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Line 106: + + − − [[File:OGS-Protocol-Webpage-Image.jpg|thumb|350px|Performance testing of an OGS unit in St Anthony Falls Laboratory in Minnesota (Saddoris, et al. 2010)<ref>Saddoris, D.A., McIntire, K.D., Mohseni, O., and J.S. Gulliver, 2010. Hydrodynamic Separator Sediment Retention Testing – Final Report. Minnesota Department of Transportation, St. Paul, MN.</ref>]]
→Performance Test Results
* '''Group 1''' includes traditional designs (n=10) with large openings and limited flow restriction. Results for these OGS types were relatively consistent at low flows and slightly more variation at high surface loading rates.
* '''Group 1''' includes traditional designs (n=10) with large openings and limited flow restriction. Results for these OGS types were relatively consistent at low flows and slightly more variation at high surface loading rates.
* '''Group 2''' units with debris filters, fine meshed debris screens or coalescing plates (n=2) showed higher performance (group 2). These units force water to flow through smaller orifices, which increase the risk of [[clogging]], leading to higher maintenance costs in the long run. Test plans for these units should include a scenario that evaluates system hydraulics and removal rates under a scenario where a portion of the small orifices are clogged. If this has not been done, it would be reasonable to apply a factor of safety to verified results to account for clogging potential over the maintenance cycle.
* '''Group 2''' units with debris filters, fine meshed debris screens or coalescing plates (n=2) showed higher performance (group 2). These units force water to flow through smaller orifices, which increase the risk of [[clogging]], leading to higher maintenance costs in the long run. Test plans for these units should include a scenario that evaluates system hydraulics and removal rates under a scenario where a portion of the small orifices are clogged. If this has not been done, it would be reasonable to apply a factor of safety to verified results to account for clogging potential over the maintenance cycle.
[[File:OGS-Protocol-Webpage-Image.jpg|thumb|420px|Performance testing of an OGS unit in St Anthony Falls Laboratory in Minnesota (Saddoris, et al. 2010)<ref>Saddoris, D.A., McIntire, K.D., Mohseni, O., and J.S. Gulliver, 2010. Hydrodynamic Separator Sediment Retention Testing – Final Report. Minnesota Department of Transportation, St. Paul, MN.</ref>]]
In general, OGS should not be installed as stand-alone units for [[water quality]] treatment. While every effort has been made to ensure that the ISO 14034 verified lab test is an accurate representation of actual performance, there remains uncertainty about how lab results translate to the field, particularly for group 2 technologies. Installing OGS only as [[pretreatment]] to other downstream practices helps to mitigate this uncertainty and risk because downstream stormwater treatment practices can be relied on to provide a second line of defense.
In general, OGS should not be installed as stand-alone units for [[water quality]] treatment. While every effort has been made to ensure that the ISO 14034 verified lab test is an accurate representation of actual performance, there remains uncertainty about how lab results translate to the field, particularly for group 2 technologies. Installing OGS only as [[pretreatment]] to other downstream practices helps to mitigate this uncertainty and risk because downstream stormwater treatment practices can be relied on to provide a second line of defense.
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