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 comparison of data collected during wet weather conditions, i.e., the ambient sample data are used as a baseline to compare pre- vs. post-stormwater runoff water quality.

The parameters discussed below 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 that are monitored vary based on individual watersheds.