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-   -   rain water entry direct into septic tank? (http://www.diychatroom.com/f7/rain-water-entry-direct-into-septic-tank-174342/)

denemante 03-12-2013 10:51 PM

rain water entry direct into septic tank?
 
Hey all - it's a long story, but I'll cut to the chase. Our basement toilet doesn't work in times of heavy rain because the septic tank floods with rainwater. A new field was installed 4 years ago with excellent grading above it. But the old field is still there. There is a diverter valve between them. I was lucky enough to have the guy who installed the new field over today.

I'm presently running on the new field. I thought the diverter valve was faulty and halfway between both fields. The old field gets boggy above it, so I figured rainwater was coming back from the old field and entering my tank.

Not so, according to him. He thinks everything is probably working as it should, and I'm 100% on the new field. Given the grading and new-ness of the new field - it should purge well even during rain and not backfill my tank.

Instead - he thinks the area over my old field - which will have an inch+ of standing water in huge areas during heavy rain - is just sort of generally funneling water back in the general direction of the tank. That unused field still fills with water - and since fields purge, water from 50-70 feet away from the tank enters that field from above - and makes it's way back to the portion of the field right near the tank.

He says that tanks are not 100% watertight, so lots of water right around the tank could in fact be what's flooding it (not water entering directly from the fields backwards into the outlet fields.

He said the low area over the old field and the boggyness of that ground is where he would start - regrade and create a natural slope down off the back of my property to keep that old, unused field dry.

It's a lot of work, but I don't know what else to try. I can't believe that there are enough places for water to enter my tank aside from the inlet/outlet valves that it would fill up. But maybe so.

I don't know whether the inlet and outlet pipes in the tanks just run through, or are caulked tight. But both would seem to be below the water table during heavy rain. I thought perhaps I should dig them up and somehow seal them - but he thought no.

Could regrading, given this scenario, be my solution?

TOOL82 03-13-2013 07:22 AM

Your tank could be leaking from many places & septic tanks are supposed to be watertight
If it is a mid-seam tank they have been known to leak at the joint.
If the access cover is buried or if has a riser could be leaking at the top slab.
How old is your house?
Did they replace the outlet pipe from the tank to the D-box when they put the new field in ?
The outlet pipe could be partly clogged.
When your basement toilet is working fine check where the water level is at the outlet pipe inside the tank.
It should be at the bottom of the pipe.
If the pipe has water in it. It has a clog.
If the pipe is cast iron or orangeburg replace it.

denemante 03-13-2013 09:55 AM

The tank/house is 15 years old. Two cement access covers are buried in the dirt. Can't speak for the condition of the outlet pipe, but when I had the tank emptied, the outlet filter was perfect and the tank otherwise got a clean bill of health.

When everything is working, the water level in the tank is in fact at the bottom of the outlet pipe.

When the basement toilet slows down during heavy rain, I can open the washout access point (before the tank in my patio) and it's full - meaning the tank is 100% full and the main drain is full and backing up towards my house. As soon as the rain subsides, everything goes back to normal and levels drop.

If this guy's theory is right, volumes of ground water around the tank are finding their way into it. He said that yes, ideally the tank would be totally sealed - but he said it's never really 100%.

So my question is....is it reasonable to think there are access points for water into the tank, and while not ideal - they aren't really a problem - so long as the tank isn't surrounded by ground water?

His other point/theory was that regrading was the easiest "fix" and the fact that I have standing water in my backyard during heavy rain is definitely an issue that needs to be fixed regardless. So I should fix that and see what happens.

He recommended surface grading. I suggested a french drain ( I already have a few and all my downspots run to corregated pipe under my backyard. So I figured I could locate a run, add a french drain in the trouble spots, and tap into an existing corregated pipe run. He didn't like this idea as much because he said they could be 10 foot sections stuck together and may already be leaking a little underground at those points. And they may not be able to handle all the new water.

TOOL82 03-13-2013 11:06 AM

Quote:

Originally Posted by denemante (Post 1136199)
The tank/house is 15 years old. Two cement access covers are buried in the dirt. Can't speak for the condition of the outlet pipe, but when I had the tank emptied, the outlet filter was perfect and the tank otherwise got a clean bill of health.

When everything is working, the water level in the tank is in fact at the bottom of the outlet pipe.

When the basement toilet slows down during heavy rain, I can open the washout access point (before the tank in my patio) and it's full - meaning the tank is 100% full and the main drain is full and backing up towards my house. As soon as the rain subsides, everything goes back to normal and levels drop.

If this guy's theory is right, volumes of ground water around the tank are finding their way into it. He said that yes, ideally the tank would be totally sealed - but he said it's never really 100%.

So my question is....is it reasonable to think there are access points for water into the tank, and while not ideal - they aren't really a problem - so long as the tank isn't surrounded by ground water?

His other point/theory was that regrading was the easiest "fix" and the fact that I have standing water in my backyard during heavy rain is definitely an issue that needs to be fixed regardless. So I should fix that and see what happens.

He recommended surface grading. I suggested a french drain ( I already have a few and all my downspots run to corregated pipe under my backyard. So I figured I could locate a run, add a french drain in the trouble spots, and tap into an existing corregated pipe run. He didn't like this idea as much because he said they could be 10 foot sections stuck together and may already be leaking a little underground at those points. And they may not be able to handle all the new water.


Then I would grade the backyard & add polylok risers to the 2 access holes.
To add Polylok risers you dig down to the top of tank, remove the concrete covers, attach a starter ring by silconing the ring & screwing it to the tank with tapcons, then add risers until you reach about 6" above grade & put polylok cover on the last riser.

You can get them from Polylok or from a local septic tank dealer.

jagans 03-13-2013 11:23 AM

A pretty smart guy once told me that people listen to those that they pay. Apparently the gentleman that gave you the advice to regrade so the water runs off your property did not charge you, so you aren't going to listen to him, and you are going to do it your way.

If you go outdoors and stand where your system is located, and everything from there is uphill, you are sitting in a bowl, and it needs to be corrected.

You need to think like water. I know this sounds funny as hell, but try it. Water seeks the easiest route back to the sea. I don't understand sealing the tank, as water can flow back into the tank from the leach field, can it not?

denemante 03-13-2013 11:57 AM

The gentleman I had out did come by freely. And he's an educated and very nice guy. My only concern about him is that he is the same guy who installed the new field and did septic work for my previous owner 4-5 years ago. And now I have problems. So in the back of my mind, you have to wonder a little whether he's thinking "man, I really screwed this job up - what problems this guy has - I can't admit that - gotta shift focus - hey, grading! I'll get him thinking about that which keeps my reputation clear. Plus, I'm out here freely, so that goes a long way too." Not like I could hold him liable or anything. But still...

There is no question - one area of my backyard over the old field has become a bowl. And I do buy his theory that even though that field is not in use, it can still take on water and effectively pipe it back 60-70 feet towards the vacinity of the tank. The real question is whether that matters. It assumes my tank has leaks - enough so to allow a normally working tank to flood quickly during rain.

And yes, on my new/currently used field - sure - water can come right back into the tank through the outlet from the field. To me - that just really seems like the easiest entry point - not some general leaks in the tank where groundwater enters directly.

Yet that new field was property designed - and the area over that field is graded perfectly. The entire area is a slight hump, and the runoff is great. That's another reason why he thinks that's not the main point of water entry.

What frustrates me is that even if I do a major regrade of my backyard and get perfect runoff - I'd still think some water would enter the ground, and I may still have the same issue.

Or - maybe it is the new field allowing water into the tank through the outlet. Or maybe there is a break in the lines somewhere around my tank.

I suppose it's just a process of elimination, and unfortunately, the regrade does seem like the only logical first step.

AllanJ 03-13-2013 03:06 PM

First order of business, stop water from pooling up over the septic tank and over the leach fields. Regrade as needed.

You can install a French drain consisting of buried perforated pipe bedded in gravel. It must be below the level of the pipe going between the septic tank and leach field. Don't forget that any water that collects in the perforated pipe must be channeled someplace away from the house and, if the water does not emerge onto the ground surface somewhere downhill then you need to have a dry well with a sump pump out there.

denemante 03-13-2013 03:52 PM

Thanks Allan - regarding the french drains - why the gravel? Those black corregated flex pipes should be watertight so what would gravel add/do?

Secondly - I'd have to get a laser level, but my entire backyard has about a 4 foot grade across the entire 170 foot width. The tank is buried in about the middle where this is about 2 foot grade. But of course, the tank inlet/outlet is buried probably 3 feet.

Moving away and "downhill" from the tank go the fields. Across this area it generally flattens out. I already have two french drains in the vicinity, and there are 2-3 downspout drains - all run all the way across my property and into a far drainage ditch.

The boggy area in question - ground level is still probably 2 feet or so above the inlet/outlet of the tank about 50 feet away.

Thus - no reasonable way I see to put the french drain lower than the inlet/outlet of the tank without sinking the french drain about 2+ feet down. And keep in mind this is over an old septic field.

Isn't the real goal just to keep these "bowls" from harboring standing water, and simply to assure as much water as possible flows across the land (or into French drains) and is moved away from the tank?

One other note - any idea how much water a standard French drain can take? The ones I have appear to be about 1x1 foot boxes set at ground level, with the 4-6" corregated pipe running buried off the back of my property. If I repeat this in my boggy area, would one be enough?

Of course - I could skip them and rent a bobcat and just regrade from the boggy point downhill off the back of the property.


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