Stormwater Monitoring & Reporting

What is Stormwater Monitoring & Reporting?

Stormwater monitoring and reporting are regulatory requirements under the National Pollutant Discharge Elimination System (NPDES) program. Facilities must collect and evaluate stormwater samples to measure pollutant levels, verify that BMPs are effective, and demonstrate compliance while protecting local waterways. Monitoring results are reported to state or federal regulators through Discharge Monitoring Reports (DMRs) and annual compliance reports. The legal framework for stormwater permitting and monitoring is outlined in 40 CFR Part 122.

Who Needs Stormwater Monitoring & Reporting?

Stormwater monitoring requirements apply to facilities covered by industrial stormwater permits, including:

1. 1. Manufacturing and industrial operations (e.g. heavy manufacturing, hazardous waste treatment, transportation facilities, etc.)
   2. Construction sites that disturb one or more acres of land (federal threshold which might vary based upon state)
   3. Transportation, distribution, and warehousing facilities
   4. Utilities, waste treatment, and recycling operations
   5. Municipal Separate Storm Sewer System (MS4s)

Facilities with outdoor industrial activities are generally required to monitor and report results unless they qualify for No Exposure Certification.

Key Monitoring Requirements

Stormwater monitoring typically includes:

1. 1. Visual Assessments
      1. Conducted quarterly at each discharge outfall.
      2. At least one quarter per year must occur during a “qualifying storm event” (≥0.1 inch of rainfall, preceded by at least 72 hours without measurable rain).
      3. Evaluates runoff for color and clarity, odor, floating materials, or foam, oil sheen, and other indicators of contamination.
   2. Analytical Monitoring
      1. Required for many sectors based on SIC code and permit conditions.
      2. Samples analyzed by certified laboratories for pollutants such as:
         1. Total Suspended Solids (TSS)
         2. pH and Chemical Oxygen Demand (COD)
         3. Oil & Grease
         4. Heavy metals and sector-specific pollutants
   3. Sampling Protocols
      1. Samples typically collected as grab samples within first 30 minutes of discharge.
      2. Composite sampling (multiple individual samples combined into single, larger sample for analysis) may be allowed in some permits.
      3. Snowmelt events may require sampling monitoring.
   4. Special Monitoring
      1. Additional sampling is required if stormwater discharges to an impaired waterbody or one with an EPA-approved Total Maximum Daily Load (TMDL)

Core Reporting Obligations

Stormwater monitoring results must be submitted in accordance with NPDES requirements, including:

• • Discharge Monitoring Reports (DMRs) – Electronic submissions via EPA’s NetDMR system or state-specific portals.
  • Annual Reports – Summarize and documentation of monitoring activities, results, and corrective actions.
  • Exceedance Reporting – Benchmark exceedances must be investigated, corrective actions documented, and resampling performed if required

Compliance Standards

Stormwater monitoring and reporting obligations are based on:

1. 1. EPA’s Multi-Sector General Permit (MSGP) and 40 CFR 122.21 stormwater regulations.
   2. State-issued stormwater permits (e.g. Tennessee’s General NPDES Multi-Sector Permit – TMSP).
   3. Implementation of BMPs to control and minimize pollutant discharges and maintain permit compliance.
   4. Sector-specific monitoring linked to Standard Industrial Classification (SIC) codes, which categorize business activities and associated monitoring parameters.