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The PPM Blog

What Actually is A Significant Noncompliance in the NPDES Realm?

a man wearing a suit and tie smiling at the cameraContributed by Holden Volentine, Project Manager, PPM Consultants

State and Federal regulators often use the terminology “Significant Noncompliance” (SNC), specifically in regards to National Pollutant Discharge Elimination System (NPDES) permits. However, permittees don’t always fully understand what conditions actually trigger a SNC from a regulatory body. According to the EPA, there are several criteria that can trigger SNC for NPDES permit violations.

A 40% exceedance of any pollutant limits for the parameters listed in Table 1 or a 20% exceedance of any pollutant limit for the parameters listed in Table 2 at a given discharge point for any two or more months during a two consecutive quarter period is considered SNC.

                                                                                                                                                                            Table 1
Biochemical Oxygen Demand (BOD) Inorganic Phosphorus Compounds Calcium
Chemical Oxygen Demand (COD) Inorganic Nitrogen Compounds Chloride
Total Oxygen Demands Oil & Grease Fluoride
Total Organic Carbon (TOC) MBAS Magnesium
Total Suspended Solids (TSS) NTA Sodium
Total Dissolved Solids (TDS) Other Detergents or algicides Potassium
Aluminum Sulfur Sulfate
Cobalt Total Alkalinity Total Hardness
Iron Vanadium Other Minerals


                                                                                                                                                                            Table 2
Other Metals not listed in Table 1 Cyanide
Total Residual Chlorine All other Organics not listed in Table 1


Also, violation of any monthly effluent limit at a given discharge by any amount for any four or more months during a two consecutive quarter period is considered SNC. It is noted that when a parameter has both a monthly average and a non-monthly average limit, a facility would only be considered in SNC for the non-monthly limit if the monthly average is also violated to some degree (but less than SNC).

The following are other scenarios that will trigger SNC:

  • Any effluent violation that causes or has the potential to cause a water quality or human health problem.
  • Any unauthorized bypass, unpermitted discharge, or pass through of pollutants which causes or has the potential to cause a water quality problem or health problems.
  • Discharge Monitoring Reports (DMRs), POTW Pretreatment Performance Reports, or the Compliance Schedule Final Report of Progress are submitted 30 or more days late.

If you have any questions regarding Significant Noncompliance or would like our team to help you in any way, please reach out to me at

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