MEMORANDUM

DATE: January 6, 2015

SUBJECT: Technology Review for Chemical Milling Maskant Applicatio n Operations in the

Aerospace Source Category

FROM: Eastern Research Group, Inc. and EC/R Incorporated

TO: Kim Teal, OAQPS/SPPD/MMG

1.0 INTRODUCTION

Section 112 of the Clean Air Act (CAA) requires the U.S . Environmental Protection Agency (EPA) to establish technology-based standards for listed source categories. These technologybased standards are often referred to as maximum achievable control technology (MACT) standards. The Aerospace MACT (40 CFR part 63, subpart GG) r egulates HAP emissions from facilities that are major sources and are engaged, eithe r in part or in whole, in the manufacture or rework of commercial, civil, or military aerospace ve hicles or components. The rule requires the use of MACT to reduce HAP emissions from the following o perations: cleaning; primer, topcoat and chemical milling maskant application; depainting; and wa ste storage and handling.

Section 112 also contains provisions requiring the EPA to peri odically revisit these standards. Specifically, section 112(d)(6) states:

(6) REVIEW AND REVISION. – The Administrator shall r eview, and revise as necessary (taking into account developments in practices , processes, and control technologies), emissions standards promulgated under this se ction no less often than every 8 years.

To comply with this CAA requirement, the EPA conducted a technology review for the Aerospace MACT standard for major sources. This memoran dum addresses the portion of the technology review for maskant application operations.

For the purposes of reviewing a MACT standard, the EPA con siders a “development” in practices, processes, and control technologies to be:

• Any add-on control technology or other equipment that was not identified and considered during MACT development;

• Any improvements in add-on control technology or other e quipment (that was identified and considered during MACT development) that could result in significant additional emission reduction;

• Any work practice or operational procedure that was not i dentified and considered during MACT development; and• Any process change or pollution prevention alternative t hat could be broadly applied that

was not identified and considered during MACT development.

Section 2 of this memorandum presents a summary of the sources of data that were used to conduct the technology review and Section 3 presents the t echnology review for maskant application operations.

2.0 SOURCES OF AVAILABLE CONTROL TECHNOLOGY INFORMAT ION

To identify any developments in practices, processes, or c ontrol technologies that could be applicable to maskant application operations in the Aerospa ce industry, we consulted the following sources of data: RACT/BACT/LAER Clearinghouse , the California Statewide Best Available Control Technology (BACT) Clearinghouse, regulat ory actions promulgated subsequent to the Aerospace MACT, regional and state regulati ons, and correspondence with state agencies and industry.

In addition, in order to assess developments in practic es, processes and control technologies that have occurred in the aerospace manufacturing and rework i ndustry since promulgation of the MACT standards, the EPA sent out a comprehensive informa tion collection request (ICR) to all known facilities in February 2011. The ICR requested informat ion on material usage and control techniques used on all of the regulated and unregulated emissi on sources. Responses were received from 100 major source facilities and 145 synthetic m inor facilities with adequate

information to determine the current level of control of HAP emissions, as well as to calculate

HAP emissions.

2.1 RACT/BACT/LAER Clearinghouse Database

Under the EPA's New Source Review (NSR) program, if a co mpany is planning to build a new plant or modify an existing plant such that criteria ai r pollution emissions will increase by a certain amount, then the company must obtain an NSR pe rmit. The NSR permit is a construction permit which generally requires the company to minimize air pollution emissions by changing the process to prevent air pollution and/or installing air pollution control equipment.

The terms "RACT," "BACT," and "LAER" are acronyms for different program requirements relevant to the NSR program. RACT, or Reasonably Avai lable Control Technology, is required on sources in areas that are not meeting national ambien t air quality standards (non-attainment areas). BACT, or Best Available Control Technology, is required on new or modified major sources in clean areas (attainment areas). LAER, or Lo west Achievable Emission Rate, is required on new or modified major sources in non-attainm ent areas.

BACT and LAER (and sometimes RACT) are determined on a c ase-by-case basis, usually by State or local permitting agencies. The EPA established th e RACT/BACT/LAER Clearinghouse, or RBLC, to provide a central data base of air pollution t echnology information (including past BACT and LAER decisions contained in NSR permits) to pro mote the sharing of information among permitting agencies and to aid in future case-by-case determinations. However, data in the RBLC are not limited to sources subject to RACT, BA CT, and LAER requirements.Noteworthy prevention and control technology decisions and information may be included even

if they are not related to past RACT, BACT, or LAER dec isions.

The RBLC contains over 5,000 air pollution control permit de terminations that can help identify appropriate technologies to mitigate most air pollutant emission streams. It was designed to help permit applicants and reviewers make pollution prevention a nd control technology decisions for stationary air pollution sources, and includes data submitte d by several U.S. territories and all 50 States on over 200 different air pollutants and 1,000 industria l processes.

The RBLC provides several options for searching the permit database on-line to locate applicable control technologies. On December 4, 2013, we c onducted a search of the RBLC. There are no process types in the RBLC for chemical milling maskant application. We then specified processes in the Aerospace surface coating cate gory, as surface coating operations also

include controls similar to those used to control maskant application sources. The search included permits dating back to September 1, 1995, which is the promulgation date of the Aerospace MACT. The results of this search are presen ted in Appendix 1.

2.2 Subsequent Regulatory Actions

No regulatory actions promulgated subsequent to the Aerospace MACT were identified for chemical milling maskant application operations. However, various regulatory actions related to surface coating operations were reviewed as they include co ntrols similar to those used to control maskant application sources. These regulatory actions, l isted in Table 1, were reviewed for developments in practices, processes and control technol ogies.

Table 1. Subsequent Regulatory Actions for Sources Similar to

Aerospace Coating Operations

MACT Standards Subpart Date Practices, Processes, and Control Technologies

Evaluated

Surface Coating of

Metal Furniture RRRR 5/23/2003 Emission limit as mass HAP per volume solids used, add-on control devices, low-HAP, high solids

coatings Surface Coating of Wood Building

Products QQQQ 5/28/2003 Emission limit as mass HAP per volume solids used, add-on control devices, low-HAP coatings

Surface Coating of Large Appliances NNNN 7/23/2002 Emission limit as mass HAP per volume solids used, add-on control devices, low-HAP, high solids

coatings Surface Coating of

Automobiles and Light-Duty Trucks IIII 4/26/2004 Emission limit as mass HAP per volume solids used, low-hap coatings (low/ non-HAP solvents), improved capture and control systems Surface Coating of

Plastic Parts and

Products PPPP 4/19/2004 Emission limit as mass HAP per volume solids used,add-on control devices, waterborne coatings, lowHAP, high solids coatingsSurface Coating of

Miscellaneous

Metal Parts and

Products MMMM 01/02/2004 Emission limit as mass HAP per volume solids used, add-on control devices, low-HAP, high solids

coatings

Area Source

Standards Subpart Date Practices, Processes, and Control Technologies

Evaluated

Paint Stripping and

Miscellaneous Surface Coating Operations HHHHHH 1/9/2008 Confining all coating operations to a spray booth, high transfer efficiency spray guns, training and certification of spray equipment operator to optimize

transfer efficiency

Residual Risk

Standards Subpart Date Practices, Processes, and Control Technologies Identified as Developments

Magnetic Tape EE 04/07/2006 No developments

Printing and Publishing KK 4/21/2011 Permanent total enclosures installed on controlled

presses

Shipbuilding and Ship Repair II 11/21/2011 Concentrator/RTO installed on spray booths to achieve 95% control efficiency; lower VOC coating limits based on California regional rules

Wood Furniture Manufacturing JJ 11/21/2011 RTO; Lower VOC coating limits based on California regional rules, more efficient spray guns

Developments identified in the regulatory actions liste d in Table 1 will be discussed in Section 3 (Technology Review for Primer and Topcoat Application Ope rations).

2.3 State and Regional Regulations

In addition to the RLBC and subsequent regulatory actions , we examined a variety of regulations of the Bay Area Air Quality Management District (BAAQ MD), the South Coast Air Quality Management District (SCAQMD), the San Diego County Air Pollution Control District (SDAPCD), the Ventura County Air Pollution Control Dist rict (VCAPCD), and the Missouri Department of Natural Resources. These regulations gener ally address VOC emissions, rather than volatile organic HAP emissions, but in many cases include provisions to reduce organic evaporative emissions from maskant application just as i ntended for the chemical milling maskant affected source under the Aerospace MACT.

The SCAQMD and the SDAPCD provide VOC content limits fo r Type I and Type II chemical milling maskants, similar to the format of the Aerospa ce MACT. Both California rules specify a content limit for Type I chemical milling maskants of 250 grams of VOC per liter (g/L) of coating applied, which is more stringent than the VOC l imit of 622 g/L for Type I maskants set forth in the Aerospace MACT. Note that the emission l imits for VOC and HAP are identical in the Aerospace MACT standards for maskants (i.e., the HA P limit for Type 1 maskants is also 622 g/L). Because volatile organic HAP is a fraction of tot al VOC, an emission limit for HAP that is equivalent to the VOC limit of 250 g/L VOC in the SCAQMD and SDAPCD rules would be equal to or lower than 250 g/L.All four California district rules reviewed have more st ringent requirements for sources choosing

to control emissions through the use of an add-on control device. These rules specify at least an 85 percent combined capture and control efficiency, compared t o the 81 percent capture and control requirement in the Aerospace MACT.

The SDAPCD aerospace coatings standard provides additional requirements for maskants applied by dip coating application equipment that are not s pecified in the Aerospace MACT. This standard includes the following requirements:

(6) Maskant Dip Coating Application Equipment.

Except as provided in Subsections (b)(1), (b)(6), and (b)(7), a person shall not use a dip tank to apply Type I chemical milling maskants or maskants for chemical processing or component coatings of a multi-stage maskants to aerospac e parts unless:

(i) The dip tank is covered except when being accessed to add or remove materials; take samples; visually inspect the maskant leve l; clean, maintain or repair the tank; or apply maskant; and

(ii) The dip tank has a readily visible, permanent mark or line indicating the maximum allowable maskant level; and

(iii) The dip tank has a freeboard ratio greater than or equal to 0.5; and

(iv) Maskant agitation is achieved by means other than gas agitation; and

(v) Material is added to the dip tank by means of submerged fi lling; and

(vi) Any dip tank lip exhaust ventilation system with an i nlet located below the cover of the maskant application dip tank is turned off an d the ventilation duct closed when the maskant application dip tank is covered.

We did find that some California air quality management d istricts have more stringent VOC content limits than those in the Aerospace NESHAP. H owever, the EPA is not aware of any facilities located in these two districts using chemical milling maskants and that would be subject to these more stringent limits.

3.0 TECHNOLOGY REVIEW FOR CHEMICAL MILLING MASKANT

APPLICATION OPERATIONS

In the process of chemical milling, an etchant solution is used to reduce the thickness of selected areas of metal parts. The process is typically used whe n the size or shape of the part precludes mechanical milling or when chemical milling is advantageo us due to shorter processing time or its batch capability. Before chemical milling, a maskant is applied to the part, allowed to cure, and is then removed from selected areas of the part whe re metal is to be removed by the etchant. The maskant remaining on the part protects those areas f rom the etchant. Maskants are appliedby brushing, dipping, spraying, or flow coating. Organic HAP em issions occur through

evaporation of the solvent, typically toluene, xylene or perchloroethylene, as the maskant is applied and while it cures.

3.1 Summary of Existing MACT Level of Control

The Aerospace MACT standard (subpart GG) promulgated in 1995 requ ires the following organic HAP and VOC content limits for uncontrolled chemi cal milling maskants:

• Type I: 5.2 pounds organic HAP per gallon (622 g/L) less water, as applied,

• Type II: 1.3 pounds of organic HAP per gallon (160 g/L) less wa ter, as applied.

These requirements do not apply to touch-up of scratched surfa ces or damaged maskant and touch-up of trimmed edges. Alternatively, a control system can be used to capture and control emissions from the maskant application operation. The system must achieve an overall control efficiency of 81 percent.

3.2 Identified Control Measures for Chemical Milling Mask ant Application Operations

Current industry practices employed to control emission s from chemical milling maskant application operations include the use of a control device , such as oxidizers and carbon adsorbers, and product substitutions, such as waterborne ma skants.

3.2.1 Add-On Control Technology or Other Equipment Not Identified and Considere d During MACT Development

No new equipment or control technologies were identif ied that were not considered during MACT development.

3.2.2 Improvements in Add-On Control Technology or Other Equipment (That Was Identified and Considered During MACT Development)

The MACT floor HAP content limit of 1.3 lb/gal for Type II maskants was based on the emission rate of the best performing 12% of sources, which was represented by two sources. The

emission rate accounted for the control measures used a t each facility. One of these sources

utilized a carbon adsorber and the other source utilized a waterborne chemical milling maskant. Each source had the same organic HAP emission rate of 1. 3 lb/gal. Advancements in the use of add-on control technologies to achieve significantly higher emission reductions than required by the current MACT limits could constitute a development as an improvement in add-on control technology.

A summary of the controls reported in the 2011 ICR for c hemical milling maskant application operations and the average percent reduction from the con trols, is provided in Table 2.Table 2. Control Measures Reported in the 2011 ICR for Chemi cal Milling Maskant

Application Operations

Control Measure Percent Reduction Carbon adsorber, catalytic oxidizer 98
Zeolite concentrator, carbon adsorber, catalytic oxid izer 95

Carbon Adsorber 92

The types of controls that are reflected in the data c ollected through the 2011 ICR are the same types of controls that were considered in the developme nt of MACT and which are presented by the requirements in 40 CFR 63.747(d) to achieve 81 percent or gre ater combined capture and destruction or removal efficiency. South Coast Air Quality Management District (SCAQMD) rule 1124 includes requirements for the use of add-on control technology of at least 90 percent capture and 95 percent destruction or removal, for an overa ll control efficiency of 85.5 percent, compared to the overall control of 81 percent in the Aer ospace MACT. The requirements in SCAQMD rule 1124 and the Aerospace MACT are based on the s ame control technology, a carbon adsorber; however, the Aerospace MACT does not s pecify the type of control technology required. The difference in the overall minimum contr ol efficiency provided by SCAQMD and the EPA is a result of differences in assumed capture and destruction efficiencies and not in the actual performance of the control equipment. Therefore , no improvements in add-on control technology or other equipment were identified.

3.2.3 Work Practices and Procedures Not Identified and Considered During MACT Development

No additional work practices or procedures were identified t hat were not already identified and considered during MACT development.

3.2.4 Any process change or pollution prevention alternative that could be broadly applied that was not identified and considered during MACT development.

Pollution prevention measures that were considered during M ACT development include product reformulations for coatings, including waterborne and lo wer HAP maskants. No further advancements in the development or adoption of waterbor ne or lower HAP maskants have been

identified. The “uncontrolled” HAP content of the maska nts reported in the 2011 ICR are consistent with those in use during the MACT development. Rather than using low-HAP coatings, facilities are relying on add-on control techno logies to reduce emissions.