I have a 28 year old concrete 1000 gal. Dual chamber septic tank that shows evidence of flooding after big rains. It is NOT the drain field backing up (which is way
Downhill, because I tested the tank with a 50 gallon rush of water that it
Handled flawlessly). I am thinking not only is it taking on water through the
Vent stacks in the house, but also the two old access doors on each chamber,
And maybe loosened tees (except there is no smell or accelerated growth).

Should I seal the doors with plumber's putty or something? The water/scum/sludge levels
All appear normal except the baffle shows evidence of a "wave" having
Gone over it after a flooding rain, with some solids going down the
Outlet tee (which I must try to prevent). Any help would be appreciated as it has
Taken me two weeks to dig for access because I have been in physical therapy
For decades and depend on assistance, and a big hole sits open as I write this.

Thanks to any of you knowledgeable septic people...

Where's your rain water run off directed to? Is there any rain water pooling over the tank after a rain? Anywhere? If you seal off the inspection ports on the tank the only places water can enter the tank would be from the house or back from the drainfield. That is, unless you have a break in the house drain to the tank or at the manifold at the other end. This hole. Is it above a inspection port? How deep is it? Somewhere you have a opening in your septic system that shouldn't be there. You say the drainfield is downhill from the tank. Can you give me a degree of fall? A little? A lot? Let me know. Tom

There are 2 main reasons septic tanks overflow:

1. Rains. Soil is saturated with rain water unable to absorb any more water
2. Heavier Usage than Usual: More people in the house using bathrooms and/or more plumbing fixtures added since original septic installation

In both cases, you should have it pumped out to prevent further overflowing.

Back to you. Milo

Thank you for the quick response(s). I hope this message doesn't get capitalized at the beginning of every line like my last. There is a vertical clean-out from the house drain about ten feet in back of the house, and the tank is a couple feet beyond that. The tank has two concrete square doors in the top that are buried down about two feet, and the whole tank is in a natural watershed area from the rear house roof , all surrounded by concrete walkways, so the area might hold water but no water has ever visibly pooled there. I have not dug up the inlet and outlet tee connections to inspect them for leakage. Should I? The drain field is composed of two level 100 ft. laterals about three acres away gradually downhill about 5-6 feet total. There are two clean-outs at the end of these that are always dry (however, I must add they are just "stuck on elbows 3 feet down" to the ends of perforated 4in pipe, not cemented, so they would drain on their own anyway, like if I pour water in them it disappears fast). I am considering pumping but it is has maybe only a quarter inch of solid floating in the outlet partition, and maybe 3-4 inches in the primary holding area before the baffle, and almost no detectable sludge level at the bottom.
The second concrete door allows me to inspect both chambers. It sat open today as I observed stress usage: multiple showers, dishwasher, toilet flushing, etc. a little over 50 gallons in 50 minutes... the level stayed the same in both chambers and clear liquid easily flowed to the field. Yet after no rain in weeks, then one 3in rain, I found the baffle had been overflowed since solids were left on top of the baffle and no doubt had gone down the outlet tee. I noticed when I removed the concrete door it looked like there was really old putty around the opening to seal it, as the corners have worn way down over the years and soil sits in them. Would that be standard plumber's compound?

Let's see what we have so far. We have a drain field that's 5 feet lower then the tank. The terminal end of the drainfield branches are dry when the tank floods. Am I correct so far?
Now we have a 100 gallon septic tank that floods out at every heavy rain. Logic tells us that if the tan's flooded that it's backing up at the house in let but I wonder what you'd find if you dug up the manifold at the discharge end. Another factor is the fact the tank sets in a water shed. The very fact that at one time someone sealed off the inspection ports tells me that this has been a ongoing problem. I would seal off the ports. I don't know how long plumbers putty would last. How about troweling in thin-set or mortar to just cover the edges of the ports. That's the first thing I would do. If the tank sets in a watershed you don't want any places open for rain water to enter.
BUT, I keep coming back to the outlet manifold. What's the drainfield doing while all this flooding's going on?
Is it overloaded and backing up" It doesn't seem likely wit a 5 foot drop. However, it's a possibility that must be looked into. At this point ALL the possibilities must be checked out. Have I given you something to start with? Let me know, Tom

Thanks for some clues here. Yes, here is a pic of the 1000 gal (not 100) tank with the second access door shut. You can see the lid is cracked on the corners (2 are missing and a third is a large removable chip).

https://www.askmehelpdesk.com/attachment.php?attachmentid=39539&stc=1&d=1332788391

It is also worn down on the inside of the lid (the baffle is also deteriorating on top a little). I haven't inspected the other lid. It took me all day to dig this hardly impressive hole (then all the next morning in a hot tub, so I am trying to keep things to minimum).

If I seal these with mortar the idea would be to chip it out of there to do
An inspection or have it sucked out?

Also, by the "outlet manifold" are you referring to the tank outlet tee or the place where the pipe from the septic joins the drain field? I have a crude diagram of the original approval and it shows no distribution box, but a single pipe feeding drain lines in series, and it is not obvious where to start digging for that junction.

, by the "outlet manifold" are you referring to the tank outlet tee or the place where the pipe from the septic joins the drain field? Yeah! I guess the "outlet tee" would cover it.
A manifold can be any fitting or fittings that divert the tanks outlet to the different drainfield branches.

You can see the lid is cracked on the corners (2 are missing and a third is a large removable chip). If the tank's in a water shed I can see now how the rain water gets in. What so you mean. "two are missing"? Dig up all around the tank top and caulk with thin set ot motor ,(not putty) and seal off all those open cracks. If you make the tank top water proof I bet you'll survive the next heavy rain. Good luck, Tom

Thanks, I have started on this less-than-pleasant project by hauling up a bunch of old metal roof panels to cover the digging in case it rains which ought to take me about month (small issue with knee pain after digging in leg braces... I will report how this works and award credit as deserved). I have never seen a cement septic tank before this one. I assume the "tank top" is a single slab full of rebar that has a seam all around joining the tank bottom, and that's what I'll be sealing up(?) The tank doors should be a lot simpler, but please correct my stupid concern: when I seal them with "thinset mortar" that's like sealing doors shut that three years from now I'll be cold-chiseling open again to inspect and have the tank sucked out (because putty or mastic instead would liquify)? If that's what I have to do so be it (... I might mercifully die in the meantime and not have to face this again).

I'd hire someone or perhaps a good friend to dig up and bare the surface. Mortar isn't as hard as cement so opening the ports shouldn't be all that much of a hassle. Unless you want this problem to continue I'd not waste too much time go bye until you got started, Good luck, Tom

May I offer some thoughts here?

The first is that your test of 50 gallons of water in a 50 minute period in a 1000 gallon tank is not a valid test of how much water it takes to make the baffle overflow at a rate sufficient to carry solids over the baffle. That's only 1 gallon a minute and it would take a lot more than that.

The second is that I don't think that rain water in the vent pipe would provide that kind of flow either. You didn't say in what period.

You certainly can be getting ground water in the tank through the inspection holes but it seems a bit much to get enough water through the soil and through the cracks in the inspection holes to cause the tank to flood unless the flow of the output line is restricted. A 4" pipe will carry a lot of water. Normal usage might not reveal a problem but the added ground water might.

Does removal of the access panel make the input and output opens accessible? If so I would first snake the output line just to make sure that it is clear of any obstruction, although I don't know how far 3 acres is.
Next, I would block the input line and run as much water from the house as possible. If the input line doesn't back up with water that would indicate a break in the line. A break in the line might be the source of the ground water. Granted it would take a break, not just a leak to to allow enough ground water to enter to create this problem. Depending on how far underground the pipes are, you might not notice signs in normal use. Depending on terrain, ground water several feet underground could be under pressure which might explain the volume. Next I would dig around input line where it enters the tank and make sure that the pipe is sealed to the tank.

Apparently you do have ground water entering the tank but that would have to be at a tremendous volume to create this problem unless the output is restricted.

Finally, I'll differ with Tom and recommend that you clean all dirt on the tank surfaces around the edge of access panels, apply a bead of silicone or construction adhesive and then cover the access panels with some rubber shower pan material, embedding it in the adhesive. Doesn't have to be water tight, just sealed enough to prevent a volume of water from entering. Be a lot easier to remove than motor.

I'll agree with Tom, hire a laborer. Cost less than the therapy that will be needed if you do it yourself.

Dear hkstroud:

You've given me a lot to think about. Let me answer 4 of your questions:

1) I got the idea of the test from a library book. Unfortunately I had no way to measure volume except by standard household usages. I can tell you this: 40 of the 50 gallons flowed in the first ten minutes when the tank didn't even show a gurgle. The last 10 gallons was the dishwasher which took a long time to finish.

2) There are 3 vent pipes and we got about 3 inches of rain in an hour after it had rained a handful of times following a prolonged drought.

3) I snaked the septic outlet pipe 40ft. It came out clean with no resistance but it is hundreds of feet to the field. It has occurred to me that there is so much pipe even a slow field may function pretty well. I also ran a garden hose full open down it for 5 minutes and it all went down with minimal splash-back. As far as the input line, there is a vertical clean-out two feet from it that always has a small amount of water in it. The input tee itself is only accessible from the septic door I have yet to excavate but if it is a tee and under the tank lip like the output is it might be impossible to truly close it for testing.

4) An untold story. A month ago the water pressure in the whole house dropped. After extensive troubleshooting I pinpointed this fractured cut-off under a patio the former owners had impolitely poured:

https://www.askmehelpdesk.com/attachment.php?attachmentid=39603&stc=1&d=1333034852

I have tried to upload this 3X and ht URI keeps changing (it shows up on the page and later disappears) but it is not critical.

I dug under this concrete slab on my belly to take this flash picture which my wife took to Lowe's to figure out what this even was. When I pulled the pipe at one end it came out like it had rotted off. Point: this is the water main to my house, 10 feet from the septic. Now it becomes clear that the septic line runs deeper directly under it and makes an elbow just a few feet past this patio. While the well line was repaired with an accessible union it didn't seems all that saturated, but there is no telling how long this pipe lost water before failure was noticeable, and the only way I surmised the location were some palm trees growing wildly faster that some others of the same age, yet the grass was no longer. I wonder if the pipes or septic floated/shifted/flexed now that you mention this deeper water pressure theory. Maybe it's still down there?

Looks like I will have to dig up/inspect the input tee next.

Yes, I would love some help but I am in a remote area and the few who are willing to come out get a load of me and the price seems to triple... I finally have a lead on a person to dig finally. There is an oil boom in this area and there are no workers... the average HS graduate makes $$$ and it is hard to find any workers for anything... also any place to stay... people are renting space for RV's to house everyone.

So thanks for these further insights, they are appreciated; I'll be following up with findings and pictures if they will attach!