LARGER IMAGE: when you can see the SEPTIC TANK during installation or after finding it for a pumpout,
that's a good time to measure off and record the exact location of the tank and its cleanout openings. Septic Tank Condition - How to Inspect Concrete Septic Tanks

  • SEPTIC TANKS, CONCRETE - CONTENTS: Characteristics of concrete septic tanks. Guide to the properties of different 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
  • SEPTIC TANK SIZE - separate article
  • POST a QUESTION or READ FAQs about concrete septic tanks: special problems, inspection, installation, troubleshooting, repairs, age, durability
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This document describes how to inspect the condition of a septic tank, providing special considerations for inspecting concrete septic tanks. Inspecting concrete septic tanks is a key component in onsite wastewater disposal systems.

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Guide to Concrete Septic Tanks: properties, sizes, installation, maintenance, repair

PHOTO of a safe concrete septic tank cover being removed for tank pumping.

The photo shows a round concrete septic tank cover being removed to prepare for pumping a concrete septic tank. This is a safe cover and is rated thick enough to be driven-over by a car - but we do not recommend that practice.

Of course the area is quite unsafe while the septic tank cover is off - we would not leave the tank cover off and the area unattended.

Concrete septic tanks at an existing septic installation are usually viable, but might have damaged baffles or cracks that permit seepage of groundwater in or septic effluent out around the tank.

Occasionally we've seen tanks made of poor-quality concrete (insufficient portland cement) which eroded badly. If the tank outlet or absorption system have been blocked, examination of the tank interior may show that effluent is or has been above the top of the baffles (see "baffles" below) thus indicating a system failure.

Types of Damage Found at Concrete Septic Tanks

One of the most common problems found on concrete (and some other) septic tanks is tank flooding due to either a drainfield backup or due to surface runoff or groundwater entering the septic tank.

How do we know if the septic tank is flooded? See SEPTIC TANK LEVELS of SEWAGE.

Concrete tanks can crack or sections may separate causing leaks with the result of not only improper disposal of effluent (wrong location) but also subverting an attempt at a septic loading and dye test since when the system is un-used the tank liquid levels drop abnormally.

The inspector may detect this condition only if there is a tank inspection port which is readily and safely accessible for before, during, and after inspection when running a loading and dye test.

Repairs to concrete septic tanks

Repairing damaged or lost concrete septic tank baffles

On occasion we find that the baffles at inlet or outlet ends of a septic tank have deteriorated, usually due to poor original concrete mix, and occasionally due to mechanical damage. A lost or damaged baffle at a septic tank is asking for sewage backup into the building or the passage of solids into the drainfield - substantially shortening its life.

To repair or replace a damaged septic tank baffle, see SEPTIC TANK BAFFLES & SEPTIC TANK TEES

Repairing leaks into a concrete septic tank

Besides leaks due to a crack in a concrete septic tank, we find leaks into the tank due to improperly algined or placed entry or exit piping or missing, damaged gaskets at those locations. To repair septic tank leaks see SEPTIC TANK LEAKS.

In addition to sealing openings at tank piping and cracks or holes (described below) if your septic tank is being flooded from local groundwater or surface runoff, the flooded tank will also flood the drainfield or may cause a sewage back-up into the building. Some readers have suggested sealing the septic tank covers and access ports - but these need to be removable for service or repair, and really you may be treating the symptom, not the problem.

We agree that faced with a high cost of site drainage corrections, sealing the septic tank lid may be an appealing solution. First make sure that the flooded septic tank is due to surface runoff or groundwater, not a backing-up or failed drainfield, or you're simply fixing the wrong problem.

It makes sense to direct surface runoff away from the septic tank, or if necessary, install an intercept drain to keep ground water and surface water away from the tank.

Reparing cracks & holes in a concrete septic tank

It is possible to repair a crack or hole in a concete septic tank using concrete patching compounds and some foundation repair compounds, epoxies, and crack sealers. Key considerations are

  • Watch out: Safety - never enter a septic tank without special training, equipment, and assistance as gases are likely to be quickly fatal even if the tank has just been pumped and washed out
  • Concrete surfaces to be patched need to be clean of sewage and dirt or debris, and for some patch products, dry as well
  • See both Seal Cracks in Concrete, How To and Seal Cracks by Polyurethane Foam Injection

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