Gravel Bottomed Tank? Do I Have a Leach Field?

[ski]

Hi,

Last time we had our leach field pumped, the septic guy gave me a "guided tour" of the tank (from the surface :) ), explaining how it was constructed and, for the most part, how it worked. I say "for the most part" because when he pumped out all of the liquid he was puzzled because he couldn't expose the bottom of the tank; instead he hit a layer of what appeared to be gravel. It was really mucky (as you might expect) and he was reluctant to pump that stuff out to (maybe) get down to a concrete tank floor that didn't actually exist.

He said the tank was well-constructed and that it was doing its job very well, but that this system may have been built in such a way as to have concrete cover and walls, but a gravel bottom.

There is indeed an outlet pipe visible from inside the tank, and I'm assuming it's going to a leachfield. Located somewhere. I think. Maybe. After reading some of the posts on this forum, now I'm not so sure we even have a leach field in the usual sense.

So this scenario raises a few questions for me...

1. Is it possible that a septic system could have been constructed in the way I described -- with a gravel bottom?

2. If this is a possibility, is there any danger of sewage/effluent leaching downward into the ground?

3. Short of digging up the yard, is there any practical means of tracing the outlet pipe to see if it extends to a distribution box/pipes further out in the yard?

[Phil H]

Anything is possible, but many things are more likely than septic tank with no bottom. I am wondering if it could be a cesspool. It might help if you described the tank.
Are the sides concrete, brick or something else?
Does it have a baffle or seperation between two chambers?
What are the approximate dimensions?

Just so you know where I am heading with these questions. Cesspools have pourous sides to allow the water to escape; often, they are brick. Septic Tanks need a baffle, cesspools do not. Around here, cesspools are cylinderical and they extned much deeper.

Local custom may use different terms than septic tank and cesspool. Around here they are distinctly differnt and cesspools are older design that allow water to escape through the sides and bottom. Septic Tanks are sealed and water only exits through the outlet pipe. The reason septic tanks have replaced cesspools is the cesspool's potential for contaminating ground water.

[joed]

Are you sure you were in the septic tank and not the distribution tank? The septic tank should have been solid bottom. It is also two parts. You need to open two covers to see the entire tank.
Septic systems will some times flow into a distribution tank and then the leach field. The distribution tank could have gravel bottom to act as a leach tank. I have never heard of a actual septic tank having a gravel bottom.

[ski]

I really appreciate your replies. I'm going to measure the tank, take a pic, and post the info a little later today. Thanks again. To be continued...

[ski]

Camera battery is dead so I made a diagram...

As you can see, the 11' x 11' tank is separated into two sections which I labeled A and B. I'll estimate that the tank was 7' - 8' deep, and I was told it had a capacity of 1500 gallons.

There are 2 manhole covers (not indicated) but which are located on the right side of each section.

The pipe I labeled "opening" was what the septic man described as the conduit for effluent to move into "A" while the sludge concentrated/settled in "B". I don't recall exactly whether one or both sections had the gravel bottom.

When we had the house inspected prior to purchase, the inspector wasn't sure what kind of septic system it was. He did a dye test but no dye percolated to the surface that he could see. He did say, however, that this was not necessarily a bad sign.

I await your comments, with my thanks!

[Phil H]

In my opinion, it is highly unlikely that your tank does not have a bottom. But, I have no idea why it has gravel at the bottom. But, if you are still curious about the bottom, the level in the tank will drop over time without a sealed bottom. If you don't add any waste water for an extended period of time, the water level will drop. If a heavy matt (scum layer) has formed on the surface of the water, you may have to break to determine the actual level.

I am a but of a dinosaur and old cesspools do not bother me. They become problems when they are close to a well supply, aquifer. All of the cesspools I have seen have not been close to a potable water supply. But, septic systems with sealed tanks are much better.

Finding a distibution box and leach field can be like finding a needle in the hay stack. The smaller the property, the smaller the haystack. If you had to hire a professional, they might try using expensive equipment or run a snake down the pipe and use a metal detector or listen for the snake. You might try probing the ground with a thin rod. Your sucess may vary. A couple guidelines. The people who installed would perfer to use straight runs of pipe. The pipe must run down hill.

[joed]

Your description is a septic tank. The gravel bottom is very strange though. I can't explain it.

[Bumblerazz]

I agree that it is a septic tank.

The gravel may come from the openings (or lids) when the tank was installed or from repeated openings.

I know ours has plenty of pebble/rock in the bottom as we have the lids buried. When it comes time to pump, the lids are uncovered and though we try to be very carefull, invariably earth and such falls in. I also think that the crew who installed our tank didn't spend a lot of time being carefull and when spreading gravel around after inserting the tank in the hole. Some may have been dumped inside.

I always get curious nervous glances from the septic guy when he comes to pump. I just smile and thump my chest as though to say "last nights dinner... whew!!" :)