4 The record articles

Hydrogen Sulfide Accounting and Reporting in Advance of this Year’s Toxic Release Inventory Reports

Posted: February 28th, 2013

Author: All4 Staff 

As environmental personnel gear up for the suite of annual reports due each year, 2013 brings an important change to the Toxic Release Inventory (TRI) report. Beginning with the TRI report due July 1, 2013, releases of hydrogen sulfide (H2S), a colorless, flammable, gas with a characteristic “rotten egg” smell, must be reported.


On October 17, 2011, the U.S. Environmental Protection Agency (U.S. EPA) lifted an Administrative Stay of the Emergency Planning and Community Right-to-Know Act (EPCRA) section 313 TRI reporting requirements for H2S [Chemical Abstracts Service Number (CAS No.) 7783–06–4][1]. As detailed in this Federal Register notice, H2S was added to the EPCRA section 313 list of toxic chemicals in a final rule published in the Federal Register on December 1, 1993. However, on August 22, 1994, U.S. EPA issued an Administrative Stay of the reporting requirements for H2S in order to evaluate issues brought to the Agency’s attention after promulgation of the final rule concerning the human health effect basis for the listing and the Agency’s use of exposure analysis in EPCRA section 313 listing decisions. Although the final rule listing H2S under section 313 of EPCRA remained in force, the stay deferred the reporting requirements for H2S while U.S. EPA completed its further evaluation. U.S. EPA has now completed its further evaluation of additional information that has become available since the stay was put in place regarding the human health and environmental effects of H2S, and the Agency published a position that the stay should be lifted in the February 26, 2010 Federal Register document entitled ‘‘Intent to Consider Lifting Administrative Stay; Opportunity for Public Comment.’’ The October 17, 2011 action that lifted the Administrative Stay established that the first TRI reports to include H2S will be due on July 1, 2013 for reporting year 2012 TRI reports.

Sources of H2S

Hydrogen sulfide, also known as sewer gas, stink damp, swamp gas and manure gas, occurs naturally in crude petroleum and natural gas. In addition, H2S is produced by bacterial breakdown of organic materials, and is produced by human and animal wastes. In particular, sanitary and wastewater treatment operations are a primary source of H2S. Hydrogen sulfide typically is formed in wastewater collection systems that are conducive to creating septic conditions. Collection systems in warm climates that have a flat grade or do not have the flow-through velocities [minimum two (2) feet per second] to prevent the stagnation of fluid, allow the septic conditions to occur. In general, septic conditions occur when bacteria use all of the available oxygen while decomposing organic matter in wastewater for energy. Sewers with low velocities encourage the growth of anaerobic bacteria in a slime layer coating the sewer. These bacteria reduce sulfur compounds such as sulfate, thereby producing sulfides. These compounds occur naturally in domestic wastewater but also can be concentrated in industrial waste streams. Under anaerobic (septic) wastewater conditions, sulfides cannot be oxidized. Therefore, they combine with hydrogen to produce hydrogen sulfide gas, creating the “”rotten egg”” odor associated with septic wastewater[2].

Several industrial activities that emit H2S include petroleum/natural gas drilling and refining, food processing facilities (including feeding operations and rendering facilities), coke ovens, tanneries, landfills, and Kraft pulp mills[3]. Hydrogen sulfide is also known to be emitted by certain agriculture operations including those associated with confined animal feeding operations (CAFO).

Releases of H2S for TRI reporting purposes will primarily be in the form of a reaction by-product of a given process (e.g., from the generation of H2S during anaerobic wastewater treatment processes or in a landfill, or in a direct contact evaporator at a Kraft pulp mill, in which the sodium sulfide in the black liquor reacts with the carbon dioxide in the furnace exhaust). However, there are some instances in which H2S is used as a reactant in a process, such as the conversion of H2S to elemental sulfur in the Claus process[4], or as part of a contact process sulfuric acid plant that burns spent acid[5].

Armed with this general understanding of the types of industries that may release H2S, an overview of the TRI reporting basics and the threshold determination process (which establishes if a covered facility must report releases of hydrogen sulfide) is provided below for additional clarification.

Reporting Basics

As described in U.S. EPA’s annual TRI instructions[6], TRI reporting is required if certain activity threshold quantities are exceeded.  The activity threshold quantities are specific to each compound and unique to each of the three (3) types of reportable activities (i.e., manufacture, process, and otherwise use).

Let’s first review the current list of compounds that are regulated under the TRI program.  The current TRI toxic chemical list contains 593 individually-listed chemicals and 30 chemical categories [including three (3) categories containing 62 specifically-listed chemicals]. If the members of the three (3) categories are counted as separate chemicals, the TRI Program could actually be said to cover 682 combined chemicals and chemical categories [i.e., 593 + (30-3) + 62)][7]. Within this list, H2S is listed without a chemical qualifier; therefore, this means that it is potentially subject to reporting in all forms in which it is manufactured, processed, or otherwise used above its applicable activity thresholds. Since H2S is not a persistent bioaccumulative toxic (PBT chemical), it is therefore subject to the standard activity thresholds of 25,000 pounds for manufacturing, 25,000 pounds for processing, and 10,000 pounds for otherwise using. For purposes of the de minimis exemption, the 1.0% level applies to H2S because it does not meet the Occupational Safety and Health Administration’s (OSHA’s) definition of a carcinogen. Therefore, H2S could be exempt in a mixture at a concentration lower than 1.0 %[1].

What do the terms manufactured, processed, or otherwise used mean for TRI purposes? As stated in the TRI instructions[6], the term “manufacture” means to produce, prepare, compound, or import an EPCRA Section 313 chemical, where the term “import” is defined as causing the EPCRA Section 313 chemical to be imported into the customs territory of the United States. Manufacturing can either be intentional or coincidental, and this is an important distinction, especially for H2S. Coincidental manufacture of a compound can occur as either a byproduct or impurity, in which byproducts are separated from the process stream and further treated or disposed, and impurities stay with the process and end up in the final product. The de minimis exemption applies to the coincidental manufacture of an impurity, but does not apply in the case of the coincidental manufacture of a byproduct.  Therefore, the coincidental manufacture of H2S as a byproduct within, for example, a wastewater treatment or other treatment process, would not be eligible for the de minimis exemption. However, H2S could be considered an impurity in the case of a natural gas sweetening plant, in which natural gas from high-pressure wells is sweetened by absorption in an amine solution to remove the H2S [natural gas is considered “sour” if it contains H2S in excess of 0.25 grains per 100 standard cubic feet[8]]. The H2S gas stream recovered by the amine solution may be: (1) vented, (2) flared in waste gas flares or smokeless flares, (3) incinerated, or (4) utilized for the production of elemental sulfur or sulfuric acid. If the recovered H2S gas stream is not to be utilized as a feedstock for commercial applications, the gas is usually passed to a tail gas incinerator in which it is oxidized to sulfur dioxide and is then passed to the atmosphere out a stack. In such cases, as noted in Question 113 of the U.S. EPA’s 1998 EPCRA Section 313 Questions and Answers document, “The removal and destruction of an EPCRA Section 313 toxic chemical from a fuel before it is used by a facility is not considered an activity that falls under the definition of manufacturing, processing or otherwise use. Facilities that use natural gas in production processes sometimes need to remove impurities from the gas before it is used. Such a facility does not coincidentally produce toxic chemicals as byproducts, but merely separates and removes toxic chemicals already present in the gas. These chemicals would not be subject to threshold determinations for reporting under EPCRA Section 313, and would not be subject to release and other waste management reporting unless an activity threshold is exceeded elsewhere at the facility. If the facility exceeds an activity threshold elsewhere, all releases and other waste management activities from the impurity removal process would be reportable.”

The term “process” means the preparation of a listed EPCRA Section 313 chemical, after its manufacture, for distribution in commerce. Processing is usually the incorporation of an EPCRA Section 313 chemical into a product. However, a facility may process an impurity that already exists in a raw material by distributing that impurity in commerce. Processing includes preparation of the EPCRA Section 313 chemicals in the same physical state or chemical form as that received by your facility, or preparation that produces a change in physical state or chemical form. The term also applies to the processing of a mixture or other trade name product that contains a listed EPCRA Section 313 chemical as one component. To revisit the above case of the natural gas sweetening plant as an example, utilization of the recovered H2S for production of elemental sulfur or sulfuric acid constitutes “processing” for the purposes of TRI reporting.

“Otherwise use” means the use of an EPCRA Section 313 chemical, including an EPCRA Section 313 chemical contained in a mixture or other trade name product or waste, which is not covered by the terms manufacture or process. It is unlikely that H2S will be present at a facility in an “otherwise use” manner.

Release Estimation Techniques

Hydrogen sulfide calculations are performed in the same manner as a typical non-metal, non-categorical (e.g., nitrate compounds) TRI compound. Because of the nature in which H2S will be present at most TRI-covered facilities, the process used to perform the threshold determinations will typically provide the quantity of H2S released to the environment. As with most pollutants, the use of analytical data (stack testing or water quality data, for example) is the preferred method to estimate activity quantities and releases. When analytical data are not available, for sources such as wastewater treatment and landfills, computer-based models are the primary means to estimate emissions [e.g., National Council for Air and Stream Improvement’s (NCASI’s) H2SSIM model for wastewater treatment processes, and U.S. EPA’s Landfill Gas Emission Model].

For specific industrial processes, various emissions guidance is available.  U.S. EPA offers emissions calculation guidance within AP-42 specific to the solid waste industry, petroleum industry, inorganic chemical industry, food and agriculture industry, and wood products industry. NCASI offers pulp and paper mills not just emission factors within its yet-to-be published Chemical Information Sheet for H2S, but also a site-specific pond profile method which requires extensive field data collection and pond sampling, and a mechanistic model with predictive capabilities that relies on wastewater treatment plant inlet sampling.  NCASI also offers emission factors within its air toxics database, and within multiple technical bulletins (e.g., Technical Bulletins No. 956 (September 2008), No. 957 (November 2008), No. 997 (August 2012), and No. 1000 (December 2012).

Regardless of the methodology used, facilities will be required to maintain documentation regarding the source of production or operating data, as well as any analytical data or emission factors used in the calculation process following selection of this approach.

Parting Thoughts

Though H2S emissions are required to be included in TRI reports this year for the first time, some regulated facilities have been performing emission estimates for H2S as part of permit applications and emission and annual emission reports in the past. Hydrogen sulfide is regulated as part of New Source Review (NSR) air permitting requirements. Some states also have ambient air quality standards for H2S, which require facilities to quantify emissions for air dispersion modeling evaluations. State and local water effluent standards are established in terms of H2S itself, or in terms of dissolved sulfides. Lastly, indoor air quality and personal exposure data also may provide a source of emission data for unique or non-typical processes.

So why discuss TRI reporting in February when the report is not due for another five (5) months? Obviously, for facilities that do not routinely quantify H2S emissions as part of current reporting programs, time will be needed to evaluate the numerous calculation methodologies that exist and identify the best methodology to calculate emissions for TRI, particularly if sampling and analysis is required. But even for facilities with some experience reporting H2S emissions, there have been numerous updates to the recommended calculation methodologies that historically existed for this compound which need to be evaluated for both TRI and future permitting purposes.  Not to mention the burdensome process of incorporating the selected calculation approach into your existing TRI calculation reporting process. Wouldn’t it be nice to be ahead of the reporting game for once? Don’t let these new reporting requirements catch you by surprise this year.


  1. Federal Register Volume 76, Number 200, pages 64023-64037, October 17, 2011.
  2. http://www.wwdmag.com/corrosion/hydrogen-sulfide-control-wastewater-collection-systems
  3. OSHA Fact Sheet for Hydrogen Sulfide, located at www.osha.gov/OshDoc/data…Facts/hydrogen_sulfide_fact.pdf.
  4. U.S. EPA, AP-42, Compilation of Air Pollutant Emission Factors, Section 8.13, July 1993.
  5. U.S. EPA, AP-42, Compilation of Air Pollutant Emission Factors, Section 8.10, July 1993.
  6. U.S. EPA, Toxic Release Inventory Reporting Forms and Instructions, Reporting Year 2011, EPA 260-R-10-001, December 2011, located at http://www.epa.gov/tri/reporting_materials/forms/index.html.
  7. http://www.epa.gov/tri/trichemicals/
  8. U.S. EPA, AP-42, Compilation of Air Pollutant Emission Factors, Section 5.3, January 1995.


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