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[[File:OGS-Protocol-Webpage-Image.jpg|thumb|300px|In lab testing of a Stormceptor<sup>(R)</sup> OGS device, here seen testing discharge rates and sediment effluent loads at St. Anthony Falls Laboratory in Minneapolis, 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>]]
[[File:OGS-Protocol-Webpage-Image.jpg|thumb|300px|In lab testing of a Stormceptor<sup>(R)</sup> OGS device, here seen testing discharge rates and sediment effluent loads at St. Anthony Falls Laboratory in Minneapolis, 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>]]
[[File:OGS min Max.png|900px|thumb|left|Average, minimum and maximum sediment removal efficiencies for ISO 14034 verified OGS at seven surface loading rates (n = 10).]]
[[File:OGS min Max.png|900px|thumb|left|Average, minimum and maximum sediment removal efficiencies for ISO 14034 verified OGS at seven surface loading rates (n = 10).]]
==Scaling==
The ISO 14034 ETV sediment removal rate data for the tested model at specified surface loading rates may be applied to similar MTDs of smaller or larger size by proper scaling. Scaling the performance results of the tested MTD to other model sizes without completing additional testing is acceptable provided that:
# The claimed sediment removal efficiencies for the similar MTD are the same or lower than the tested MTD at identical surface loading rates; and
# The similar MTD is scaled geometrically proportional to the tested unit in all inside dimensions of length and width and a minimum of 85% proportional in depth.
Ensuring the unit is scaled appropriately in all dimensions also helps to ensure that the recommended maintenance intervals for the unit can be achieved.
==Sizing==
It is recommended that a standard sizing approach be used for all OGS units to ensure they are evaluated based on a consistent methodology. The attached OGS Review Calculator has been developed to facilitate application of ISO 14034 ETV test data through a standard approach applicable to all OGS MTD designs. The following methods and processes are built into the tool:
* Rational Method used as a basis for flow calculations (Q = CiA, where C is the site runoff coefficient, i is the rainfall intensity and A is the drainage area) - Alternatively, provide bubble link to definition of rational method
* Target treatment is based on capture and treatment of the average annual runoff volume for the site using ISO 14034 verified sediment removal test results for 7 surface loading rates
* Linear interpolation is used to calculate sediment removal efficiencies between the ISO/ETV tested surface loading rates
* Surface loading rates below the lowest ISO/ETV tested surface loading rate are assigned a sediment removal efficiency equal to that of the lowest tested rate
* Hourly historical rainfall data (minimum 20 years) are used to generate the rainfall intensity distribution curve.
* Capacity to add historical rainfall record is provided in order to generate the relationship between hourly rainfall intensities vs average annual rainfall volume for the meteorologic station of choice.