MEMORANDUM

DATE: January 21, 2009

SUBJECT: Subcategorization and MACT Floor Determination for Stationary Reciprocating Internal Combustion Engines ≤ 500 HP at Major Sources

FROM: Tanya Parise, Alpha-Gamma Technologies, Inc.

TO: Jaime Pagán, EPA Energy Strategies Group

THROUGH: Bradley Nelson, EC/R

The purpose of this memorandum is to document the subcategorization and analysis of the maximum achievable contro l technology (MACT) floor for existing stationary reciprocating internal combus tion engines (RICE) less than or equal 500 horsepower (HP) located at major source s that are subject to National Emission Standards for Hazardous Air Pollutants (NESHAP). A “major source” means any stationary source or group of stationary sources located within a contiguous area and

under common control that emits or has the potential to emit considering controls, in the aggregate, 10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air pollutants (HAP).

Introduction

The EPA is developing a regulation affecti ng existing stationary RICE less than or equal to 500 HP located at major source s that will address toxic air emissions from these engines. The regulation will be developed fo llowing criteria set forth under section 112(d) of the Clean Air Act (CAA). The MACT floor standards for existing sources must be no less stringent than the average emi ssion limitation achieved by the best performing 12 percent of existing sources. The EPA has previously issued a similar regulation affecting existing and new stati onary RICE greater than 500 HP at major sources, which was promulgated in 2004.Subcategorization

Section 112 of the CAA allows the EPA to establish subcategories among a group of sources. These subcategories are bas ed on technical criteria that differentiate sources in terms of technical feasibility or applicability of emissions control. The following subcategories are necessary in order to capture the differences which could affect the emissions of HAP from these engines:

• <50 HP

• Landfill/Digester Gas 50 ≥ HP ≤ 500

• Emergency Compression Ignition (CI) 50 ≥ HP ≤ 500

• Non-Emergency CI 50 ≥ HP ≤ 500

• Emergency Spark Ignition (SI) 50 ≥ HP ≤ 500

• Non-Emergency Two-Stroke Lean Burn (2SLB) 50 ≥ HP ≤ 500

• Non-Emergency Four-Stroke Rich Burn (4SRB) 50 ≥ HP ≤ 500

• Non-Emergency Four-Stroke Lean Burn (4SLB) 50 ≥ HP ≤ 249

• Non-Emergency 4SLB 250 ≥ HP ≤ 500 HP

EPA has previously discussed the appr opriateness of establishing the above subcategories and the rationale is not repeated in this memorandum. The rationale can be found in the memorandum titled Subcategor ization of Stationary Reciprocating Internal Combustion Engines ≤ 500 HP, available from http://www.regulations.gov as Document ID No. EPA-HQ-OAR-2005-0030-0012.

MACT Floor Determination

General Approach

The MACT floor for existing stationary RICE must be no less stringent than the average emission limitation achieved by t he best performing 12 percent of existing

sources. For the MACT floor determinati on, EPA consulted the Population Database. The Population Database was originally dev eloped for the NESHAP for stationary RICE greater than 500 HP located at major sour ces. Documentation on the Population

Database can be found in the docket for that rulemaking (EPA-HQ-OAR-2002-0059). The EPA queried the Population Database to determine how many existing stationary RICE less than or equal to 500 HP have catalyst type controls. A similar analysis was

conducted in 2006 with the results summariz ed in the memorandum titled “Analysis of the RICE NESHAP Population Database,” available from http://www.regulations.gov as Document ID No. EPA-HQ-OAR-2005-0030-0007.

In order to establish the emission limit fo r each subcategory of stationary existing engines, EPA referred to the Emissions Database. The Emissions Database was originally developed in support of regulatory development for the original RICE NESHAP addressing existing and new stationary engines greater than 500 HP located at major

sources. Documentation on the Emissions Database can be found in the docket for that rulemaking (EPA-HQ-OAR-2002-0059). The Emissions Database is an extensive compilation of criteria and HAP source test data obtained from various sources such as the California Air Resources Board, EPA’s S ource Test Information Retrieval System,tests conducted by the Gas Research Institut e, and testing conducted at Colorado State University.

EPA extracted tests from the Emissi ons Database containing formaldehyde and carbon monoxide (CO) test results. Formal dehyde is a hazardous air pollutant that is emitted by stationary engines. The tests we re divided into the subcategories listed on page 1 of this memorandum and the formaldehyde and CO emissions test data were analyzed. In some cases, the dataset for each subcategory was limited. For example, EPA only has one test for engines less than 50 HP. Therefore, the data may not be considered representative of that particular subcategory. Consequently, it would be more appropriate to use test results from all size engines within each subcategory or family of engines, where possible. This approach takes into account more variability and would be more representative of actual emissions assuming a reasonable number of tests are available. Further, for eac h subcategory, EPA selected the best performing 12 percent of engines in terms of formaldehy de. The formaldehyde emissions from the best performing 12 percent were then averaged together to obtain the average emission limitation achieved by these engines. W here possible, EPA selected the corresponding CO test results and averaged those tests to determine the CO limit. The MACT floor determination for each subcategory is described below and is summarized in Table 1.

EPA has previously conducted an analysis for the RICE NESHAP for engines greater than 500 HP at major sources, which investigated whether CO could be used as a surrogate for HAP from stationary engines. The conclusion of the analysis was that CO is a reasonable surrogate for HAP for SI lean burn engines and CI engines. However, CO was not determined to be a reasonable surrogate for HAP for 4SRB engines. It is beneficial for industry and EPA to us e CO as a surrogate for HAP if that is determined to be appropriate as it is much eas ier to test for one pollutant instead of all HAP. Testing for CO is easier and more ec onomical than testing for several HAP, and can be done either through source testing or continuous emission monitoring systems, making it more flexible than testing for several HAP.4 <50 HP

According to information in the Popul ation Database there are no existing stationary engines less than 50 HP using ca talyst type controls. Therefore, EPA

determined that the MACT floor is the emi ssion level that is achievable by existing engines of this size operating without add-on controls.

In order to determine the level being achieved by engines less than 50 HP, EPA referred to the Emissions Database. Only one test was available for engines less than 50 HP. This test was for a 4SRB engine operating on propane. EPA is not expecting any stationary CI engines less than 50 HP si nce they are typically considered nonroad mobile engines. Also, EPA does not expect any lean burn engines in this subcategory as lean burn engines tend to be found in larger engine size segments. Therefore, it is assumed that engines less than 50 HP would be 4SRB engines. Subsequently, EPA reviewed emissions from 13 tests of 4SRB engines between 50 and 500 HP plus the one test available for the less than 50 HP engi ne. EPA selected the best performing 12 percent (or 2 tests) of 4SRB engines less than 500 HP without add-on controls and averaged the formaldehyde emissions to dete rmine the MACT floor limit for engines below 50 HP. As a result, the MACT floor for engines below 50 HP is 2 parts per million by volume, dry basis (ppmvd) of formaldehyde at 15 percent oxygen (O 2 ).

Landfill/Digester Gas ≥ 50 HP

According to information in the Populati on Database there are no existing landfill or digester gas engines greater than or equal to 50 HP using catalyst type controls. Therefore, EPA determined that the MACT fl oor for this subcategory is the level achievable by existing landfill and diges ter gas engines operating without add-on

controls.

EPA consulted several sources, including the Emissions Database, in order to determine the level being achieved by landfill and digester gas engines. Based on reviewing recently obtained test reports for landfill and digester gas engines, EPA

concluded that the latest information obtai ned on the current levels being achieved by landfill gas engines is the most appropria te and representative information and was

therefore used to determine the MACT floor limit. EPA analyzed the CO emissions from landfill and digester gas test reports. EPA selected the best performing 12 percent and averaged those 12 percent to determine the MACT floor. Therefore, the MACT floor for landfill and digester gas stationary RICE greater than or equal to 50 HP is 177 ppmvd of CO at 15 percent O 2

.5 Emergency CI 50 ≥ HP ≤ 500

No existing CI emergency stationary RICE greater than or equal to 50 HP and less than or equal to 500 HP were found to have catalyst type controls in the Population Database. For that reason, the MACT floor for this subcategory is the level achievable by existing CI engines operating without add-on controls.

EPA analyzed formaldehyde emissions from 34 tests for engines of all sizes and 5 tests for engines between 50 and 500 HP without add-on controls. Due to the limited number of tests in the smaller size group, EPA believes that the average of the top 12 percent of engines between 50 and 500 HP may not be representative of what engines in this size group are achieving. Therefore, EPA believes that it is more appropriate to use the dataset containing a higher number of tests, which takes into account more variability and would be more representative of actual emissions. EPA averaged the top 12 percent (or 4 tests) for formaldehyde. CO test results of the best performing 12 percent was not available. Therefore, EPA reviewed emissions from all CO tests (10 tests) and selected the best performing 12 percent (or 1 test). As a result, the MACT floor for CI emergency stationary RICE great er than or equal to 50 HP and less than or equal to 500 HP is 4 ppbvd of formaldehyde at 15 percent O 2 or 40 ppmvd of CO at 15 percent O 2

.

Non-Emergency CI 50 ≥ HP ≤ 500

No existing CI non-emergency stationary RICE greater than or equal to 50 HP and less than or equal to 500 HP were found to have catalyst type controls, according the Population Database. For that reason, the MACT floor for this subcategory is the level achievable by existing CI engines operating without add-on controls.

In terms of non-cumulative emissions, t here is no difference between emissions from non-emergency and emergency CI engines. Therefore, the MACT floor for nonemergency CI engines between 50 and 500 HP engines is equivalent to the MACT floor for emergency CI engines between 50 and 500 HP and EPA analyzed the same data in

order to determine the MACT floor limit. As a result, the MACT floor for CI nonemergency stationary RICE gr eater than or equal to 50 HP and less than or equal to 500 HP is 4 ppbvd of formaldehyde at 15 percent O 2 or 40 ppmvd of CO at 15 percent

O 2

.

Emergency SI 50 ≥ HP ≤ 500

According to the Population Databas e there are no SI emergency stationary RICE greater than or equal to 50 HP and le ss than or equal to 500 HP using catalyst type controls. Therefore, EPA determined that the MACT floor for this subcategory is the level achievable by existing emer gency SI engines operating without add-on

controls.6 As noted above, there is no difference between emissions from emergency and non-emergency engines on a non-cumulative bas is. Therefore, emissions from emergency SI engines would be the same as from non-emergency engines. Based on industry estimates, the majority of emergen cy SI engines are 4SRB engines. Therefore, the MACT floor for emergency SI engines is equivalent to the level achieved by 4SRB engines operating without add-on controls. Consequently, the MACT floor for SI emergency stationary RICE gr eater than or equal to 50 HP and less than or equal to 500 HP is 2 ppmvd of formaldehyde at 15 percent O 2

.

Non-Emergency 2SLB 50 ≥ HP ≤ 500

According to the Population Databas e, no existing SI non-emergency 2SLB stationary RICE greater than or equal to 50 HP and less than or equal to 500 HP were found to have catalyst type controls. Therefor e, the MACT floor for this subcategory is the level achieved by 2SLB engines operating without add-on controls.

EPA analyzed formaldehyde emissions from 16 2SLB tests for engines between

50 and 500 HP without add-on controls. T hen, EPA took the average of the best performing 12 percent (or 2 tests) of engines, found the corresponding CO tests and averaged those tests as well. As a resu lt, the MACT floor for non-emergency 2SLB stationary RICE greater than or equal to 50 HP and less than or equal to 500 HP is 16 ppmvd of formaldehyde at 15 percent O 2 or 85 ppmvd of CO at 15 percent O 2

.

Non-Emergency 4SLB 50 ≥ HP ≤ 249

According to the Population Databas e, there are no non-emergency 4SLB stationary RICE greater than or equal to 50 HP and less than or equal to 249 HP using catalyst type controls. Therefore, the MACT floor for this subcategory is the level achieved by 4SLB engines 50 to 249 HP operating without add-on controls.

EPA analyzed formaldehyde emissions from 34 4SLB tests for engines of all sizes without add-on controls. All 34 tests were for 4SLB engines above 500 HP. Therefore, the entire data set was analyzed to determine the MACT floor. EPA took the average of the best performing 12 percent of engines (or 4 tests) for formaldehyde and identified the corresponding CO values from the top 12 tests for formaldehyde. The corresponding CO values were then averaged. As a result, the MACT floor for 4SLB stationary RICE greater than or equal to 50 HP and less than or equal to 249 HP is 2 ppmvd of formaldehyde at 15 percent O 2 or 95 ppmvd of CO at 15 percent O 2

.

Non-Emergency 4SLB 250 ≥ HP ≤ 500

For non-emergency 4SLB engines between 250 and 500 HP, EPA found that 31 out of 538 engines are using catalyst type contro ls. This means that 5.7 percent of the non-emergency population of 4SLB engines between 250 and 500 HP are controlled with aftertreatment that yields HAP reductions. This percentage is below the criteria for7 a MACT floor that would require add-on c ontrols for non-emergency 4SLB engines in this size range. Therefore, the MACT floor for this subcategory is the level achieved by 4SLB engines 250 to 500 HP operating without add-on controls.

EPA analyzed formaldehyde emissions from 34 4SLB tests for engines of all sizes without add-on controls. All 34 tests were for 4SLB engines above 500 HP. Therefore, the entire data set was analyzed to determine the MACT floor. EPA took the average of the best performing 12 percent of engines (or 4 tests) for formaldehyde and identified the corresponding CO values from the top 12 tests. The corresponding CO values were then averaged. As a result, the MACT floor for 4SLB stationary RICE greater than or equal to 250 HP and less than or equal to 500 HP is 2 ppmvd of formaldehyde at 15 percent O 2 or 95 ppmvd of CO at 15 percent O 2

.

Non-Emergency 4SRB 50 ≥ HP ≤ 500

For SI non-emergency stationary 4SRB engi nes greater than or equal to 50 HP and less than or equal to 500 HP, EPA found that 197 out of 3,533 are using catalyst type controls, according to the Population Da tabase. This equates to a percentage of 5.6 percent, which is below the criteria for a MACT floor based on add-on control. Therefore, the MACT floor for this subcat egory is the level achieved by 4SRB engines 50 to 500 HP operating without add-on controls.

EPA analyzed formaldehyde emissions from 21 tests for engines of all sizes and 13 tests for engines between 50 and 500 HP. EPA believes the number of tests

available between 50 and 500 HP is a reas onable amount and would be representative of 4SRB engines in this size category. Therefore, EPA used the dataset between 50 and 500 HP. EPA averaged the formaldehyde emissions from the best performing 12 percent of engines (or 2 tests) without add-on c ontrols. As a result, the MACT floor for 4SRB stationary RICE greater than or equal to 50 HP and less than or equal to 500 HP is 2 ppmvd of formaldehyde at 15 percent O 2

.8 Table 1. Summary of MACT Floor Dete rmination for Existing Stationary RICE

Subcategory MACT Floor

<50 HP 2 ppmvd CH 2 O @15% O 2

Landfill/Digester Gas 50 ≥ HP ≤ 500 177 ppmvd CO @15% O 2

Emergency CI 50 ≥ HP ≤ 500 4 ppbvd CH 2 O @15% O 2

or 40 ppmvd CO @15% O 2

Non-Emergency CI 50 ≥ HP ≤ 500 4 ppbvd CH 2 O @15% O 2

or 40 ppmvd CO @15% O 2

Emergency SI 50 ≥ HP ≤ 500 2 ppmvd CH 2 O @15% O 2

Non-Emergency 2SLB 50 ≥ HP ≤ 500 16 ppmvd CH 2 O @15% O 2

or 85 ppmvd CO @ 15% O 2

Non-Emergency 4SLB 50 ≥ HP ≤ 249 2 ppmvd CH 2 O @15% O 2

or 95 ppmvd CO @15% O 2

Non-Emergency 4SLB 250 ≥ HP ≤ 500 2 ppmvd CH 2 O @15% O 2

or 95 ppmvd CO @15% O 2

Non-Emergency 4SRB 50 ≥ HP ≤ 500 2 ppmvd CH 2 O @15% O 2