Cost-Effectiveness Calculations Using Alternate Metrics of Stormwater Control Measure Pollutant Removal Performance

The hydrologic and pollutant removal effectiveness of structural stormwater control measures (SCMs) is subject to a significant amount of variability, attributable to the episodic and stochastic nature of stormwater flows. This variability can be seen by the range of an SCM's " percent removal" metric -the proportion of the influent that does not appear in the effluent -as estimated across varying precipitation characteristics. As the percent removal metric is commonly used in practice for the selection and design of SCMs for post-development runoff control, and for estimating progress toward total maximum daily load (TMDL) waste load allocations (WLAs), the variability in performance confounds straightforward cost-effectiveness calculations. This research presents alternate methods for characterizing SCM performance, discusses the use of these methods for cost-effectiveness estimation, and compares the outcomes to the cost-effectiveness as estimated using a static percent removal value. The importance of the SCM performance method employed on the selection of the "optimal" SCM is discussed, as is the effect of the various methods on progress toward a TMDL waste load allocation.