Abandoned, Dis-Used, or New Septic System Test Guide
How to test a septic system that has never been used or has been out of use

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How to inspect or test abandoned, disused, or new unused septic systems:

Here we provide suggestions for evaluating the condition of an abandoned, un-used, or new and un-used septic tank and drainfield. Septic systems that have never been used or systems that have been un-used or even abandoned for months or years present special concerns, and the evaluation of the condition of such a system requires different steps than for a working and in-use septic tank and drainfield.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

How to Evaluate the Condition of an Abandoned or Un-Used Septic System

Determining the Condition of Never-Used Septic Systems

A septic system that has never been used should not be evaluated by a loading and dye test because chances are the septic tank is empty - the loading test volume of water run into the system is unlikely to even fill the septic tank during the test interval.

If the a septic tank is not full to normal operating level, placing a test volume of water into the septic tank will not move any test water out to the drainfield - the drainfield or absorption system will remain un-tested, and its problems will remain undiscovered.

What to Inspect & Test a Septic System is New & Un-Used

In almost any location where building codes and health codes are enforced, a building permit, a septic system design, soil percolation tests, and approval of the septic system design are required by local health or building department officials.

  1. Contact the building department and health department to ask:
    1. Was a septic design submitted and approved?
    2. Are there drawings, inspection, or test result documents available (obtain copies)?
    3. Was there a final inspection to confirm that the septic system was built as proposed?
    4. Confirm that a septic construction permit was obtained and the system was inspected and approved as built
  2. Identify the septic contractor who installed the system;
    1. Ask for a site tour (offer to pay the contractor for his time) at which the contractor points out (and you mark) the location of septic components (tank, distribution box, drainfield, other site drainage components that may have been installed).
    2. Ask if the septic contractor had to make changes to the original plan. A septic contractor might encounter a buried surprise - rocks, boulders, changes in lot or building plans, that lead to last-minute changes in the septic system layout or in the location of its components.
    3. Ask when the work was completed and whether or not all connections (tank to house, tank to D-box, D-box to drainfield) were completed.
  3. Septic drawing: if an accurate sketch is not already provided, locate and sketch the measurements to and location of all septic system components. See SEPTIC TANK, HOW TO FIND. Confirm that the as-built (which may be different than the as approved design) septic system meets all of the setback requirements - distance from well, property lines, streams, etc.
  4. Inspect the septic system site, tank, septic distribution box, septic drainfield: 
    1. A septic tank that has never been used should be empty of sewage and water. It is possible that a small amount of water has run into a septic tank during installation if the tank was set during very wet weather, but that's an abnormal circumstance. If there is significant water in the septic tank, more than an inch, the concern is that surface runoff or ground water may be leaking into (and flooding) the septic tank: look for stains at the inlet piping, baffles, covers, tank sides, that might indicate places where water is leaking into the septic tank.
    2. Inspect the septic tank further using the criteria that we list below,
    3. Inspect the site for evidence of settlement, un-wanted surface runoff, or other changes that might have affected the condition of the septic system such as evidence that vehicles have been driven over the drainfield. See Septic Site Inspection Procedure and see Failure Causes - Septic Drainfields.
    4. If the distribution box has tipped, or if there is evidence that surface water is entering the distribution box, these conditions will need to be corrected.
    5. Make certain that the septic tank has save and secure covers. See SEPTIC & CESSPOOL SAFETY

If the septic system is reported to be new and never used, the septic tank should be empty. Inspecting the septic tank by finding and opening its service ports will yield important data such as evidence that surface or groundwater are leaking into the septic tank (and flooding the system).

If the septic system is new and never used, the distribution box should show no evidence of flooding or ground water leaking into that part of the system.

What to Inspect & Test If an Un-used Septic System is Old & of Unknown Age

Opening an older septic tank (C) Daniel FriedmanIf a septic system is old, perhaps of un-known age, and it is reported that the system has been un-used for a long time, special inspection and test considerations apply.

  1. Contact the building department and/or health department to ask if there was a septic plan, inspection, approvals for the site, and if drawings are on file. Above we suggest details that might be asked.
  2. Inspect the septic system site, septic tank, and distribution box: find the septic tank , have the tank opened (be careful not to fall into a tank with an unsafe cover, and never enter a septic tank).
    1. If the septic tank is empty and clean inside it has either been pumped or has never been used. There should be no standing water or debris in the septic tank. A steel, plastic, or concrete septic tank that has never been used will have clean sides with no sewage staining.
    2. While the septic tank is open, look for evidence of places where ground water might be leaking into the tank (DO NOT ENTER THE SEPTIC TANK) - and check the condition of the septic tank inlet and outlet baffles to be sure they are in place.
    3. If the septic tank is not empty inspect the sewage and effluent levels. A septic tank that was in active use but has been unused for a year or even longer should still be nearly full to the point just below its outlet pipe. A septic tank that has been un-used for many years may have lower sewage and effluent level.

      But if the septic tank has no effluent, just a dried crust of sewage sludge on its bottom, it is possible that the tank has been damaged and is leaky. Something is probably wrong. A steel septic tank is at risk of having rusted through and lost its liquid volume, so unless the test volume of water is more than tank volume you won’t be testing the drainfield. A concrete septic tank might be cracked and leaky too – but this is less common.
    4. If the septic system's distribution box has tipped, or if there is evidence that surface water is entering the distribution box, these conditions will need to be corrected.
    5. Make certain that the septic tank has save and secure covers.
  3. Inspect the septic system site for evidence conditions that suggest damage to the drainfield, un-wanted surface water, etc: Site conditions may have changed since the original septic tank or drainfield installation, such as changes in surface runoff, subsidence, nearby construction, vehicle traffic on the drainfield, or even damage to the septic tank, distribution box, or drainfield piping.
    See Septic Site Inspection Procedure.
    1. Settlement of the septic tank, tank cover, distribution box, or settlement of areas in the drainfield. Any of these may mean that septic components have become tipped or even disconnected. For example, a poor-quality installation of septic drainfield piping with uneven trench excavation, inadequate gravel, un-compacted backfill, may have led to drainfield pipes that have become tipped, disconnected, or blocked with soil. Even a new septic drainfield, just a few months old, might fail under these conditions.
    2. Un-wanted surface runoff that directs water onto the septic tank, distribution box, or drainfield can flood the system and may significantly shorten the life of the drainfield.
    3. Other changes that might have affected the condition of the septic system such as evidence that vehicles have been driven over the drainfield. Driving over the drainfield compacts soil that needs to breathe, and it risks crushed or broken drainfield piping or distribution boxes.
    4. Soil test: You might want to do a soil perc test to see if the soil drains as was claimed when the septic drainfield was built.
  4. Septic drawing: if an accurate sketch is not already provided, locate and sketch the measurements to and location of all septic system components.
    See SEPTIC TANK, HOW TO FIND. Confirm that the as-built septic system meets all of the setback requirements - distance from well, property lines, streams, etc.
  5. Septic loading and dye test for an un-used septic system? If inspection of the septic tank shows that the tank is full or nearly full, then a septic loading and dye test has a chance of disclosing a damaged, blocked, or failed septic drainfield. We find enough septic failures with this procedure that it's worth performing, but beware: a drainfield that has rested for a few months and that is tested during the dry season might still have a short functional life when it is restored to year round use. Septic loading and dye tests and septic tank inspections should be accompanied by an expert visual inspection of the site as well as a collection of any available historical data.
    See Dye Tests
    and also
    see Dye Amounts, Water Volume

  6. Septic maintenance history may be available from local septic tank pumping companies. If a few telephone calls can locate a septic pumper who has serviced the property be sure to ask the contractor's opinion of the condition of the septic system.

How to Inspect a Septic System that has been Shut Down for Six Months or Longer

Reader Question: how long should water be turned on before a septic inspection can be performed on a vacant home?

How long should the water be turned on before a septic inspection can be performed on a home that has been vacant for 1 year? - Anonymous, Mortgage Loan Resource Desk Analyst


A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. For example, one might learn something about the type of septic system installed, whether or not there are grinder pumps, effluent pumps, a septic tank vs cesspool, separate drywells taking graywater - all of which would be crucial in understanding possibly significant issues about the condition of the system. You will find additional depth and detail in articles at our website.

The short answer is easy but dangerous: run the standard septic test volume

The short answer is: run water long enough to get the minimum standard test volume into the septic system. That's at least 50 gallons per bedroom or 200 gallons, whichever is more.

Longer or more water is a better test as long as the total volume does not exceed a normal family's daily use - which could exceed the septic system's design level. At InspectApedia we give tables of those volumes based on septic tank size and other variables.



For example, if we know (direct measurement is often easy) the size of the septic tank we know the average daily wastewater flow for which it was designed. I'll repeat that septic tank size and water usage volume data here.

Table of Required Septic Tank Size for Daily Water Usage Volume in Gallons

Average Sewage Wastewater
Flow - Gallons Per Day
Minimum Septic Tank Size in Gallons of Effective Capacity Needed (1)
0-500 900
601-700 1200
801-900 1500
1001-1240 1900
2001-2500 3200
4501-5000 5800

The left column in this table gives the average daily wastewater flow for which the tank and septic system were (or should have been) designed. That same figure would be the maximum water that can be run into the septic tank without worry of exceeding the system design volume and thus without being blamed for doing something wrong.

Technical note: in fact since wastewater flow into a septic tank is normally not uniform but instead surges at the start and end of the day, running water into the system more slowly, over the entire day is probably a bit less aggressive and thus safe. I am not recommending using these test volumes as they significantly exceed our minimum test volumes given earlier.

But it is reasonable to conclude that running water in the building at a rate not to exceed 500 gallons over 24 hours is an aggressive but "safe" septic loading test provided other safety checks I describe below are also made.

Reasons why running any septic loading test without knowing more are risky

Watch out: a fundamental and very significant risk, especially for a bank assuming financial responsibility for a property, is that of permitting a "pro-forma" or "going through the motions" test or inspection that is not a true or valid inspection or test. Making such a mistake significantly increases the risk of an expensive surprise. And there are several critical stumbling blocks that mean to me that simply requesting that a volume of water be run, without checking some other critical parameters first, is a significant mistake.

OK so How Much Water DO We Need to Run to Test a Shut-Down Septic?

Therefore while I completely understand the appeal of a simple answer like

"Turn on the water for one hour" or some variation, such an answer would be, frankly, ridiculous if I were to offer just that.

So we need an approach that makes a credible attempt at addressing these fundamental questions.

When you ask how long water should be "turned on" I imagine you mean left running. But un-stated is at what rate the water is running - the flow rate in gpm, and at how many fixtures simultaneously. We need to either know something more about the house, or make some assumptions.

How long to run water = how much water do we need to run:

It is reasonable to assume that a home water system, whether on well or municipal water supply, delivers between 1 and 3 gallons per minute at a kitchen sink faucet or bath tub faucet. So if we can determine how much water we need, we can calculate the water-on time.

A bare minimum septic test needs to run at least 200 gallons or at least 50 gallons per bedroom into the septic system for an in-use septic system OR for a septic system that has not been in use for some time.

Other Instructions to the Septic Inspector to Reduce Risks & Hazards at the Septic System, Site, & Well Pump

Your instructions to the inspector need to include some effort at determining the following:

  1. What is the actual water flow rate ( it's trivial to measure it with a container and a stopwatch) - run the water long enough to achieve the necessary volume
  2. What is the water source: if it is a private well, there is risk that if water is left running unattended, say at a slow rate overnight or longer, if the well runs dry the inspector could be charged with running the well pump dry - which in some systems can destroy the well pump.
  3. What is the condition of the building drain system. If water is left running unattended and a drain is blocked, a backup and flood in the building could cause costly damage.
  4. What is the type and condition of septic system. If a visual inspection could have disclosed an unsafe septic tank cover, for example, and your representative was on-site performing a test and failed to detect this potentially fatal hazard, should there be an accident there would be hell to pay. Also the observation that the system uses septic grinder pumps, effluent distribution pumps or other equipment is important in understanding how the system can be tested.

    For example, if a sewage pump is part of the system and the power to the pump is left off the system cannot be safely tested. SEWAGE EJECTOR / GRINDER PUMPS and SEPTIC PUMPS

    Further, some idea of the type, location, & condition of the septic system informs the test that can or should be performed. For example a dosing system can be flooded by some septic tests and could be damaged, while a conventional septic tank and drainfield would not be unless the system were itself already damaged or defective.

Keep in mind that we are testing the effluent disposal system, the drainfield, not the septic tank, except that if the tank and system include pumps and filters etc. those too are being exercised and thus tested by the septic loading and dye test.

Condition of the septic tank: Impact on Testing a Septic System that Has Been Out of Use

IF the system is a conventional septic tank and drainfield, and if the septic tank is un-damaged, that is, not leaking, after even a year of non-use, the septic tank will be nearly full of sewage. The losses by evaporation or transpiration through a closed septic tank are practically nil.

Therefore pushing a standard minimum test volume, say 50 gallons per bedroom or 200 gallons, whichever is greater, would be a minimum water volume. A safe maximum test volume, as I established above, is 500 gallons of water over 24 hours. In fact, since in most U.S. jurisdictions the minimum permitted tank size for new septic installations is 1000 gallons this is a pretty safe number.

Watch out: if a septic tank has a leak, its in-tank sewage level may have fallen significantly. If so, all of our "test water" or a good part of it, is remaining in the tank - so we never tested the drainfield at all. A "false test".

Watch out also: if the septic tank was pumped and never re-filled by normal use we are sitting there with 1000 gallons or so of empty volume into which all of our test water runs - the septic "test" would have been false if this condition is not discovered. Therefore the un-used septic system test needs to include, if possible, an effort to open and inspect the levels in the septic tank before doing anything. This step also allows an effort at assuring that the septic tank cover is safe and secure.

Weather, Season, & Condition & Location of the Septic Drainfield: Impact on Disused-Septic System Testing

The condition absorption bed or drainfield condition is a different question. There are ample visual signs of trouble or likely trouble at the septic drainfield even before a septic test is performed.

One would think that a drainfield that has been un-used for a year would have had a rest period that should have improved its performance.

Watch out: that is not necessarily true. There may be critical seasonal variations. For example a drainfield in a low wet area may show failure but only in wet weather, regardless of how long it's been out of use . So a site inspection that notes that the known or apparent or only possible drainfield location is alongside a stream or lake, for example, would be important.

Watch out for unsafe site conditions like missing or unsafe septic covers, and subsidences:


For these reasons, a "disused septic system test" that does not include an inspection for these critical pieces of information, is not valid, and exposes all parties to liability, loss, and aggravation.

Reader Question: upstream "septic drywells" don't work. What's a septic drywell, what's a cesspool, what's the difference & who cares?

2016/09/13 VanCoerte said:

We just discovered that of our two septic drywells, one is at 85% capacity and the other one is empty, because the pipe to it is actually running uphill. (!!) This means that the functioning drywell was the only one in use for - wait for it - 56 years!!

SO: we're going to properly hook up the empty drywell, of course. But I'm wondering: if we cap off the other drywell now, how long do you think it would take for it to become usable again? I heard one estimate of 20 years, but I think the facts that our soil is clearly excellent for drainage and that it hasn't actually failed yet should be taken into consideration. Could it be as soon as 10 years??

DETAILS: The 85% capacity drywell is 8x6 (200 sf) for a 4 bedroom house, in which usually only 2 - 4 people lived.


A dope, like me or like Barnum's "Sucker" is born every minute. According to my sister Linda, one was born on my own birthday. But most septic people know that sewage doesn't flow uphill.

A "septic drywell" is properly called a seepage pit or CESSPOOLS or cesspit - detailed at

while a "drywell" strictly speaking, is used to receive graywater. A cesspool that no longer absorbs effluent can be slightly and temporarily pepped up by probing and jamming around the bottom - an approach that is short in benefit and can result in death to site occupants if the fooling around causes the system to collapse - that happened in a case on Long Island in New York.


So usually we leave the failed cesspool alone and daisy-chain on a new one.

Left alone a cesspool that no longer absorbs won't recover itself in your lifetime nor mine nor the two of them together. There is just too much solid waste, scum, slime in the pit and in the surrounding soil. It's not like resting a drainfield.

I'd plan on either adding a sewage grinder pump to send waste up to the higher cesspool or I'd dig a new one downhill.

BE SURE that the covers over these units are safe against collapse or fall-in. See CESSPOOL SAFETY WARNINGS

Reader follow-up: why can you rest a drainfield but not a seepage pit?

Anonymous said:

Yes -- it is beyond my comprehension that, even 56 years ago when it was installed, someone would run pipe UPHILL to drain sewage.

Also yes -- I suppose what we have is a seepage pit. But here it's called a drywell by the septic companies and the health department.

Ours is man-made (in 1960) of concrete block and crushed stone and is about 5 feet underground. I believe its size is 8' x 6' - although they say it's 200 square feet, so I don't understand any of that.

If you don't mind taking the time - could you explain WHY you can rest a drainfield and not a man-made drywell (seepage pit)?

Moderator reply: depth, thickness & nature of waste & clogging in the soil

Not to be goo glib but one thing about it: the installer could have given a written guarantee that the uphill cesspool would never clog with sewage.

I understand that sounding like nit-picking over words can be annoying, but misunderstanding about just what is installed, how it works, how it should be designed, how it should be maintained, and what are its failure criteria also causes trouble for owners and occupants anywhere. So it's nice to be clear about blackwater. If it won't annoy your local officials you are welcome to print out and give free copies of the articles in this series explaining drywell and cesspool to anyone who wants them. We appreciate criticism, gripes, questions, feedback: working together makes us smarter.

So thanks for asking.

The distinction between "drywell" and "seepage pit" and "cesspool" can be confusing but also can be important as designs, maintenance, usage, and failure criteria are not identical.

DRYWELL DESIGN & USES (for graywater disposal and sometimes for stormwater buffering or disposal - found at discusses: What is a drywell or "septic drywell", seepage pit, and how is it different from a cesspool? How are drywells or seepage pits constructed? What care is needed for a drywell? Do we need to filter wastewater entering a drywell? What is the failure criteria for a drywell?

CESSPOOLS - used to dispose of sewage wastewater - at discusses: Septic cesspool design, construction, installation, inspection, maintenance & repair advice. Definition of a cesspool, why a cesspool is not a drywell, why their function is limited. How is a cesspool cleaned or maintained? Does cleaning the cesspool extend its life? What about hydrojetting cesspools to break up sludge? How do cesspools fail? How old is the cesspool? How long should a cesspool last? Should I put additives or chemical treatments into the cesspool to extend its life?

See also CESSPOOL / DRYWELL PIT COLLAPSE or FAILURE How to detect a drywell or seepage pit failure; What causes seepage pit failure? What causes drywell failure; How to avoid seepage pit or drywell early failure? What care is needed for a drywell? What is the failure criteria for a drywell?

You can rest a drainfield trench because we're talking about a small diameter trench, perhaps a couple of feet across and near the soil surface where there's both anaerobic and aerobic bacteria who eat away at the biomass that has formed, typically an inch or so thick, in the soil around the perimeter of the trench. That's an inch or so of biomass near the ground surface. In proper use, a drainfield receives ONLY clarified effluent, that is, no solids, no feces, no toilet paper, no grease - or at least very little of those materials and only in ultrafine particulates.

A cesspool is going to be 4 to 20 feet deep and at the end of its life will be filled with nearly solid sewage; that's a mass of solid waste close to say 4-5 feet in diameter by 4 to 20 feet deep. The cesspool, depending on how it was constructed, was surrounded by gravel and backfill soil. More solids, grease, fecal waste, as well as biomass have formed in the gravel and soil around the cesspool and still more thickly at its bottom.

A cesspool receives all of the solid waste: feces, toilet paper, grease, crud. Therefore the soils around the cesspool will become clogged by much more than the mere biomass produced by soil bacteria.

It's clogged by 6" to 24" (typically) of sewage, grease, solids, as well as by the biomass formed by bacteria. That thickness is not going to be easily removed by soil bacteria for two reasons: 1. It's enormous in thickness compared to a leachfield biomass and 2. it most of the cesspool it's much deeper in the soil where there is no aerobic bacteria.

Think of an outhouse privy pit. When filled the pit is abandoned. That now covered-pit will remain full of nearly-solid sewage for 10 to 20 years or longer. The breakdown is very very slow because of the thickness and mass of the waste.

Some cesspool "restoration" services in some areas pump out cesspools - a dangerous approach if the cesspool is home made as it can lead to a collapse such as one that killed a homeowner on Long Island. Others try toxic caustic chemicals that, even if they de-grease or de-sludge, also kill bacteria and poison groundwater and are illegal in many jurisdictions.

Other cesspool services will hydrojet the bottom of the cesspool to "restore" soil absorption of effluent - a partly-effective but rather short-lived "repair".

Those conditions mean that the usual approach when a cesspool has failed (failure criteria are in the article I cited above) it is abandoned or at most daisy-chained to pass on sewage to a new cesspool just downstream.


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