NPDES Permits IllinoisNational Pollutant Discharge Elimination System (NPDES) permits are being reissued now with new, revised and expanded special conditions. The special conditions include:

  • A New Phosphorus Feasibility Study
  • A New Phosphorus Optimization Plan
  • A Revised Storm Water Pollution Prevention Plan; Revised (SWPPP)
  • New 85% Removal of BOD and TSS Special Condition
  • Expanded Capacity Management Operation and Maintenance (CMOM) Requirements

Over the last couple years the United States Environmental Protection Agency (USEPA) has raised several issues of concern with the Illinois Environmental Protection Agency (IEPA) and as a result a backlog of NPDES permits waiting to be reissued developed. Recently this has changed as IEPA and USEPA have finally reached a compromise on several new special conditions to include in NPDES permits. IEPA is now reissuing NPDES permits with the new special conditions outlined.

NEW SPECIAL CONDITION: A Phosphorus Feasibility Study

IEPA is requiring a Phosphorus Feasibility study for plants larger than 1 MGD within 18 months of the effective date of the permit.

NPDES permit holders are now required to submit a feasibility study to identify the capital and operational costs for providing different levels of phosphorus removal. The NPDES permit requires a feasibility study of the efforts required to meet possible future effluent limitations of 1 mg/l, 0.5 mg/l, and 0.1 mg/l.

IEPA has stated they will not make a determination if any NPDES permit holder needs to take specific action based upon their feasibility study. All feasibility studies are being collected as part of the broader State Nutrient Reduction Strategy, and will be used by Illinois to weigh the costs and benefits of adopting additional nutrient criteria. These studies may be preliminary in nature, assuming the NPDES permit holder does not already have a compliance mandate to reduce their phosphorus discharge. A more detailed level of planning may be expected during the facility planning phase in the event of a more stringent regulatory requirement for treatment.

Plants located within the Fox River Watershed have been receiving similar permit language. However, these permits include a compliance schedule to meet a new phosphorus limit, and the language in those permits is customized to reflect the on-going efforts to reduce phosphorus loading to the Fox River.

NEW SPECIAL CONDITION: A Phosphorus Optimization Plan

IEPA is requiring a Phosphorus Discharge Optimization Plan for plants larger than 1 MGD within 18 months of the effective date of the NPDES permit.

This plan should examine industrial users in the service area and consider opportunities to reduce phosphorus loading through industrial pretreatment programs. The plan should also consider opportunities to optimize the current plant for phosphorous removal. Examples include:

  • modifications to the operations of the existing facilities, or
  • low cost changes in the configuration of existing tanks.

NEW REVISED SPECIAL CONDITION: A Storm Water Pollution Prevention Plan

IEPA has revised the special condition it includes in some permits requiring a Storm Water Pollution Prevention Plan. This revised special condition is only included in permits that have had the previous version the Storm Water Pollution Prevention Plan language, or in cases in which the owner requests it. Permit holders with an existing SWPPP will be required to review and update their SWPPP within 30 days of the effective date of the permit. Permit holders without a SWPPP will be required to prepare and submit a SWPPP within 6 months of the effective date of the permit.

All domestic wastewater facilities with a capacity of 1 MGD or greater are subject to federal stormwater regulations given in 40 CFR 122.26. Historically, most plants in Illinois have applied for stormwater coverage under the IL General Permit ILR00 – Stormwater Discharges from Industrial Facilities. However, some plants requested the stormwater requirements be added to their plant NPDES permit so they would not have to apply for a separate stormwater permit. The original version of this special condition was developed for those situations.

IEPA has revised the original special condition so it is better orientated towards wastewater facilities. IEPA has pointed out the language in the original special condition was written generically towards any industrial facilities, and it was not always clear how, and if, some of the language was applicable to wastewater plants.

Plants with the previous version of this special condition in their permit will automatically receive the revised version upon permit renewal. Other permit holders can request for this special condition to be added during their permit renewal. IEPA will consider these requests on a case-by-case basis. The advantage of adding the SWPPP special condition to a NPDES permit application is the elimination of the need for a separate stormwater permit and the associated fee. The disadvantages are that it adds to the length of the permit, and the added special condition is subject to public comment or objections (along with the rest of the permit).

NEW SPECIAL CONDITION: 85% Removal of BOD and TSS Special Condition

IEPA is requiring an 85% monthly average removal of BOD and TSS. This new special condition is being added to all NPDES permits in accordance to the federal requirements for secondary treatment.

In the case of facilities with excess flow, compliance with the 85% monthly removal special condition must include the removal efficiency of the excess flow treatment. In this case the NPDES permit holder needs to calculate:

  • the total pounds of influent and effluent pollutants from both the main treatment and excess flow systems, and
  • the net removal efficiency based upon the total monthly average of both influent and effluent total pounds.


  • CSO treatment facilities are not being included in this calculation unless the flow diversion to the CSO treatment facilities occurs after the main headworks of the wastewater treatment plant.
  • IEPA is not requiring this information to be reported on the monthly DMRs. However, records of the influent and effluent data must be available on site for IEPA inspection and review.

EXPANDED SPECIAL CONDITION: Capacity Management Operation and Maintenance (CMOM) Requirements

In the past, IEPA has included CMOM requirements in NPDES permits for CSO communities, plants with excess flow, or communities with a past history of SSOs. Recently, the draft permits issued by IEPA indicate IEPA has expanded the permit scope to include CMOM requirements for all plants 1 MGD and larger. This may not be the case and some permits may be issued without the expanded CMOM requirements.

The expanded CMOM requirements are based upon USEPA 2005 CMOM Guidance and are intended to encourage optimal collection system management. The expanded CMOM requirements contain language that specifically requires the NPDES permit holder to develop an asset management program which will identify:

  • all owned assets,
  • the conditions of each,
  • level of service,
  • identification of critical assets,
  • life cycle costs, and
  • long-term funding strategies.

Also, the expanded CMOM requirements place an increased emphasis on tracking basement backups, identifying sources of inflow and infiltration, and developing plans for their removal.

NPDES Permit holders who have not previously developed and submitted a CMOM plan will be required to do so in the time frame outlined in the NPDES permit. NPDES Permit holders who have previously submitted a CMOM plan will be expected to review their existing program, to make any modifications required, and to resubmit to IEPA within the time frame in the NPDES permit. The time frame can vary depending upon the site specific situations, however twelve months seems to be the most common.

Authored by:
Nate Davis, Crawford, Murphy & Tilly Water Resource Engineer Specializing in Wastewater Treatment
Direct: 217-572-1137

Please feel free to contact Nate if you have thoughts, suggestions and/or questions.