Section 5.2.5. - Stormwater (page 16)
Oil/Grit separators are only credited for 50% suspended solids removal. The value of 50% is not supported by independent test data from the ETV Canada separator protocol. This data suggests up to 70% removal at very low flow rates. Further, this high removal rate is based on a solids distribution where 20% of the particles are less than 8 um and 50% of the particles are less than 70 um. Municipalities around Ontario use different particle size distributions (PSD) in their design criteria. For example, in the City of Toronto particle size distribution there are no particles smaller than 20um and the d50 is 100 um. Therefore, higher rates of TSS removal are achievable with this distribution than the values tested under the ETV protocol since the particle size distribution (PSD) is coarser. Similarly, the City of Kitchener's design PSD has a d50 of 425 um which is much coarser than the ETV PSD.
Therefore, the efficiency of oil/grit separators (OGS) depends on the design PSD, which in turn, can be dictated by the local municipality. Even if a municipality adopts the ETV PSD the ETV data indicates that OGS systems would be able to meet the basic water quality level (60%). In other areas for municipalities that choose a coarser PSD, OGS systems could meet 70% or even 80% annual levels.
Unless the province is willing to mandate a design PSD to the municipalities the level of efficiency provided in section 5.2.5. is inaccurate and misleading. Even if the province mandates the ETV Canada PSD, the 50% value is misleading since OGS systems can meet the basic requirements (60%) as shown by ETV test data.
Several municipalities have put together spreadsheets to determine the efficiency of OGS products based on their own PSD criteria based on the ETV test data.
Considering all of the aforementioned information, we recommend removing 5.2.5 altogether.
Table 3 in Schedule B (page 4).
The table is blank for oil and grit separators in terms of treatment status. Depending on the municipality design PSD for water quality, the OGS could achieve either basic, normal, or enhanced status as noted above. The problem with the table is that it is generic. Different design standards dictate the level of treatment. It would be misleading to state one level of treatment for all OGS systems since the level depends on the PSD criteria and how the OGS is sized.
This is the same for any treatment practice such as dry ponds, wet ponds, wetlands, LID practices, etc.
Many of the old treatment numbers coming from manuals based on the Center for Watershed Protection or monitoring databases are flawed since there was not uniform monitoring standards, monitoring equipment, weather, treatment practice design parameters (L to W to D, etc.), site PSD, etc., etc. Field monitoring of OGS systems has found to have had poor correlation with controlled laboratory tests (ETV Canada) demonstrating that generic efficiencies based on field monitoring are unreliable with questionable transfer-ability.
Allowing the municipalities to fill out Table 3 based on their own design criteria makes comparison of this table across municipalities meaningless. Recommend removing the levels of treatment and just providing system totals.
Submitted August 27, 2020 12:10 PM