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The United States Environmental Protection Agency (EPA) issued the "Identification of Non-Hazardous Secondary Materials (NHSMs) that are Solid Waste" final rule (Current NHSM Rule) under 40 CFR Part 241 on March 21, 2011.  EPA received several comments from the regulated community and stakeholders requesting clarification on definitions and provisions contained in the Current NHSM Rule.  On December 23, 2011, EPA proposed amendments to certain provisions of the Current NHSM Rule (Proposed NHSM Rule Revisions).


The Current NHSM Rule was developed under the Resource Conservation and Recovery Act (RCRA) in conjunction with National Emission Standards for Hazardous Air Pollutants for Boilers (the Boiler NESHAP) and revisions to the Commercial and Industrial Solid Waste Incinerator (CISWI) Rules under the Clean Air Act (CAA).  Combustion sources utilizing solid waste would be subject to the CAA Section 129 requirements (i.e., CISWI Rule) while combustion equipment utilizing non-waste fuel would be subject to the CAA Section 112 requirements (i.e., Boiler NESHAP).  Therefore, it is critical to accurately classify NHSMs as solid waste or non-waste fuel in order to determine whether a combustion unit is subject to a CAA Section 112 or a CAA Section 129 regulation.1

In general, the Current NHSM Rule identifies NHSMs burned in combustion units as solid wastes unless the material falls into one of the following categories, has not been discarded, and meets the following legitimacy criteria:

  • Material used as a fuel that remains within the control of the generator
  • Scrap tires that have not been discarded and are managed under the oversight of an established tire collection program
  • Resinated wood that has not been discarded
  • Material used as an ingredient2
  • Material produced from the processing of NHSMs

The Current NHSM Rule also specifies that EPA may grant a non-waste determination on a case-by-case basis (case-by-case determination) for an NHSM used as a fuel and not managed within the control of the generator, not discarded, and thus not a solid waste when combusted.  Note that to obtain this case-by-case determination from EPA, the NHSM must also meet the legitimacy criteria requirements that are described below.

Any NHSM that is not a traditional fuel must meet the following legitimacy criteria to avoid classification as a solid waste.  Under the Current NHSM Rule, the legitimacy criteria for materials used as a fuel are as follows:

  • Managed as a valuable commodity such that the storage of the NHSM does not exceed reasonable time frames, and releases to the environment are prevented
  • Meaningful heating value (typically around 5,000 Btu/lb or greater) and used as a fuel in a combustion unit that recovers energy
  • Contains contaminants at levels comparable in concentration or lower than those in traditional fuels which the combustion unit is designed to burn
Key Revisions

EPA limited the scope of the Proposed NHSM Rule Revisions to updating key definitions, revising the contaminant legitimacy criteria for NHSMs used as fuels, providing categorical non waste determinations for select NHSMs, adding a petition process for facilities to request EPA to add a categorical non-waste determination to 40 Part 241.4(a), and clarifying other miscellaneous provisions.  The key proposed changes to the Current NHSM Rule are summarized below.

Revised Definitions
EPA is proposing to update the definition of clean cellulosic biomass by adding a number of specific examples of materials that are considered clean cellulosic biomass (explicitly not a solid waste) such as wood pellets and hogged fuel.  Although EPA added several new materials to the definition, the preamble to the Proposed NHSM Rule Revisions is clear that the list of materials provided in the definition of clean cellulosic biomass is not exhaustive.3  If a combustion unit burns a type of clean cellulosic biomass that is not specifically listed in the revised definition of clean cellulosic biomass, the facility should verify that the biomass fuel does not contain contaminations at concentrations higher than virgin biomass materials.

EPA is also proposing to revise the definition of contaminants in order to clarify how a facility can determine if a NHSM meets the legitimacy criteria.  The current definition of contaminant includes all pollutants listed in CAA Section 112(b) and Section 129(a)(4).  As part of the Proposed NHSM Rule Revisions, EPA is proposing to clarify which pollutants listed under either section of the CAA will or will not be considered a contaminant.  Refer to Table 1 for a list of pollutants that will or will not be considered as contaminants per the Proposed NHSM Rule Revisions.  Note that if a pollutant is not specifically excluded from the contaminant definition and is listed in either CAA Section 112(b) or Section 129(a)(4), that pollutant will be considered a contaminant under the proposed revisions.  EPA’s rationale on updating the definition of contaminants is to clearly identify the elements and compounds that are expected to be found in the NHSM and ultimately result in air emissions of a regulated pollutant under CAA Sections 112 and 129.

NHSM Table 1 Spring 2012


In the Current NHSM Rule, it is unclear whether the contaminant threshold should be compared to the emissions emitted from the stack or compared to the pollutant concentration contained in the non-burnt NHSM.  Due to this ambiguity, EPA is proposing to remove the phrase "that will result in emissions of air pollutants" from the current definition of contaminants in order to clarify that the pollutant concentration in the NHSM itself should be evaluated and not the emissions generated by the combustion unit.

EPA is proposing to revise the definition of established tire collection program to include tire retailers and manufacturers that generate scrap tires that are sold to a combustor.  EPA has determined that tires can be routed to a combustor and treated as a commodity via two mechanisms where the tires have never been discarded: 1) through a state run tire collection program and 2) through a contractual agreement between tire manufacturers and the combustor where scrap/off-spec tires are sent directly as fuel.

Fuel Legitimacy Criteria Revisions
In the Proposed NHSM Rule Revisions, EPA is proposing two key changes to the contaminant legitimacy criteria for NHSMs used as fuel.  The first revision includes replacement of the term “contaminants” with the phrase “contaminants or groups of contaminants” to allow flexibility when determining whether an NHSM meets the contaminant legitimacy criteria.  It is now possible to group similar contaminants (e.g., volatile organic compounds [VOCs] or total selected metals [TSM]) in order to satisfy the legitimacy criteria.  Under the Current NHSM Rule, contaminant levels could only be compared on a pollutant-by-pollutant basis.  This revision clearly gives industry the necessary flexibility to demonstrate that the contaminant portion of the legitimacy criteria is achieved for select NHSMs.

The second revision to the legitimacy criteria revolves around exactly what traditional fuels can be selected to compare against the NHSM contaminant levels.  EPA is proposing to allow all traditional fuels that the combustion unit is designed to burn, regardless of whether the unit is “permitted to burn that traditional fuel” for comparison to the NHSM.  Under the Proposed NHSM Rule Revisions, it will be possible to select the highest concentration of a contaminant or group of contaminants from all traditional fuels the combustion unit is designed to burn for comparison with the NHSM.

It should be noted that the contaminant legitimacy criteria determinations do not mandate testing of contaminant levels in either NHSMs or traditional fuels.  Expert or process knowledge may be used to justify contaminant concentrations for comparison.  Examples of acceptable means to obtain contaminant thresholds may include generic laboratory test results or industry-recognized values provided by a national trade organization.

Categorical Non-Waste Determinations and the Proposed Petition Process
In the Current NHSM Rule, both resinated wood and scrap tires would need to meet the legitimacy criteria in order to qualify as a non-waste NHSM.   However, in the Proposed NHSM Rule Revisions, EPA would grant a categorical non-waste status to resinated wood and scrap tires and as a result, it would be unnecessary to review the legitimacy criteria for these two NHSMs.  This change is proposed to be codified at 40 CFR Part 241.4(a).  EPA reviewed the legitimacy criteria for these two NHSM fuel types, balanced the criteria against other factors such as industrial process changes to accommodate the NHSM fuel type, and determined that the overall picture of how facilities treated resinated wood and scrap tires indicated the materials were treated as a fuel and not a solid waste by industry.

In addition to previously identified non-waste fuels, EPA solicited comments on whether to include pulp and paper sludge that is generated on-site and coal refuse from legacy piles that are processed sufficiently in the non-waste fuel category.  Based on the collected data, EPA believes that these NHSMs already meet the legitimacy criteria; as such, there is no need to specifically list pulp and paper sludge and coal refuse from legacy piles as categorically exempt from meeting the legitimacy criteria.4

It is likely that there are other NHSM fuels that EPA did not identify as non-waste fuels during the NHSM rulemaking.  As such and under the proposed rule revisions, if the NHSM doesn’t fall into one of the prescribed categories described previously in this article, EPA can make a determination on the NHSM solid waste status through two processes:

  1. Case-by-case determinations: Under 40 CFR Part 241.3(c), a facility can apply to its Regional EPA Administrator for a determination on NHSMs that are not generated on-site, not discarded, and which meet the legitimacy criteria. Under this option, EPA would make a preliminary decision on the solid waste status of the NHSM and the decision would go through a public comment period.  This option remains unchanged from the Current NHSM Rule.
  2. Proposed petition process: EPA is proposing to add a petition process to the Current NHSM Rule.  Under the proposal, industry can petition EPA to specifically list NHSM as a non-waste fuel at 40 CFR Part 241.4(a) similar to how resinated wood and scrap tires are listed.  Industry would need to demonstrate that the NHSM could potentially be categorized as a non-waste fuel due to balancing the legitimacy criteria against other external factors.  It would be necessary to submit the following information to EPA:
    • Demonstration that the NHSM is critical to the production process
    • If the NHSM does not meet the legitimacy criteria, an explanation of why EPA should consider the NHSM as non-waste fuel by balancing the legitimacy criteria against other relevant factors
    EPA’s preliminary decision would be proposed in the Federal Register and a public comment period would ensue. Should EPA grant the NHSM non-waste fuel status, 40 CFR Part 241.4(a) would be updated granting the NHSM categorical exemption from meeting the legitimacy criteria.  Although EPA does not foresee the proposed petition process becoming time- and resource-intensive, it certainly could become a lengthy undertaking depending on the complexity of the case.


Contained Gaseous Material
Among the regulated community, the Current NHSM Rule created concerns that EPA had changed a long-standing interpretation of what constitutes a “contained gaseous material” for defining the term solid waste under RCRA.5  Specifically, EPA’s response to comments on the Current NHSM Rule alluded to the fact that any gaseous NHSM transported to a combustion unit through a pipeline could be considered as a ‘contained gaseous material’ and as a result, should be assessed against the legitimacy criteria.  Historically, EPA considered gases stored in a closed container (e.g., cylinder of butane) to be a ‘contained gaseous material’ when the container is combusted.  In the Proposed NHSM Rule Revisions, EPA confirmed that “we are not changing any of our previous interpretations as it relates to whether “contained gaseous material” is a solid waste.”6  Additionally, EPA clarified that burning of gaseous material in devices such as fume incinerators or air pollution control equipment, will not be considered as a treatment or other management of a solid waste.7


NHSM Table 2 Spring 2012


Case Study

The following hypothetical case study demonstrates the process a facility could use to determine if a non-traditional fuel qualifies as a non-waste fuel by utilizing the proposed revisions to the NHSM Rule.  A boiler located at a utility facility is designed to burn the following traditional fuels: coal and virgin wood.  The boiler also combusts scrap wood chips and scrap tires.  Scrap wood chips are generated on-site, contain traces of paint, and do not meet the definition of resinated wood; as such, these chips do not meet a definition of clean biomass.  The scrap tires are received under an established tire collection program.  All of these materials have a heating value of greater than 5,000 Btu/lb.  These materials are stored inside the warehouse and are used within 20 days from the date of shipment.  A sampling of metal contaminant concentrations for these fuels is provided in the Table 2 above.  The fuel contaminant concentrations provided are for illustration purposes only.

All of these NHSMs can be categorized using the following procedure:

  • Coal and virgin wood are traditional fuels and therefore, no further analysis is required.
  • Scrap wood chips are generated on-site and remain within the control of the generator.  These chips meet the criteria for valuable commodity and are used within a reasonable time period.  As shown in Table 1, the lead contaminant concentration of the scrap wood chips exceeds the lead concentration of both coal and virgin wood.  Under the Current NHSM Rule, the legitimacy criteria would not be met and thus, the scrap wood chips would be considered a solid waste.  Under the Proposed NHSM Rule Revisions, the scrap wood chips may not be considered a solid waste because by “grouping the contaminants,” the TSM concentration is higher in coal than that of the scrap wood chips.
  • Scrap tires are not discarded and are received under an established tire collection program.  The scrap tires would be classified as a non-waste fuel under a categorical exemption listed in the proposed rule revisions.

Approach to Qualifying Solid Waste

In conclusion, assuming that the Proposed NHSM Rule Revisions are incorporated in the Current NHSM Rule, the following step-by-step procedure can be utilized to determine if a non-traditional fuel qualifies as a solid waste:

  1. List all types of fuels combusted and categorize them as traditional fuels or NHSMs.  No further evaluation is required for traditional fuels.
  2. Identify which NHSMs meet categorical exemptions such as the exemption for scrap tires or resinated wood.  No further analysis is required for those NHSMs that qualify under a categorical exemption codified at 40 CFR Part 241.4(a) under the proposed rule revisions.
  3. For NHSMs generated on-site or processed sufficiently before being burned as a fuel, check whether the NHSMs meet the legitimacy criteria by identifying if the NHSM can be classified as a valuable commodity, has a "meaningful" heat value (typically 5,000 Btu/lb or higher), and has contaminant concentrations (based on individual contaminant or group of contaminants) comparable to that of traditional fuels combusted.  Maintain adequate documentation to support the non-waste classification of those NHSMs.
  4. For NHSMs that are not generated on-site, not discarded, and meet the legitimacy criteria, prepare a case-by-case application and submit it to the Regional EPA Administrator for further review.
  5. For NHSMs that do not meet the legitimacy criteria but for which other relevant factors may balance the legitimacy criteria, prepare a petition for submittal to EPA.  EPA will respond by either denying the petition or adding regulatory text to 40 CFR Part 241.4(a) listing the NHSM as a non-waste fuel exempt from the legitimacy criteria.


In spite of EPA guidance documents, clarifications to definitions, and response to the regulated community’s questions, the Current NHSM Rule and the Proposed NHSM Rule Revisions continue to be a complex undertaking when categorizing NHSM and identifying compliance obligations.  This rule is especially critical for combustors that combust several non-traditional fuels (e.g., cement kilns and solid fired boilers).  It will be challenging to classify each NHSM appropriately.  Although the revised contaminant legitimacy criteria added flexibility by allowing groups of contaminants to be compared to the contaminant thresholds in traditional fuels, such comparisons can become quite convoluted.  Given the complexity of this regulation and potential regulatory liability, industry may benefit from expert advice on categorizing NHSMs and identifying current or future compliance obligations.

1 Per Section 129(h) of the Clean Air Act, if an emission unit becomes subject to a Section 129 Regulation, such as the CISWI Rules, the emission unit will not be subject to the Section 112 Regulations (NESHAP Subparts).
2 The Proposed NHSM Rule Revisions only provided clarification for NHSM used as fuel.  As such, NHSMs used as ingredients are not discussed further in this article.
3 Federal Register, Volume 76, Number 247, Page 80470.
4  Federal Register, Volume 76, Number 247, Page 80486.
5 “Responses to Comments Document for the Identification of Non- Hazardous Secondary Materials that are Solid Waste”, February 2011.
6 Federal Register, Volume 76, Number 247, Page 80473.
7 Ibid.