The Wisconsin Department of Natural Resources (WDNR) promulgated
NR 439 in September of 1986 to codify the requirements for reporting, recordkeeping, testing, inspection, and determination of compliance requirements. The WDNR have made updates to the rule since promulgation, however, most of these have been very minor changes, and the rule is largely written as it was when promulgated. NR 439 applies to all air contaminant sources and their owners and operators and sets a baseline for the majority of ongoing compliance for permitted facilities. For example, NR 439.04 states all records that the WDNR requires facilities keep, such as sampling, testing, and monitoring, any records that demonstrate compliance with any applicable emission limitations, etc.
Proposed NR 439 Updates
The WDNR has stated that the proposed changes to NR 439 will bring the rule into the 21st century, especially in regard to monitoring requirements, as new technologies have been implemented since the rule was originally written. The WDNR initiated the process of updating the rule in the summer of 2021 with
stakeholder listening sessions, published a Statement of Scope in August 2022 where the WDNR published the comments from the listening sessions, and continued development with further input from the public on the economic impact of the proposed rule and a general public comment session. The WDNR published a response to comments from both the economic impact analysis and the public comment period, with updates on how the DNR would address the concerns of both industry and the public. Major changes expected to the rule are as follows:
- Align rule language with federal requirements
- This will help standardize the Wisconsin regulations with the United States Environmental Protection Agency (USEPA) and allow consistent language across the rule
- Reporting – NR 439.03
- Create a new citation for the requirement of immediate reporting of hazardous substance air releases to clarify that other types of deviations in NR 439.03(4) do not require immediate reporting
- Next-business day reporting requirement: Revision of requirement for emission limitation exceedances to a tiered approach where emission limitation exceedances require a two-business day notification to the Department, with a submitted report within 10 calendar days
- Other deviations from permit requirements that are not emission limitation exceedances would be submitted no later than the due date of the monitoring report required in NR 439.03(1)(b)
- Expansion of the opacity reporting requirements from 10% above the opacity limit to 20%, and revise the requirement to use six-minute averaging periods, consistent with federal requirements
- Recordkeeping – NR 439.04
- Flexibility in records that can be maintained as paper, digital, or electronic formats
- Clarification of what sources are required to keep records, as well as what records are required to be kept
- Determining compliance with instrumentation – NR 439.055
- Update to yearly calibration requirement to allow for calibration of parametric monitoring devices per the manufacturer’s specifications or as required by an applicable standard
- Removal of equipment-specific monitoring parameters and frequencies
- Identification of specific records sources are required to keep for demonstration of compliance
- Methods and procedures for determining compliance with emission limitations – NR 439.06
- Addition of alternative federal test methods for PM10, organic compounds, sulfur compounds, lead, and nitrogen compounds
- Alignment of test methods for carbon monoxide, nitrogen compounds, sulfur compounds, and visible emission continuous emission monitoring systems (CEMS) with federal standards
- Period compliance emission testing – NR 439.07
- Clarification that compliance emission testing shall be performed under conditions resulting in maximum emissions, with control devices operating, and at capacity
- Allow for alternative test methods for determining gas flow rate, heat input, boiler emission rate, and organic compound emission limit determination
- Period fuel sampling and analysis – NR 439.08
- Update to fuel sampling and analysis methods for current standards and available methods
- Continuous emissions monitoring – NR 439.09 & NR 439.095
- Addition of federal performance specifications for pollutant CEMS that have been developed since the previous rule revision
- Clarification of when an excess emission report or summary excess emission report is required
- Simplification of the averaging period used to determine if excess emissions have occurred from sources monitored by CEMS
- Inclusion of a deadline for submission of a CEMS QA/QC plan
- Malfunction Prevention and Abatement Plans (MPAP) – NR 439.11
- Update the definition of an MPAP
- Limitation that only malfunctions that may cause an applicable emission limit to be violated or may cause air pollution shall be required in an MPAP
- Reduction of requirements for MPAPs to only include sources with have a control device
- Clarification on which emission units, operations, and activities require an MPAP, exempt smaller emission units, operations, and activities
- Clarification on required plan content and submittal requirements
- Addition of MPAP recordkeeping requirements for demonstration of implementation
- Clarification when MPAP review and updates are required
Summary & What to Expect
The proposed changes to NR 439 should allow greater flexibility for facilities, and clarify vague pain points in the rule, but will also place new requirements on sources. Facilities should be ready to update existing MPAPs and Environmental Management Information Systems (EMIS) and read the draft and final rule to understand the new changes to recordkeeping and reporting for continued compliance.
The WDNR filed for publication of the rule on May 5, 2025, with the Wisconsin Legislative Bureau as CR 24-030, and has stated that the rule is expected to be published on June 30, 2025, with an effective date of July 1, 2025. As facilities may know, Part 2 of a WDNR issued air permit includes many references to and requirements from NR 439. The WDNR has stated that they view the Part 2 permit as an individual permit attached to the Part 1 permit, so the WDNR will be able to update the Part 2 permit separately from the Part 1 permit. Facilities should expect to receive an updated Part 2 permit around September 2025, however, the WDNR has not previously issued permits in this manner, so some delays or changes to the method outlined may be present at the time of issuance.
Additional Resources
If you have any questions about the proposed changes to NR 439 or how they may impact your facility, please contact Trinity’s
Wisconsin office at
262.200.0200.
