5.1 Each device has unique flow patterns and turbulence characteristics. In addition, each device exhibits a wide range of efficiencies as discharge, particle-size distribution, particle density, and flow viscosity (that is, water temperature) change. In order to properly compare performance, the inherent factors, flow patterns and turbulence, must be isolated from the environmental factors, particle and water properties. The testing procedures described in Sections 7 and 8 provide a method of measuring the removal efficiency of these devices under a given flow condition, particle-size distribution, particle density, and fluid viscosity. Therefore, the results of testing represent performance only under this specific set of conditions.

5.2 Since this test is for only a single size unit it does not generate sufficient data for prediction of scaling unless the test is repeated for multiple unit sizes or scaling is in accordance with Practice C1893.

1.1 This test method concerns measurement of the efficiency of hydrodynamic separators and underground settling devices in removing suspended sediment from simulated stormwater runoff under conditions defined herein. This test method is intended to be applied in a laboratory setting to provide a common basis for comparing system performance. This test method is not intended for use in determining field removal efficiency.

1.2 This test method is intended to provide accurate, repeatable data for any stakeholder interested in evaluating HDS performance. Meeting the requirements of the test does not necessarily mean any given Authority Having Jurisdiction (AHJ) will certify the results. AHJs should be consulted prior to undertaking testing since some AHJs may require certain modifications, exclusions of certain methods, or additional criteria be met for HDS certification. This test method does not certify HDS devices; it is up to the AHJ to certify results from this test method and to certify that a given HDS’s performance will meet their specific performance goals.

1.3 Units tested shall be of a size commonly manufactured and available for purchase. In order to facilitate testing it is permissible to substitute alternate materials for the housing and structural components of the test units if operational components are at full size, with identical dimensions, configurations and materials specified for commercial use. Scale models are not permissible. This test method is not intended to address product scaling.

1.4 This test method is not for measuring the removal efficiency of filters or the scouring potential of hydrodynamic separators and underground settling devices.

1.5 This test method addresses gravity flow operation only. It does not address performance of units operating under pressurized or surcharge conditions.

1.6 The values stated in inch-pound units are to be regarded as standard, except for methods to establish and report sediment concentration and particle size. It is convention to exclusively describe sediment concentration in mg/L and particle size in mm or µm, both of which are SI units. The SI units given in parentheses are mathematical conversions, which are provided for information purposes only and are not considered standard. Reporting of test results in units other than inch-pound units shall not be regarded as non-conformance with this test method.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.