Technical Guidance

This page provides guidance on the following topics.  If you do not see the topic you are looking for, please contact Brianna Young for assistance.

Permit and Certificate of Coverage Numbers

Each facility has a specific permit number.  For general and individual permits, the number is 3 letters followed by 6 numbers.  For general permits, the first two numbers denote the type of general permit applicable to the facility.  For No Exposure Certifications, the number is "NCGNE" followed by 4 numbers. See the table below for more information.

Number Starts With

Permit Type




General Permit

The first two numbers denote the general permit type



Individual Permit




No Exposure

Only has 4 numbers




Permit Types

Permit Type

General Permit Most industrial facilities in North Carolina are covered under a General Permit; there are 21 General Industrial Permits.  Industries that are eligible for one of the General Industrial Permits are issued a Certificate of Coverage (COC). Each facility's COC contains the same requirements as for all other facilities covered under the same General Permit. For more information, see the General Permit section of our website (found here).
Individual Permit Industries that are not eligible for any of the General Permits may be required to obtain an individual permit. These permits are more tailored for a specific facility. As a result, the application and approval process is more arduous than for General Permits. For more information, see the Individual Permit section of our website (found here).
No Exposure Certification

Facilities with stormwater discharges "associated with industrial activity" may be excluded from permit coverage if industrial materials and operations are not exposed to stormwater.  For more information, see the No Exposure section of our website (found here).

Stormwater Benchmarks

Benchmarks are numerical action levels for pollutants that may be present in industrial stormwater.  All NPDES Stormwater Industrial permits include a table that lists the parameters that an industrial facility is required to monitor and the benchmarks associated with each parameter.  Benchmarks are different from effluent limits because a stormwater discharge concentration that exceeds a benchmark concentration in the permit table is not a violation of a stormwater permit.  However, a permittee who fails to conduct the required investigations to determine the source of the exceedance or who fails to take the required actions to correct the exceedance is in violation of his/her stormwater permit.

The Stormwater Program provides benchmarks with assistance from the Division of Water Resources’ Classifications and Standards, Rules Review Branch.  These DWR staff members use data from multiple sources to develop stormwater benchmarks, including EPA’s National Recommended Water Quality Criteria, the National Primary Drinking Water Regulation (40 CFR 141.11), and NC Surface Water Quality Standards (15A NCAC 02B .0200). When these resources do not contain information for a particular pollutant of concern, benchmarks are calculated per 15A NCAC 2B .0200 using peer-reviewed toxicity data. 

Another important point about benchmarks is that they are set for each pollutant based on the effects on aquatic life from acute (short-term) exposure to the pollutant.  The effects that are considered include both mortality and impairment to biological functions like feeding, movement, and predation.  Acute rather than long-term impacts of pollutants are considered because rainfall events occur sporadically.   

There are a few reasons for the differences between stormwater benchmarks and water quality standards:

  • Benchmarks are based on acute (short-term) rather than chronic (long-term) pollutant levels.
  • Different technical sources may be used to develop a stormwater benchmark than a water quality standard.
  • Benchmarks for metals are based on total pollutant concentrations (the sample is not filtered before analysis), and (most) water quality metals standards are based on dissolved pollutant concentrations (the sample is filtered before analysis).  

Monitoring and Sampling

See EPA's Industrial Stormwater Monitoring and Sampling Guide.

No Discharge

A “No Discharge” report means that no discharge occurred from a stormwater outfall for the entire monitoring period.  For this reason, permittees should begin outfall monitoring efforts with the first measurable storm even in the monitoring period that occurs during the facility's normal operating hours.  Not all outfalls must be sampled during the same storm event, so permittees are required to continuously attempt to sample each outfall until the end of the monitoring period.  Waiting until the last month of the monitoirng period to begin monitoring efforts and then recording "No Discharge" does not comply with permit conditions.

If there is no discharge from an outfall during the entire monitoring period, the permittee shall:

  • Report “No Discharge” in the DMR,
  • Note “No Discharge” in the SWPPP, and
  • Submit the DMR within 30 days after the end of the monitoring period.

As individual and general permits are renewed, this requirement will be clarified.   

Sample Analysis

For Stormwater Discharges North Carolina certification procedures do not apply to stormwater-only discharges at this time.  However, any monitoring of discharges under an NPDES permit (including stormwater) must be conducted in accordance to test procedures approved under federal regulations in 40 CFR §136.  This includes measuring pH properly within the 15-minute hold time.  All labs certified by North Carolina perform analyses in accordance with federal procedures.  So, even if your facility is not classified as a Water Pollution Control System, using a North Carolina certified lab is often the easiest way to comply with NPDES Program requirements.  A list of North Carolina certified labs can be found here.
For Wastewater Discharges

North Carolina certification procedures apply to wastewater discharges originating from Water Pollution Control Systems defined under T15A NCAC 8G .0300 and classified by the Technical Assistance and Certification Unit.  However, wastewater treatment facilities at most mines and ready-mixed concrete plants under General Permits NCG020000 and NCG140000 are not classified at this time.  Because state Operator and Laboratory Certification programs currently do not address these treatment facilities, there are no certification requirements for entities performing wastewater sample analysis (including field measurements like pH) at these sites right now, unless an exception is classified by the TACU.  Whether certified or not, discharge monitoring under an NPDES permit must be conducted in accordance to test procedures under 40 CFR §136.

Extra Samples

If a permittee monitors any pollutant more frequently than required by a General Permit using test procedures approved under 40 CFR Part 136 and at a sampling location specified in this General Permit, then the results of such monitoring shall be included in the data submitted on the DMR.  Analytical results within the monitoring period shall be submitted no later than 30 days from the date the facility receives all the sampling results.  For purposes of benchmark comparison and Tiered response actions, the permittee shall use the analytical results from the first sample with valid results.  The permittee is encouraged to take more samples than required by permit during a monitoring period to help identify potential causes of exceedance(s).  When taking additional samples, the permittee may not use the additional sample with lowest results for compliance purposes to avoid taking actions to identify causes of parameter exceedances. Additional sampling is only for informational purposes.

Tier Responses

The Tier Response system is the method that NCDEQ’s stormwater program uses to help industrial facilities identify and correct stormwater discharge deficiencies. Please email or call the appropriate Regional Office to inform them of benchmark/limit exceedances as needed.

If a parameter exceeds its benchmark, all parameters at that outfall will go into Tier 1 status. If the same parameter exceeds its benchmark twice in a row, all parameters at that outfall will go into Tier 2 status. If the same parameter exceeds its benchmark four times in any five year period, all parameters at that outfall will go into Tier 3 status. Below is a summary of this system, but a more in-depth explanation can be found in the applicable permit. 


Tier 1

Tier 2

Tier 3

How does an outfall get into this Tier?

A parameter exceeds its benchmark

A parameter exceeds its benchmarks twice in row

A parameter exceeds its benchmark 4 times within a five year period

How does an outfall get out of this Tier?

3 consecutive samples are under benchmark

3 consecutive samples are under benchmark

3 consecutive samples are under benchmark or if the local Regional Office waives

How often do parameters need to be sampled while in this Tier?

Quarterly or Semi-annually, depending on the permit.



Stormwater Pollution Prevention Plans (SWPPPs)

EPA resouress to assist with SWPPPs:

Non-polar Oil & Grease/TPH by Method 1664 (SGT-HEM)

There has been confusion over this parameter in recent permits (mainly for vehicle maintenance monitoring), and we want to clear it up.  This description refers to ONE test:  Non-polar Oil &Grease using EPA Method 1664 with the silica gel treatment step, in addition to hexane extraction (not JUST HEM).  This gravimetric test method is an alternative way of estimating Total Petroleum Hydrocarbons (TPH), without using the more expensive gas chromatographic analysis.  This parameter does not refer to TPH analysis by gas chromatograph.  Future permits and DMR forms will be updated with language to avoid confusion about the term.  [Please note that currently labs in NC are being certified for Revision B to that Method under 40 CFR 136.]

There is also guidance on the Oil Spill Information Sheet.

Vehicle Maintenance Activity (VMA)

If my facility uses more than 55 gal/month of motor oil BUT performs all vehicle maintenance indoors, do we still have to monitor VMA parameters in the permit?

Probably.  Even when all maintenance is performed inside, the NPDES program considers parking lots used to store vehicles prior to maintenance as a component of the vehicle maintenance activity (VMA).  The facility must still monitor any outfalls draining those areas for VMA-related parameters if the parking area for these vehicles is exposed.

If all vehicles awaiting maintenance are not stored outside or otherwise exposed to stormwater, EPA guidance is not clear about whether monitoring applies when the minimum motor oil usage (indoors) is exceeded.  NC's NPDES Stormwater Program interprets current permit conditions to allow permittees to forgo VMA monitoring as long as no vehicle maintenance materials, maintenance activities, or vehicles are exposed in any drainage area.

Vehicle Washing

Vehicle pressure washing wash water is a wastewater, and discharge to surface waters through storm drains is not authorized by any NPDES stormwater permit.  You should check with your local government, as some may require a permit.  This fact sheet has additional details and information.  (Also see the NPDES Wastewater Guidance website.)  See the the Vehicle Washing Information Sheet for more guidance.

Facilities with Multiple SIC Codes

What would a facility do if they have multiple outfalls, but each stormwater outfall is associated with industrial activity classified under different general permits? Would they apply for coverage under each applicable general permit, or would they have to get an individual permit?

It depends.  If their primary activity (or what constitutes the most exposure potential) is associated with one General Permit, and the monitoring requirements in that GP were sufficient to cover other outfalls with different types of industrial activity (i.e., the potential pollutants are covered in the GP we’re considering anyway), then we just cover the facility under the one General Permit.  If the activities really are diverse enough that the one General Permit is adequate, we’d have to take them the individual permit route.  This is a lot more involved for the permittee, we understand, but unfortunately, we don’t have a Program set up the same way as the EPA Multi-Sector permit, which requires facilities to follow every portion of the permit that pertains to their activities.