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How to inspect the condition of a septic tank: this document describes in detail how to inspect the condition of a septic tank - a key component in
onsite wastewater disposal systems.
We describe what to look for at three distinct septic tank inspection points: before pumping, during pumping, & after the septic tank has been emptied.
After discussing a list of things to watch for before, during, and after pumping or cleaning out
a septic tank, we discuss specific septic system inspection details and concerns for
steel septic tanks, concrete septic tanks, home made septic tanks, fiberglass or plastic septic tanks, and the condition of
septic tank baffles.
The purpose of the treatment tank or "septic tank" is to contain solid waste and to permit the beginning of
bacterial action to process sewage into a combination of clarified effluent, settled sludge, or floating scum in the
An intact, un-damaged septic tank is normally always filled with these materials.
However the inspector
performing a "visual" check of the septic system needs to be alert
for some important findings which we describe below.
How to Inspect the Septic Tank Before & After Pumping
If you have not already reviewed
SEPTIC TANK SAFETY please
do so before continuing in this section. There are serious risks of injury, explosion, and
death if safe procedures are not followed when working on septic systems.
Septic Tank Safety Warnings
Don't work alone: Falling into a septic tank or even leaning over a septic tank can be fatal.
Do not work on or at septic tanks alone - workers can become suddenly overcome by methane gas.
Do not ever go into a septic tank to inspect or repair it unless you are specially trained and are wearing the
special equipment and gear for that purpose, including self-contained breathing apparatus.
Don't enter the septic tank to rescue someone: Never go into a septic tank to retrieve someone who has fallen in and was overcome by toxic gases
without a self-contained breathing apparatus (SCBA). if a SCBA is not available, call for emergency services and put a
fan at the top of the tank to blow in fresh air.
Don't even lean over the septic tank openings: Do not lean over or stick your head into the septic tank to examine its interior - you could fall in to the
tank or become overcome by gases and fall into the tank, an event which is likely to be fatal.
Don't ignite flames near the septic tank: Do not light a flame at or near the tank - methane gas is explosive.
At one tank pumpout my client described
the explosion and burns received by the pumping contractor when he stood by the tank and lit a cigarette. Another exploded their septic tank by burning brush that was piled over the tank.
Work area around the septic tank must be ventilated: Decomposing wastes in the septic tank produce toxic gases (such as methane) which
can kill a human in a matter of minutes. When working on a tank be sure the area is well ventilated.
Rope off Dangerous Septic Tanks, Cesspools, Drywells, Work Sites: If your inspection discover that there are dangerous conditions, such as
an unsafe tank cover, tank collapse, or a home-made septic tank or cesspool (which are at increased risk of sudden collapse)
such areas should be roped off and clearly marked as dangerous to prevent access until proper evaluation and repairs can be made.
If you have not already reviewed SEPTIC TANK SAFETY please
do so before continuing in this section. There are serious risks of injury, explosion, and death if safe procedures are not followed when working on septic systems.
A Septic Tank Inspection Checklist
Inspecting the Septic Tank and Septic Tank Area Before Opening the Septic Tank
Subsidence (depressions or low areas in the soil) at the septic tank location - may risk dangerous, potentially fatal collapse
Recent work, excavation, modifications: Evidence of recent work which may need to be investigated to understand the condition of the septic system
Important Safety Check: Inspect the Condition of the Septic Tank Covers:
Condition and safety of the tank and access covers.
In the photo shown here
a round concrete septic tank cover was placed over collapsing concrete blocks stacked to provide an access to a septic tank.
There was a septic tank collapse risk and a possible fatal hazard which at this property was an area only three meters
from a children's playground.
The stacked concrete blocks were tumbling and the opening into the septic tank was larger
than the cover.
We covered the area with plywood, roped it off, and informed the appropriate parties including the property owner.
A safe septic tank cover on a concrete tank is shown in a photo below where we discuss
concrete septic tanks.
Inspecting the Septic Tank After Opening the Septic Tank but Before Pumping
After Opening But Before Pumping the Septic Tank: When the septic tank is opened before it has been pumped out or cleaned, important information about the condition of
the septic system is available:
Thickness of scum and sludge levels: Septic tank maximum scum and sludge buildup prior to pump out, and instructions for measuring the floating scum
layer thickness and settled sludge layer thickness in a septic tank are available in a separate chapter
at SEPTIC TANK PUMPING SCHEDULE.
At SEPTIC TANK LEVELS of SEWAGE we explain the meaning of thick or thin scum or sludge levels and high or low levels of sewage in the septic tank.
Back-flow of effluent into the tank during pumpdown - an indicator of flooded leach fields
Condition of the Septic Tank Baffles: damage to the tank baffles. Evidence of a broken concrete septic tank baffle
is shown below at our discussion of home made site built tanks, and a rusted-steel septic tank baffle is shown
in other photographs on this page.
See SEPTIC TANK BAFFLES for an explanation of how to observe clues at the septic tank baffles or tees to look for signs of tank flooding when opening the septic tank for cleaning, pumping, or inspection.
Liquid and waste level in the tank: evidence of waste passing over the baffles - a flooded system, an indicator of septic system failure.
Evidence of sewage flowing over the septic tank baffle is shown in a photo below where we describe septic tank baffles.
Unusually high levels of sewage in the septic tank - suggesting a blocked outlet or drainfield. The drainfield may be failing due a damaged or clogged pipe, a clogged, failing drainfield, or due to groundwater leaks into the septic tank or groundwater that saturates the drainfield.
Unusually low levels of sewage in the septic tank - suggesting that the septic tank has a leak, can have several causes depending on the tank age and the material from which it was built.
Low Sewage Levels in Concrete septic tanks: If the tank is made of concrete
it should be pumped and cleaned thoroughly so that your contractor can inspect the tank for cracks or other damage.
Low Sewage Levels in Plastic/Fiberglass septic tanks: after pumping the tank, look for a lost drain plug in the tank
bottom. Even pumping the tank can accidentally remove this plug - a condition you won't notice until the next time it's pumped.
Low Sewage Levels in Steel Septic Tanks: Pump the tank completely, clean and inspect for rust holes - it's common for the
bottom of such tanks to rust completely away.
Low Sewage Levels in Home Made or Site Built Septic Tanks:
Watch out: there is risk of tank collapse or leaks when septic tanks
are site-built such as using concrete blocks or stone. Leaks are likely. Similarly, pumping out a site-built cesspool or drywall also risks fatal collapse hazards.
See SEPTIC TANK LEAKS - for an explanation of how and why septic tank leaks cause septic system failures.
See SEPTIC TANK LEVELS of SEWAGE for an a discussion of: What Do the Levels of Sewage in the Septic Tank Mean about Septic Tank Condition, Septic Tank Leaks, & the Timing of Septic Tank Pumping.
Septic Tank Inspection During Tank Pumping
During Septic Tank Pumping: if the pumper observes (or hears) septic effluent flowing back into the septic tank
from the tank outlet pipe this is a sure indication that the drainfield or soil absorption system is waterlogged, and
indicates a system failure needing further investigation.
The photo shows a concrete septic tank during pumping.
As the effluent level dropped
below that of the bottom of the tank baffles, we stopped pumping briefly to listen for the sound of effluent flowing back into the
tank from its outlet.
Septic tank pumping is best performed from an access cover at the center of the tank if one is provided (as in this photo).
This gives best access to the pumper to clean sludge and debris from all areas of the tank bottom.
Septic Tank Inspection After the Septic Tank has Been Pumped Out
Only by pumping and visual inspection can actual tank capacity and condition be
completely determined. Probing in the area of a tank, without excavation, is not recommended as the probe may damage a steel or fiberglass tank.
When a tank is uncovered for pumping additional critical details may be observed before the pumping operation begins
After the septic tank has been pumped out it may be useful to inspect its interior for evidence of cracks, settlement,
or damage to its baffles, or perhaps to confirm the tank size if most of the tank has remained buried.
If a septic tank has been serviced by removing a cover over the entire tank all of these conditions can
be seen easily. But more often the tank is pumped by access through a center cleanout port.
If there is no center cleanout port on a septic tank (some older concrete tanks) it is pumped preferably at the outlet end of the tank but
possibly at the inlet end. Septic pumpers may use a tool such as the one shown here,
a combination of a mirror at the end of a pole and a flashlight to look at the tank interior.
Look for Evidence of damage to the tank itself such as cracks, leaks, or additional evidence of damaged tank baffles.
SAFETY WARNING: Do not enter
or lean down over or into any septic tank unless you're wearing special breathing apparatus and have
a second worker watching you for safety - methane gas in the tank can cause fatal asphyxiation.
It should never be necessary to enter a septic tank. Any work to replace the baffles
or repair the tank should be done from the outside.
SEPTIC TANK SOLIDS & SCUM - thickness, net free area, effluent retention time
Solids entering a septic tank are intended to remain there until pumped out during tank service. A large
portion of solids settle to the bottom of the tank as sludge.
Grease and floating scum remain at the top of the
sewage in the tank. Baffles (discussed above) help keep solids, scum, and grease in the tank. Bacterial action
in the tank make a modest reduction in the solids volume and begin the processing of sewage pathogens, a step
later completed by soil bacteria in the absorption fields.
Net free area in the septic tank: If the sludge level becomes too high or the floating scum layer too thick, in addition to risking passage of
solids out of the tank (damaging the absorption system), the remaining "net free area" of liquid in the tank is reduced.
When the net free area becomes too small, there is insufficient time for waste entering the tank to settle out as
bottom sludge or top floating scum.
The time allowed for sewage to separate and settle out as sludge or
collect as floating scum is called septic tank retention time. Retention time is discussed further at EFFLUENT RETENTION TIME "Septic Effluent Retention time and Effective Septic Tank Volume - Why pump a septic tank before it is "full" of solids and grease?".
For an in-use septic tank with a small net free area, and therefore a short septic effluent retention time, the frequent entry of
solid and liquid waste will keep the tank debris agitated, thus forcing floating debris into the absorption system where the
life of that component will be reduced (due to soil clogging).
The importance of keeping an adequate net free area in a septic tank is the reason that tanks need to be pumped
at regular intervals. Building owners who never pump a tank until it is clogged have already damaged the
absorption system and reduced its future life expectancy.
Continue reading at SEPTIC TANK LEVELS of SEWAGE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see SEPTIC TANK PUMPING PROCEDURE - home. Below at in the form of individual detailed articles are the Steps in Septic Tank Cleaning Procedure in the order that they should be performed
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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.
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.
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
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