40 CFR Part 64 Subpart FFFF establishes National Emission Standards for Hazardous Air Pollutants (NESHAP) for Miscellaneous Organic Chemical Manufacturing (MON). This subpart establishes requirements to demonstrate initial and continuous compliance with the emission limits, operating limits, and work practice standards. Under subpart FFFF, a wastewater stream from a miscellaneous organic chemical manufacturing process unit (MCPU) would be subject to the rule if it has a concentration of greater than five parts per million by weight (ppmw) of any of the HAPs listed in Table 8 or Table 9. Once determined that a source meets this threshold, it must be further categorized as a Group 1 wastewater (>1,000 ppmw HAP), or Group 2 wastewater (<1,000 ppmw HAP).


The MACT rule is a minimum standard that industry meet to be compliant based on emissions levels that are already being achieved by the best controlled and lowest emitting sources in the identified industry. This ensures MACTs are realistic and incentivizes the development of further control technologies.

The EPA uses Residual Risk and Technology Reviews (RTR) to develop standards of particular industries, i.e., MON. The new MON rule is the result of the EPA finalizing decisions of a recent RTR that went into effect August 12, 2020.

Testing to Determine Applicability and Group 1 Group 2 Determination

To determine applicability, an owner or operator shall determine the annual average concentration for Subpart FFFF Table 8 and/or Table 9 compounds. New sources shall determine both the flow weighted total annual concentrations for Table 9 compounds and the flow weighted annual average concentration for each Table 8 compound. Existing sources shall determine the flow weighted total annual average concentration for Table 9 compounds. The annual average concentration is a flow weighted average representative of the actual or anticipated operation of the chemical manufacturing process unit generating the wastewater over a designated 12-month period.

Wastewater is collected in a way that minimizes the loss of organic compounds during sampling and analysis. An acceptable sampling procedure is outlined in EPA Method 25D, “DETERMINATION OF THE VOLATILE ORGANIC CONCENTRATION OF WASTE SAMPLES.” EPA Method 25D calls for the samples to be collected in VOA vials containing 30 mL of Polyethylene Glycol (PEG), which minimizes the loss of VOCs during sample collection. Approximately 10g of wastewater is added to vials containing PEG weighed to the nearest 0.01g. Vials are immediately capped and stored chilled. For ease of collection and to minimize headspace, 40mL VOA vials are typically used. A minimum of three samples from each wastewater stream shall be taken, and it is recommended that each sample be collected in duplicate.

Method 25D can be used to determine the total VOC content of a waste stream and would be a suitable method for determining annual concentrations for Table 9. However, a more robust analytical method would need to be deployed to determine individual VOC concentrations identified in Table 8. One such method is EPA Method 305, “MEASUREMENT OF EMISSION POTENTIAL OF INDIVIDUAL VOLATILE ORGANIC COMPOUNDS IN WASTE.” Method 305 builds upon the sampling and analytical techniques outlined in method 25D but adds speciated measurements using Gas Chromatography (GC) or High-Performance Liquid Chromatography (HPLC) with appropriate detectors. An individual recovery efficiency determination is made for each of the target compounds in the waste sample. This recovery efficiency determination is used to calculate an adjusted total weight for each compound detected in each sample.

The sample concentrations and weight value averages are used with the flow rates determined for each stream to calculate the flow weighted total annual concentrations and ultimately if the waste stream is subject to the MON rule and subsequent grouping. It should be noted the owner/operator is not required to determine the concentration of Table 8 or 9 compounds that are not reasonably expected to be in the process and therefore waste stream.


With this newly enacted MON rule, the EPA estimates a reduction in HAP emissions by this source category by approximately 107 tons per year. By categorizing and monitoring wastewater streams, facilities can target new ways to reduce emissions and optimize process efficiency.

You can find information about the MON rule here, and information on NESHAP wastewater regulations for the organic chemical manufacturing industry here.

If you have any questions regarding sampling and analytical techniques and how Enthalpy may be able to assist with your regulatory needs, please click here to start a conversation.

Taylor Gross

Business Development Manager

Taylor Gross holds a B.S. in Biology with a focus on the environment and natural resource management. He pulls from over 5 years of technical sales and project management experience, to solve environmental testing needs with Enthalpy’s analytical solutions.