Septic tank tank leaks are one of the things to check for during a septic tank inspection.

Here we explain where and why septic tanks might leak, why surface water or runoff leaking into a septic tank is bad, and why septic effluent leaking out of a septic tank can also be a problem.

We explain why pumping a flooded septic tank does not usually fix anything. Leaks in either direction, into the septic tank or out of the septic tank can be a problem.

Causes, Effects, & Repair of Leaks Out of or Into the Septic Tank

Leaks at septic tanks leaks into and out of the septic tank cause different sorts of problems.

Leaks out of the septic tank ultimately risk a sewage backup in the building and also prevent testing the septic drainfield.

Leaks into a septic tank can flood the tank and destroy drainfield, also risking a sewage backup into the building.

Here we'll explain the causes of septic tank leaks, their effects, and the proper repair. We also warn that pumping out a flooded or leaky septic tank dosn't fix anything. We also include a description of test standards for septic tank water tightness.

Our page top photo and the closer view just above show water ponding at the connection of a sewer line to a septic tank.

Because this sewer line runs downhill from the house to the septic tank it was particularly good at collecting surface water and aiming it all at the septic tank entry port. Because the sewer line was not sealed at the tank, water entered and flooded the septic tank and drainfield.

Article Contents

• WHERE DO SEPTIC TANK LEAKS OCCUR?
• PUMPING a FLOODED SEPTIC TANK?
• SEPTIC TANK LEAK TESTS & STANDARDS

Where do Septic Tank Leaks Occur?

A septic tank can develop a leak at just about any location but here are some common ones.

Our photo shows concrete poured around a waste line entering the septic tank. You can see that just as the concrete pooled in this location, the trench dug for the sewer line would, in wet weather, collect and aim a large volume of water into the septic tank.

• At the sewer line entering the septic tank, or the effluent line leaving the septic tank may leak:
  
  if the pipe is not sealed in that location; many older septic tanks provided no sealant unless some home-made system was used. Some installers pour concrete around the waste pipe entering the tank - which can work but it makes future repairs more troublesome.
  
  Modern septic tanks may include a rubber gasket to help seal at the tank entry and exit openings. But if the waste lines entering or the effluent lines leaving the septic tank are at a sharp angle with respect to the tank, the gasket may not seal properly.
• Any damaged sewer piping
  
   and even effluent piping might permit ground water or surface runoff to flow into the septic tank or into the drainfield.
• A septic tank cover or cleanout port,
  
  especially one that is below ground may permit surface water to enter the septic tank. (Make sure septic tank covers are sound - falling into a septic tank is likely to be fatal).
• Rust damage to a steel septic tank
  
   can let effluent out of the tank and water leak in depending on weather conditions.
• Cracks in a concrete septic tank
  
  also can let effluent leak out or water leak in - though we have not found these occurring as often as rusted out steel septics
• Damaged fiberglass or plastic septic tanks
  
  can also leak at a seam or point of damage - though we heard few reports of this problem.

You can reduce the chances of water leaking into a septic tank by making sure that roof runoff and surface drainage are directed away from the septic tank as well as the drainfield.

Leaks out of the septic tank prevent testing the septic drainfield

Leaks out of the septic tank can occur if the tank has a hole (for example a rusted-out metal septic tank) or if a concrete, fiberglass, or plastic tank is cracked or damaged. A leaky septic tank means that effluent may not be properly treated since it is not reaching the drainfield.

A leaky septic tank also means that a septic loading and dye test to attempt to check on the condition of the drainfield may fail to work. Particularly if the septic system has been unused for some time, and if the leak is near the bottom of the septic tank, the liquid level in the tank will drop very low.

The result is that a normal septic dye test volume will simply be filling up the septic tank rather than pushing water out into the drainfield.

In turn this condition means that the septic test could not test the function of the drainfield. The risk is that new owners moving into the property will very quickly discover the bad news that not only has the septic tank got a leak but the drainfield may not really be functional.

A septic tank that is not in use and leaks out may also produce solidified scum and sludge that collect low in the septic tank or on its bottom - making septic tank cleaning extra difficult.

If there is a port to permit safely looking into the septic tank before an inspection or test, be sure to check the sewage level in the tank.

Leaks into a septic tank can flood the tank and drainfield

Leaks into the septic tank can occur if ground water or surface runoff are directed towards the septic tank or pipes that carry sewage into the tank (or effluent out of the tank).

Any opening that permits surface runoff to enter the septic tank risks flooding the tank. In rainy weather the result can be a water overload in the septic tank, reducing the level of treatment in the septic tank.

Perhaps more of a problem, the same water running into the tank may also push its way into the drainfield, flooding the septic drainfield.

If extra volume of the water entering the septic tank also prevents adequate settling time for sewage entering the tank then an excessive level of suspended solid waste may be forced of the septic tank and into the drainfield, further reducing the life of that component.

Leaks into a septic tank can also occur if the drainfield is so flooded that water is flowing backwards through the drainfield piping and back into the septic tank through its outlet.

Pumping a Flooded Septic Tank - Does that Fix Anything?

Pumping the septic tank won't fix any of these flooded septic tank conditions. A septic tank is normally always "full" to just below the septic tank outlet opening.

But pumping a flooded septic tank might be performed for the following reasons:

1. Flooded septic tank needs cleaning:
   
   If the septic tank was exposed to area flooding it may have become loaded up with mud and silt and needs to be cleaned in order to work at all. In this case, the septic drainfield piping, distribution boxes, and similar components need to be excavated sufficient to permit their inspection as well.
2. Diagnose a flooded septic tank:
   
   If the septic tank appears to be filling from surface runoff or ground water leaking into the tank, pumping the tank permits the owner or septic service company to look for these problems by observing the empty tank for signs of effluent or ground water back-flowing into the tank.
   
   See SEPTIC TANK BACK FLOODING for details.
3. Permit temporary use of a flooded septic tank:
   
   if the tank is emptied, and if the building occupants make a maximum effort to minimize unnecessary water usage (showers, laundry, bathing), then the occupants may be able to use the septic system and thus the building and site in a sanitary way, without further contaminating the neighborhood, for a few days to a week, depending on the tank size, number of building occupants, frequency of toilet flushes, etc.
4. Is your septic tank flooded?
   
   See SEPTIC TANK LEVELS of SEWAGE for details on normal and abnormal levels and what they mean.

In our OPINION, if the septic tank floods once in 20 years, under exceptional conditions, no design changes or repairs may be needed other than cleaning the septic tank when floodwaters subside.

But if this condition happens frequently, the septic system is unsanitary and may be a health risk to the building occupants or its neighbors.

 

Septic Tank Leak Test - Water-tightness Test Standards

The following describe septic tank water-tightness test standards & procedures. While these septic tank leak test procedures focus on the tank's abiltiy to prevent sewage or wastewater leaks out of a septic tank, indirectly they also address in part the risk of groundwater or surface runoff leaking into a septic tank. Keep in mind that these tests do not address:

• Water leaking into a septic tank at poorly-sealed inlet our outlet piping connections
• Water leaking into a septic tank at covers, access covers
• Drain-back: wastewater flowing backwards into the septic tank from a failed drainfield
• Other sources of leakage into septic tanks discussed in the article above

Notes to the table above

Note that these tests do not require absolute water tightness or air tightness.

Adapted from US EPA Septic Design Manual Table 4-14 Watertightness testing procedure/criteria for precast concrete septic tanks

Also see SEPTIC TANK DESIGN SPECIFICATIONS

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical reviewers are welcome and are listed at "References."

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Kathy How do I get a Dye Test on my C3 Septic System?

How is a dye test performed on a c3 septic system rated at 1000 litres per day - On 2020-05-30 by

Reply by (mod) -

Kathy:

Details of how a septic loading and dye test are performed are given starting at

SEPTIC LOADING & DYE TEST PROCEDURE

Please take a look there and don't hesitate to ask follow-up questions.

How to stop leaks at a septic tank made of concrete blocks

The tank is built out of blocks. Water is leaking from the side of the tank

Want to stop the leak-what shall I use - On 2020-05-30 by Soma

Reply by (mod) - keep people away from the concrete block septic tank - it's unsafe

Soma:

Watch out: a septic tank built of concrete blocks and leaking is at risk of sudden collapse;

If someone falls-in it's a quick and nasty death.

Keep people away, rope off the area, and then, to understand what's leaking at your septic tank, call a septic contractor for an inspection: I suspect the tank should be replaced.

The contractor will need to empty the septic tank and clean it to see where the damage is and what repair is possible.

But in general, a septic tank made of concrete blocks is unsafe and is likely to leak or collapse.

Septic holding tank seems to be leaking - groundwater fills the tank

I have a 1200-1500 gallon cement holding septic tank. Not a mound system, just holding tank at a cabin.

So once full needs to be pumped out. It has cracks in the bottom of the tank. Have paid someone to go down when empty and did not find any cracks in the sides.

They tried putting sealer in some cracks in floor of tank. Helped only a little.

In the spring or when heavy rains and the ground water is high it will fill the tank when we are not even there using it. Can the tank be pumped out and then pour 2-3 inches of cement and see if that will stop the ground water from coming in? - On 2020-05-21 by Jerry

On 2020-05-22 by (mod) - before "repairing" the leaky septic tank, identify the leak point

Jerry

Watch out: it is extremely dangerous and often fatal for someone to enter a septic tank even if it has been pumped out. A person can become overcome by methane gas in moments, and anyone entering the tank to try to rescue them can also be overcome in moments.

Only a professional, working with an assistant, and wearing appropriate safety gear should even consider entering a septic tank.

That said, pouring a couple of inches of high Portland cement on the bottom of the tank may indeed cure your bottom leak provided we can get a decent bond between the poor and the tank surface. If there is algae or sewage on the septic tank bottom the band may be poor and leaky.

But

Watch out: it's very common for ground water to leak into a septic tank, even one that's only a holding tank, that is, not connected to a drainfield. I don't assume the problem is cracks in the tank bottom as you've described.

Water may enter at the septic tank top edges, at its covers, at its sewer line connection to the cabin, or surface runoff may be leaking into the sewer pipe itself.

You might want a contractor who has a sewer line inspection camera to to check your sewer piping.

On 2020-05-27 by Jerry

Thanks for the info back. I was not planning on climbing down in. Would take cover off and scrape and power wash and have the pumping guy stick around while I do that to clean as much as possible. Then would create a long trough to pour the cement down. Thought I would make it wetter than usual so it spreads out easier.

 

How to fix a leak at the septic aerator line

How to fix an air leak from where the aerator line goes into septic tank gurgling on outside of tank? -

Reply by (mod) - To fix an aerator air-line leak on an aerobic septic tank system

To fix an aerator air-line leak on an aerobic septic tank system we need first to identify just what part is leaking and where.

If the leak is at the connector the repair could be as simple as tightening a stainless steel hose clamp or if the connector is damaged, as troublesome as replacing that part.

If the leak is in the tubing in my opinion it should be replaced.

Both of these are inexpensive parts.

Also see

AEROBIC ATU SEPTIC PROBLEMS

and for parts
see

AEROBIC SEPTIC SYSTEM ATU SUPPLIERS & MANUALS

 

Septic tank sat idle, now it's just half full: is there a leak?

Septic tank has not been used in over a year. On inspection the tank is only half full. Does this mean there is a leak? - On 2019-11-15 by Rod

On 2019-11-15 - by (mod) - probably

That seems like a distinctive possibility. It would make sense to have the tank cleaned which may require adding some water to enable it to be pumped out. When the tank is pumped and claimed that it should be inspected for cracks or other damage. Of course if it's a steel tank it's even more likely but it's rusted out.

 

Diagnose & fix intermittent septic effluent pump cycling

Our effluent tank pump comes on every couple of hours during the night when nobody is putting any water into it. Where do you think it’s coming from? - On 2019-05-09 by David -

Reply by (mod) - is it a leak into the tank or water running in the building?

The two common explanations for the effluent pump appearing to run for no reason are one that there is actually water running somewhere in the building, such as a running toilet that you haven't noticed, there were two that there's ground water leaking into the pumping chamber or leaking into the septic tank from a flooding field or failure condition and that in turn could be backing up into the pumping chamber

Typically you would take one of two approaches to solve the problem of a flooding holding tank. What is the direct surface runoff away from the area and the other is to make sure that the tank top and any pipe connections into it are sealed.

Septic holding tanks take in water during wet spring

Have 2 holding tanks, 45 years old, that take in groundwater during wet spring conditions. Any suggestions on cause and cure? - On 2019-05-09 by jpbill

Reply by (mod): where to look for septic tank leaks

Look for leaks

around the septic tank top or lid

at the septic tank access covers

at the septic tank pipe connection(s)

If those look good, have the tanks emptied and cleaned to inspect the tank sides and bottom.

...

Continue reading  at SEPTIC TANK INSPECTION PROCEDURE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SEPTIC TANK LEAK FAQs - questions & answers about leaks into or out of septic tanks, posted originally at the end of this page

Or see these

Recommended Articles

• CAULK & SEALANT CHOICES, products list for possible septic tank lid or pipe connection sealants to keep water out of the tank
• INSPECT the SEPTIC TANK BEFORE PUMPING
• INSPECT the SEPTIC TANK DURING PUMPING
• INSPECT the SEPTIC TANK AFTER PUMPING where we describe septic tank inspection mirrors, cameras & other tools
• MEASURE SEPTIC TANK SCUM & SLUDGE how we measure the thickness of septic tank floating scum and bottom sludge levels.
• SEAL CRACKS in CONCRETE
• SEPTIC TANK BACK FLOODING - a common source of flooded septic tanks: failed drainfield / soak bed
• SEPTIC TANK INSPECTION PROCEDURE
• SEPTIC TANK LEAKS
• SEPTIC TANK LEVELS of SEWAGE for a discussion of the normal levels of sewage found in a septic tank.

Suggested citation for this web page

SEPTIC TANK LEAKS 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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