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Community and Q&A

Optimal Exit Location for Sewer to Septic System

idahobuild | Posted in Energy Efficiency and Durability on

I am working on the septic system placement for my house.  There are basic distance requirements in Idaho from the well of 100 ft. (partial circle on attached image) and other general requirements for depth of leach field and distance from structure.  What I am wondering is; are there any best practices for placement to make the sewage drainpipe installs better or easier?

The lot is about as flat as a lot can be (less than 2 feet elevation change across the entire width (600 ft.). 

I am thinking of using option 2 (out the front of the house) to make future access during cleanout of the tank easier — for truck access.  But I don’t feel like I want to sit on the front porch and see that lid out there.

Any advice would be greatly appreciated.


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  1. onslow | | #1


    There are several questions that arise. Where is the old septic field? Where is your old tank? Is the tank broken? How much depth of suitable soil do you have in the proposed areas. Do you know which form of leach field you are planning on? (the diagram infers two possible choices) Does the elevation change drop away from the direction of the well? What is the elevation below grade for the current waste line in your house? Can you provide enough pitch from house to a new tank without digging down too much?

    With a lot that flat the underlying soil profiles may be hard to determine without exploratory trenches. If you have a hidden incline of rock that slopes away from the well, I would use that feature to ensure the wells continued purity. If the well bore is sleeved down to bedrock the risk of cross contamination is probably minimal for either location, but better further than closer. Knowing the depth of the well and the water depth in the well would be handy to know. If the rock is highly porous go for the further location. If you know that a lower rock layer is present and tilted, do consider where the neighbors wells reside.

    Of greater importance to your design decision is the available soil depth and choice of leach method. If you fall under a local jurisdiction that requires an engineered system then you may be limited by requirements not covered in your question. In my location, the state regulates all septic installations and they have greatly altered requirements from past years. My percolation rate was not great, so providing capacity for 5 bedrooms resulted in my field size being quite large. Fortunately, I was able to use leach field chambers directly on native soil, which sizes the area differently from the more traditional perforated field pipes in controlled bedding. I also avoided bringing in a very large amount of approved bedding that a traditional leach field would have required.

    I have much greater elevation drop from the house to the septic field than you have so my exit elevation from house to tank is nearly below the frost line. The tank exit elevation and drop to first field distribution box also played out favorably given that my soil profile was just enough to meet code. My site is sandstone bedrock with 3-6' of over burden, so if I was a flat site there would be little room for the drops in elevation between house, tank and field. I might have been forced to put in a "pump and dump" system, a very costly option. I also believe that there are limits to the depth a traditional leach field may be set, so knowing your soil profile is critical. It will also help to know how much excavation work will be needed.

    As for the admittedly ugly above grade access hatches, try to make it part of the landscaping or hidden by landscaping. A planter box with a seating square on one end to cover the offending hatch will make your view from the patio more pleasant. If not that, evergreen shrubs can provide visual relief. Like the software people say, "It's not a bug, it's a feature".

    1. idahobuild | | #5

      Thanks Onslow - great input. We'll have a soil perc test done with the county health dept. and a geotech. firm will be on site the same day for foundation recommendations and soil test. At that time, and while the backhoe is on site, we'll dig some test trenches in the proposed locations for soil conditions and depth. I also hadn't considered the 'hide the lid' option. New construction, so no existing tanks/fields.

  2. Expert Member


    I've had tanks pumped that were +-40 feet below the truck and at least 100 feet distant. I wouldn't use proximity of the truck parking as a determinant. If the two sites are equally suitable, put it where you would most want it.

    1. idahobuild | | #6

      Thanks Malcolm.

  3. plumb_bob | | #3

    If the main issue is not enjoying looking at the tank, it is an easy matter to build a structure over it as part of the landscaping. In the past I have stacked rough cut cedar timbers to build a box on top, and the wife will put baskets of flowers on top. Looks quite nice. When it is time to access the tank, simply tip the box off.
    It is also an additional visual clue for snow plows or other machines when the tank is buried by snow in the winter.

    1. idahobuild | | #8

      Thanks Plumb_bob.
      Do you know if sewage generally creates a smell in the area around the tank?

      1. plumb_bob | | #9

        Sewage tanks should be well sealed so smells do not escape, and other things like ground water, pests etc. cannot enter.

        1. idahobuild | | #10

          Makes sense. Thanks Again.

  4. Expert Member
    BILL WICHERS | | #4

    Usually you try to put the septic system on the opposite side of the house from the well, to maximize seperation. You want the septic tank accessible for service, but you don't want the tank or the drain field in an area where there will be heavy traffic, and you don't want the truck t have to drive over any part of the septic system to get to it for service. I would try to get the system placed so that the truck can stay in the driveway and just run hose to the tank for service. If you call around to your local septic service companies, they can tell you how much hose they usually carry, and if there is any magic number above which they charge extra. Size things for maintenance while still protecting the system from damage.

    You can screen the lid with some shrubs, just leave one side open for access. You can also bury the lid under a thin layer of an inch or two of soil to make it "grass over-able", but still easy to dig up for service work (mine is this way).

    Your primary concern should be keeping the drain field well away from the house and in an area where it won't ever see heavy traffic. That means keep the drain field well away from the driveway, and also out of any utility easements. After that, I'd just try to put the drainfield as much "downhill" from the house as possible, if you have any amount of slope at all to your land.


    1. idahobuild | | #7

      Thanks Bill,
      I'll call around tomorrow and see what the service folks say.

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