E

C

/R Incorporated Providing Environmental Technical Support Since 1989

501 Eastowne Drive, Suite 325  Chapel Hill, North Carolina 27514

Telephone: (919) 484-0222  Fax: (919) 484-0122

 

MEMORANDUM

DATE: August 10, 2010

SUBJECT: MACT Floor and MACT Determination for Existing Stationary Non-Emergency

SI RICE <100 HP and Existing Stationary Emergency SI RICE Located at Major 

Sources and GACT for Existing Stationary SI RICE Located at Area Sources

FROM: Tanya Parise, EC/R, Inc.

TO: Melanie King, EPA OAQPS/SPPD/ESG

1.0 PURPOSE

The purpose of this memorandum is to document the analysis of the maximum 

achievable control technology (MACT) floor and MACT for existing stationary non-emergency

spark ignition (SI) reciprocating internal combustion engines (RICE) less than 100 horsepower 

(HP) and existing stationary emergency and black start SI engines located at major sources. The 

generally achievable control technology (GACT) determination for existing stationary SI RICE 

located at area sources of hazardous air pollutants (HAP) emissions that are subject to National 

Emission Standards for Hazardous Air Pollutants (NESHAP) is also presented in this 

memorandum. 

The analysis for existing stationary non-emergency SI engines greater than or equal to 

100 HP and less than or equal to 500 HP located at major sources of HAP emissions is presented 

in a separate memorandum titled “MACT Floor and MACT Determination for Existing 

Stationary SI RICE ≤500 HP Located at Major Sources,” which is available in the rulemaking 

docket (EPA-HQ-OAR-2008-0708). 

2.0 INTRODUCTION

EPA proposed NESHAP for existing stationary SI engines at area sources and existing 

stationary SI engines that are less than or equal to 500 HP at major sources on March 5, 2009 (71 

FR 9698). The EPA previously promulgated NESHAP for existing stationary SI engines greater 

than 500 HP that are located at major sources, which were published on June 14, 2004 (69 FR 

33474). The final NESHAP for existing stationary SI engines at area sources and existing 

stationary SI engines that are less than or equal to 500 HP at major sources will add requirements 

to 40 CFR part 63, subpart ZZZZ, for these engines. 
2

The regulation was developed following criteria set forth under section 112 of the Clean 

Air Act (CAA). Section 112(d) of the CAA stipulates that EPA must promulgate emission 

standards that require the maximum degree of HAP reduction. According to 112(d)(3)(A) of the 

CAA, the emission standards for existing major sources must be no less stringent than the 

average emission limitation achieved by the best performing 12 percent of existing sources for 

which the Administrator has emissions information. For existing area sources, EPA has the

option under 112(d)(5) of the CAA to promulgate emission standards or requirements, which 

provide for the use of generally available control technologies (GACT) or management practices 

in order to reduce HAP emissions. 

Section 112 of the CAA outlines the statutory requirements for the EPA’s stationary

source air toxics program. Section 112(k) of the CAA requires the development of standards for 

area sources which account for 90 percent of the emissions in urban areas of the 33 urban HAP 

listed in the Integrated Urban Air Toxics Strategy (UATS). These area source standards can 

require control levels which are equivalent to either MACT or GACT, as defined in the CAA 

under section 112(d)(2) and (3) and section 112(d)(5), respectively. Section 112 of the CAA 

allows the EPA to establish subcategories among a group of sources. EPA has determined that 

the following subcategories are necessary to distinguish between existing stationary RICE 

located at area sources:

 Non-emergency 2-stroke lean burn (2SLB) stationary SI RICE; 

 Non-emergency 4-stroke lean burn (4SLB) stationary SI RICE; 

o ≤500 HP

o >500 HP

 Non-emergency 4-stroke rich burn (4SRB) stationary SI RICE;

o ≤500 HP

o >500 HP

 Non-emergency landfill and digester gas stationary SI RICE; and

 Emergency stationary SI RICE.

EPA has discussed the appropriateness of distinguishing stationary engines by fuel, mode of 

operation (emergency versus non-emergency), burn type (lean burn versus rich burn), and 

number of strokes (2-stroke versus 4-stroke) in a previous memorandum.1 The rationale 

provided in that memorandum supports establishing the subcategories listed above. 

In addition to the above subcategories established for existing stationary RICE located at area 

sources, this memorandum will also discuss the MACT floor and MACT for existing nonemergency stationary SI RICE less than 100 HP that are located at major sources and existing 

emergency and black start stationary SI RICE that are located at major sources.

EPA believes that previous determinations regarding the appropriateness of using 

formaldehyde levels in concentration (parts per million (ppm)) as surrogates for HAP for 4SRB 

stationary SI RICE, and carbon monoxide (CO) levels in concentration for all other stationary SI 

 

1 Memorandum from Jennifer Snyder and Tanya Parise, Alpha-Gamma Technologies, Inc. Subcategorization of 

Stationary Reciprocating Internal Combustion Engines ≤500 HP. May 15, 2006. EPA-HQ-OAR-2005-0030-0012.
3

RICE, are still valid. Consequently, EPA is finalizing formaldehyde standards for 4SRB RICE 

and CO standards for other SI RICE to regulate HAP emissions.

3.0 MACT FLOOR AND MACT DETERMINATION

Non-Emergency SI Engines <100 HP

For stationary SI engines less than 100 HP, EPA determined that it is not feasible to 

prescribe or enforce an emission standard because the application of measuring methodologies to 

this subcategory of engines is not practicable due to technological and economic limitations. In 

order to measure the formaldehyde or CO emissions from these engines in terms of volumetric 

concentration on a dry basis and corrected to 15 percent oxygen (O2), the following test methods 

are required:

 EPA Method 1 or 1A for selection of sampling ports;

 EPA Method 3, 3A, or 3B or ASTM Method D6522-00 (2005) for determining the O2

concentration;

 EPA Method 4 for measuring the moisture content;

 EPA Method 10 or ASTM Method D6522-00 (2005) for measuring the carbon 

monoxide (CO) concentration; and

 EPA Method 320 or 323 or ASTM Method D6348-03 for measuring the 

formaldehyde concentration.

The test methods require the sample point to be a certain distance between the engine and 

the exhaust. Because engines below 100 HP often have exhaust pipes with very small diameters 

and lengths, stack testing using these methods could require a modification or extension of the 

exhaust pipe to accomplish the test. Furthermore, the cost of performing a stack test ranges from 

approximately $1,000-$2,000 depending on the method used. The cumulative cost of testing 

existing stationary non-emergency engines below 100 HP at major sources would be high. EPA 

estimates that there are more than 67,000 of these engines and to test them engines could cost as 

much as $135 million. Given the cost of the testing itself, the physical adjustments necessary to 

accomplish the test, and the particular circumstances pertaining to engines below 100 HP, EPA

believes that the application of measurement methodology to this class of engines is not 

practicable due to technological and economic limitations. Therefore, work practices are the 

MACT floor for existing stationary non-emergency SI engines less than 100 HP. This is 

consistent with decisions made for existing stationary non-emergency compression ignition (CI) 

engines less than 100 HP, which EPA finalized requirements for on March 3, 2010 (75 FR 

9674). 

To determine the work practices, EPA reviewed information obtained from different 

manufacturers and operators of SI engines. The EPA has determined that the maximum 

achievable control, based on the work practices of the best controlled engines, is to maintain and 

replace the following stationary engine components: oil and oil filter, spark plugs, hoses, and 

belts. According to information received from manufacturers and operators of stationary

engines, these parameters are the most appropriate to ensure proper operation for minimizing 

HAP emissions. Each of these work practices limit HAP emissions by allowing the engine to 
4

operate at peak efficiency. Changing the oil and oil filter reduces the wear on the pistons and 

cylinders and limits the amount on worn metals that may be introduced to the exhaust stream. 

Maintaining efficient spark plugs reduces the potential for inefficient combustion and reduced 

efficiency, preventing higher emissions. Inspecting the belts and hoses ensures that the engines 

cooling and electrical systems are operating, therefore eliminating the burning of oil and 

ensuring that the electrical systems are functioning as intended.

Intervals for checking, inspecting and replacing the oil and oil filter, spark plugs, hoses, 

and belts vary with engine makes and models, application, location, and other factors, therefore 

making it difficult to define specific maintenance intervals that would be represent the operation 

of the best controlled engines. However, EPA must promulgate specific requirements pursuant 

to section 112(d) of the CAA and the information indicates that there are commonalities in 

maintenance interval frequencies for the best controlled engines. Based on the information 

provided, EPA believes that the work practices below are what the best controlled existing 

stationary non-emergency SI engines less than 100 HP are currently doing and for that reason the 

MACT floor for these engines except 2SLB engines is work practices as follows:

 Change oil and filter every 1,440 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,440 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 1,440 hours of operation or annually, whichever comes 

first, and replace as necessary.

The following work practices are what the best controlled stationary non-emergency 2SLB 

engines less than 100 HP are currently doing and is therefore the MACT floor:

 Change oil and filter every 4,320 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 4,320 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 4,320 hours of operation or annually, whichever comes 

first, and replace as necessary.

Two stroke lean burn engines have a longer maintenance interval than 4-stroke engines 

because 2SLB engines do not have as much oil contamination and also operate at lower speeds 

and temperatures so spark plugs do not fire as frequently and fire at lower temperatures than 4-

stroke engines. Further rationale for longer maintenance intervals for 2SLB engines in general is 

discussed in the section on 2SLB engines in this memorandum. 

As discussed above, current maintenance procedures vary from engine to engine based on 

a number of factors including engine design, fuel, and operating characteristics. Maintaining the 

oil however, is, one of the most important activities operators can perform to minimize emissions 

and to ensure proper operation and performance. 
5

In addition to following a set schedule for checking and replacing the oil, it is also 

common that the oil is monitored through an oil analysis program where the oil is periodically

sampled to determine oil quality. Based on the oil sample that is extracted, an oil analysis can be 

performed that can indicate if it is time to replace the oil or if the existing oil has not reached 

condemning limits it can continue to be used. Based on the analysis a decision can be made 

whether to drain and replace the oil or if the oil change interval can be extended if the properties 

of the oil are within acceptable limits. Appropriate parameters and condemning limits that 

would indicate oil degradation and the presence and quantity of contaminants varies. However, 

EPA has determined that the parameters that would most appropriately indicate the oil quality 

are the total acid number (TAN), viscosity, and water content. The TAN is an indication of the 

acidity of the oil and the viscosity of the oil is a measure of how well the oil flows and these 

parameters are, along with water content, measures of the condition of the oil. If the following 

levels below as measured through an oil analysis program are exceeded, EPA has determined 

that an oil change must be performed:

 TAN increases by more than 3.0 milligrams (mg) potassium hydroxide per gram 

(KOH/g) from the TAN of the oil when new; or

 viscosity of the oil changes by more than 20 percent from the viscosity of the oil when 

new; or

 percent water content (by volume) is greater than 0.5. 

No other regulatory options beyond the MACT floor were identified as appropriate for 

existing stationary non-emergency SI engines below 100 HP. Therefore, MACT for HAP 

emissions is equivalent to the MACT floor for these engines. 

Emergency SI Engines

For existing stationary SI emergency engines located at major sources, EPA determined it 

is not feasible to prescribe or enforce an emission standard because the application of 

measurement methodology to this class of engine is impracticable due to the technological and 

economic limitations. This is consistent with decisions made for existing stationary emergency

CI engines, which EPA finalized requirements for on March 3, 2010 (75 FR 9674). Emergency

engines typically only operate during emergencies or during periods of routine testing and 

maintenance. EPA determined that application of the emissions measurement methodologies 

during either of these periods is not practicable. It is impracticable to test emissions from 

stationary SI emergency engines during periods of routine testing and maintenance using the test 

procedures specified in the rule because it would increase the required number of hours of 

operation of the engine beyond the routinely scheduled reliability testing and maintenance 

operation, thereby increasing emissions. While emergency engines have periods of operation for 

scheduled maintenance and reliability testing, those periods are usually several hours shorter 

than the number of hours that would be required to run the necessary emissions tests under 40 

CFR part 63, subpart ZZZZ. It is also impracticable to apply the testing methodologies required 

in this rule to test the stationary engines during periods of emergency operation because 

emergencies are unplanned events and implementation of the procedures specified in 40 CFR 

part 63, subpart ZZZZ require advance planning before tests are conducted. In an emergency, 
6

the owner/operator does not have the advance planning time necessary to implement 40 CFR part 

63, subpart ZZZZ. In addition, it would be costly to test existing stationary SI emergency

engines at major sources. EPA estimates that there are close to 1,600 existing stationary SI 

emergency engines from 100 HP to 500 HP at major sources that are subject to this rulemaking. 

The cost for testing these engines could be as high as $3 million. 

For these reasons, work practices are appropriate and justified for this group of stationary

engines because the application of measurement methodology is not practicable due to 

technological and economic limitations. Consequently, work practices are the MACT floor for 

existing stationary emergency SI engines located at major sources. 

Again, in order to determine the work practices for stationary emergency engines at 

major sources, EPA reviewed information obtained from different manufacturers and operators

of SI engines. For the same reasons as discussed above for existing stationary non-emergency SI

engines less than 100 HP at major sources, EPA has determined that maximum achievable 

control, based on the work practices of the best controlled emergency engines, is to maintain and 

replace the following stationary engine components: oil and oil filter, spark plugs, hoses, and 

belts. EPA discussed above the effect that maintaining these parameters have on HAP 

emissions. 

As stated, intervals for checking, inspecting and replacing these components vary from 

engine to engine and determining specific maintenance intervals that would be represent the 

operation of the best controlled emergency engines is challenging. However, EPA must 

promulgate specific requirements pursuant to section 112(d) of the CAA and the information 

indicates that there are commonalities in maintenance interval frequencies for the best controlled

engines. Based on the information provided, EPA believes that the below maintenance practices 

are what the best controlled existing stationary emergency SI engines are currently doing and for 

that reason, the MACT floor for these engines is maintenance practices as follows:

 Change oil and filter every 500 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,000 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 500 hours of operation or annually, whichever comes 

first, and replace as necessary.

The changing of oil and the oil filter for stationary emergency engines is more frequent on an 

hourly basis than for non-emergency engines because of the nature of operation of these engines, 

which is for standby and intermittent use, and thus requires less hourly use over the same period 

of time, and oil quality is reduced over time even during periods when the engine is not used. 

Emergency SI engines also have the option to use an oil analysis program to determine if 

it is time to replace the oil or if the existing oil has not reached condemning limits it can continue 

to be used. The provisions of the oil analysis program are the same discussed above for nonemergency SI engines less than 100 HP.
7

No other regulatory options beyond the MACT floor were identified as appropriate for 

existing stationary emergency SI engines at major sources. Because these engines are typically 

used only a few number of hours per year, the costs of emission control are not warranted when 

compared to the emission reductions that would be achieved. The cost per ton estimates for 

stationary emergency SI engines can be found in the memorandum entitled “Cost per Ton of 

HAP Reduced for Existing Stationary SI RICE” in the rulemaking docket (EPA-HQ-OAR-2008-

0708). Therefore, MACT for HAP emissions is equivalent to the MACT floor for these engines.

Black Start Engines

Black start engines are used solely to start up combustion turbines. They operate for very

short durations and have the same issues as emergency SI engines based on their unique and 

limited operation. According to information received during the public comment period, black 

start engines typically operate no more than 10 minutes at a time and only operate during 

emergencies or during periods of high demand (see for example EPA-HQ-OAR-2008-0708-0088 

and 0129). The short time of operation makes testing of black start engines using the required 

procedures impracticable. Therefore, work practices are the MACT floor for existing stationary

black start engines located at major sources and are as follows: 

 Change oil and filter every 500 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,000 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 500 hours of operation or annually, whichever comes 

first, and replace as necessary.

As with stationary emergency SI engines, no other regulatory options beyond the MACT 

floor were identified as appropriate for existing stationary black start engines at major sources. 

The limited operating time also makes applying aftertreatment to black start engines not 

effective. In addition, these engines operate a few hours per year, making further regulation of 

these engines economically impractical. Therefore, MACT is equivalent to the MACT floor for 

these engines.

4.0 REQUIREMENTS FOR ENGINES AT AREA SOURCES

Under CAA section 112(d)(5), EPA may elect to promulgate standards or requirements 

for area sources "which provide for the use of generally available control technologies or 

management practices by such sources to reduce emissions of hazardous air pollutants." 

Additional information on generally available control technologies or management practices 

(GACT) is found in the Senate report on the legislation (Senate report Number 101-228, 

December 20, 1989), which describes GACT as:
8

. . . methods, practices and techniques which are commercially available and appropriate 

for application by the sources in the category considering economic impacts and the technical 

capabilities of the firms to operate and maintain the emissions control systems.

Determining what constitutes GACT involves considering the control technologies and 

management practices that are generally available to the area sources in the source category. 

EPA also considers the standards applicable to major sources in the same industrial sector to 

determine if the control technologies and management practices are transferable and generally 

available to area sources. In appropriate circumstances, EPA may also consider technologies and 

practices at area and major sources in similar categories to determine whether such technologies 

and practices could be considered generally available for the area source category at issue. 

Finally, as EPA has already noted, in determining GACT for a particular area source category, 

EPA considers the costs and economic impacts of available control technologies and 

management practices on that category. 

For existing stationary SI engines less than or equal to 500 HP, EPA is requiring

management practices. This determination is consistent with comments received on the 

proposed rule, as well as other information submitted to EPA post-proposal. Comments EPA 

received on the proposed rule indicated that EPA had underestimated the cost of emission 

controls and overestimated how many engines were already using these controls. Engine 

owners/operators have indicated that most of these smaller area source engines are not equipped 

with the control technologies required to meet these limits. For example, the American 

Petroleum Institute (API) said that the estimate of 4SRB engines currently equipped with add-on 

controls that EPA used for the proposal (80 percent), was greatly overestimated.2The Gas 

Processors Association indicated that few, if any, engines below 500 HP are currently equipped 

with add-on controls.3 Several comments received on the proposed rule supported the use of 

management practices where EPA proposed that for certain engines, and further recommended 

that EPA establish management practices for other engines at area sources. Commenters 

indicated that the management practices EPA proposed are generally available, although they did 

have comments on the maintenance intervals. More information on the management practice 

recommendations submitted by commenters is summarized in the response to comments 

document for the final rule, available from the rulemaking docket. EPA reevaluated the cost 

impacts associated with establishing numeric emission limitations for these engines and 

determined that the cost impacts would be unreasonable for most engines given the expected 

emission impacts both with and without the expectation of use of emission control technologies. 

Specific costs for each engine type are provided in the sections that follow. 

Based on this information, EPA determined that management practices for these 

stationary SI RICE less than or equal to 500 HP located at area sources of HAP are generally

available and cost effective and these procedures will ensure that emissions are minimized and 

engines are properly operated. EPA believes that requiring management practices instead of 

 

2

Pages 80-81 of Comments on the Proposed Revisions to the National Emission Standards for Hazardous Air 

Pollutants for Reciprocating Internal Combustion Engines. Prepared by American Petroleum Institute. June 3, 

2009. EPA-HQ-OAR-2008-0708-0242.2.

3

Page 9 of Comments on the Proposed Revisions to the National Emission Standards for Hazardous Air Pollutants 

for Reciprocating Internal Combustion Engines. Submitted by Gas Processors Association. June 2, 2009. EPAHQ-OAR-2008-0708-0112.1.
9

specific emission limitations and/or control efficiency requirements on the majority of existing 

stationary SI engines at area sources alleviates concerns regarding costly and burdensome 

requirements for rural sources and other area sources. 

Similarly, as discussed below, for engines above 500 HP, EPA determined, based on its 

reevaluation of the cost impacts associated with establishing numeric emission limitations for 

emergency engines, black start engines, 2SLB engines and landfill and digester gas engines, that 

the cost impacts would be unreasonable for these engines given the expected emission impacts 

both with and without the expectation of use of emission control technologies. EPA also 

determined that management practices are generally available for these engines.

Therefore, EPA is finalizing management practices for area source engines that are 

existing stationary non-emergency 2SLB engines, existing stationary non-emergency 4SLB less 

than or equal to 500 HP, existing stationary non-emergency 4SRB engines less than or equal to 

500 HP located at area sources of HAP, existing stationary non-emergency landfill and digester 

gas engines, and existing emergency stationary SI engines. Finalizing management practices for 

most existing stationary SI engines at area sources minimizes the burden of the final rule, 

particularly on small businesses and individual owners and operators. 

For existing non-emergency 4SRB engines greater than 500 HP at area sources and nonemergency 4SLB stationary engines greater than 500 HP at area sources, EPA determined that it 

is appropriate to set numerical emission limits, which are expected to be met using emission 

control technologies. Additional discussion and the basis for EPA’s final determination are

provided in the sections that follow.

Non-Emergency 2SLB

For existing stationary non-emergency 2SLB engines, EPA determined that management 

practices are generally available. EPA looked at promulgating further requirements beyond 

management practices for non-emergency 2SLB engines at area sources. The first option EPA 

looked at was having a CO emission limit for these engines based on emission levels expected 

without using add-on controls. EPA looked at the costs associated with this option, which 

includes the cost of performance testing, monitoring, recordkeeping and reporting. These costs 

are estimated to be more than $3,000 on an annual basis per engine. On a cumulative basis, the 

yearly compliance cost would be close to $35 million. However, a CO emission limit based on 

what a 2SLB engine could achieve without oxidation catalyst would not result in any emissions 

reductions beyond what would occur with proper management practices. EPA believes the costs 

associated with this option are unreasonable given there would be no emissions reductions 

achieved. 

The second option EPA looked at was going beyond management practices for nonemergency 2SLB engines at area sources by requiring emission limits based on levels expected 

using oxidation catalyst. Although add-on controls are technically feasible for these engines 

located at area sources, EPA does not believe oxidation catalyst is generally available for 2SLB 

engines. In addition, control costs are high and it is possible to achieve reasonable controls using 

management practices. For example, the cost per ton of HAP removed associated with requiring 
10

oxidation catalyst control on a 250 HP engine is $224,000. For a 500 HP engine, the cost per ton 

of HAP removed is $128,000 and for a 1,000 HP engine, the cost is $80,000 per ton of HAP 

removed. Information on how EPA estimated the cost per ton for oxidation catalyst on 2SLB 

engines and for specific costs for different size 2SLB engines, please refer to the memorandum 

“Cost per Ton of HAP Reduced for Existing Stationary SI RICE,” available from the docket 

(EPA-HQ-OAR-2008-0708). EPA determined that it is not appropriate to go beyond 

management practices for existing non-emergency 2SLB engines. Management practices 

represent what is generally available among such engines to reduce HAP, and the practices will 

ensure that emissions are minimized and engines are properly operated. Therefore, going 

beyond management practices is not justified and for existing stationary non-emergency 2SLB 

engines EPA is requiring management practices. 

Regarding what management practices are required, EPA has determined that 

maintaining and replacing the following stationary engine components is generally available 

management practice: oil and oil filter, spark plugs, hoses, and belts. In order to determine the 

specific intervals for management practices for stationary non-emergency 2SLB engines at area 

sources, EPA reviewed information obtained from different manufacturers and operators of SI 

engines. 

Two stroke lean burn engines have a longer maintenance interval than 4-stroke engines 

because 2SLB engines do not have combustion blow-by gases entering the crankcase due to the 

engine configuration and therefore do not have as much oil contamination from the combustion 

blow-by gases. The 2SLB engines also operate at lower speeds and temperatures than 4-stroke 

engines, consequently the spark plug does not fire as frequently and fires at lower temperatures 

than 4-stroke engines. Therefore, 2SLB engines should have longer maintenance practice 

intervals than 4-stroke engines and consequently EPA has determined that the proper interval for 

stationary non-emergency 2SLB engines is every 4,320 hours of engine operation or annually, 

whichever comes first. Intervals for checking, inspecting and replacing the oil and oil filter, 

spark plugs, hoses and belts vary with engine makes and models, application, location, and other 

factors. This makes it difficult to define specific maintenance intervals that would be 

representative of every possible operating scenario. However, EPA must finalize specific 

management practices. Based on comments received on the proposed rule and more specifically 

information received post-proposal from Exterran, JW Power Company, and CSI (EJC)4

indicates that a maintenance frequency of every 4,320 hours of operation is common practice and 

generally available. This specific recommendation is supported by INGAA and API. A 

maintenance interval of every 4,320 hours of engine usage will ensure that the components 

remain in proper condition and continue to perform the necessary functions to support proper 

engine operation, reduce HAP, and minimize emissions. Specifically, EPA is requiring the 

following management practices:

 Change oil and filter every 4,320 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 4,320 hours of operation or annually, whichever comes first, 

 

4 Memorandum from Rebecca Rentz, Bracewell and Giuliani to Melanie King, EPA. Spark Ignited (SI) 

Recommended Management Practices. January 27, 2010. EPA-HQ-OAR-2008-0708-0354.1. 
11

and replace as necessary; and

 Inspect all hoses and belts every 4,320 hours of operation or annually, whichever comes 

first, and replace as necessary.

EPA has discussed above the effect that maintaining these parameters have on HAP 

emissions and believes that the above management practices will ensure that HAP emissions are 

minimized. EPA also determined that it would be appropriate to include the option to use an oil 

analysis program in the final rule. 

Non-Emergency 4SLB ≤500 HP

For existing stationary non-emergency 4SLB engines less than or equal to 500 HP 

located at area sources, EPA determined that management practices are generally available. 

EPA looked at promulgating further requirements beyond management practices for nonemergency 4SLB engines less than or equal to 500 HP at area sources. The first option EPA 

looked at was having a CO emission limit for these engines based on emission levels expected 

without the use of add-on controls. EPA looked at the costs associated with this option, which 

include the cost of performance testing, monitoring, recordkeeping and reporting. These costs 

are estimated to be more than $3,000 on an annual basis per engine. On a cumulative basis, the 

yearly compliance cost would be close to $121 million. However, a CO emission limit based on 

what a 4SLB engine could achieve without oxidation catalyst would not result in any emissions 

reductions beyond what would occur with proper management practices. EPA believes the costs 

associated with this option are unreasonable given there would be no emissions reductions 

achieved. 

The second option EPA looked at was going beyond management practices for nonemergency 4SLB engines less than or equal to 500 HP at area sources by requiring emission 

limits based on levels expected using oxidation catalyst. Again, add-on controls are technically 

feasible for these engines located at area sources, but control costs are high when compared to 

the amount of reductions achieved. Information on the cost of control and the potential HAP 

reductions achieved with oxidation catalyst for different size 4SLB engines is presented in the 

memorandum “Cost per Ton of HAP Reduced for Existing Stationary SI RICE,” available from 

the docket (EPA-HQ-OAR-2008-0708). Requiring emission limits on this segment of engines 

that would require the use of oxidation catalyst would result in a significant burden, especially on 

small businesses. For example, in the 250 HP to 500 HP size range, 40 percent of the population

consists of agricultural engines, which are typically located at small businesses. For larger size 

engines, i.e., those above 500 HP, engines used for agricultural purposes represent only 14 

percent of the total population. EPA does not believe the costs of requiring aftertreatment are 

reasonable and therefore, going beyond management practices is not justified and GACT for 

existing stationary non-emergency 4SLB engines less than or equal to 500 HP is management 

practices. Management practices represent what is generally available among such engines to 

reduce HAP and the practices will ensure that emissions are minimized and engines are properly

operated. EPA does not believe that management practices would be a substantial burden on 

owners and operators such as homeowners and small entities. 
12

EPA has determined that for existing stationary non-emergency 4SLB engines less than 

or equal to 500 HP, the management practices shall be performed every 1,440 hours of engine 

operation or annually, whichever comes first, which reflects the management practices that are 

generally available. Again, intervals for checking, inspecting and replacing the oil and oil filter, 

spark plugs, hoses and belts vary with different 4SLB engine makes and models, application, 

location, and other factors. This makes it difficult to define specific maintenance intervals that 

would be representative of every possible operating scenario. However, EPA must finalize

specific management practices. Based on comments received on the proposed rule and more 

specifically information received post-proposal from Exterran, JW Power Company, and CSI

(EJC),3 which is supported by industry groups INGAA and API, indicates that a maintenance 

frequency of every 1,440 hours of operation is common practice and generally available. A 

maintenance interval of every 1,440 hours of engine usage will ensure that the components

remain in proper condition and continue to perform the necessary functions to support proper 

engine operation, reduce HAP, and minimize emissions. Therefore, EPA is requiring the 

following management practices for existing stationary non-emergency 4SLB engines less than 

or equal to 500 HP at area sources:

 Change oil and filter every 1,440 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,440 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 1,440 hours of operation or annually, whichever comes 

first, and replace as necessary.

Non-Emergency 4SLB >500 HP

For existing stationary non-emergency 4SLB engines greater than 500 HP located at area 

sources, EPA determined that management practices are generally available. EPA looked at 

promulgating further requirements beyond management practices for non-emergency 4SLB 

engines greater than 500 HP at area sources that are operated more than 24 hours per calendar 

year. EPA considered having a CO emission limit for these engines based on emission levels 

expected without add-on controls. Compliance costs are estimated to be more than $3,000 on an 

annual basis per engine and cumulatively close to $28 million on a yearly basis. Again, a CO 

emission limit based on what a 4SLB engine could achieve without oxidation catalyst would not 

result in any emissions reductions beyond what would occur using proper management practices. 

EPA believes the costs associated with this option are unreasonable given there would be no 

emissions reductions achieved. 

The second option EPA considered was going beyond management practices for nonemergency 4SLB engines greater than 500 HP at area sources that are operated more than 24 

hours per calendar year by requiring emission limits based on levels expected using oxidation 

catalyst. EPA believes that oxidation catalyst is readily available and feasible for all existing 

stationary non-emergency 4SLB engines above 500 HP generally regardless of location. Further, 

EPA has determined that costs and economic impacts associated with implementing HAPreducing technologies are reasonable and justified. For example, the cost per ton of HAP 
13

removed for a 750 HP engine is about $20,000 and is around $16,000 for a 1,000 HP engine. 

Information on the specific add-on control costs and cost per ton estimates can be found in the 

memorandum “Cost per Ton of HAP Reduced for Existing Stationary SI RICE,” available from 

the docket (EPA-HQ-OAR-2008-0708). Also, the controls that are expected to be used on these 

engines will have the co-benefit of reducing volatile organic compounds (VOC) and CO 

emissions as well. The reductions estimated from installing controls on non-emergency 4SLB 

engines greater than 500 HP at area sources are 3,500 tons of HAP, 33,000 tons of CO, and 

18,000 tons of VOC. Based on this, EPA believes it is appropriate to go beyond management 

controls for existing stationary non-emergency 4SLB engines greater than 500 HP at area 

sources. Therefore, EPA has determined that the final emission limits should be based on the use 

of oxidation catalysts for existing stationary non-emergency 4SLB engines greater than 500 HP 

that are located at area sources. 

To determine the final emission limits, EPA looked at the CO emissions data from 4SLB 

engines less than or equal to 1,000 HP that are equipped with oxidation catalyst control. EPA 

has test results from 4 existing 4SLB engines with oxidation catalyst. Next, EPA followed the 

MACT floor approach using the upper prediction limit, which was discussed in a separate 

memorandum5, to establish the concentration. This resulted in a concentration of 47 ppm by

volume, dry basis (ppmvd) of CO at 15 percent O2. A summary of the test data that was used to 

set the concentration standard is available in Appendix B-2 of the memo titled “MACT Floor and 

MACT Determination for Existing Stationary SI RICE ≤500 HP Located at Major Sources.” 

Next, EPA looked at the test results6obtained during testing at Colorado State University (CSU)

for the 4SLB engines equipped with oxidation catalyst. The data from CSU indicate that 

oxidation catalysts on 4SLB engines are capable of reducing CO emissions by 93 percent or

more. A control efficiency of 93 percent is also currently the CO percent reduction required for 

new and reconstructed stationary 4SLB engines greater than 500 HP and located at major sources 

that are equipped with aftertreatment under 40 CFR part 63, subpart ZZZZ. Consequently, for 

existing stationary non-emergency 4SLB engines greater than 500 HP located at area sources

that are operated more than 24 hours per calendar year, the final emission limit is 47 ppmvd of 

CO at 15 percent O2 or a CO reduction of 93 percent. 

Non-Emergency 4SRB ≤500 HP

For existing stationary non-emergency 4SRB engines less than or equal to 500 HP 

located at area sources, EPA determined that management practices are appropriate for GACT. 

EPA looked at promulgating further requirements beyond management practices for nonemergency 4SRB engines less than or equal to 500 HP at area sources. The first option EPA 

looked at was going beyond management practices by having a formaldehyde emission limit for 

these engines based on emission levels expected without add-on controls. EPA looked at the 

costs associated with this option, which would include the cost of performance testing, 

monitoring, recordkeeping and reporting. These costs are estimated to be nearly $4,000 on an 

annual basis per engine. On a cumulative basis, the yearly compliance cost would be more than 

 

5 Memorandum from Tanya Parise, EC/R to Melanie King, EPA. MACT Floor and MACT Determination for 

Existing Stationary SI RICE ≤500 HP Located at Major Sources. August 10, 2010.

6 Memorandum from Melanie Taylor and Jennifer Snyder, Alpha-Gamma Technologies, Inc. to Sims Roy, EPA 

OAQPS ESD Combustion Group. January 7, 2004. EPA-HQ-OAR-2002-0059-0665.
14

$123 million. However, a formaldehyde emission limit based on what a 4SRB engine could 

achieve without oxidation catalyst would not result in any emissions reductions beyond what 

would occur with proper management practices. EPA believes the costs associated with this 

option are unreasonable given there would be no emissions reductions achieved.

The second option considered by EPA was going beyond management practices for nonemergency 4SRB engines less than or equal to 500 HP at area sources by requiring emission 

limits based on levels expected using add-on control technology. The applicable control 

technology for reducing HAP is non-selective catalytic reduction (NSCR), which is technically

feasible for these engines located at area sources. However, control costs are high for these 

engines. For example, the cost per ton of HAP removed associated with requiring NSCR control

on a 250 HP engine is $167,000. Information on the cost per ton of HAP reduced with NSCR 

for different size 4SLB engines is presented in the memorandum “Cost per Ton of HAP Reduced 

for Existing Stationary SI RICE,” available from the docket (EPA-HQ-OAR-2008-0708). 

Requiring emission limits on this group of engines necessitating the use of aftertreatment would 

result in a significant burden, especially on small businesses. As previously stated in this 

memorandum, in the 250 HP to 500 HP size range, 40 percent of the population consists of 

agricultural engines, which are typically located at small businesses. Although there are cobenefits with using NSCR on 4SRB engines, EPA does not believe that this co-benefit outweighs 

the other considerations discussed above and does not justify going beyond management 

practices for existing non-emergency 4SRB engines less than or equal to 500 HP at area sources. 

Management practices represent what is generally available among such engines to reduce HAP, 

and the practices will ensure that emissions are minimized and engines are properly operated. 

EPA determined that it is not appropriate to go beyond management practices for existing nonemergency 4SRB engines less than or equal to 500 HP. 

 

EPA does not believe the costs of requiring aftertreatment are reasonable and therefore, 

going beyond management practices is not justified and GACT for existing stationary nonemergency 4SLB engines less than or equal to 500 HP is management practices. EPA does not 

believe that management practices would be a substantial burden on owners and operators such 

as homeowners and small entities. 

EPA has determined that for stationary non-emergency 4SRB engines at or below 500 

HP, it is appropriate for the management practices to be performed every 1,440 hours of engine 

operation or annually, whichever comes first, which reflects the management practices that are 

generally available. As with 2SLB and 4SLB engines, intervals for checking, inspecting and 

replacing the oil and oil filter, spark plugs, hoses and belts vary between 4SRB engines based on 

different makes and models, application, location, and other factors. This makes it difficult to 

define specific maintenance intervals that would be representative of every possible operating 

scenario. However, EPA must finalize specific management practices. Based on comments 

received on the proposed rule and more specifically information received post-proposal from 

Exterran, JW Power Company, and CSI (EJC),3 which is supported by industry groups INGAA 

and API, indicates that a maintenance frequency of every 1,440 hours of operation is common 

practice and generally available. A maintenance interval of every 1,440 hours of engine usage 

will ensure that the components remain in proper condition and continue to perform the 

necessary functions to support proper engine operation, reduce HAP, and minimize emissions. 
15

Therefore, for existing stationary non-emergency 4SRB engines less than or equal to 500 HP at 

area sources, EPA is requiring the use of management practices as follows:

 Change oil and filter every 1,440 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,440 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 1,440 hours of operation or annually, whichever comes 

first, and replace as necessary.

Non-Emergency 4SRB >500 HP

For existing stationary non-emergency 4SRB engines greater than 500 HP located at area 

sources, EPA determined that management practices are generally available. EPA looked at 

promulgating further requirements beyond management practices for non-emergency 4SLB 

engines greater than 500 HP at area sources that are operated more than 24 hours per calendar 

year. EPA considered having a formaldehyde emission limit for these engines based on emission 

levels expected without add-on controls. Compliance costs are estimated to be almost $4,000 on 

an annual basis per engine and cumulatively more than $28 million on a yearly basis. Again, a 

formaldehyde emission limit based on what a 4SRB engine could achieve without oxidation 

catalyst would not result in any emissions reductions beyond what would occur with proper 

management practices. EPA believes the costs associated with this option are unreasonable 

given there would be no emissions reductions achieved. 

The second option EPA considered was going beyond management practices for nonemergency 4SRB engines greater than 500 HP at area sources that are operated more than 24 

hours per calendar year by requiring emission limits based on levels using aftertreatment. 

Aftertreatment controls (NSCR) for existing non-emergency 4SRB engines greater than 500 HP 

are readily available and feasible regardless of location. Non-selective catalytic reduction, the 

technology applicable to 4SRB engines for HAP reduction is generally available. Further, costs 

and economic impacts associated with implementing HAP-reducing technologies are reasonable 

and justified. The cost per ton of HAP removed from a 750 HP engine is about $68,000 and 

$56,000 for a 1,000 HP engine. Information on the specific add-on control costs and cost per ton 

estimates can be found in the memorandum “Cost per Ton of HAP Reduced for Existing 

Stationary SI RICE,” available from the docket (EPA-HQ-OAR-2008-0708). In addition, the 

controls that are expected to be used on these engines will have the co-benefit of reducing VOC,

CO emissions and NOx emissions. For example, co-benefits of NOx reductions can be achieved 

at a favorable cost effectiveness of less than $1,000/ton for a 750 HP engine and $720/ton for a 

1,000 HP engine. EPA believes that this co-benefit adds to the justification for establishing 

emission limits based on the use of NSCR for these engines. The reductions estimated from 

installing controls on non-emergency 4SRB engines greater than 500 HP at area sources are 

1,200 tons of HAP, 64,000 tons of CO, 96,000 tons of NOx, and 6,400 tons of VOC. For these 

reasons, EPA believes it is appropriate to go beyond management practices for existing 

stationary non-emergency 4SRB engines greater than 500 HP at area sources. Therefore, EPA 
16

has determined that the final emission limits should be based on the use of NSCR for existing 

stationary non-emergency 4SRB engines greater than 500 HP that are located at area sources. 

To determine the final emission limits for non-emergency 4SRB engines greater than 500 

HP located at area sources that are operated more than 24 hours per calendar year, EPA looked at 

the formaldehyde emissions from 51 uncontrolled 4SRB engines and determined the average 

uncontrolled formaldehyde concentration. The average uncontrolled formaldehyde 

concentration was 11.3 ppmvd at 15 percent O2. Next, EPA applied a 76 percent formaldehyde 

control efficiency to the uncontrolled formaldehyde level. The 76 percent formaldehyde control 

efficiency is based on test results7used to set the final standards for stationary 4SRB engines 

greater than 500 HP at major sources and is consistent with the current requirement for these 

engines. As a result, the final emission limit for existing non-emergency 4SRB engines greater 

than 500 HP is 2.7 ppmvd formaldehyde at 15 percent O2 or a 76 percent formaldehyde 

reduction.

Emergency SI 

For existing stationary emergency SI engines located at area sources, EPA believes that it 

is appropriate to set GACT to be the same requirements as is required for emergency engines at 

major sources because the same issues that were discussed above for stationary emergency SI 

engines at major sources apply to emergency SI engines at area sources. Again, this is consistent 

with how EPA treated existing stationary emergency CI engines in the requirements finalized on 

March 3, 2010 under 40 CFR part 63, subpart ZZZZ. There is no reason why the requirements 

for engines located at area sources pursuant to GACT should be different than those for engines 

located at major sources. The management practices are generally available and being located at 

an area source does not prevent the engine from being maintained appropriately and according to 

how engines at major sources are being maintained. Further, the management practices do not 

present an economic burden on area source engines. Therefore, GACT for existing stationary

emergency SI engines at area sources is the use of management practices as follows:

 Change oil and filter every 500 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,000 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 500 hours of operation or annually, whichever comes 

first, and replace as necessary.

As discussed above for major sources, these sources may utilize an oil analysis program in order 

to extend the specified oil change requirement specified above. 

Black Start Engines

 

7 Memorandum from Melanie Taylor and Jennifer Snyder, Alpha-Gamma Technologies, Inc. to Sims Roy, EPA 

OAQPS ESD Combustion Group. January 7, 2004. EPA-HQ-OAR-2002-0059-0665.
17

For existing stationary black start engines located at area sources, EPA believes that it is 

appropriate to set GACT to be the same requirements as is required for black start engines at 

major sources because the same issues that were discussed above for stationary black start 

engines at major sources apply to these engines at area sources. There is no reason why the 

requirements for area sources pursuant to GACT should be different than those for black start 

engines at major sources. Therefore, GACT for existing stationary emergency SI engines at area 

sources is the use of management practices as follows:

 Change oil and filter every 500 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,000 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 500 hours of operation or annually, whichever comes 

first, and replace as necessary.

Non-Emergency Landfill and Digester Gas

For existing stationary landfill and digester gas engines located at area sources, EPA 

determined that management practices are appropriate for GACT. EPA looked at going beyond 

management practices for non-emergency landfill and digester gas engines at area sources. The 

first option EPA looked at was going beyond management practices by having a CO emission 

limit for these engines based on levels expected without add-on controls. EPA looked at the 

costs associated with this option, which would include the cost of performance testing, 

monitoring, recordkeeping and reporting. These costs are estimated to be between $3,000 and 

$4,000 on an annual basis per engine, depending on the engine type. On a cumulative basis, the 

yearly compliance cost would be close to $2.5 million. However, a CO emission limit based on 

what landfill and digester gas engines could achieve without add-on controls would not result in 

any emissions reductions beyond what would occur with proper management practices. EPA 

believes the costs associated with this option are unreasonable given there would be no emissions 

reductions achieved. 

The second option EPA looked at was going beyond management practices for nonemergency landfill and digester gas engines at area sources by requiring emission limits based on 

levels expected using add-on controls. However, add-on controls are not technically feasible for 

these engines and it is possible to achieve reasonable controls using management practices. 

Therefore, going beyond management practices is not justified and GACT for existing stationary

non-emergency landfill and digester gas engines is management practices. Management 

practices represent what is generally available among such engines to reduce HAP, and the 

practices will ensure that emissions are minimized and engines are properly operated. 

Regarding what management practices are required, EPA has determined that 

maintaining and replacing the following stationary engine components is generally available 

management practice: oil and oil filter, spark plugs, hoses, and belts. These same components 

must be maintained for the existing engines at major sources where MACT is work practices, 

and EPA believes these practices are transferable and generally available to area sources. There 
18

is nothing preventing existing non-emergency landfill and digester gas engines at areas from 

maintaining and replacing these engine components. 

To determine the specific intervals for management practices for stationary nonemergency landfill and digester gas engines at area sources, EPA reviewed information obtained 

from different manufacturers and operators of SI, including operators of landfill and digester gas

engines. Based on the information reviewed, it appeared that the management practices for 

landfill and digester gas engines are comparable to those of 4-stroke engines in general. 

Typically, engines operating at landfills or that use digester gas fuels are either 4SLB or 4SRB. 

Also, based on information available to EPA, the majority of landfill gas fired engines at 4SLB 

engines and digester gas engines are 4SRB. Therefore, management practices for landfill and 

digester gas engines are the same as for 4-stroke engines. Specifically, GACT for existing 

stationary non-emergency landfill and digester gas engines at area sources is the use of 

management practices as follows:

 Change oil and filter every 1,440 hours of operation or annually, whichever comes first, 

except that sources can extend the period for changing the oil if the oil is part of an oil 

analysis program as discussed below and none of the condemning limits are exceeded; 

 Inspect spark plugs every 1,440 hours of operation or annually, whichever comes first, 

and replace as necessary; and

 Inspect all hoses and belts every 1,440 hours of operation or annually, whichever comes 

first, and replace as necessary.