STORMWATER MONITORING REQUIREMENTS – AMBIENT SAMPLING
Phase I MS4s conduct ambient monitoring of surface waters, such as lakes, streams, and rivers, during normal (non-storm) events to establish baseline conditions, i.e., water quality without direct effects from stormwater runoff. While these conditions are considered normal, that is not to say impacts are not identified. In fact, several of the parameters measured and identified during ambient sampling events can only be a direct result of human impacts and are examples of residual impacts from stormwater runoff. The data also provide a reference point for wet weather conditions, i.e., a baseline to compare pre- vs. post-runoff water quality. The parameters discussed are by no means intended to be an all-inclusive list; instead, they are examples of commonly sampled parameters used to establish the presence/absence of chronic stormwater contamination or water quality impairment. Specific parameters vary based on individual watersheds.