MPCA: Industrial stormwater sampling requirements – what’s next?

The current general permit was issued April 2015, and all permittees were required to “restart” sampling quarterly, for four quarters to start, starting July 2015.  New applicants started sampling the next full calendar quarter after receiving permit coverage.

This means that June 30, 2016 marks the end of the first four quarters of industrial stormwater sampling requirements for most permittees.

Did you collect samples during four separate quarters?  If not, continue sampling.  If you were able to collect stormwater samples from four different quarters during the past year, calculate the rolling average value of each parameter’s monitoring results and compare with the benchmark values listed in the general permit.  If your average value is less than the benchmark value, you’re done monitoring for that parameter.  If your average value is more than the benchmark value, continue sampling until your averaged values fall below the benchmark values.

The concept of “the rolling average” is new for the 2015-2020 general permit.  Make sure you are averaging the sample results from the four most recent quarters, and compare those with the general permit values.  If no sample was collected for a quarter, send in the sampling form with a “No Flow” explanation.  In the example below, no sample was collected in Quarter 5 and Quarter 10, and the permittee needs to collect only one sample during the following quarter.  You no longer have to “collect two samples in the next quarter to make up for not being able to collect samples the previous quarter” as required in the 2010-2015 permit.  This example below is for Total Suspended Solids (TSS), with a permit benchmark value of 100 mg/L.

Use this handy “Industrial Stormwater Sampling Worksheet” to help you record and review your sampling data.  Previously, we had “sampling results” and “sampling calendars” on our website to let permittees know if they had to continue sampling.  Due to our agency-wide data system upgrade, that functionality is currently not available but we are working on bringing that functionality back.  If you are unsure whether or not you have to continue sampling, please contact any industrial stormwater technical staff and we’ll be happy to help you.

No exceedances?  No problem!

Were you below the permit benchmark values for all of your parameter(s) at all of your monitoring location(s) You do not need to notify the MPCA that you’re “done” with the sampling requirements.  Keep the individual and averaged results documented within your Stormwater Pollution Prevention Plan.


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