Changes

The whisker plot figures to the right show combined stormwater effluent quality monitoring results from STEP monitoring projects conducted over a 25-year time period (between 1997 and 2021) at sites within Greater Toronto Area municipalities.<br>

The whisker plot figures to the right show combined stormwater effluent quality monitoring results from STEP monitoring projects conducted over a 25-year time period (between 1997 and 2021) at sites within Greater Toronto Area municipalities.<br>

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Median concentrations of Total Suspended Solids (TSS) in untreated stormwater and oil and grit separator (OGS) outlet locations were found to typically exceed 30 mg/L.  Median TSS concentrations at stormwater detention pond and chamber system outlet locations was found to be below 30 mg/L, but exceeded the guideline value in 36% of the monitored storm events.  Median TSS concentrations at bioretention, permeable pavement and infiltration trench outlet locations were found to be all below 30 mg/L.  TSS concentrations in effluent from bioretention was found to exceed 30 mg/L in only 15% of the 301 monitored storm events, and in only 12% of the 296 monitored events for permeable pavements.<br>

Median concentrations of Total Suspended Solids (TSS) in untreated stormwater and oil and grit separator (OGS) outlet locations were found to exceed 30 mg/L.  Median TSS concentrations at stormwater detention pond and chamber system outlet locations were found to be below 30 mg/L, but exceeded the guideline value in 36% of the 231 monitored storm events.  Median TSS concentrations at bioretention, permeable pavement and infiltration trench outlet locations were found to be all below 30 mg/L.  TSS concentrations in effluent from bioretention was found to exceed 30 mg/L in only 15% of the 301 monitored storm events, and in only 12% of the 296 monitored events for permeable pavements.<br>

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Median concentrations of Total Phosphorus (TP) in untreated stormwater and all stormwater facility type outlet locations were found to exceed 0.03 mg/L. Untreated stormwater was found to exceed 0.03 mg/L in between 96 to 98% of the 545 monitored storm events.  Stormwater detention pond or chamber system effluent was found to exceed 0.03 mg/L during 91% of the 211 monitored events. Effluent from bioretention outlet locations was found to exceeded 0.03 mg/L during 86% of the 355 monitored events.  Effluent from permeable pavement outlet locations exceeded 0.03 mg/L during 62% of the 300 monitored storm events.<br>

Median concentrations of Total Phosphorus (TP) in untreated stormwater and all stormwater treatment facility type outlet locations were found to exceed 0.03 mg/L. Untreated stormwater was found to exceed 0.03 mg/L in between 96 to 98% of the 545 monitored storm events (Asphalt Reference and SWM Inlet data sets).  Stormwater detention pond or chamber system effluent was found to exceed 0.03 mg/L during 91% of the 211 monitored events. Effluent from bioretention outlet locations was found to exceeded 0.03 mg/L during 86% of the 355 monitored events.  Effluent from permeable pavement outlet locations exceeded 0.03 mg/L during 62% of the 300 monitored storm events.<br>

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It is notable that infiltration trench results are from only one site and based on a relatively small number of storm events (25).

It is notable that infiltration trench results are from only one site and based on a relatively small number of storm events (25).