Septic Tank Driveway

[Pirate]

Bought this house about 3 years ago. It was built in 1993. The tank is 8 feet from the back of the house, directly under the gravel drive for the basement garage. The other side of the tank is the gravel driveway to the front of the house.

I'm becoming worried about cracking this tank. Right now my son parks his small car in the basement garage. Last time I had it pumped out I put a 1/2 steel plate over the access hole since the cement cover was broken (another stupid move on my part, I should have used aluminum). I recently told him to stop parking in that garage and to not park over the tank.

I'm wonder is there is a way to pour a "bridge" or something over that tank so we can drive cars over it. I'm a bit pissed off the county allowed him to put the tank where they did. I was septic stupid when I bought the house so it didn't click in my giant brain that I may have a problem. Moving this tank would be a major undertaking as I live in the woods and don't want any trees cut down. I won't even bring up my drain field location.

I did some internet reading and only found one idea - put a riser on the tank access and then pave over area with thick concrete slab. I think that might work but I can't get past the riser idea. If a vehicle tire is directly on the riser, I think all of the weight is transferred directly to the top of the tank, thus I wouldn't put a riser on even though last 2 septic pumpers recommended it. Tank is about 2.5 feet deep, I don't mind digging the dirt/gravel off the lid.

 

[Oldtrout]

OK...Now how can we help??

 

[LBrown59]

Bought this house about 3 years ago. It was built in 1993. The tank is 8 feet from the back of the house, directly under the gravel drive for the basement garage. The other side of the tank is the gravel driveway to the front of the house.

I'm becoming worried about cracking this tank. Right now my son parks his small car in the basement garage. Last time I had it pumped out I put a 1/2 steel plate over the access hole since the cement cover was broken (another stupid move on my part, I should have used aluminum). I recently told him to stop parking in that garage and to not park over the tank.

I'm wonder is there is a way to pour a "bridge" or something over that tank so we can drive cars over it. I'm a bit pissed off the county allowed him to put the tank where they did. I was septic stupid when I bought the house so it didn't click in my giant brain that I may have a problem. Moving this tank would be a major undertaking as I live in the woods and don't want any trees cut down. I won't even bring up my drain field location.

I did some internet reading and only found one idea - put a riser on the tank access and then pave over area with thick concrete slab. I think that might work but I can't get past the riser idea. If a vehicle tire is directly on the riser, I think all of the weight is transferred directly to the top of the tank, thus I wouldn't put a riser on even though last 2 septic pumpers recommended it. Tank is about 2.5 feet deep, I don't mind digging the dirt/gravel off the lid.

It's not a good idea to drive over or park on the tank. as it could cave in from the weight.

 

[Pirate]

It's not a good idea to drive over or park on the tank. as it could cave in from the weight.

I know this. I'm looking for a solution to keep using the garage drive other than moving the tank.

 

[Tig]

Be careful with the riser idea, it could have the opposite effect of what you want to do. As you described it will focus the weight on the tank. Right now you have 2.5 feet of earth distributing the weight.
Something like curbstones upside down and flush with the ground would distribute the weight even further. You can remove them to access the tank. You could even hide them under 4" of gravel.
How wide it the tank? 2.5 feet deep is quite deep. Possible deep enough that there is no issue for a car.
What is the tank made of?
Just my $.02 CDN

 

[CurlyDave]

I am afraid that the safest thing to do is put a white picket fence around the tank.

I suppose you could dig footings on opposite sides of the tank for footings, and then build a bridge of sorts over it. The problem I can see is that one false move with a backhoe will crack the tank. I am not even certain that you could dig around that tank without creating a problem. The pressure of the earth on the sides probably counteracts the pressure from the liquid inside.

I would avoid a thick concrete slab over the tank. It will probably weight more than a car, and could crack your tank, especially while it is being poured when it has all the mass, but none of its final strength. While I can think of worse situations, the concept of several tons of wet concrete mixing with a thousand or more gallons of sewage, all right in my backyard gives me the willies.

The most cost-effective solution I can think of is a new carport or even a garage, somewhere else.

Explain the consequence of a collapse, with his car falling into the contents of the tank, to your son...

 

[Tig]

My tank is about 3' by 6' and made of concrete. I would not like it in my driveway but if it were there and 2.5' deep I would probably do the curbstone bridge.

 

[JB4310]

I'm no septic tank expert though I have 3 on my property, one of mine is about 2 feet below my back gravel driveway to my shop.
I never gave it any thought till reading your thread, but I honestly don't think you have anything to worry about with light vehicle traffic, I'm driving a 12,000 pound truck over mine. Mine's concrete reinforced with steel, it's already built like a bridge. Yours being 2.5 ft deep is added protection, might be more worried if it was very shallow.

Just have to warn equipment operators of the tanks location, I've heard of guys with tree bucket trucks finding them the hard way when all the weight is on an out-rigger on top of a tank.

If your not going to sleep well worrying about this though, I have a solution. Dig down about half way and lay a heavy plate of steel down, something like what they use to cover trenches in the road, 3/4-1" thick and 4'x8' wont be cheap but that would spread the weight, bridging the tank like you said to the surrounding area around the tank. you would need a hole in the plate for access which you could cover with steel also, Don't know why you would need aluminum, if your worried it will corrode? not in your lifetime. Cover it back over with the gravel you dug out.

You could do it cheaper substituting wood for the steel, screw 2 pcs of 3/4" PT or marine plywood together, could stiffen it up more by framing the wood platform with 2x4-6.

I know, wood in the ground, doesn't sound that great but I would think it would last many, many years.

If you did the riser and concrete slab, just don't bring the riser into the slab, have it just below the slab and have a recessed steel access cover in the slab, this way driving on the cover would not push on the tank. I personally think that's a little over kill going that whole route but it would make it easier to service the tank if needed..

Good Luck, JB.

 

[LBrown59]

Be careful with the riser idea, it could have the opposite effect of what you want to do. As you described it will focus the weight on the tank. Right now you have 2.5 feet of earth distributing the weight.
Something like curbstones upside down and flush with the ground would distribute the weight even further. You can remove them to access the tank. You could even hide them under 4" of gravel.
How wide is the tank? 2.5 feet deep is quite deep. 1*Possible deep enough that there is no issue for a car.
What is the tank made of?
Just my $.02 CDN

1* I wouldn't want to bet on that.
A few years ago a distant neighbor crashed his riding mower through his concrete tank while driving over it.

 

[LBrown59]

Explain the consequence of a collapse, with his car falling into the contents of the tank, to your son...

A neighbor of mine had to do just that only it wasn't his car it was his riding lawn mower.