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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.
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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.
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.
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.
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: 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)|
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.
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.
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.
Your instructions to the inspector need to include some effort at determining the following:
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.
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.
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.
See SEPTIC FAILURE SIGN
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.
See SEPTIC BIOMATS)
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.
See SOAKBED SOIL CONDITIONS
Watch out for unsafe site conditions like missing or unsafe septic covers, and subsidences:
See SEPTIC SYSTEM SAFETY WARNINGS
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.
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 inspectapedia.com/septic/Cesspool_Guide.php
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.
Also see DRYWELL / SEEPAGE PIT SPECIFICATIONS
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
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)?
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 inspectapedia.com/septic/Drywell_Design.php 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 inspectapedia.com/septic/Cesspool_Guide.php 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.
Continue reading at DISPOSAL vs TREATMENT or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see SEPTIC DRAINFIELD RESTORERS?
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(July 22, 2015) irene said:
septic tank has not been used for 3 years and now is dry is this common?
"Dry" may be subjective. If the sewage level in the tank were down even a foot I'd not be worried but if sewage levels have fallen to the bottom of the tank I suspect it is leaking.
(Sept 1, 2015) cherm32 said:
We moved on a property that has not had a house on it for about 30+ years, we recently found an old PVC pipe sticking out of the ground next to an area of dirt where there is no grass which is directly behind where the old house used to be. My husband dug up part of the pipe and the rest broke of the dirt was wet a a frog came out of the piece of pipe that was still in the ground that appeared to be filled with dirt.
Questions: is it probable this is the old septic system? if so would it still have water after so many years, and could recent heavy rains fill it up? how do we get rid of this thing. I am really concerned for our and our childs safety.
While there could certainly be other reasons that you'd find a bit of dirt-filled pipe sticking up out of the ground, an old, failed or possibly abandoned septic is a good guess. The no-grass area may mark a septic tank.
To avoid possibly killing someone, rope off and keep people away from the suspected septic area until you've had a contractor excavate to see what's there. An old steel tank or home made system could have a failing cover that could suddenly collapse - falling into such an opening can be fatal.
When the tank is found you want to know that it was properly abandoned -for safety - as described in the article ABANDONED or NEW SEPTIC SYSTEM TESTS
(Jan 26, 2016) Geoff said:
I'm looking into purchasing a home that has a septic system. Unfortunately, the septic system was not used for about a year. Because of this, the real estate listing agent has informed us that the home will need an entirely new septic system.
What I was curious about the possible problems (though I would imagine from reading the article and comments that the system is leaking) to ask about if we pursue the property further.
Also, would you ever recommend fixing any of the possible problems without replacing the entire septic system, but instead using a product like aero stream?
Thanks in advance.
Please see HOME BUYERS GUIDE to SEPTIC SYSTEMS for suggestions of how to get an idea what's there. It's safe to say you need a "whole new system" but that may not be so. OR the realtor knows something that's not been disclosed.
Also see OTHER PEOPLE's MONEY - why consultants spend your money to reduce their risk.
(Mar 18, 2016) Lenny said:
My wife and I recently purchased a new home with a septic system - we've always lived in homes with "city sewer/water." In Colorado, the existing septic system must pass inspection and re-certified prior to the home being turned over to the new owners; i.e., the seller is on the hook to fix any problems with the septic system.
Well it was found that the leach field needed to be completely rebuilt/replaced. So knowing nothing about these systems the contractor said he is providing a new "tank" behind the existing tank which makes me think, he will use the existing tank as the front tank to the leach field. I asked him why he just didn't pull the existing tank out and use the new tank (apparently the new is the "latest and greatest" where the existing tank is not) I didn't understand his answer that the new tank will "interface" with the existing tank?
Then I asked him, what if the existing tank goes "south" he said, well I guess you'll have to get another tank. Any info would be appreciated.
A better approach might be to empty, then abandon the existing septic tank, presuming it's not serviceable. Be sure the work actually addresses the drainfield that has failed - the comments you report don't do so.
(Mar 20, 2016) Lenny said:
Thanks .... The contractor did state he hadn't fully inspected the existing tank, but felt it most likely was in "code" shape.
His work is primarily focused on the leach field which was the failure requiring the rework; apparently it was invaded by existing tree roots and required the removal of two large pine trees to rebuild the drainfield including re-soiling(?). I guess I don't understand the need for the existing tank when a new and improved tank is being installed.
Not to be too much of a stickler, "code shape" is an undefined term. In fact there is almost no building code written for in-service septic systems.
When the tank is pumped and cleaned it should be inspected for damage such as holes, cracks, missing baffles.
If you want to abandon the existing tank have it emptied and filled-in.
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