Site Conditions


What is an ideal soil for an on-site system?

The soil used for an on-site system needs to be unsaturated. With unsaturated soil, effluent flow through the biomat is slower. This enables the microorganisms, who live in the soil, to treat the effluent as it flows through the soil system.

What is T-time? And why is it important?

The T-time, or percolation time, is the average time, in minutes, that it takes for water to drop 1 cm during a percolation test or as determined by a soil evaluation or analysis. It is important because it allows us to see how the system would operate.

What is the required T-time for a standard in-ground system? 

A standard in ground system must have a T-time between 1min/cm and 50min/cm. If it is higher, you will have to decide one of the following:

  • Consider a system other than a class 4
  • Use a raised leaching bed
  • Use a shallow buried trench if the soil has a high percolation time
  • Use a raised filter bed

How should the surface of the bed be shaped? 

The surface of the leaching bed must be shaped to shed water and shall be protected from any erosion. Drainage should be directed away from the bed.

What is the maximum slope of the area upon which a leaching bed can be built? 

A slope of 1 vertical unit to 4 horizontal units. (25%) However, a slope greater than 10% may require excessive grading.

Clearance Distances

The Ontario Building Code has strict requirements on the distances from the on-site system to any nearby structures, wells, watercourses or property lines. It is important for installers to take note of these at the site prior to installation.


clear Clearance Distances for Class 1, 2 and 3 Sewage Systems
Table Minimum Clearances for Distribution Piping
Table Minimum Clearances for Holding Tanks
Table Minimum Clearances for Treatment Units

Remember, always install the the best system for the site!