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Under the 40 CFR 63 Subpart ZZZZ National Emission Standard for Hazardous Air Pollutants for Reciprocating Internal Combustion Engines (the “RICE MACT”), the April 17th deadline is fast approaching for initial performance testing, or catalyst activity testing, as applicable, for two broad categories of engines with emissions standards: (1) existing SI RICE between 100 and 500 hp at major sources, and, (2) existing 4S SI RICE greater than 500 hp at non-remote area sources. To comply with the RICE MACT emissions standards, EPA assumes that the majority of these engines will need catalytic control, i.e., oxidation catalyst for the lean burn engines and three-way / non-selective catalyst for the rich burn engines. For any engine controlled by catalyst and subject to initial performance testing, the RICE MACT requires ongoing monitoring of parameters established during the testing. This monitoring must be completed according to a site-specific monitoring plan, and this plan should be in place by the date of the initial performance test, which, for the engine categories mentioned above, is just around the corner. Along with the 60-day notice and other items on your performance test to-do list, plan to carve out some time for developing your monitoring plan(s). Some details of what goes into the required monitoring plan are discussed below.

Although EPA may approve alternatives in some cases, the standard monitoring parameters are catalyst inlet temperature and pressure drop across the catalyst bed. The maximum allowable values for each should be established during the initial performance test, and the rule provides some minimum standards for measurement frequency, sensor accuracy, compliance tolerance, operational load, and periodic performance evaluations. Otherwise, the monitoring plans will be engine-specific, addressing items such as instrument/equipment design, performance criteria, data acquisition and averaging, auditing procedures, and planned maintenance. Each requirement of the continuous parametric monitoring system (CPMS) and each required part of a RICE MACT site-specific monitoring plan is summarized below.

Important Applicability Notes:
  • Monitoring plans are not required for existing, non-remote area source 4S SI RICE greater than 500 hp that are equipped with automatic high-temperature engine shutdown equipment and for which initial and annual catalyst activity checks are performed.
  • Many other categories of existing engines are subject to RICE MACT monitoring requirements and the development of site-specific monitoring plans; for these engines the deadlines for monitoring plan develop have already passed.
  • Where applicable, the monitoring and monitoring plan requirements described here are the same for new (as defined in the rule) engines as for existing engines; only the deadlines are different.
  • Measurement frequency: Catalyst inlet temperature must be recorded every 15 minutes at all times except during monitor malfunctions, repairs, and QA/QC activities, but including shutdowns and re-starts.  Pressure drop measurements are required monthly except for months during which the engine does not operate.
  • Data reduction: The 15-minute temperature data should be reduced to 4-hour rolling averages, based on 1-hour block average values.
  • Sensor/thermocouple accuracy: Five (5) degrees Fahrenheit or one (1) percent of measurement range, whichever is larger
  • Pressure drop tolerance: Two (2) inches of water from values measured during a performance test
  • Performance evaluation: Initially (during or before the initial engine performance test) and at least once per year via comparison to a second thermocouple
  • Engine load restrictions: Depends on the specific engine category
  • Design specifications of all monitoring system equipment, including the data recording system
  • Installation of equipment, considering possible sources of interference, and representativeness of measured values
  • Auditing and quality control procedures
  • Preventative maintenance and spare parts inventory
  • Program of corrective actions for anticipated monitor malfunctions such as loss of power, transmitter failure, and data acquisition failure
  • Availability of and reporting of measured data and records of monitor downtime


Keep the plans as simple as possible. One approach is to reference other, already established plans/manuals where appropriate. And as always, establishing a system to document compliance with the plan may be the most difficult part. For assistance with developing a plan or a compliance system, or for other related questions, please call your local Trinity office or (800) 229-6655.