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Septic Drainfield Layout & Shape

Septic soakaway bed / drainfield shape & layout guidelines:

This septic system design article discusses determination of a conventional drainfield shape or layout.

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How to Determine Septic Absorption Field Shape or Layout

Drainfields, also called leach fields, absorption beds, soil absorption systems, and leaching beds, perform the functions of septic effluent treatment and disposal in onsite wastewater treatment systems, conventionally called "septic systems".

We discuss several different conventional soil absorption systems: absorption fields: conventional trench, deep trench, shallow trench, cut-and-fill, and gravelless septic systems. Then we discuss septic absorption beds, and seepage pits.

Septic Field Shape or Layout Specifications: Septic Leach Field or Septic Absorption Field Design

Typical drainfield layout - USDA - DJFThe shape or footprint, of a septic system drainfield or leaching bed is determined by the following considerations:

Once we know the total area of effluent disposal system needed, such as

length in feet of gravel-filled perorated pipe trenches (or galleys or gravelless or whatever)

then the septic system installer will excavate to prepare the drainfield in a pattern or shape that divides that length into sub-lengths of parallel (or other) trenches or pits or whatever,

and the location, routing, etc. of these will be determined by the lot size and shape so that the necessary septic system components fit

AND are separated by the reacquired distances from one another and from site boundaries and other site features like the well or buildings, driveways, and the like.

The specific shape and dimensions for a specific property, soil characteristics, and septic system type can't really be specified precisely here since we know the detailed answers to the septic system drainfield design considerations listed above.

But we have posted addition articles on septic system drainfield design that give the general septic system specifications that should be helpful.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-09-18 by Anonymous

thank!
But what if the mound is made with sand, then gravel. Will the sand be tamped before this or not? If so, how to do it correctly? Is it enough to spill sand with water or just tamp with an excavator bucket?

And is it possible to do without a junction box if there are 3 pipe lines of 20 feet each? How will it be correct?

On 2020-09-16 21:50:53.246179 - by (mod) -

Sasha

If the excavator digs the trench too deeply or unevenly and if the soil is not subsequently-compacted, the risk of subsidence as you describe is quite real. Moreso with flexible piping systems.

Properly the trench bottom is on virgin soil or on compacted soil or fill, along with being set on and surrounded by gravel (except in a "no-rock" system)

On 2020-09-16 by sasha

How to avoid sagging (deflection) of the pipe as a result of soil subsidence? This can happen with a new trench or mound system after backfilling with gravel and soil. I'm afraid the pipes will sag and the field will absorb unevenly gray water.

On 2019-09-04 - by (mod) -

If the drain line slopes 1/8" to 1/4" per foot AND is laid out so as not to have trouble from spots of too much slope it should be ok

For a distance that far - 280 ft - I'd expect the installer to have put some cleanouts along the route- good spots to take a look at what happens when you flush solids down the john.

On 2019-09-04 by Anonymous


My septic tank is 15' feet from house following leach is 280' feet away from Septic tank and farthest end of leach field is almost 7' foot drop in elevation. Wisconsin Leech field was built on slope. Downward end of field has a mound spanning the length of leach field. (Supposedly to deter runoff, but...)

On 2018-09-15 - by (mod) -

I don't know of a fixed number.

The maximum distance is going to depend on the site, size, layout, slope, and dips involved. After all your effluent has to drain by gravity so the slope is typically going to be a quarter of an inch or perhaps an eighth of an inch per foot.

On 2018-09-14 by Tony

What is the maximum distance a leach field can be from tank discharge

On 2018-06-15 by (mod) - How far from someones property ine can a septic drain field be

See SEPTIC CLEARANCE DISTANCES

On 2018-06-15 by Anonymous

How far from someones property ine can a septic drain field be


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