Information provided for reference purposes only

Note: This information is provided for reference purposes only. Although the information provided here was accurate and current when first created, it is now outdated. All the links in the document have been removed.

NPDES Storm Water MSGP: Analytical Monitoring

Analytical monitoring is required only for the industry sectors or sub-sectors which were determined to have a high potential to discharge a pollutant at concentrations of concern. Monitoring provides feedback to the facility operator to assess the effectiveness of the facility's storm water pollution prevention plan.

Which Pollutants Need To Be Monitored?

The Analytical Monitoring Table identifies specific parameters that must be monitored for each industry sector or sub-sector required to perform analytical monitoring of their storm water discharges. In addition to the requirements listed in this section, facilities must also comply with any state-specific and Regional requirements as listed in Part XII of the MSGP. 

When Does Analytical Monitoring Need to be Performed?

Analytical monitoring must be performed on a quarterly basis in years two and four of the permit. The second and fourth years of the MSGP do not correspond to calendar years, and they differ from region to region.


Geographic Location of Facility

Analytical Monitoring Schedule

DMR Postmark Deadlines

Facilities in all areas of coverage other than Alaska or Guam:

Years 2 and 4:
October - December (1996, 1998)
January - March (1997, 1999)
April - June (1997, 1999)
July - September (1997, 1999)

March 31 (1998, 2000)

Facilities in Alaska:

Years 2 and 4:
January - March (1997, 1999)
April - June (1997, 1999)
July - September (1997, 1999)
October - December (1997, 1999)

March 31 (1998, 2000)
Facilities in Guam:

Years 2 and 4:
October - December (1997, 1999)
January - March (1998, 2000)
April - June (1998, 2000)
July - September (1998, 2000)

March 31 (1999, 2001)

Analytical Monitoring In Year Four May Not Need to be Performed. Here’s Why…

  • If the average pollutant level of the four quarterly samples from year two is LESS than the benchmark levels listed here, the facility may waive analytical monitoring for year four, unless otherwise directed by EPA.

NOTE: This waiver is available ONLY to those facilities which have completed four monitoring quarters according to the specifications of the MSGP. If a facility obtained MSGP coverage in year two and performed three quarters of monitoring in year two, it would need to complete one additional quarter of monitoring before it would be eligible for this waiver.

Do All Discharge Points Need to be Sampled?

No. Under certain conditions, a facility may determine one outfall to be a Representative Discharge. That is, the facility reasonably believes the discharge from two or more outfalls is substantially identical and therefore sampling from only one outfall is necessary. Facilities must document their rationale for considering two outfalls to be identical. More information on Representative Discharges can be found in the Introductory Fact Sheet to the MSGP (Section VI.E.6).

Sampling Waivers

The MSGP allows for waivers from analytical monitoring requirements under two circumstances: adverse weather conditions, and unstaffed and inactive sites. In addition, facilities may obtain an exemption from monitoring through an alternative certification as described below. It should be noted that these waivers cannot be used for compliance monitoring requirements associated with effluent limitations.

Adverse Weather Waiver

The permit allows for temporary waivers from analytical monitoring based on adverse climatic conditions. If samples cannot be collected within a specified sampling period due to insurmountable weather conditions such as drought or dangerous conditions (e.g., lightning, flash flooding, or hurricanes), the discharger must collect a substitute sample from a separate qualifying event in the next sampling period. This substitute sample must be taken in addition to the routine monitoring required in that period. Both samples should be analyzed separately.

Unstaffed and Inactive Site Waiver

If a facility is both inactive and unstaffed, and the ability to conduct sampling within permit specifications is not possible, then the discharger must certify in the DMR that the facility is inactive and unstaffed and that the ability to conduct sampling within the specifications is not possible.

Alternative Certification Waiver

A facility can obtain an exemption from monitoring for any particular pollutant if the facility operator can certify that there is no source of that pollutant which is exposed or potentially exposed to storm water during the certification period. This certification must be submitted as part of the DMR in lieu of monitoring data. The alternative certification is not available for compliance monitoring for effluent limitation guidelines.

Parameter Benchmark Values For Analytical Monitoring 


Benchmark Level (mg/l unless otherwise noted)


Benchmark Level (mg/l unless otherwise noted)

Aluminum, Total Recoverable


Mercury, Total Recoverable




Nitrate + Nitrite Nitrogen


Arsenic, Total Recoverable


Nitrogen, Total Kjeldahl


Biological Oxygen Demand (BOD5)


Oil & Grease


Cadmium, Total Recoverable



6.0 to 9.0 s.u.

Chemical Oxygen Demand (COD)




Copper, Total Recoverable


Selenium, Total Recoverable


Cyanide, Total


Silver, Total Recoverable


Iron, Total Recoverable


Total Organic Carbon (TOC)


Lead, Total Recoverable


Total Suspended Solids (TSS)


Magnesium, Total Recoverable


Zinc, Total Recoverable



How Are Analytical Monitoring Results Reported?

Upon completion of each monitoring year, analytical monitoring results must be submitted on a Discharge Monitoring Report (DMR) form (and DMR form instructions) to the appropriate NPDES Permitting Authority authority by March 31 of the following year.  For more information, please download the Guidance Manual for the Monitoring and Reporting Requirements of the NPDES Storm Water Multi-Sector General Permit. 


Disclaimer: The information contained on these pages is a general statement of policy. It does not establish or affect legal rights or obligations. It does not establish a binding norm and is not finally determinative of the issues addressed. Agency decisions in any particular case will be made by applying the law and regulations to the specific facts of the case. This applies to all pages in the NPDES Storm Water Program web hierarchy (