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Just Where to Look to Find the Septic Drainfield InspectAPedia®  -

• How to find the septic drainfield or leach field - where are the most likely locations?
• Where to look to find septic system components - key visual clues help locate septics
• What visual clues tip off probable location of septic components

This article and our accompanying septic system location videos explains how to find the leach field or drainfield portion of a septic system. We include sketches and photos that help you learn what to look for, and we describe several methods useful for finding buried drainfield components. (Septic drain fields are also called soil absorption systems or seepage beds.) Also see How to Find the Septic Tank.

The septic system video#3 at right describes walking an 18 year old homesite by a lake to find the septic system components. We observe one area that by its space and absence of trees and rocks is almost certainly the drainfield location - a fact later confirmed by the owner. This particular drainfield is uphill from the septic tank and the home which it serves. A septic pumping system will be needed. More videos on septic system location & maintenance are at SEPTIC VIDEOS.More videos on septic system location & maintenance are at SEPTIC VIDEOS.

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This is a chapter of Inspecting, Testing, & Maintaining Residential Septic Systems an online book on septic systems.

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Visual Clues that Indicate Drain Field Location

Where should we expect to find a septic system drainfield or leachfield when we're exploring an existing homesite?

Suppose we have no documentation and no idea where the drainfield is located. You can walk the building site looking for where a septic field could possibly be placed based on space, soil, and terrain conditions as well as distances from property boundaries and from a well if one is present. Our video at the top of this page gives a site walkthrough example of that procedure.

If you cannot find any candidate locations for a drainfield, go back to "square one" and start with our Septic Tank Location article. Once we can find the septic tank itself, the septic tank outlet defines the location of the effluent drain line that leads to the leach field. But remember that a drainfield may not be installed at all. There could be a seepage pit, or nothing, yet the septic system may appear to be working, depending on the level of its usage and soil characteristics.

An experienced contractor or inspector can often tell where the leach field is by a simple visual check of the property since s/he knows the typical size, elevation, and soil requirements - in other words, we look to see where a leach field could possibly be fit at a property.

In the photo our client is pointing to a filled-area at the front of his home - which we determined was the probable drainfield area. Unfortunately the installer put his fill right across a creek bed (look in the upper photo at the natural lay of the land). So the drain field did not have much of a life before its effluent leaked into groundwater, appearing in our test as pink-dyed effluent in a nearby stream.

Our article Absorption Field Design discusses how to locate the septic field and how to determine septic field size for a conventional drain field. Knowing these most basic design considerations can tell you where to look for septic fields at a building site by knowing where a working field might be expected to be installed.

If a property has an alternative design system such as a mound or raised bed or other special absorption field designs, those will be more obvious as a terrain feature. You'll see a rather large, rather flat area of raised soil or filled soil on the property. Sizes can vary widely but a small constructed drainfield made of fill might be 30' wide x 50' long. In the photo a two-level or "tiered" septic mound was installed perhaps 20 years ago; the lower mound is visible in the foreground. The shrubs are a bit close to the septic field, which we found was in failure - dyed septic effluent appeared in the driveway in the close foreground, and could be seen quickly in this drain basin intended we were told to remove water from the driveway. Actually it was removing septic effluent from the drive.

There may be good visual clues that indicate the drainfield location, especially if you know what to look for.

Areas Cleared of Rocks and Major Trees Often Marks the Location of an Older Drainfield

This older and mature lawn is free of large trees and rocks though those items are found at other areas of this building site. This is where we expected to find the septic tank and drainfield.

Often it is possible to see long parallel depressions which mark leach field trenches. You cannot see them in this photo (a tank and seepage pit were found later) but you can see them in the next section of this article. These depressions are caused by earth fill settlement over the drainfield trenches.

They may be visible in systems of almost any age. Long parallel depressions, perhaps 24 to 30" wide and many feet long, perhaps 20' to 40' and spaced perhaps 4' to 6' apart are suggestive of drain field trenches.

Wet Areas may Show a (failing) Drainfield Location

It's too bad, but sometimes the leaching bed or drainfield location becomes obvious because it is in failure mode.

If a drainfield is failing by pushing effluent to the surface that is a rather obvious clue of the field location.

The effluent breakout most-often occurs at the low-end of the failing drainfield line(s), but it can occur anywhere that a pipe is clogged, damaged, or leaking. In this photo, which we discuss in more detail below, the septic system failure and thus the septic field location was visually evident even under deep snow cover.

Often it is possible to see an area of raised-fill which was built to house the leach field.

Visual Clues to Location contains additional clues that telltale where you can expect to find the septic drainfield.

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SEPTIC DRAINFIELD LOCATION
  Why Look For the Drainfield?
  Using Septic System Records
  Where to Look
  Areas Not Likely
  Locate Piping Precisely
  Excavating to find Drainfield
  Surprising Leachfield Locations
  SEPTIC VIDEOS show how to find the drainfield and tank

Detailed Guide for Finding Other Septic System Components

More Information on Building Diagnostic Inspections and Repairs

• The Septic System Information Website home page for septic system design, installation, maintenance, repair
• Buyer's Guide Home Buyer's Guide to Septic Systems Inspection & Testing - What to Do, Step by Step.
• Septic Drainfields, Leach beds, Drwells, Absorption Systems
  • Absorption Field Design size and specifications for leach fields, absorption beds, gravelless systems, seepage pits
  • How Big Should the Leach Field Be? - table of soil percolation rate vs. field size
  • Planting Over Septic Systems: trees, shrubs, groundcover over the septic system: what can you plant over or near septic system components without causing a problem?
  • Septic System Drainfield Absorption System Biomat Formation - what leads to drain field clogging and expensive drainfield repairs
  • Table of Required Septic Tank, Drainfield, & Well Clearances: Distances Between Septic System & Wells, Streams, Trees, etc
  • SEPTIC SYSTEM DESIGN BASICS
  • Septic System DESIGN ALTERNATIVES
• Septic Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location
• Septic Tank Pumping Guide: When, Why, How to pump the septic tank
• How to Measure the Distance From the House to the Septic Tank gives details of making a septic location sketch.
• Distribution Box design, inspection, testing, and maintenance of the septic system D-box

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