Normalized Technology Verification of Structural BMPs, Low Impact Development (LID) Designs and Manufactured BMPs

Three rainfall-runoff events between September and October 2004 were monitored for a suite of structural BMPs, Low Impact Development designs, and manufactured BMPs. The range of 12 stormwater unit processes include: infiltration devices, filtration devices, treatment wetlands, conveyance structures, detention ponds, and manufactured BMPs; all of which were evaluated for water quality performance and storm volume reduction. Stormwater management strategies were tested in parallel, with uniformly sized unit processes targeted for a rainfall-runoff depth of 25.4 millimeters that is equivalent to 90% of the annual volume of rainfall. Under the parallel and uniformly sized configuration, a normalized performance evaluation is possible because unit processes of the same scale receive runoff from events of the same duration, intensity, antecedent dry period, and watershed. Water quality contaminants monitored include nutrients, hydrocarbons, metals, solids, and other routine parameters. Runoff constituent analyses routinely include total suspended solids (TSS), diesel range organics (DRO), nitrate (NO₃), phosphate (PO₄), chloride (Cl), zinc (Zn). A range of water quality parameters (temperature, dissolved oxygen, pH, conductivity) were monitored continuously as real-time data for influent and effluent waters. Previous research has demonstrated that treatment performance by stormwater control measures varies widely depending on both the design of stormwater treatment measures, as well as the variations in contaminant loading functions from site to site. In many cases it has been shown for stormwater BMPs that contaminant effluent concentrations exceed influent concentrations, particularly those major classes of stormwater devices functioning within the design criteria for treating 90% annual rainfall-runoff volume. The ranges of devices have distinct trends and performance differences.