Tutorial - Leach Trenches

Leach Trench Construction

A typical trench is 3-ft to 4-ft deep, about 2-ft to 4-ft wide, and may be 30-ft to 100-ft long. 


The bottom of the trench is filled with leach stone (0.75-inch to 1.5-inch washed stones) to a depth of 1.5-ft to 2.5-ft.  A perforated pipe is placed in the top of the leach stone for the length of the trench. A 2-inch to 3-inch layer of peastone is placed over the leach stone as a barrier to topsoil mixing into the leach stone. About 1-ft of topsoil is placed over the leach trench to match the surface grade.  Typically, grass is planted over the area to stabilize soils and to prevent deep rooted plants from growing over the trenches.  Deep rooted plants can quickly clog a leach system. 

If site conditions are favorable for leach trenches, this is often the preferred system for the following reasons:

  • The leach trench is efficient, using sidewalls as well as bottom area for flow dispersal.
  • If abused, the leach trench may take longer than other systems to fail. If the bottom plugs, the sidewalls may remain effective. 
  • This soil absorption system has a relatively low cost to construct