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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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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.
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 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.
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.
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:
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.
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