How do you know if your stormwater control measures are working? Sampling your stormwater discharges, compare your results to the benchmark value(s) listed in the permit, and either take action if results are high or continue utilizing your control measures to protect our surface waters and groundwater.

image of staff collecting a stormwater sample through the grab sample method
Collecting a stormwater sample the right way is important.

Need your facility-specific sampling form? Visit the Permit Information Access tool.

Permittees are required to sample quarterly until results from four separate quarters average below the permit benchmark value(s):

  • Quarter 1:July, August, September 2015 (form due no later than October 21, 2015)
  • Quarter 2: October, November, December 2015 (form due no later than January 21, 2016)
  • Quarter 3: January, February, March 2016 (form due no later than April 21, 2016)
  • Quarter 4:April, May, June 2016 (form due no later than July 21, 2016)

If you were you unable to collect samples during Quarters 1-4 or your averaged results were above the permit benchmark value(s), continue sampling:

  • Quarter 5: July, August, September 2016 (form due no later than October 21, 2016)
  • Quarter 6: October, November, December 2016 (form due no later than January 21, 2017)
  • Quarter 7: January, February, March 2017 (form due no later than April 21, 2017)
  • Quarter 8: April, May, June 2017 (form due no later than July 21, 2017)
  • Quarter 9: July, August, September 2017 (form due no later than October 21, 2017)
  • Quarter 10: October, November, December 2017 (form due no later than January 21, 2018)
  • Quarter 11: January, February, March 2018 (form due no later than April 21, 2018)
  • Quarter 12: April, May, June 2018 (form due no later than July 21, 2018)
  • Quarter 13: July, August, September 2018 (form due no later than October 21, 2018)
  • Quarter 14: October, November, December 2018 (form due no later than January 21, 2019.

Check out the Monitoring Guidance Manual For Minnesota’s Industrial Stormwater Multi-Sector General Permit to learn the answers to these questions:

  • Who needs to collect stormwater samples?
  • What do I need to sample for?
  • When do I take my sample?
  • Where do I take my samples?
  • How do I sample?
  • How do I report my sampling results?

Permittees may use any Minn. Department of Health Certified Testing Laboratory to conduct analyses required by the permit. Click on the "customized searches" tab and select "Minnesota" in the state/province drop down option. Fill out and send in the sampling form to the MPCA.

Determine when to sample Permittees can take a stormwater sample anytime there is a measurable runoff event, which means any volume flowing past/through their monitoring location that allows you to collect a sample. You can collect either from a rain event or a snow-melt event. You should take samples within 30 minutes of the start of a measurable discharge. If you aren't able to collect a sample within 30 minutes of flowing stormwater, still collect a sample and record on the SWMR why a sample could not be collected within the first 30 minutes of a measurable runoff event. Be sure it's been dry for at least 72 hours (3 days) since the last time you collected a sample.

Tip: If faced with collecting a sample after 30 minutes of discharge leaving your monitoring location or trying to sample another day, do not wait another day. Collect the sample now.

Winter thaw storm event

Because you are required to collect four benchmark samples in four separate quarters, winter thaw or winter rains will occur and collecting stormwater samples in the winter is often obtainable state-wide. Snow melt has the potential to carry significant accumulations of pollutants offsite.

Guidance materials and resources:


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This page was last edited on 6 June 2018, at 14:28.

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