Placing house in relation to existing septic tank, drainfield

[susanneb]

We will soon be building a small house and removing the old "tin cabin" (mobile home). Well, septic system, electricity and phone are already in place; a septic tank sized for a 3 bedroom house was installed in 2004. The drainfield is in excellent condition.

We originally planned to build the new house on the same footprint as the mobile, but logistics would be much, much simpler if we could wait to remove the mobile until after construction (or perhaps keep it as a storage building). We are limited as to where we can build, but we have an alternative building site that is equally nice in relation to access, drainage, views, existing trees, proximity to neighbors, etc.

The septic tank is roughly 15 feet away from the mobile home, with the drainfield running parallel to (lengthwise) and away from the end of the mobile. Our alternative location would be on the same side of the drainfield, but at the opposite end. Both sites are level with the drainfield.

Can we attach to the existing tank and drainfield from this position, or are we limited where we can site the house in relation to tank and drainfield?

I realize our county building department has the final say, but I'm hoping to get preliminary opinions on whether or not this is do-able, cost-effective, and/or ultimately wise. My uneducated thought is that we would just trench back to the tank (about 40 ft), and then the tank and drainfield would function as they do now, but what do I know?

Are there issues I'm not considering here? Any ballpark guesses on cost?

Thanks for putting your minds to this.

[Stann]

I got my septic done recently, in 2010. The permit cost $567. I'm in Coos County. It's actually DEQ (Oregon Department of Environmental Quality) who controls septic usage. Obtain a “Repair Permit”, which is less demanding than the other “New Septic” permit. For the new home, they'll probably require DEQ sign off your septic and a the permit to change or trench to the drainfield.

The house must be at least 10 feet away from the drain field and underground utilities must be at least 10 feet away from the drain field. The driveway must be at least 10 feet away from the drainfield.

For gravity fed systems, the distance from the house to the tank, yours is 40 ft, requires that the pipe elevation drop at least a certain number of inches. I don't know what that number is. You may want to ask a septic tank contractor that question before you go to DEQ... it's best to get it right the first time!!!

Good luck!!!

[Pouncer]

So, you want to run your discharge line from new location, to current installed one, no problem usually. However, your local regulators may require an additional cleanout (or two) to make that 180 degree turn back to the inlet. I've seen septic intalls at over 100 lineal foot to tank, or to drainfeild before, so it's possible-don't know whether it is okay in Oregon though. Typical drop on the line here is 1/4 inch. Too shallow, the pipe does not drain. Too steep, and the liquids outrun the solids over a lengthy run of piping. JMO.

I am sure the septic experts will chime in shortly

[Cabin Fever]

In Minnesota, the minimum required slope for a 4” sewer line from the home to the septic tank is 1" per 8ft. If the length of sewer pipe is greater than 50-feet, the minimum slope is 1" per 4ft. These slope requirements are for gravity flow, not pumped sewage.

In your situation, “long sweep” elbows would be needed for the two 90º bends in the sewer line to the septic tank inlet. And, I’d suggest two cleanouts. (One cleanout is required for every 50 feet of sewer line length.)

Keep in mind, the distance from the septic tank inlet to the new house may be only 40 feet, but the actual length of sewer line needed may be closer to 50 feet. Assuming a 50 foot length, the horizontal run of sewer line would have to start at an elevation 12.5 inches higher than what it currently is in the trailer home. (50’ x 1"per 4’ = 12.5") So, hopefully the new home would be built at a slightly higher elevation than the current trailer house.

[SteveO]

Cabin Fever I think you meant 1inch in 8ft or a max of 1inch in 4 ft if the slope is to steep your solids will not go with the flow if you know what I mean.

You need to know how deep the inlet to your tank is than see if thereis enough slope to get where you want to go. Who wver is going to put in the new house fountaion should be able to check that for you.

Steve

[Cabin Fever]

DOH! I should stick with the soil end of things! I'll go back and amend my post.

Thanks!

[gila_dog]

You don't want to be driving cars over your septic tank. Over the drain field isn't too bad, but not over the septic tank itself.

[susanneb]

You guys are wonderful -- thanks for the great information!

The tank and drainfield are well away from the driveway -- they are under the lawn/meadow, so nothing would be driven over heavier than a lawn tractor. The sewer pipe from house to tank would run along the edge of the driveway. Will the sewer pipe need to be protected from the occasional errant drive-over?

I'm searching for the copy of our septic permit, which is somewhere on my computer...hoping they include info on height of input.

[texican]

Originally Posted by gila_dog

You don't want to be driving cars over your septic tank. Over the drain field isn't too bad, but not over the septic tank itself.

Tractors either... ask my father's ghost why! He mowed for decades over one of the septic tanks at our home... till one day, he and the tractor 'fell in'.

[Robotron]

Septic tank at my place was placed center of the drive. Of course this was done probaly 70-80 years ago. Also the tank is much thicker concrete wise than anything I have seen for sale. Hatch is over 12 inches thick. Also I would not drive anything larger than a lawn tractor over the fields. This is where compaction can lead to serous problems.

[susanneb]

As stated, the tank and drainfield are safe from all except occasional mowing (with us, that can be very occasional...).

[Stann]

Tip for finding the existing septic pipe pathway location from the mobile home to the tank... Oregon law requires that a length of wire be placed on top and following the path of the pipe (usually black plastic pipe) so that a metal detector can be used to detect, find, and identify the pipe's path. The contractors call it "green wire" and it's about 18 AWG and underground rated (the color look's blue-ish-green , to me lol). Good luck (haven't tried the metal detector searcher, myself )

[Ross]

If you go with a pumped system (the house drains into a tank and it pumps to the septic tank/field) you have a great deal more options where to locate the house. You shouldn't drive on the tank or field, in my experience. pvc pipe is not very strong.

[Robotron]

If you need to drive on PVC pipe you need to get schedule 80 pipe. The cost is about $25 per 10' length. DWV pipe is way thin to hold any weight.
Schedule 40 pipe is what I use where there is no load.

[meanwhile]

I do not know the rules about where to place the drain field but I do know that when we moved here there was a nice big garden used by the former owners. After we moved in we found a huge pile of leaves covering a wide area behind the garden. When we started to rake and clean it up. there was standing water that smelled horrible! It was septic water.

We called the man who had put in the septic and drain field for them and he said they had deliberately put the garden over the drain field and made it drain where they had planned to put fruit trees! We had to get him to bring in a couple loads of dirt to cover the area. It was a nasty mess.

So - be sure to protect the drain field so that nothing comes to the top.