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Old 02-13-2013, 08:44 AM   #1
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why do septic fields and tank get saturated


Help me with this example:

A home has septic that has always worked fine. A new "state of the art" field was installed 5 years ago by a professional known as the best in the business. The owners have the tank emptied and everything inspected. It appears perfect. A few weeks later, the owners go away for a very long vacation. During that time, a neighbor comes in and flushes a few toilets on occasion. It doesn't rain hardly at all during that time and conditions are generally dry. The homeowners return. The owner decides to look into the washout that's about 15 feet before the tank. It's empty as it should be.


Just then a typhoon hits, flooding their backyard. They don't use any of the home plumbing, and none of the fixtures are leaking.

8 hours later the owner opens the washout again to find it totally full, and finds he cannot flush his basement toilet.

With no use of indoor water and nothing leaking in the house, this backup was 100% caused by rain.

But how? And where would rainwater be leaking into the system?

I know septic tanks are only supposed to be full to the level of the inlet/outlet valves. Yet to backup into the main drain line and stop a basement toilet from working, that tank would seem to be 100% full, then the drain to the house starts to fill as well.

Is rainwater getting in through the lids of the tank? Enough to cause this so quickly?

Is rainwater simply and easily getting into the fields, going the wrong direction, and backfilling the tank, etc?

Is it a combo of both, or is one more likely the cause?

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Old 02-13-2013, 09:02 AM   #2
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why do septic fields and tank get saturated


Soil conditions, using a garbage disposal will have a lot to do with it.
Not sure how things work there but before any septic goes in around here a soil sciencetest comes in and takes soil samples to figure out how to design the system.
Things like clay soils will need a much bigger wider leach field.
Picture a leach field as a coffee filter, with no coffee in the wilter water runs right through, keep adding more and more coffee and after a while it over flows.

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Old 02-13-2013, 09:40 AM   #3
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why do septic fields and tank get saturated


The localized(perched) water table may have been created/caused by the "typhoon" and with heavy soil, it will take time to lower (if at all).

An engineering firm could punch a few holes (hand augered) at a reasonable price to determine if the local water table has risen or there may be a problem with the septic system operation or maintenance. An engineer friend of mine frequently does hand augered holes to determine soil situations and can go 30 miles each way and auger 4 or 5 holes in less than 2 hours.

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Old 02-13-2013, 09:40 AM   #4
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why do septic fields and tank get saturated


The outlet of the septic tank has drain lines that leach the water into the ground. By their function they can not be sealed. When you get heavy rain the reverse action happens. The water in the ground leaks into the drain lines and back into the tank. As the ground dries out the water goes out of the tank again.
The best solution is proper drainage patterns that keep water away from the leach field. An alternate solution used here when soil conditions are poor is to install a raised bed using properly selected sandy draining soil. It looks like large mound in your yard. The water from the septic tank is pumped up to the leach field.
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Old 02-13-2013, 09:44 AM   #5
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why do septic fields and tank get saturated


Thanks Joe...I understand your explanation with the coffee filter and garbage disposal. Those add solids to the tank.

Let me revise my scenario. The tank is emptied and all checks out 100%. For two months, the homeowner never puts a single solid into the tank. They simply take showers and do laundry.

So the tank only has liquid in it, and it's full to the inlet/outlet.

Then comes a heavy rain, and at the same time, all water use from the house is halted.

The tank fills up 100% and water backs up into the main drain line of the house.

How? And from where?
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Old 02-13-2013, 09:48 AM   #6
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why do septic fields and tank get saturated


If the leach field is not draining into the ground, where else it it going to go?
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Old 02-13-2013, 10:12 AM   #7
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No question rain water is coming back into the tank. I'm simply trying to troubleshoot whether this scenario would happen most largely from rainwater coming back in the outlet valve from the fields....or if somehow, water is directly entering the tank via some other means. Like there is a crack in the top of the tank, a lid has shifted under the soil, etc.

If excessive water is somehow getting directly into the tank - the the soil around the fields has nothing to do with it. Yet if direct entry of water to the tank is probably unlikely - then it is time to point at the fields/soil as the culprit.
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Old 02-13-2013, 10:38 AM   #8
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why do septic fields and tank get saturated


I need to add something here - real this time.

We have two fields with a diverter valve (Bull Run Valve http://www.americanonsite.com/american/catalog/brv.html).

I'm currently on my new field, which has very good drainage/sloping, etc. around it. Even in a typhoon, all the rain runs off and away and the ground doesn't get spongy.


The old field location, however, is toast. It's low-lying and has standing water during rain.


On the diverter valve (A, B fields) I've been unable to get it 100% over to A (our new field). Just 95% there. I spoke with the manufactuerer about this. Something could be stuck in there. Sand/dirt may have gotten into the top of the valve, etc. It's "easy" and cheap to replace. Lots of digging though since it's about 3-4 feet down in a standpipe.


Thus, 95% is going out to the new field and 5% still goes to the old field.


The new field is newer and high and well drained. It doesn't really make sense that the ground around it would get saturated to the point of backup, especially since "the best in the business" installed it.


But there is that 5% opening in the valve coming from the old field. It may perhaps be a 1/4 inch gap.


So if the old field (unused) is faulty or simply floods easily with rainwater, it it logical to think it could be like turning on a faucet back into my tank?


In other words, hardly any rainwater is actually coming back into the tank from my new field. Yet that 5% opening to the old field - could water be just pouring back into the tank?


I wish I had a tiny camera I could put between the tank outlet and the valve. Then wait for heavy rain. I wonder if I'd see just a ton of water pouring back towards the tank coming from the old field.


Could enough water come back in reverse from a field through just a tiny opening in the valve to quickly fill the tank and backup my system?


And in any scenario - I also wonder if my backyard is dumping "waste" into the tank - like a reverse system. I wonder if the field filters out dirt, sand, etc and only water pours back into the tank (and in reverse through the outlet filter) - or if it's mostly just water...
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Old 02-13-2013, 10:54 AM   #9
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why do septic fields and tank get saturated


denemante -

Where in the world are you located? Your profile does not give a clue.

Standards, profiles and local practices can vary according to the location. I don't think there are many "typhoons" in the U.S., which indicates you may have a system designed for localized conditions and a short term storm could cause problems.

What did the respected local system installer have to say about the situation?

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Old 02-13-2013, 11:14 AM   #10
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I'm in Atlanta....

I tracked down the guy who put in the new field (for previous owner) - the guy is very well respected. He didn't 100% remember my job and was only able to tell me what many say: "yeah, sometimes saturated field from heavy rain can cause the system to slow".

We don't get typhoons. But we have bouts of heavy/extreme rain - and this is when I have the issue. Thankfully it's only a few times per year. But unfortunately, it always seems to happen around holidays when we have guests here - and my wife is ready to move because she so embarrassed the basement toilet won't flush for her mother one morning.

I've seperately had at least a dozen other septic "experts" out but sent every one away. They were all obvious snake oil salesman telling me I needed everything under the sun. I balance what they all say against what I know and what I learn here.

I have 360+ days of a perfectly working system. Not to bad in my eyes. I was about to close the case and just say it is what it is.

But now I'm hopeful a real solution is at hand. The new field is well drained and is NOT flooding my tank with rainwater. Instead, a slight gap in the valve is allowing rainwater from the old/shoddy field into the tank. I replace that valve - problem solved? Only one way to find out.

I'm also hopeful it works because it still just doesn't make sense that a "state of the art" field (5 years old) installed by a pro would allow so much rain back into the tank. He did note that on any job he does, the soil it totally tested, prepped, etc. etc. etc. And he does all the grading as well. If you could see it - even during downpours - you can see that the landscape over this new field is just "right".
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Old 02-13-2013, 12:40 PM   #11
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why do septic fields and tank get saturated


Nevermind.
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Last edited by drtbk4ever; 02-14-2013 at 09:35 AM.
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Old 02-13-2013, 04:32 PM   #12
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why do septic fields and tank get saturated


If the leach field is saturated enough from storm water and is also not muchlower (downhill) from the septic tank then it can send water back to the septic tank.
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Old 02-13-2013, 11:23 PM   #13
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Allan - I believe and trust that you're right given that I'm experiencing rainwater impacting my tank.

But it doesn't make sense.

A field has to be downhill from a tank by design. How much downhill - I'm sure that's variable.

Imagine a large tank of water sitting out on the ground. Put a PVC pipe into the side about 3/4 of the way up, then angle that PVC pipe downward a bit. Water will rush out that PVC pipe until inside the tank it's level with that outlet pipe.

Now put a baby pool under the end of that slightly-down-angled outlet pipe and have the pipe go right into it.

The baby pool sits at a height about midway up the tank. The baby pool fills with water, of course. Fill the tank with more water, and more water flows into the baby pool until it overflows (purges). That's septic design 101.

Now introduce massive rain. The baby pool either fills, or was already full. But in no way could water flow uphill back into the tank.

Now start jacking up the baby pool. Now, of course water could flow back into the tank.

But you don't put square wheels on a car. Who would install a septic field nearly level with the outlet on a tank?

My system works fine 360 days a year - so in fact the fields must be downhill enough to make it work.

Come to think of it, I just can't picture any scenario where water could flow uphill.

The tolerance/variance for that would have to be less than the diameter of the pipe just after the tank outlet. During dry times, that pipe is empty and water flows easily downhill. During wet times, that pipe fills up and is suddenly 1/2 full of water, with more water wanting to come back into the tank, overpowering any that wanted to leave it.

Who would be idiotic enought to install such a major aspect around a home like this? Make the field 6 inches deeper - and it would seem that this issue would be impossible.

Yet - perhaps that's what I have in my backyard.

This begs a question. Why couldn't I install some kind of pump just after the tank outlet? So the water flows out of the tank into some other tank and is instantly pumped upward 4 feet. From there, it's released to the field.

Now, there is 100% no way for any rainwater to backfill my tank.

Yet if the fields are saturated as usual - that pump wouldn't be able to send anything else out. What happens then?
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Old 02-14-2013, 10:07 AM   #14
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wow I didn't think we had THAT much rain here in Atlanta! For those of member not from around here - we have a mostly clay soil which does not drain well. Visualize the perforated pipes sitting in a clay dish filled with water.... water that won't drain off very fast...

If your old field was totally saturated, you have to realize that "top" of the water is the top surface of the saturated soil on the old field, not the level of buried pipes themselves... water in the soil is pushing down the water in the gravel filled channels the pipes are in.

That water has been leaking back 24/7 for how long? I doubt the tank was 'completely empty' to begin with... and only has 1000-1500 gallon capacity.

The pipes in your field are more horizontally level than you visualize.... if the pipe in the field were downward sloped, all the water would collect at the end of the pipe instead of being evenly distributed throughout the field to allow for even discharge.

Perhaps switch back to the old field during droughts to give the new field a 'rest' sometimes?

Also... water runoff management... where did all the rainwater from the roof go? Is is directed far away from the septic tank field? General slope of the yard? Is it level, concave or convex? Pics of the yard, old and new site? Just curious....
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Old 02-14-2013, 10:18 AM   #15
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why do septic fields and tank get saturated


Quote:
But it doesn't make sense.
Ayuh,... It makes Perfect sense,...

It seems you just don't understand that water seeks it's own Level, 'n when the ground is saturated, that's the Water Level, until such time it soaks into the ground, or runs off...

If you have standing water, on top of yer drain field, I'd suspect the finish grade needs to be adjusted, so's the surface water, runs Away, insteada sittin' there, soakin' in, raisin' the water level of the drain field...

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