A.J. Erickson, P.T. Weiss, J.S. Gulliver, R.M. Hozalski
Summation of load and event mean concentration (EMC) efficiency are two methods for estimating stormwater treatment practice performance from monitoring data that result in a single value for performance with associated uncertainty. The exceedance and effluent probability methods are graphical comparisons of data (typically inflow and outflow) that illustrate trends for the entire range of data values. The summation of load and EMC efficiency methods are both recommended for analysis of single storm events to determine the total pollutant load, EMC, and associated reduction efficiencies. The exceedance method is recommended for analysis of long-term performance because it can be performed with most commercially available spreadsheet software and it provides an illustration of performance for the entire range of data. The exceedance method can also be used to compare performance from different time periods, sites, or practices.