The state of a new art: Monitoring stormwater quality BMPs

Virtually all stormwater treatment systems work quite well at the low operating rates that occur during routine rainstorms and virtually all experience some drop-off, in efficiency at the higher operating rates that result from heavy rainstorms. Some systems may fail, i.e. operate at negative efficiency meaning that they lose previously captured pollutants, when subjected to high enough loading rates. A premise of this paper is that no system's performance has been thoroughly documented until the highest operating rate at which it can perform acceptably has been documented. The three components of a monitoring program are: 1) sampling (including rain gauging and/or flow measurement) 2) testing 3) reporting. None are overly complex, but since every site and every monitoring program is unique, there is wide variability in how best to carry them out. The outline that follows is offered as a practical set of methods to carry out each component to get the best results from available resources.