Submit stormwater sampling/monitoring reports through e-Services.

Industrial stormwater permittees are required to sample quarterly. Permittees may use any Minn. Department of Health Certified Testing Laboratory to conduct analyses required by the permit:

If you do hire a lab, be sure to ask if the lab is certified for the type of analysis you need. Ask about the cost of the service, turnaround times, and bottle delivery responsibilities. Can the lab analyze the pollutant parameters you are sampling for? What is its reporting methodology?

Monitoring locations

Benchmark monitoring locations should be below the most down-gradient best management practice (BMP) from the source of industrial activity or significant material, but prior to discharging from the permittee’s operational control. If applicable, effluent monitoring locations should be located immediately below the most down-gradient BMP from the specific industrial activity that has a numeric effluent limit, but prior to where the discharge co-mingles with stormwater from other sources.

Effluent limit monitoring

Permittees with effluent limit monitoring requirements must collect an additional, separate stormwater sample once a year. If you had no off-site surface water discharges, you are still required to submit the sampling form with a "no flow" explanation. It's a requirement for:

  • Sector A: Discharges from wet decking storage areas
  • Sector C: Runoff from phosphate fertilizer manufacturing facilities that comes into contact with any raw materials, finished product, by-products or waste products (SIC 2874)
  • Sector D: Runoff from asphalt emulsion facilities
  • Sector E: Runoff from material storage piles at cement manufacturing facilities (NOT Ready-Mix facilities!)
  • Sector K: Runoff from hazardous waste landfills See Sector K
  • Sector L: Runoff from non-hazardous waste landfills See Sector L
  • Sector O: Runoff from coal storage piles at steam electric generating facilities
  • Sector S: Existing and new primary airports with 1,000 or more annual jet departures that discharge wastewater associated with airfield pavement deicing that contains urea commingled with stormwater.

Use the discharge monitoring report (DMR) for effluent monitoring results.

Sampling guidance

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 should take samples within 30 minutes of the start of a measurable discharge. If you aren't able to collect a sample in 30 minutes of flowing stormwater, still collect a sample and record why a sample could not be collected in the first 30 minutes. Be sure it's been dry for at least 72 hours since the last time you collected a sample.

Tip: If you're deciding whether to collect a sample after 30 minutes of discharge vs. collect a sample another day, do not wait. Collect the sample now.

You must collect samples each quarter, including in the winter, but collecting stormwater samples in the winter is often obtainable statewide. Snow melt has the potential to carry significant accumulations of pollutants offsite.

Required sampling equipment

  • Flashlight (non-sparking)
  • Hard hat
  • Safety goggles
  • Reflective vests
  • Gloves (latex or nitrile)
  • Rain gear
  • Safety shoes
  • Traffic cones
  • Rain gauge
  • Eye wash bottle
  • Paper towels  
  • Ice cooler/shipping cooler
  • Field sampling notebook
  • Waterproof pens
  • pH meter
  • Sampling bottles
  • Preservatives   
  • Waterproof labels      
  • First aid kit

Averaged results exceeded? Modify/add new BMPs

If you collected four samples over four separate quarters and your averaged results were above the permit benchmark values, you are required to continue quarterly sampling until four results in a row average below the benchmark values.

First, determine which parameters you will be required to re-sample.Second, identify the significant material or industrial activity that the exceedance is connected to. Consider:

  • What BMPs you can modify and change at your facility?
  • Can you move that material or conduct that activity indoors or within a permanent, storm-resistant shelter?
  • If not, are there other BMPs you can add to minimize or eliminate the contaminants of concern?

What other areas may be causing you to exceed? Are there structural and/or non-structural BMPs that can help pass your benchmark monitoring requirements?

Monitoring waivers

Permittees may use various types of monitoring waivers. Waivers and adjustment for hardness-dependent metals may be done through the permitting process in e-Services. 

General benchmark monitoring waiver

Permittees are not required to conduct benchmark monitoring if an infiltration or pond system has been designed, constructed, and maintained in accordance with the permit.

Run-on demonstration waiver

If the average concentration of any benchmark parameter sampled over the course of a sampling year shows that a benchmark value has been exceeded and you believe that drainage onto the site from run-on has contributed to or caused the benchmark value exceedance, you can discontinue monitoring for that pollutant parameter if terms and conditions of the run-on demonstration waver are met:

  1. Sample the run-on prior to co-mingling with other stormwater discharges, and analyze the run-on against the pollutant parameter for which the benchmark value was exceeded.
  2. Include with the SWPPP a run-on demonstration narrative that explains the nature of the run-on, a description of the neighboring property and activities, dates and lab results of the samples taken for comparison purposes, a statement that you have assessed and assured the run-on is directly affecting the specific benchmark monitoring location for which a benchmark value has been exceeded, efforts you've taken to divert/minimize run-on to the facility, and other relevant information supporting your use of this waiver.
  3. Complete and submit the appropriate sections of a stormwater monitoring report .
  4. Address the use of this waiver in annual report submittals.

Natural background pollutant waiver

If the average concentration of a benchmark parameter exceeds a benchmark value, and you demonstrate that the exceedance is attributable to natural background pollution, your aren't required to perform corrective actions or additional benchmark monitoring of that benchmark parameter provided that:

  1. You demonstrates that the average of all samples taken of a specific benchmark parameter of the natural background is causing the benchmark value exceedance at the monitoring location.
  2. You document in the SWPPP the supporting rationale for concluding the benchmark value exceedance is attributable to natural background pollutant levels. Include any previously collected data that describes the levels of natural background pollutants in the industrial facility stormwater discharge.
  3. You notify the MPCA in the stormwater monitoring report that the benchmark value exceedance is attributable to natural background pollutant level, and address the use of this waiver in annual report submittals.

If you qualify for the benchmark monitoring waiver, use this form:

Hardness-dependent metals adjustment

The MPCA allows adjustment of benchmark values for seven hardness-dependent metals (cadmium, chromium +3, copper, lead, nickel, silver, and zinc) to provide flexibility in compliance with benchmark values in this permit. For any sector required to conduct benchmark monitoring for a hardness-dependent metal, the agency includes “hardness ranges” from which benchmark values can be determined.