4 The record articles

Proposed Changes to New Hampshire Air Toxics Rules and Potential Ramifications to Stakeholders

Posted: September 22nd, 2021

Authors: John H.  Dan D.  Ryan C. 

ALL4 is pleased to continue providing updates regarding changes to New Hampshire air toxics rules and the impacts to stakeholders responsible for compliance.  In April 2021, ALL4 presented, “Changes to the New Hampshire Air Toxics Rule:  What Could it Mean for You”, the first in a series of articles detailing proposed revisions to the New Hampshire Code of Administrative Rules Part Env-A 1400 (Rule).  This article serves as the second part in the series, intended to provide updates to recent developments associated with the proposed revisions and to provide a high-level overview of one implication of the revisions: considerations for conducting air dispersion modeling at a facility.


In 1987, the New Hampshire Legislature established its Air Toxic Control Act to promote public health and reduce human exposure to toxic chemicals.  The act regulates releases of Regulated Toxic Air Pollutants (RTAP) into ambient air and requires any facility that uses substances containing RTAP to conduct an Air Toxics Compliance Demonstration to determine compliance with ENV-A 1400.

Env-A 1400 is applicable to facilities that use products containing RTAP and therefore applies even if an air emissions permit is not required for a facility.  Examples include manufacturing facilities, facilities burning a non-exempt fuel, such as landfill gas and resinated wood products for heat or power, and facilities producing a renewable fuel, such as dried wood chips, pellets, and Renewable Natural Gas (RNG), the biogas product of the decomposition of organic matter.

Proposed changes to Env-A 1400

On August 16, 2021, the New Hampshire Department of Environmental Services (NHDES) provided notice of rulemaking for Env-A 1400.  As part of the notice, a public hearing has been scheduled for September 29, 2021, and written public comments will be accepted through October 8, 2021.  The public hearing will be held in person at NHDES offices in Concord, New Hampshire and will be made accessible virtually.

The intent of the proposed changes to Env-A 1400 is to clarify aspects of the Rule to make it easier to understand and follow.  Sections have been reorganized and renumbered, and terminology has been added or redefined.  Several noteworthy changes to the Rule that could potentially necessitate compliance activities, including air pollution dispersion modeling, are:

  • Addition, or incorporation of, 121 RTAP,
  • Removal of 21 RTAP,
  • Modification to aspects of over 150 RTAP (e.g., compound description, de minimis and Ambient Air Limits (AAL) thresholds, toxicity class), and
  • Redefinition of the compliance boundary for leased properties and inclusion of a provision for proposing an alternate compliance boundary other than the boundary in which an emissions source is located.

Overview of Env-A 1400

Env-A 1400 defines the applicability of air emissions sources and exemptions to the Rule, permit requirements and application procedures, and the classification of RTAP.  Under the Rule, NHDES established de minimis levels and AAL for over 700 RTAP, including lead.  The Rule applies to a stationary source with new, modified, or an existing process or device that emits RTAP, unless exempted under Env-A 1402.01 (e.g., normal agricultural operations and emissions of RTAP from mobile sources or resulting from combustion of virgin petroleum products) or Env-A 1402.2 (e.g., combustion of certain fuels, gasoline dispensing, and spray coating operations).

Compliance with the Rule can be demonstrated based on a sequence of evaluation methods specified in the Rule, in the following order:

  • De minimis emission level method,
  • In-stack concentration method,
  • Adjusted in-stack concentration method, and
  • Air dispersion modeling analysis.

The Rule also provides the option for an applicant to submit a request for approval of an alternative compliance demonstration using air dispersion modeling to NHDES.

Requirements for performing compliance demonstrations vary across the methods.  The de minimis emission level method requires emissions rates when airflow exiting the stack is vertical and unobstructed.  Both the in-stack concentration and adjusted in-stack concentration methods require the emissions rate, in pounds per hour, of each RTAP from each stack.  The in-stack method also requires volumetric flow rates for each stack, whereas the adjusted in-stack methods requires distances from each stack’s associated building to the nearest compliance boundary.  The air dispersion modeling analysis method has specific procedural requirements specified by NHDES, and has additional data requirements, including emissions rates, stack parameters, meteorological data, and terrain data.  Regardless of the selected method, compliance must be demonstrated relative to the de minimis or AAL levels defined in the Rule.

Modeling Associated with Env-A 1400

Under the proposed Env-A 1404.02, if an air dispersion modeling analysis is performed, the owner or operator must conduct the analysis in accordance with Env-A 606 requirements to demonstrate that the concentration of emissions of each RTAP is equal to, or below, the corresponding AAL at and beyond the compliance boundary.

In addition, NHDES modeling guidance requires the use of one of the United States Environmental Protection Agency (U.S. EPA) recommended models, AERMOD or AERSCREEN, in conformance with the “Guideline on Air Quality Models” (Appendix W to 40 CFR Part 51).  For any compliance demonstration associated with a permit application, NHDES requires, by rule, submittal of a modeling protocol documenting the proposed modeling methodology and input parameters, prior to submittal of the compliance demonstration.  Following acceptance of an approved protocol, results of the compliance demonstration, in the form of a report and associated modeling files, must also be submitted to NHDES.  Even if the compliance demonstration is not associated with an air emissions permit, it is recommended that the final report be kept on-site, in the event the facility is inspected in the future.

Potential Impacts and Benefits to Stakeholders

The proposed changes to Env-A 1400 could have significant impacts on existing facilities that emit RTAP.  The addition of RTAP may require an updated compliance demonstration, possibly including modeling for facilities that have previously demonstrated compliance, whereas the removal of one or more RTAP or the increase in de minimis threshold or AAL may present facilities with an opportunity to remove or relax permit limits on some processes.  The modification of RTAP thresholds may require updated analyses, either to demonstrate compliance with more restrictive limits, or to increase permit limits due to more lenient limits.  Similarly, the redefinition of the compliance boundary may impact compliance or offer the opportunity to modify permit limits.

In addition to updating previous compliance demonstrations for existing facilities, the proposed Rule changes may prompt a change in a facility’s compliance demonstration strategy.  A different approach may become more cost-effective or offer a facility additional operational flexibility.  Facilities, and the individuals responsible for maintaining their compliance, should review the Rule revisions and carefully consider their impacts on costs and production flexibility, to realize effective and efficient operations.

Stakeholders – Actions to Consider

Stakeholders should begin the evaluation process to determine how they may be impacted by the proposed Rule changes.  The evaluation should include:

  • Determining if Env-A 1400 applies to a facility. If a facility is not exempt, perform a compliance demonstration.
  • While performing the compliance demonstration, evaluating the most effective compliance strategy, such as initiating a product substitution, changing production goals, installing an emissions control device, requesting an alternative compliance boundary, or performing air quality dispersion modeling.
  • Assessing if Env-A 1400 will require an air emissions permit. Compliance must be evaluated and demonstrated, with supporting documentation kept on-site, even if an air emissions permit is not required.

Contact John Hinckley at jhinckley@all4inc.com (802-359-7295), Dan Dix at ddix@all4inc.com (610-422-1118), or Ryan Cleary at rcleary@all4inc.com (919-230-0716) for more information.


    Sign up to receive 4 THE RECORD articles here. You'll get timely articles on current environmental, health, and safety regulatory topics as well as updates on webinars and training events.
    First Name: *
    Last Name: *
    Location: *
    Email: *