Know your Sewage System Classes: Class 2 - Grey Water System

This is the second  post in a series titled 'Know your Sewage System Classes' about the different classes of onsite sewage systems regulated under the Ontario Building Code (OBC). This second post will summarize Class 2 sewage systems.

                                                          (Source:  Grey Bruce Health Unit)


Class 2 sewage systems are systems that receive only grey-water which comes from plumbing fixtures such as sinks, showers, or laundry machines. They are not to be used for the disposal of toilet waste. 

Leaching pits are used to treat and dispose of the grey water.  Since they are considered a sewage system they must be inspected and approved under the OBC.

A system cannot be constrcuted where the daily flow exceeds 1000 L/day.The total design flow for a Class 2 sewage system is calculated based on the fixtures discharging to the system as follows:

(a) 200 L per fixture unit where there is a supply of pressurized water, and
(b) 125 L per fixture unit where there is no supply of pressurized water

When considering a location of a leaching pit, caution must be taken to ensure that the minimum setbacks are strictly adhered to.  The following are just minimum distances and may have to be increased if the soil conditions are not ideal. Greywater sewage will contaminate ground water if not properly located and constructed.
                    
15 m (50 feet) from any lake, pond, river, stream or any water course
15 m (50 feet) from any dug well, sand point well, spring or any source of potable water

The leaching pit should be constructed in an area that is elevated and well drained.  Low lying areas are subject to excessive surface run-off which will overload the leaching pit and saturate surrounding soils.  This will result in poor treatment of the greywater and increase the possibility of ground water contamination.

Construction requirements are as follows:
(1)  The bottom of the pit shall be at least 900 mm above the high ground water table.
(2)  The pit shall be constructed in such a manner as to prevent the collapse of its sidewalls.
(3)  Material used to support or form the sidewalls must be open jointed materials that allow leaching.
(4)  The pit must have a tight, strong cover at all times except for removing greywater or maintenance.
(5)  The earth around the perimeter of the pit must be raised or mounded to a heigth of 150 mm above ground.
(6)  The ground in the pit area must be graded so that surface drainage is diverted away from the pit.