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• How to inspect the condition of a septic tank - detailed procedures
• Septic tank inspection checklist
• Types of Septic Tanks: steel septic tanks, concrete septic tanks, fiberglass septic tanks, home made septic tanks - definitions and characteristics of various types of septic tanks
• Inspection specifics each different type of septic tank
• Inspection specifics for septic tank baffles, septic tank sludge and scum levels or thickness

This document describes in detail how to inspect the condition of a septic tank - a key component in onsite wastewater disposal systems. 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. \

This is a chapter of Septic Systems Inspection, Testing our online book about septic system inspection procedures, defects in onsite waste disposal systems, septic tank problems, septic drainfield problems, checklists of system components and things to ask. Also see The Septic Information Website our main page of articles and information about septic systems and onsite wastewater disposal systems inspection, testing, diagnosis, maintenance, and repair.

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INSPECTING TANKS - How to Inspect the Condition of A Septic Tank

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 tank. 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 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: 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 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 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.
• Site 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 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.

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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
• Evidence of recent work which may need to be investigated to understand the condition of the septic system
• Evidence of backup or effluent breakout at the surface in the septic tank area

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.

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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 Guide
• 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.
• 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 discuss septic tank baffles.
• Unusually high levels of sewage in the septic tank - suggesting a blocked outlet or drainfield.
• Unusually low levels of sewage in the septic tank - suggesting that the 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: there is risk of tank collapse or leaks when septic tanks are site-built such as using concrete blocks or stone. Leaks are likely.

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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.

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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.

A separate document, MEASURE SCUM & SLUDGE, discusses how and why to measure septic tank scum and sludge

Net free area: 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.

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SEPTIC SYSTEMS ONLINE BOOK
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEMS INSPECTION COURSE
SEPTIC INSPECTION TYPES & LEVELS
SEPTIC INSPECTION WORK SHEETS
SEPTIC TANK PUMPING
  TANK PUMPING FREQUENCY TABLE
  WHY DOES A TANK NEED PUMPING?
  EFFLUENT RETENTION TIME
  WHEN NOT TO PUMP A SEPTIC TANK
SEPTIC TANK PUMPING PROCEDURE
TANK INSPECTION PROCEDURE
  SEPTIC TANK INSPECTION CHECLIST
  STEEL SEPTIC TANKS
  CONCRETE SEPTIC TANKS
  FIBERGLASS / PLASTIC SEPTIC TANKS
  HOME MADE SITE BUILT TANKS
  SEPTIC TANK BAFFLES
  SEPTIC TANK SOLIDS & SCUM
MEASURE SCUM & SLUDGE
CLEANING SEPTIC TANKS
SEPTIC PUMPING CONCLUSIONS
SEPTIC LIFE EXPECTANCY
SEPTIC TANK SAFETY
SEPTIC FIELD INSPECTION
INSPECTING SEPTIC D-BOX
SEPTIC VIDEOS
SEPTIC TREATMENTS

TANK PUMPING FREQUENCY TABLE
EFFLUENT RETENTION TIME
WHEN NOT TO PUMP A SEPTIC TANK
SEPTIC TANK PUMPING PROCEDURE
MEASURE SCUM & SLUDGE - How and Why to Measure Septic Tank Scum and Sludge in the Septic Tank
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?

The Septic Systems Online Book - Where Are We?

More Information on Building Diagnostic Inspections and Repairs

• Inspecting Septic Systems: 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.
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Septic Tank Pumping Frequency Table
• The Septic System Information Website - Extensive, Detailed Consumer and Industry Information on Septic System Inspection, Testing, Maintenance, Alternatives for on-site waste disposal
• Alternative & Advanced Designs for Septic Systems for discussion and links to (on-site waste disposal) System Designs for Problem Sites & Soils. Books, Consultants, Engineers, Designers. Alternative septic system designs can substantially reduce the normal required distances between septic system components and wells, lakes, streams, and property boundaries.

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