NPDES Permitting Overview - Discharge Permits Under the Clean Water Act

Overview

The National Pollutant Discharge Elimination System (NPDES) is the federal permitting program that regulates point source discharges of pollutants to waters of the United States under the Clean Water Act (CWA). If you discharge wastewater, stormwater, or any other pollutant from a discrete conveyance (pipe, ditch, channel) to a surface water body, you likely need an NPDES permit.

NPDES permits are authorized under CWA Section 402 (33 U.S.C. 1342). Most states are authorized by EPA to administer the NPDES program within their borders. In Ohio, NPDES permits are issued by Ohio EPA’s Division of Surface Water.

Who Needs an NPDES Permit

Any person or entity that discharges pollutants from a point source to waters of the United States needs an NPDES permit. Common activities requiring permits include:

Industrial discharges - process wastewater, cooling water, and other industrial effluent
Municipal wastewater treatment plants - treated sewage discharge
Construction stormwater - runoff from construction sites disturbing one acre or more
Industrial stormwater - runoff from industrial facilities with exposed materials or activities
Municipal separate storm sewer systems (MS4s) - stormwater collected by municipal storm drain systems
Concentrated animal feeding operations (CAFOs) - discharge from large livestock operations
Mining operations - discharge from mining activities
Remediation discharges - treated groundwater or dewatering water from environmental cleanup activities

Environmental consultants most commonly encounter NPDES requirements in two contexts: construction stormwater permits (often linked to SWPPP requirements) and discharge permits for remediation activities (pump-and-treat system effluent, dewatering during excavation).

Types of NPDES Permits

Individual Permits

Individual permits are site-specific permits tailored to a particular facility’s discharge. They contain facility-specific effluent limits, monitoring requirements, and compliance schedules. Individual permits are required for:

Large or complex discharges
Discharges to impaired water bodies
Facilities with significant environmental impact
Situations where a general permit is not available or not appropriate

Individual permits are issued after a detailed application review, public notice, and public comment period. They are typically valid for five years and must be renewed.

General Permits

General permits cover categories of similar discharges. Rather than developing a site-specific permit for each facility, EPA or the authorized state issues a general permit that applies to all facilities in the category that meet specified conditions. Facilities obtain coverage by submitting a Notice of Intent (NOI).

Common general permits include:

Construction General Permit (CGP) - covers stormwater discharges from construction activities disturbing one acre or more. In Ohio, this is the OHC000005 permit.
Multi-Sector General Permit (MSGP) - covers stormwater discharges from industrial facilities in designated sectors. In Ohio, this is the OHR000007 permit.
Small MS4 General Permit - covers stormwater discharges from small municipal storm sewer systems

General permits are faster to obtain and less expensive than individual permits, but they have less flexibility in their terms and conditions.

What an NPDES Permit Contains

Effluent Limitations

The core of any NPDES permit is the effluent limitations - the maximum allowable concentrations or mass loadings of pollutants in the discharge. Effluent limits are based on:

Technology-based limits - the minimum level of treatment required for the type of discharge, based on available treatment technology. For industrial discharges, these are typically Effluent Limitations Guidelines (ELGs) published by EPA for specific industry categories.
Water quality-based limits - more stringent limits required when technology-based limits alone are not sufficient to meet water quality standards in the receiving water body. These are calculated using the receiving water’s designated uses, ambient conditions, and applicable water quality criteria.

The permit contains the more stringent of the two for each parameter.

Monitoring and Reporting

NPDES permits require regular monitoring of the discharge and submission of Discharge Monitoring Reports (DMRs). Monitoring requirements specify:

Which parameters to monitor (pH, BOD, TSS, specific pollutants)
How often to sample (daily, weekly, monthly, quarterly)
What type of sample to collect (grab, composite, continuous)
Where to sample (outfall location)

DMRs must be submitted to the permitting authority on the schedule specified in the permit (typically monthly or quarterly). DMR data is publicly available through EPA’s ECHO database.

Special Conditions

Permits may include additional requirements such as:

Best management practices (BMPs)
Toxicity testing (whole effluent toxicity)
Pollution prevention plans
Spill prevention and response plans
Reporting of noncompliance, bypasses, and upsets

Stormwater Permitting

Stormwater is a major component of the NPDES program and the most commonly encountered permit type for environmental consultants.

Construction Stormwater

Construction activities that disturb one acre or more (or are part of a common plan of development that will disturb one acre or more) require NPDES stormwater permit coverage. This involves:

Developing a Stormwater Pollution Prevention Plan (SWPPP) before construction begins
Submitting a Notice of Intent (NOI) to the permitting authority
Implementing erosion and sediment controls per the SWPPP
Conducting regular inspections
Submitting a Notice of Termination (NOT) when final stabilization is achieved

Industrial Stormwater

Industrial facilities in designated sectors that have stormwater discharges associated with industrial activity must obtain NPDES stormwater permit coverage. This requires:

Determining whether the facility’s SIC/NAICS code falls within a covered sector
Developing a SWPPP with sector-specific BMPs
Submitting an NOI
Conducting quarterly visual assessments and benchmark monitoring
Annual reporting

Enforcement

NPDES violations can result in:

Administrative orders requiring compliance
Civil penalties (up to $64,618 per day per violation under federal law, as of 2024)
Criminal penalties for knowing violations
Citizen suits under CWA Section 505

Common violations include exceeding effluent limits, failure to monitor, failure to submit DMRs, and unauthorized discharges. EPA and authorized states track permit compliance through the ECHO database, which is publicly searchable.

NPDES and Environmental Remediation

Environmental consultants encounter NPDES requirements when cleanup activities generate wastewater that must be discharged. Common scenarios include:

Pump-and-treat systems that extract and treat contaminated groundwater before discharge to surface water
Dewatering during excavation at contaminated sites
Discharge of treated groundwater from remediation systems

These discharges typically require either an individual NPDES permit or coverage under a general permit for remediation discharges (if available in the state). The permit will specify treatment requirements and effluent limits for the contaminants of concern.

Source

Clean Water Act Section 402 (33 U.S.C. 1342). 40 CFR Parts 122-125 (NPDES regulations). EPA NPDES Permit Basics website.