First, a very quick summary of the impaired waters monitoring program:
One MS4 monitoring requirement is that MS4s conduct wet weather monitoring of all outfalls that discharge directly to stormwater impaired waterbodies which can be impaired by bacteria, nitrogen, phosphorus, or other pollutant of concern. Impaired waterbodies can be seen on the MS4 map viewer: https://nemo.uconn.edu/ms4/tools/ms4map.html.
The clarification: Total coliform only needs to be measured when the outfall discharges to an AA waterbody – which indicates is a potential source of drinking water.
The recap: If you have a bacteria-impaired freshwater body, sample for E. Coli. And only sample for total coliform if it’s classified as an AA waterbody.
Please let me know if you have any questions!