The AOWMA continues to draw Municipal Affair’s attention to member concerns regarding specific components of the 2009 Standard of Practice. Two such issues are the additional flow volume required based on fixture unit allocations and the use of gravel under chambers when used in treatment mounds.

On January 25, 2012 Municipal Affairs issued province wide variances on these two subjects.  Copies of the variances are available for download here (Variance PS03.12 and Variance PS04.12).

These variances provide designers and installers the option of not using gravel under chambers used in treatment mounds. The second variance allows a higher fixture unit allowance in a home before additional flow volume must be added. This variance impacts Article 2.2.2.2 and Table 2.2.2.2.A  in the SOP.  The variance allows the designer to use the criteria used in the adjusted table to assess additional loading.  Floor drains have now been removed from the fixture units.  The result of this is that there will be very few instances in which added daily flow must be included in the system design.

These variances are effective immediately. While these are not embedded in the Standard of Practice, installers are permitted to apply these variances in their system designs.

The AOWMA expects that the concepts set out in these province wide variances will be part of the next version of the Standard of Practice.

These are important moves forward as the industry works to reduce system costs and sizes without adversely affecting performance and safety.