Industrial Stormwater General Permit

What is it?

The General Permit for the Discharge of Stormwater Associated with Industrial Activity (“Industrial General Permit”) addresses point source pollution caused by industrial activities. The permit requires a Stormwater Pollution Prevention Plan (SWPPP) and the monitoring of outfalls for every registered facility to mitigate and prevent exposed materials and potential pollutants from discharging in stormwater runoff and entering local waterways.

Why do we need it?

Industrial activities of all kinds can be the source of various pollutants discharging into waterways. Materials, equipment, and general maintenance activities are often exposed at these industrial areas, allowing for runoff from storm events and snow melt to come in contact and transport pollutants into local waters. These pollutants can have negative impacts on water quality, aquatic life and habitats, ecosystems, and more. For more information, visit our Stormwater Basics page.

Frequently Asked Questions

Since when has this General Permit been in place?

The effective date for this General Permit is Oct. 1st, 2021. It expires Sept. 30th, 2024.

Who needs a permit?

Any person or municipality that initiates, creates, originates, or maintains a discharge authorized by the Industrial General Permit must register.

How do I register?

Registration can be done through DEEP’s ezFile instructions. Information of the specifics of what is required within the registration form can be found on pages 13-15 of the Industrial General Permit. With your registration, you must provide a description of the stormwater discharge, a map of the location of the facility and the area within a one mile radius of the facility, and the Stormwater Pollution Prevention Plan. More guidance on the SWPPP can be found here. Registration can be filed at the following address:


HARTFORD, CT 06106-5127

For certain small-scale composting facilities specialized in horse manure and bedding, the SWPPP and registration must be reviewed and approved directly by the Commissioner.

What is needed for the Stormwater Pollution Prevention Plan (SWPPP)?

A SWPPP must be developed for each site at the time of registration and signed by a duly authorized representative. More guidance on the SWPPP can be found here. The SWPPP must be accompanied by a “Plan Certification” and be retained on site at all times, ready for copy if requested by the Commissioner and or the operator of an involved municipal system or public water supply company. The SWPPP must also be ready for amendment for any necessary changes such as a change on site which may impact the potential to cause pollution, failure of the plan to ensure protection against pollution, etc. Amendments must take place within 120 days of the registrant becoming aware that a change is needed. For details on what is needed within the plan, continue down the page to our SWPPP section.


What inspections are needed?

Qualified personnel must conduct site inspections semi-annually and must occur more than twice a year. These inspections are for areas that are potential sources of pollution and to inspect and evaluate the stormwater management and treatment devices in place to prevent pollution. Qualified personnel must also conduct routine inspections at least monthly to inspect equipment and sensitive areas to the site. Keep a record of all inspections, both semi-annual and routine maintained in the SWPPP at all times. Semi-annual inspection reports must be signed by the permittee.

What about off-site and natural background pollutants?

Natural background pollutants are substances which naturally occur in rainfall, soils, or groundwater. They do not include legacy pollutants from earlier activity on the site.

After the first 4 semiannual samples for monitoring have been taken, if any exceedances can be proven to be attributable solely to the presence of that pollutant in the natural background or in “run-on” entering rom off-site, no corrective action or additional monitoring is necessary as long as the following conditions are being met:

  • The average concentration of the monitoring results is less than or equal to the natural background pollutant concentration or off-site run-on;
  • The registrant has documented and maintained the evidence that the exceedance is solely due to natural background pollutants or off-site run-on within the SWPPP;
  • The permittee demonstrates that the diversion of off-site run-on containing these pollutants levels is not feasible;
  • The permittee has notified the commissioner; and
  • The commissioner issues a written approval of the documentation.


Conditions of the Industrial General Permit

Certain Sectors should also see section 5(f) for more information on additional requirements.

  • Asphalt plants; non-metallic mines and quarries; refuse systems; auto salvage yards; scrap recycling facilities; steam electric power generation; transportation and public works facilities; marinas, yacht clubs, and boat dealers; ship and boat building and repair; and small scale composting facilities

Conditions Applicable to Certain Discharges

  • Any person or municipality who initiates, creates, or originates a discharge of stormwater associated with industrial activity after Oct. 1st, 1997 which is located less than 500 ft from a tidal wetland (not fresh-tidal) must discharge the stormwater through a system designed to retain the volume of stormwater runoff generated by 1 in of rainfall on the site. If retention cannot be completed, the registrant must provide documentation of the limitations.
  • Any person or municipality who discharges stormwater below the high tide line into coastal, tidal, or navigable water needs to also register for the Structures and Dredging Act permit or Tidal Wetlands Act permit
  • There can be no visible floating scum, oil or other matter in the discharge
  • The discharge can’t result in pollution due to acute or chronic toxicity to aquatic and marine life, impair biological integrity of ecosystems or pose unacceptable risk to human health
  • The discharge shall not cause or contribute to an exceedance of applicable Water Quality Standards
  • New stormwater discharges to high quality waters must be discharged in accordance with the Connecticut Anti-Degradation Implementation Policy

Control Measures

The following control measures is a brief summary of the Best Management Practices required by the general permit to minimize the discharge of pollutants. These must be implemented to assist in reducing and or eliminating discharges to the maximum extent practicable.

    Good Housekeeping

    Maintain clean facility in all areas exposed to rainfall and could be a potential source of pollutants

    Roof Areas

    Identify and inspect roof areas which may be subject to drippage, dust or particulates from exhausts or vents or other sources of pollution and determine any potential sources of stormwater pollution

    Management of Runoff

    Investigate the need for, implement, and maintain stormwater management or treatment measures to minimize the discharge of pollutants from the site. When implementing measures, avoid ground water contamination. Where feasible, divert uncontaminated run-on to avoid areas that may contribute pollutants

    Employee training

    Train employees who may be involved with water quality and ensure they know the SWPPP

    Vehicle or Equipment Washing

    No washing or rinsing or equipment, buildings, or vehicles to be allowed at the site in which the washing would enter storm drains or surface waters

    Minimize Exposure

    Minimize exposure to stormwater of materials with permanent roof or cover or provide stormwater treatment. If a cover is not feasible, submit areas in question and limitations with  SWPPP

    Preventive Maintenance

    Inspection and maintenance of stormwater management devices and equipment which could contribute to polluted discharges

    Non-stormwater discharges

    Eliminate all non-stormwater discharges

    Floor Drains

    All floor drains must be sealed; OR the registrant must be authorized by a local authority to discharge to a sanitary sewer; OR have approval by DEEP

    Sediment and Erosion Control

    Identify areas with potential for soil erosion and implement measures to limit and stabilize

    Spill Prevention and Response Procedures

    • Containment
      • Stationary storage or storage areas
      • Mobile or portable storage
      • Containment exemption for certain stationary above-ground storage tanks, containers, and areas
    • Dumpsters
      • Ensure watertight condition with covers and drain plugs intact or are roofed
    • Loading Docks
      • Have a permanent roof to prevent direct rainfall

    Solid De-icing Material Storage

    With the exception of the bulk solid deicing material storage facilities:

    Ensure storage areas for de-icing materials are in an enclosed or covered structure. No new storage can be located within an 100-year floodplain, within 250ft of a potable drinking well, or within a Level A aquifer protection area.

    Stormwater Pollution Prevention Plan (SWPPP)

    Shall be developed and maintained on-site for the duration of the construction activity. For more guidance on this plan, consult the SWPPP Guidance Doc.

    Contents of Plan

    • Facility description and general location map
    • Pollution prevention team
      • Team is responsible for implementing SWPPP, assisting in implementation, maintenance, and development of revisions to SWPPP, maintaining control measures, and taking corrective actions where required
    • Potential pollutant sources
      • Map and describe the potential sources of pollutants that may be expected to affect stormwater quality or result in discharges during dry weather
        • Description to include inventory of exposed materials, summary of potential pollutant sources, and a list of spills and leaks
    • Control Measures implemented
    • Non-stormwater discharge certification signed certification by professional engineer


    • Consistency with other plans and permits
      • Demonstrating compliance with MS4 permit if applicable
      • Spill Prevention Control and Countermeasure (SPCC)
      • Resource Conservation and Recovery Act (RCRA)
    • Future Construction
      • Construction that disturbs more than one acre must register with Construction GP
      • Follow Erosion Guidelines and Stormwater Manual
    • Monitoring Program description
    • Schedules and Procedures
      • For implementation of control measures, monitoring, and inspections


    Standard Monitoring Procedures

    Visual monitoring

    • Frequency: once each quarter of the entire permit term
      • Quarter starts: Jan. 1, April 1, July 1, Oct. 1
    • Activity: collect stormwater sample from each outfall and conduct visual assessment
      • Color, odor, clarity, floating solids, settled solids, suspended solids, foam, oil sheen, any other obvious indicator of stormwater pollution

    General monitoring requirements

    • Frequency: semiannually
      • One between oct 1 and march 31
      • Another between April 1 and sept 30
      • Events must be separated by at least 30 days
    • Activity: Conduct for:
      • Chemical Oxygen Demand (75), Total Oil and Grease (5), pH (5-9), Total Suspended Solids (90), Total P (0.40), TKN (2.30), Nitrate as N (1.10), Total Cu (0.059), Total Pb (0.076), Total Zi (0.160), aquatic toxicity (for the first two years)
    • Not exceeding:
      • If the average of four monitoring values for any parameter do not exceed benchmark, the monitoring requirement for that parameter is fulfilled
    • Exceeding:
      • If the average of the four semiannual monitoring values for any parameter exceeds the benchmark, the SWPPP must be reviewed and determine if modifications are necessary
      • See the Natural Background Pollutant and Off-Site Run-On FAQ for more information regarding this exceedance.

    Monitoring of Discharges to Impaired Waters

    • Impaired water without a TMDL
      • Monitor annually for any indicator pollutants contributing to the impairment
      • Monitoring requirement does not apply after the first year of monitoring if the indicator pollutant is not detected above natural background levels or is the result of run-on entering from offsite
    • Impaired water with a TMDL
      • Permittee not required to monitor for any indicator pollutant identified in the TMDL unless notified otherwise
        • After the first year of sampling, if the indicator pollutant is not detected, further sampling can be discontinued, unless notified otherwise
        • If the pollutant indicated is identified within the first year of sampling, annual monitoring must continue through the term of the permit, unless notified otherwise.
    • To learn more about if you discharge to an impaired water or if your impaired water has a TMDL, consult the Impaired Waters Table

    Stormwater Monitoring Procedures

    • All samples collected from discharges from a storm event occurring at least 72 hrs after any pervious storm event generating discharge
      • Snow or ice must be identified on report form
    • If discharge is through a detention basin or other stormwater management structure, sample must be collected from there.
      • If no discharge, mention on report form
    • Grab samples collected during first 30 min of a storm event discharge
    • Representative discharge
      • Two or more outfalls which discharge identical effluents, the permittee may test one outfall and report that it is identical, along with a rationale of why they are representative discharges
    • Storm Event Information
      • Collect with sample:
        • Date, discharge temp, time of start of discharge and sampling, magnitude (in) of storm event
        • pH of uncontaminated rainfall (before it hits the ground)
        • duration between storm event sampled and more recent storm event with discharge
      • If sample cannot be taken, document in stormwater monitoring report form with reasons why