above.
Scum distance to baffle bottom: The distance between the two marks gives the distance from the bottom of the scum layer to the (lower) bottom of the outlet baffle. If the bottom of the scum layer is within 3 inches of the bottom of the baffle the tank needs to be pumped.
Scum distance to baffle top: By visual inspection, if the top of the floating scum layer in the septic tank is within 1 inch of the top of the outlet baffle, the septic tank also needs to be pumped.

A similar sludge & scum measuring procedure is provided in 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.

What is The floating scum layer in a septic tank

The floating scum layer in a septic tank includes oil and grease which, if pushed into the leach field, will clog that component of the septic system.

Oil and grease are particularly harmful to the aerobic portion of septic effluent treatment in the soil absorption system.

Therefore we want to clean the septic tank if the scum layer has thickened to the point of risking pushing grease and oil out of the tank.

The septic tank needs to be pumped when the floating scum layer has accumulated to reach 3 inches of the bottom of the outlet baffle or tee.

See SEWAGE LEVELS in SEPTIC TANKS for details on normal and abnormal levels and what they mean.

WHEN TO PUMP - 3 Rules on How thick can the septic tank sludge and scum layer be before septic tank cleaning is needed?

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%.

Similar rules of thumb offered by USDA on how much sludge or scum mean the septic tank needs cleaning include:

1/3 of tank depth: Pump the septic tank when the total depth of scum plus sludge layers equals one-third of the depth of the tank

Less than 3" between scum bottom & outlet baffle: 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)

Less than 6" from sludge top outlet baffle bottom: 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

Watch out: 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.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

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 Contaminants, identifying - what are the contaminants produced by septic systems and what can be done about them if they escape initial treatment?
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 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 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. 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 & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
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  Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
  Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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  Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
  Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
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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 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 804-747-7747 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."

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.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Inspecting Septic Systems: Online Book, Inspection, Test, Diagnosis, Repair, & Maintenance: our Online Septic Book: Septic Testing, Loading & Dye Tests, Septic Tank Pumping, Clearances, details of onsite waste disposal system inspection, testing, repair procedures.
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.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

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.


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