The National Pollutant Removal Performance Database, version 2 (Winer, 2000) consisted of 139 individual best management practice (BMP) performance studies published through 2000. An update of the database has since been conducted to include an additional 27 studies published through 2006. The source information for these additional studies is listed in the References section of this document. The updated database was statistically analyzed to derive the median and quartile removal values for each major group of stormwater BMPs. All BMP studies considered for inclusion into the database were reviewed with respect to three target criteria: (1) Five or more storm samples were collected; (2) Automated equipment that enabled flow or time-based composite samples were used, and (3) The method used to compute removal efficiency was documented. Pollutant removal efficiency, usually represented by a percentage, specifically refers to the pollutant reduction from the inflow to the outflow of a system. The two most common computation methods are event mean concentration (EMC) efficiency and mass or load efficiency.