Emission Guidelines: Municipal Waste Combustors

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 60

[AD-FRL-5068-6]

Emission Guidelines: Municipal Waste Combustors

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed guidelines and notice of public hearing.

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SUMMARY: The EPA is proposing new subpart Cb ``emission guidelines'' to

be used by States in developing State regulations to control emissions

from existing municipal waste combustors (MWC's). Today's proposed

guidelines would apply to MWC's for which construction, modification,

or reconstruction began on or before September 20, 1994.

Today's proposal would implement sections 111 and 129 of the Clean

Air Act (Act). The proposed guidelines would apply to existing MWC

units at facilities with capacities to combust greater than 35

megagrams per day (Mg/day; a megagram is a metric ton, and one megagram

is equal to 2,204 pounds or about 1.1 short tons) of municipal solid

waste (MSW) and would require sources to achieve emission levels

reflecting the maximum degree of reduction in emissions of air

pollutants that the Administrator determines is achievable, taking into

consideration the costs, non-air-quality health and environmental

impacts, and energy impacts. The proposed guidelines would establish

emission limits for MWC acid gases (sulfur dioxide (SO2) and

hydrogen chloride (HCl)), MWC metals (particulate matter (PM), opacity,

cadmium (Cd), lead (Pb), and mercury (Hg)), MWC organics (dioxins/

furans), nitrogen oxides (NOX), and MWC fugitive fly ash/bottom

ash emissions. The proposed guidelines would also establish

requirements for MWC operating practices (carbon monoxide (CO), load,

and flue gas temperature), and operator training and certification.

DATES: Comments. Comments must be received on or before November 21,

1994.

Public Hearing. A public hearing will be held about 15 days

following proposal. See SUPPLEMENTARY INFORMATION for additional

information regarding the public hearing.

ADDRESSES: Comments. Comments on the proposal should be submitted (in

duplicate, if possible) to: Air and Radiation Docket and Information

Center (Mail Code 6102), ATTN: Docket No. A-90-45, Room M1500, U.S.

Environmental Protection Agency, 401 M Street, SW, Washington, DC

20460. See SUPPLEMENTARY INFORMATION for additional information

regarding submittal of comments.

Background Information. Key background information for the proposal

includes: (1) A document entitled ``FACT SHEET: Existing Municipal

Waste Combustors--Proposed Subpart Cb Emission Guidelines,'' which

succinctly summarizes the proposal, and (2) several technical documents

listed under SUPPLEMENTARY INFORMATION, including all of the background

information documents that supported the proposal and promulgation of

the subpart Ca emission guidelines. See SUPPLEMENTARY INFORMATION for

instructions for obtaining these documents.

Docket. Docket Nos. A-90-45 and A-89-08, containing supporting

information used in developing the proposed emission guidelines, are

located at the EPA's Air and Radiation Docket and Information Center,

Waterside Mall, Room M1500, Central Mall, 401 M Street, SW, Washington,

DC 20460. The docket may also be accessed by calling (202) 260-7548.

See SUPPLEMENTARY INFORMATION for further information regarding the

docket.

FOR FURTHER INFORMATION CONTACT: Mr. Walter Stevenson at (919) 541-5264

or Mr. Fred Porter at (919) 541-5251, Standards Development Branch,

Emission Standards Division (MD-13), U.S. Environmental Protection

Agency, Research Triangle Park, North Carolina 27711.

SUPPLEMENTARY INFORMATION:

Background Information

On December 20, 1989, the EPA proposed emission guidelines for

existing MWC's in subpart Ca of 40 CFR part 60. The subpart Ca emission

guidelines were promulgated on February 11, 1991 and were developed

under authority of section 111 of the Act of 1977. The Act of 1990

requires the EPA to review and revise, as necessary, the subpart Ca

guidelines. The EPA has reviewed the subpart Ca emission guidelines and

has concluded that they are not adequate to comply with the

requirements of section 129 of the Act of 1990. In a separate notice in

today's Federal Register, the EPA is proposing to withdraw the subpart

Ca emission guidelines that were promulgated on February 11, 1991.

Today's proposed subpart Cb guidelines would fully comply with the

requirements of section 129 of the Act of 1990.

The Federal Register notices for the proposed emission guidelines,

withdrawal of the subpart Ca emission guidelines, and a proposed EPA

test method that is associated with the proposed guidelines, and the

economic impacts analysis associated with the proposed emission

guidelines are listed below and are available on the EPA's Technology

Transfer Network (TTN) electronic bulletin board. Also listed below and

available on the EPA's TTN is a FACT SHEET, which succinctly summarizes

the proposal and is suggested reading for persons requiring a limited

overview of the proposal. The TTN contains 18 electronic bulletin

boards, and the items listed below are included in the Clean Air Act

Amendments (CAAA) bulletin board and the Emissions Measurement

Technical Information Center (EMTIC) bulletin board. The FACT SHEET can

also be obtained by calling Ms. Cassie Posey at (919) 541-0069.

MWC Items in the CAAA Electronic Bulletin Board

(1) ``FACT SHEET: Existing Municipal Waste Combustors--Proposed

Subpart Cb Emission Guidelines.''

(2) Federal Register notice for this proposal: ``Emission

Guidelines: Municipal Waste Combustors'' (this document).

(3) Federal Register notice: ``Withdrawal of the 1991 Emission

Guidelines for Municipal Waste Combustors.''

(4) ``Economic Impact Analysis for Proposed Emission Standards and

Guidelines for Municipal Waste Combustors,'' EPA-450/3-91-029, March

1994.

MWC Items in the EMTIC Electronic Bulletin Board

(1) ``Emissions Test Method 29: Determination of Metals Emissions

from Stationary Sources (1994 Proposal),'' EPA-454/R-94-016, April

1994, (which includes both the Federal Register proposal notice

(chapter 1) and the full text of the rationale and test method for the

proposal (chapter 2)).

The TTN is accessible 24 hours per day, 7 days per week, except

Monday morning from 8 a.m. to 12 p.m., when the system is updated. The

service is free, except for the cost of the phone call. Dial (919) 541-

5742 to access the TTN. The TTN is compatible with up to a 14,400 bits-

per-second (bps) modem. Further instructions for accessing the TTN can

be obtained by calling the help desk at (919) 541-5384.

The background information for today's proposal includes all of the

documents that supported the proposal and promulgation of the subpart

Ca emission guidelines (Docket No. A-89-08), as well as information in

Docket No. A-90-45. Key background information documents used in

developing the subpart Ca emission guidelines as well as today's

proposed guidelines are as follows:

(1) ``Municipal Waste Combustors--Background Information for

Proposed Guidelines for Existing Facilities,'' EPA-450/3-89-27e, August

1989;

(2) ``Municipal Waste Combustors--Background Information for

Proposed Standards: Post-Combustion Technology Performance,'' EPA-450/

3-89-27c, August 1989;

(3) ``Municipal Waste Combustion Assessment: Combustion Control at

Existing Facilities,'' EPA-600/8-89-057, August 1989;

(4) ``Municipal Waste Combustion Assessment, Technical Basis for

Good Combustion Practices,'' EPA-600/8-89-063, August 1989;

(5) ``Municipal Waste Combustors--Background Information for

Proposed Standards: Cost Procedures,'' EPA-450/3-89-27a, August 1989;

and

(6) ``Economic Impact Analysis for Proposed Emissions Standards and

Guidelines for Municipal Waste Combustors,'' EPA-450/3-91-029, March

1994.

Docket Nos. A-90-45 and A-89-08 are available for public inspection

and copying between 8:00 a.m. and 4:00 p.m., Monday through Friday, at

the location specified in the ADDRESSES section of this preamble. A

reasonable fee may be charged for copying. Additionally, the docket may

be accessed by telephone, as specified in the ADDRESSES section.

Comments. Today's action is a proposal and comments are requested.

The MWC regulations are complex, and the EPA expects to receive

numerous comments on this proposal. The EPA has specifically requested

comments on items fundamental to the proposal, including but not

limited to the MACT floor, MACT performance levels, and a consideration

of materials separation requirements for existing MWC's. The EPA seeks

full public participation in arriving at its final decisions, and

strongly encourages comments on all aspects of this proposal from all

interested parties. Whenever applicable, full supporting data and

detailed analyses should be submitted with all comments to allow the

EPA to respond to the comments.

Commenters wishing to submit proprietary information for

consideration should clearly distinguish such information from other

comments, and clearly label it ``Confidential Business Information.''

Submissions containing such proprietary information should be sent

directly to the following address, and not to the public docket, to

ensure that proprietary information is not inadvertently placed in the

docket: Attention: Mr. Walter Stevenson, c/o Ms. Melva Toomer, U.S. EPA

Confidential Business Manager, 411 W. Chapel Hill Street, Room 944,

Durham, North Carolina 27701. Information covered by such a claim of

confidentiality will be disclosed by the EPA only to the extent allowed

and by the procedures set forth in 40 CFR part 2. If no claim of

confidentiality accompanies a submission when it is received by the

EPA, it may be made available to the public without further notice to

the commenter.

Public Hearing. The public hearing will be held to provide

interested parties an opportunity for oral presentation of data, views,

or arguments concerning the proposed guidelines (see DATES for the

hearing schedule). The public hearing will be held at Research Triangle

Park, North Carolina, and will start at about 9 a.m. Persons wishing to

present oral testimony at the public hearing should call Ms. Julia

Latta at (919) 541-5578 at least 2 days in advance of the public

hearing. Persons interested in attending the hearing should also call

Ms. Latta to verify the time, date, and location of the hearing.

Persons may call (919) 541-5264 to hear a recorded message that

provides current information on the status of the public hearing.

Preamble Outline. The following outline is provided to aid in

locating information in this preamble.

I. Introduction

A. Summary of Regulatory History

B. Emission Guidelines--General Goals

C. Overview of this Preamble

II. Summary of the Proposed Subpart Cb MWC Emission Guidelines

A. Source Category to be Regulated

B. Pollutants to be Regulated

C. Format for the Proposed Guidelines

D. Proposed Emission Guidelines

E. Comparison of the 1991 Guidelines and Today's Proposal

F. Performance Testing and Monitoring Requirements

G. Reporting, Recordkeeping, and Compliance Schedule Guidelines

III. Impacts of the Proposed Emission Guidelines

A. Air Impacts

B. Water and Solid Waste Impacts

C. Energy Impacts

D. Cost and Economic Impacts

IV. Rationale for the Proposed Guidelines for MWC Emissions

A. Background

B. Selection of Source Category

C. Modification or Reconstruction of Existing MWC's

D. Selection of Designated Pollutants

E. Selection of Designated Facilities

F. Selection of Maximum Achievable Control Technology

G. Selection of Format for the Proposed Guidelines

H. Performance Test Methods and Monitoring Requirements

I. Reporting, Recordkeeping, and Compliance Schedule

Requirements

V. Rationale for the Proposed Guidelines for Fugitive Fly Ash/Bottom

Ash Emissions

A. Background

B. Fugitive Emission Control Techniques

C. Proposed Fugitive Emissions Guidelines

VI. Proposed Guidelines for Air Curtain Incinerators

VII. Comparison of the Proposal and European Emission Limits

VIII. Miscellaneous

IX. Administrative Requirements

A. Public Hearing

B. Docket

C. Clean Air Act Procedural Requirements

D. Executive Order 12866 Review

E. Regulatory Flexibility Act Compliance

I. Introduction

This section provides an introduction to the proposed rule by: (1)

Summarizing the history of the development of emission guidelines for

existing MWC's over the past 7 years; (2) summarizing the general goals

of the proposed rule that are specified by sections 111(d) and 129 of

the Act of 1990; and (3) providing a brief overview of the major issues

discussed in this preamble.

A. Summary of Regulatory History

Today's proposal is a result of a series of regulatory decisions

that were initiated in 1987. During the early and mid-1980's, studies

were performed to determine whether MWC emissions should be regulated

and, if so, under what section of the Act. As set forth in the advance

notice of proposed rulemaking (52 FR 25399, July 7, 1987), the EPA

decided to regulate air emissions from MWC's under section 111 of the

Act as it existed prior to the 1990 Amendments. Section 111 of the Act

required that the regulations be based on best demonstrated technology

(BDT). On December 20, 1989, the EPA proposed new source performance

standards (NSPS) for new MWC's and emission guidelines for existing

MWC's (54 FR 52251 and 54 FR 52209, respectively). On November 15,

1990, the Act Amendments of 1990 were enacted and added section 129 to

the Act. Section 129 of the Act specifies that revised NSPS and

emission guidelines must be developed for MWC's in accordance with the

requirements of sections 111 and 129. Section 129 further specifies

that revised NSPS and emission guidelines be developed for both large

and small MWC's and that the NSPS and emission guidelines must reflect

certain standards of performance. Section 129 includes a schedule for

revising the 1991 emission guidelines. When the EPA did not comply with

that schedule, the Sierra Club and the Natural Resources Defense

Council (NRDC) filed a complaint with the U.S. District Court for the

Eastern District of New York. The resulting consent decree requires the

EPA Administrator to sign a notice of proposed rulemaking not later

than September 1, 1994 and a notice of promulgation not later than

September 1, 1995 (Nos. CV-92-2093 and CV-93-0284).

The NSPS and guidelines promulgated on February 11, 1991 (56 FR

5488 and 56 FR 5514, respectively) apply to MWC's with unit capacities

above 225 Mg/day and reflect BDT as determined by the Administrator at

the time those guidelines were issued. Today's notice therefore

proposes to create new emission guidelines to be fully consistent with

sections 111 and 129 of the Act and to extend coverage of the

guidelines to existing MWC units located at MWC facilities with

aggregate plant capacity above 35 Mg/day. In a separate notice in

today's Federal Register, the EPA is proposing to withdraw the subpart

Ca emission guidelines that were promulgated on February 11, 1991.

Under a separate regulatory action in today's Federal Register, a

new subpart Eb NSPS for new MWC plants with aggregate capacities above

35 Mg/day of MSW that are constructed after September 20, 1994 is being

proposed pursuant to sections 111(b) and 129 of the Act. Even though a

new subpart Eb NSPS is being proposed, the February 11, 1991 subpart Ea

NSPS will remain in effect. Municipal waste combustors constructed,

modified, or reconstructed after December 20, 1989 but on or before

September 20, 1994 would be subject to both subpart Ea (NSPS)

requirements and today's proposed subpart Cb (guideline) requirements.

In most cases, the control technologies being used to meet the 1991

subpart Ea NSPS emission limits would be able to comply with the

proposed subpart Cb guidelines, except that additional controls would

be required to reduce Hg emissions, dioxin/furan emissions, and

fugitive fly ash/bottom ash emissions.

B. Emission Guidelines--General Goals

The Act requires the promulgation of performance standards under

section 111 for categories of new and existing stationary sources that

may contribute to air pollution that may reasonably be anticipated to

endanger public health or welfare. Section 129 of the Act specifies

that NSPS and emission guidelines must be developed for MWC's in

accordance with the requirements of sections 111 and 129. Section

129(a)(2) provides that emission guidelines for existing MWC's reflect

the maximum degree of reduction in emissions of designated air

pollutants, taking into consideration the cost of achieving such

emission reduction, and any non-air-quality health and environmental

impacts and energy requirements that Administrator determines is

achievable for a particular category of sources (this standard is

commonly referred to as ``maximum achievable control technology, or

``MACT''). Additionally, section 129 provides that the emissions

limitations in the guidelines for existing MWC's may not be less

stringent than the average emissions limitation achieved by the best

performing 12 percent of units in the category. This is referred to as

the ``MACT floor.''

According to sections 111(d) and 129(b), States must submit to the

Administrator, within 1 year of the EPA's promulgation of the

guidelines, a plan that accomplishes the following: (1) Establishes for

existing sources emission standards for designated pollutants; and (2)

provides for implementation and enforcement of the emission standards.

Section 129(b) provides that a State plan for existing MWC's be at

least as protective as the emission guidelines.

As specified in section 129 of the Act, States are required to

submit to the Administrator a plan implementing the emission guidelines

within 1 year after the promulgation of the guidelines. This proposal

further requires that a State plan shall provide that each unit subject

to the guidelines shall be in compliance with all requirements of the

State plan within 3 years following issuance of a revised construction

or operation permit, if a permit modification is required, or within 3

years following approval of the State plan, if a permit modification is

not required. Section 60.24(e)(1) of subpart B of part 60 requires that

any compliance schedule extending more than 1 year from adoption of a

State plan shall include legally enforceable increments of progress to

achieve compliance for each designated facility. The proposed emission

guidelines include this requirement. This proposed compliance schedule

is more comprehensive than the compliance schedule and timetable

specified in the subpart Ca emission guidelines promulgated on February

11, 1991 (56 FR 5514). The Act specifies that the procedure for State

submission of a plan shall be similar to the procedure for submission

of State implementation plans under section 110. Section 129 specifies

that the EPA, in reviewing State plans for any variation from the

emission guidelines, must ensure that State plans and their resulting

MWC control requirements are at least as protective as the EPA

guidelines, including incorporation of the compliance scheduling

requirements established by the guidelines. The Act also provides that

the EPA shall prescribe a plan according to procedures similar to those

in section 110(c) if a State fails to submit a ``satisfactory plan.''

Moreover, States that believe additional control is desirable may

require more extensive controls, which might have the effect of closing

otherwise marginal facilities or banning a particular category of

sources outright.

C. Overview of This Preamble

This preamble will:

(1) Summarize the proposed guidelines by discussing the conclusions

reached with respect to each of the elements in the decision summary;

(2) describe the environmental, energy, and economic impacts of

these proposed guidelines;

(3) present a rationale for each of the decisions associated with

this proposal;

(4) present a regulatory flexibility analysis; and

(5) discuss administrative requirements relevant to this action.

II. Summary of the Proposed Subpart Cb MWC Emission Guidelines

This section presents a summary of the proposed emission

guidelines, including identification of the source category and

pollutants that would be regulated under the proposal, discussion of

the format of the proposed guidelines, and presentation of the proposed

guidelines and their associated performance testing, monitoring,

recordkeeping, and reporting requirements. This section also provides a

comparison of the emission guidelines in this proposed subpart Cb

versus the 1991 emission guidelines (subpart Ca).

A. Source Category To Be Regulated

Today's proposed emission guidelines would require States to

develop emission regulations limiting air emissions from each existing

MWC unit located at an MWC facility that has an aggregate existing

plant capacity to combust over 35 Mg/day of MSW, for which

construction, modification, or reconstruction commenced on or before

September 20, 1994. The proposed guidelines would apply to more than 99

percent of all existing MWC capacity. Additionally, plants with an

aggregate capacity to combust between 25 and 35 Mg/day would be

required to submit an initial report of their location and facility

capacities, but would not be subject to any provisions of the

guidelines.

The aggregate design capacity of all existing MWC's at an MWC plant

would be considered in determining: (1) Whether a plant is subject to

the guidelines; and (2) what control levels are applicable. The

capacity of new MWC's (i.e., those that commenced construction,

modification, or reconstruction after September 20, 1994) that are

located at the MWC plant would not be considered in determining

applicability of the emission guidelines to existing MWC's, but would

be considered in determining the applicability of the subpart Eb NSPS.

Only MWC units constructed, modified, or reconstructed on or before

September 20, 1994 would be used for determining the applicability of

subpart Cb guidelines. Modification of an existing MWC to comply with

the emission guidelines would not bring an existing MWC under the NSPS

for new MWC's.

An MWC is defined as any setting or equipment that combusts MSW.

Municipal waste combustion includes the burning (or pyrolysis) of MSW

in any type of setting or equipment, including combustion equipment

with and without heat recovery. This definition has been slightly

modified from the February 11, 1991 guidelines and is discussed below.

Municipal solid waste is defined as either a mixture or a single-

item stream of household, commercial, and/or institutional discards.

This would include discards such as paper, wood, yard wastes, tree

trimmings, plastics, leather, rubber, glass, metals, and other

combustible and noncombustible materials. The MSW definition includes

household discards as well as discards from institutional and

commercial sources, but does not include industrial process or

manufacturing discards. The MSW definition also includes refuse-derived

fuel (RDF), which is made from MSW that is shredded (or pelletized) and

classified by size before combustion. Municipal solid waste does not,

however, include wastes that are solely segregated medical wastes.

However, if segregated medical wastes are mixed with MSW, the resulting

mixture is considered to be MSW, and the proposed guidelines would

apply if the aggregate plant capacity exceeded 35 Mg/day. Minor editing

is proposed in the definition of MSW to clarify this point.

Air curtain incinerators that combust MSW are MWC's. However, air

curtain incinerators that burn only yard wastes, tree trimmings, and

clean untreated lumber would be covered under a separate set of

proposed opacity emission levels, and no other part of the proposal

would apply. Air curtain incinerator opacity requirements are discussed

in section VI of this preamble.

B. Pollutants To Be Regulated

Section 129 of the Act requires the EPA to establish numerical

emission limits specifically for SO2, HCl, PM, opacity, Cd, Pb,

Hg, dioxins/furans, CO, and NOX. Section 129 specifies that the

EPA may also:

* * * promulgate numerical emission limitations or provide for

the monitoring of post-combustion concentrations of surrogate

substances, parameters, or periods of residence times in excess of

stated temperatures with respect to pollutants other than those

listed [above] * * *.

Therefore, the EPA is proposing guidelines for load and flue gas

temperature at the PM control device inlet as additional indicators of

MWC operating practices. The EPA is also proposing a guideline emission

level for fly ash/bottom ash fugitive emissions because these emissions

include Cd, Pb, Hg, and dioxins/furans (see section V of this preamble

for further discussion of the EPA's decision to regulate fugitive

emissions from MWC's).

The February 11, 1991 guidelines include emission limitations for

all of the pollutants listed above except Cd, Pb, Hg, NOX, and fly

ash/bottom ash fugitive emissions. The proposed guidelines would

establish guidelines for all of the pollutants listed above. The

proposed guidelines for the same pollutants regulated by the February

11, 1991 guidelines (i.e., SO2, HCl, PM, opacity, dioxins/furans,

CO, load, and flue gas temperature at the PM control device inlet) have

been revised to reflect the requirements of section 129.

C. Format for the Proposed Guidelines

The format of the proposed emission guidelines is similar to the

format of the February 11, 1991 guidelines. In most cases, the format

is in the form of an emission level (concentration).

The format of the dioxin/furan guideline would be revised in

today's proposal. In the 1991 guidelines, dioxin/furan emissions were

reported as a concentration (nanograms per dry standard cubic meter

(ng/dscm), corrected to 7 percent oxygen (O2), dry basis) on a

total mass basis (i.e., the mass of all tetra- through octa-congeners

were added together). In today's proposal, dioxin/furan emissions could

be reported in units of either ng/dscm total mass or ng/dscm toxic

equivalency (TEQ). Reporting in TEQ units is done by first measuring

the total mass of dioxin/furan congeners and then adjusting the results

to account for the varying toxicity of each congener. The same test

method (Method 23) is used in either case. See section II.F of this

preamble for further discussion of the proposed method of reporting

dioxin/furan emissions in terms of TEQ.

The February 11, 1991 guidelines specify guideline emission levels

for PM and opacity. Particulate matter is measured as a concentration

(milligrams per dry standard cubic meter (mg/dscm)) and is corrected to

7 percent O2, and opacity is measured on a percentage basis. The

format for the PM and opacity guidelines would not change, but Cd, Pb,

and Hg emission guideline limits would be added. Emissions of Cd, Pb,

and Hg would be calculated as a concentration (mg/dscm) corrected to 7

percent O2. For Hg, the proposed emission guidelines would also

establish an alternative percentage reduction requirement. A new method

(Method 29) that would measure these pollutants is being proposed in a

separate part of today's Federal Register.

The February 11, 1991 guidelines establish control requirements for

SO2 and HCl (MWC acid gases) by specifying both numerical emission

levels, calculated as parts per million by volume (ppmv) corrected to 7

percent O2, dry basis, and percentage reduction requirements for

both SO2 and HCl. Today's proposed guidelines would also be based

on the same format.

Today's proposal would also establish a guideline emission level

(ppmv) for NOX emissions. The NOX guideline emission level

would apply to MWC units at MWC plants with capacities to combust

greater than 225 Mg/day.

In addition to controlling stack emissions, the February 11, 1991

emission guidelines establish combustion operating guidelines for

MWC's. These operating guidelines are part of good combustion practices

(GCP) and ensure that emissions of MWC organics (dioxins/furans) are

minimized on a continuous basis. The GCP requirements are included in

today's proposal, but they are being extended to apply to MWC's at

plants of 35 Mg/day aggregate capacity or larger. Additionally, some

minor revisions are being proposed. The proposed revisions would

include: (1) A requirement that all shift supervisors and chief

facility operators obtain full (as opposed to provisional) operator

certification; (2) ``stand in'' authority for MWC control room

operators; and (3) required training of MWC shift supervisors. These

items are discussed below.

The February 11, 1991 emission guidelines require provisional

certification of the chief facility operator and shift supervisors by

the American Society of Mechanical Engineers (ASME) or a State

certification program. Development of a site-specific training manual

to be used for training other MWC personnel is also required. Today's

proposal would require that the chief facility operator and shift

supervisor obtain both provisional and then full operator

certification.

Today's proposal would allow for the optional certification of one

or more control room operators. Under the February 11, 1991 guidelines,

all chief facility operators and shift supervisors must be certified,

and one of these individuals must be onsite during all periods of MWC

operation. Under today's proposal, a provisionally certified control

room operator may ``stand in'' for the chief facility operator or shift

supervisor during periods in which the certified chief facility

operator or certified shift supervisor is offsite, in order to fulfill

the requirement that a certified individual be on site during all

periods of MWC operation. This would provide additional operating

flexibility. Today's proposal would also require that all chief

facility operators, shift supervisors, and control room operators

complete the MWC training program developed by the EPA or a State

program. The EPA has developed a model training program that has been

distributed to State air pollution control agencies, EPA Regional

Offices, and MWC industry groups. The EPA believes that operator

training is an integral part of the implementation of GCP.

Today's proposed guidelines also establish guidelines for fugitive

fly ash/bottom ash emissions from ash handling facilities. These

guidelines would establish a no visible emissions level, and would

apply to all buildings, external ash transfer equipment, and ash

handling areas at the MWC facility.

D. Proposed Emission Guidelines

Today's proposal would establish emission guidelines for MWC

organics (dioxins/furans), MWC metals (PM, opacity, Cd, Pb, and Hg),

MWC acid gases (SO2 and HCl), and NOX. The guidelines also

propose requirements for fly ash/bottom ash fugitive handling, MWC

operating practices (CO, load, and flue gas temperature), and operator

training and certification.

The proposed guidelines would divide the MWC population into two

subcategories: The first would be for MWC units located at small MWC

plants (i.e., those with aggregate capacities to combust greater than

35 Mg/day of MSW but equal to or less than 225 Mg/day), and the second

would be for MWC units at large plants (i.e., those with aggregate

capacities to combust more than 225 Mg/day of MSW). The aggregate

capacity of all existing MWC units at one site would be added together

to define aggregate MWC plant capacity for the purposes of the emission

guidelines. The proposed emission guidelines for each subcategory and

subclass of MWC's are summarized in table 1.

Table 1.--Summary of Proposed Emission Guidelines for Existing MWC's

[Subpart Cb]a

------------------------------------------------------------------------

Plant size (MSW combustion

capacity) Requirement

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Applicability

The proposed guidelines would apply to existing MWC's located at plants

with capacities to combust greater than 25 Mg/day of residential,

commercial, and/or institutional discards.b Industrial discards are not

covered by the proposed guidelines.

25 Mg/day.......... Not covered by guidelines.

> 25 Mg/day but 35 Initial report of MWC design

Mg/day. capacity and startup date.

> 35 Mg/day but 225 Subject to provisions listed below.

Mg/day (referred to as small

MWC plants).

> 225 Mg/day (referred to as Subject to provisions listed below.

large MWC plants).

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Good Combustion Practices

Applies to large and small MWC plants.

A site-specific operator training manual would be required to

be developed and made available for MWC personnel. The EPA or a State

MWC operator training course would be required to be completed by the

MWC chief facility operator, shift supervisors, and control room

operators.

The ASME or a State MWC operator certification would be

required to be obtained by the MWC chief facility operator

(mandatory), shift supervisors (mandatory), and control room

operators (optional).

The MWC load level would be required to be measured and not to

exceed the maximum load level as demonstrated during the most recent

dioxin/furan performance test.

The maximum PM control device inlet flue gas temperature would

be required to be measured and not to exceed the level demonstrated

during the most recent dioxin/furan performance test.

The CO level would be required to be measured using a CEMS,

and the concentration in the flue gas would be required not to exceed

the following:

------------------------------------------------------------------------

MWC type CO levelc Averaging time

Modular starved-air and excess-air...... 50 ppmv 4-hour.

Mass burn waterwall and refractory...... 100 ppmv 4-hour.

Mass burn rotary refractory............. 100 ppmv 24-hour.

Fluidized-bed combustion................ 100 ppmv 4-hour.

Coal/RDF mixed fuel-fired............... 150 ppmv 4-hour.

RDF stokers............................. 200 ppmv 24-hour.

Mass burn rotary waterwall.............. 250 ppmv 24-hour.

MWC Organic Emissions (measured as dioxin/furan)c,d

Dioxins/furans (compliance test by EPA Reference Method 23)

Large MWC plants............... 30 ng/dscm total mass or 0.5 ng/

dscm dioxin/furan TEQ.

Small MWC plants............... 60 ng/dscm total mass or 1.0 ng/

dscm dioxin/furan TEQ.

Basis for dioxin/furan guideline

Large MWC plants............... GCP and SD/ESP/CI or GCP and SD/FF/

CI.

Small MWC plants............... GCP and DSI/ESP/CI.

MWC Metal Emissionsc

PM (compliance test by EPA Reference Method 5)

Large MWC plants............... 27 mg/dscm (0.012 gr/dscf).

Small MWC plants............... 69 mg/dscm (0.030 gr/dscf).

Opacity (compliance test by EPA Reference Method 9)

Large and small MWC plants..... 10 percent (6-minute average).

Cd (compliance test by EPA Reference Method 29)e

Large MWC plants............... 0.040 mg/dscm (18 gr/million dscf).

Small MWC plants............... 0.10 mg/dscm (44 gr/million dscf).

Pb (compliance test by EPA Reference Method 29)e

Large MWC plants............... 0.50 mg/dscm (200 gr/million dscf).

Small MWC plants............... 1.6 mg/dscm (700 gr/million dscf).

Hg (compliance test by EPA Reference Method 29)e

Large and small MWC plants..... 0.080 mg/dscm (35 gr/million dscf)

or 85-percent reduction in Hg

emissions.

Basis for PM, opacity, Cd, Pb, and Hg guidelines

Large and small MWC plants..... See basis for dioxin/furan

guidelines.

MWC Acid Gas Emissionsc

SO2 (compliance test by CEMS)

Large MWC plants............... 35 ppmv or 75-percent reduction in

SO2 emissions (24-hour).

Small MWC plants............... 80 ppmv or 50-percent reduction in

SO2 emissions (24-hour).

HCl (compliance test by EPA Reference Method 26)

Large MWC plants............... 35 ppmv or 95-percent reduction in

HCl emissions.

Small MWC plants............... 250 ppmv or 50-percent reduction in

HCl emissions.

Basis for SO2 and HCl guidelines

Large and small MWC plants..... See basis for dioxin/furan

guidelines.

Nitrogen Oxides Emissionsc

NOX (compliance test by CEMS)

Large MWC plants............... 180 ppmv (except mass burn/

refractory MWC's).

Mass burn refractory MWC plants No NOX control requirement.

Small MWC plants............... No NOX control requirement.

Basis for NOX guideline

Large MWC plants............... SNCR.

Mass burn refractory MWC plants No NOX control requirement.

Small MWC plants............... No NOX control requirement.

Fly Ash/Bottom Ash Fugitive Emissions

Fly Ash/Bottom Ash (compliance test by EPA Reference Method 22)

Large and small plants......... No visible emissions from

buildings, ash transfer points, or

ash handling areas.

Basis for fugitive emission Wet ash handling or enclosed ash

guideline. handling.

Compliance Testing/Monitoring Requirements

Load, flue gas Continuous monitoring systems, 4-

temperature. hour arithmetic average.

CO..................... CEMS, 4- or 24-hour arithmetic

average, as applicable.

Dioxins/Furans,d PM, Cd, Pb, Hg, and HCl

Large MWC plants............... Annual stack test.

Small MWC plants............... Annual or third year stack testf.

Opacity................ COMS (6-minute average) and annual

stack test.

SO2.................... CEMS, 24-hour geometric mean.

NOX (large MWC plants CEMS, 24-hour arithmetic average.

only).

Fly ash/bottom ash Annual test.

fugitive emissions.

Compliance Schedule:

State plans would be required to include one of the following

two schedules for compliance with regulatory requirements: (1) Full

compliance within 1 year following approval of the State plan; or (2)

full compliance within 3 years following issuance of a revised

construction or operation permit, if a permit modification is

required, or within 3 years following approval of the State plan, if

a permit modification is not required, provided the State plan

includes measurable and enforceable incremental steps of progress

toward compliance.

State plans would be required to specify that all MWC's at

large MWC plants for which construction, modification, or

reconstruction is commenced after June 26, 1987 comply with the

emission guidelines for Hg and dioxins/furans within 1 year following

issuance of a revised construction or operation permit, if a permit

modification is required, or within 1 year following approval of the

State plan, if a permit modification is not required.

State plans would be required to require compliance with the

MWC operator training and certification requirements by 1 year after

promulgation of the guidelines.

aDefinition of abbreviations used in table:

ASME=American Society of Mechanical Engineers

Cd=cadmium

CEMS=continuous emission monitoring system

CO=carbon monoxide

COMS=continuous opacity monitoring system

DSI/ESP/CI=dry sorbent injection/electrostatic precipitator/activated

carbon injection

GCP=good combustion practices

gr/dscf=grains per dry standard cubic foot

gr/million dscf=grains per million dry standard cubic feet

HCl=hydrogen chloride

Hg=mercury

mg/dscm=milligrams per dry standard cubic meter (100 mg/dscm=0.044 gr/

dscf)

Mg/day=megagrams per day (1 Mg/day=1.1 short tons/day (2,204 pounds/

day))

MSW=municipal solid waste

MWC=municipal waste combustor

ng/dscm=nanograms per dry standard cubic meter (1,000,000 ng=1 mg)

NOX=nitrogen oxides

Pb=lead

PM=particulate matter

ppmv=parts per million by volume

RDF=refuse-derived fuel

SD/ESP/CI=spray dryer/electrostatic precipitator/activated carbon

injection system

SD/FF/CI=spray dryer/fabric filter/activated carbon injection system

SNCR=selective noncatalytic reduction

SO2=sulfur dioxide

TEQ=toxic equivalency of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (1989

North Atlantic Treaty Organization (NATO) international criteria)

Total mass=total mass of tetra- through octa-chlorinated dibenzo-p-

dioxins and dibenzofurans.

bAir curtain incinerators that combust only yard waste, tree trimmings,

and/or clean untreated lumber would be subject to an opacity

guideline, but to no other parts of the proposed emission guidelines.

Air curtain incinerators that combust other MSW are subject to all

requirements under the proposed emission guidelines.

cAll concentration levels in the table are converted to 7 percent O2,

dry basis.

dDioxins/furans are measured as tetra- through octa-chlorinated dibenzo-

p-dioxins and dibenzofurans. For plants complying with the TEQ format,

TEQ is determined using 1989 international toxicity equivalency

factors.

eMethod 29 is being proposed in a separate notice in today's Federal

Register.

fThe proposed guidelines include provisions that would allow small MWC

plants to conduct performance tests for dioxin/furans, PM, Cd, Pb, Hg,

and HCl every third year if the MWC meets certain specified criteria,

as discussed in section II.F of this preamble.

The proposed guideline limits are summarized below.

1. Municipal Waste Combustor Organics

The proposed guidelines would require existing MWC's at large MWC

plants to meet a dioxin/furan emission level of 0.50 ng/dscm TEQ or 30

ng/dscm total dioxins/furans, corrected to 7 percent O2. Existing

MWC's located at small MWC plants would be required to meet a dioxin/

furan level of 1.0 ng/dscm TEQ or 60 ng/dscm total dioxins/furans,

corrected to 7 percent O2. The TEQ emission levels would be

calculated using the 1989 North Atlantic Treaty Organization (NATO)

international toxic equivalency factors (TEF's), using the methods

described in section II.F of this preamble and section 60.58b of

subpart Eb of today's proposed NSPS.

2. Municipal Waste Combustor Metals

The proposed emission guidelines would require MWC's at large

plants to control PM to a level of 27 mg/dscm corrected to 7 percent

O2. The emission guideline PM level proposed for MWC's at small

plants is 69 mg/dscm, corrected to 7 percent O2. Municipal waste

combustors at both small and large existing MWC plants would be

required to meet an opacity level of 10 percent using a 6-minute

averaging period.

The proposed emission guidelines would also establish specific

emission levels for Cd, Pb, and Hg. The proposed guidelines would

require existing MWC's at large plants to meet a Cd emission level of

0.040 mg/dscm, a Pb emission level of 0.50 mg/dscm, and an Hg emission

level of 0.080 mg/dscm or an 85-percent reduction in Hg emissions.

For existing MWC's at small plants, the emission guidelines would

be 0.10 mg/dscm for Cd, 1.6 mg/dscm for Pb, and 0.080 mg/dscm or an 85-

percent reduction in Hg emissions.

3. Municipal Waste Combustor Acid Gases

The proposed emission guidelines for acid gases would require all

existing MWC's located at large plants to control SO2 emissions to

a level of either 35 ppmv or 75-percent reduction (at 7 percent

O2, dry basis) on a 24-hour geometric mean basis and HCl emissions

to a level of either 35 ppmv or 95-percent reduction (at 7 percent

O2, dry basis). All existing MWC's located at small plants would

be required to meet an SO2 emission level of either 80 ppmv or 50-

percent reduction (at 7 percent O2, dry basis) on a 24-hour

geometric mean basis and an HCl emission level of either 250 ppmv or

50-percent reduction (at 7 percent O2, dry basis).

4. Good Combustion Practices

Today's proposed emission guidelines would require all existing

MWC's at plants with capacities above 35 Mg/day to comply with

specified operating practices that reflect GCP. These operating

practices include CO levels, combustor load levels, and flue gas

temperatures and are specified below.

The GCP levels remain unchanged from the February 11, 1991

guidelines. For modular starved-air and modular excess-air types of

MWC's, the CO emission limit would be 50 ppmv (at 7 percent O2,

dry basis) on a 4-hour block average basis. For mass burn waterwall,

mass burn fixed-wall refractory, and fluidized-bed types of MWC's, the

CO emission limit would be 100 ppmv (at 7 percent O2, dry basis)

on a 4-hour block average basis. For mass burn rotary refractory MWC's,

the CO emission limit would be 100 ppmv (at 7 percent O2, dry

basis) on a 24-hour block average basis. For mass burn rotary waterwall

MWC's, the CO emission limit would be 250 ppmv (at 7 percent O2,

dry basis) on a 24-hour block average basis. For RDF-stoker MWC's, the

CO limit would be 200 ppmv (at 7 percent O2, dry basis) on a 24-

hour block average basis. For coal/RDF mixed fuel-fired MWC's, the CO

limit would be 150 ppmv (at 7 percent O2, dry basis) on a 4-hour

block average basis.

Municipal waste combustors would be allowed to operate up to 110

percent of the maximum capacity, as achieved during the most recent

dioxin/furan compliance test. Maximum capacity would be based on the

steam flow rate, which would be continuously monitored according to the

ASME Power Test Code (PTC) for Steam Generating Units (PTC4.1 and

PTC19.5). This requirement is unchanged from the February 11, 1991

emission guidelines. The EPA requests comments on this method of

measuring load for steam-generating MWC's. Specifically, the EPA has

questions regarding the requirement for calibration of the measuring

device (e.g., orifice plate) before and after each dioxin/furan

compliance test. The EPA is concerned that this calibration requirement

may be overly burdensome because the main steam line that contains the

orifice plate may need to be cut in order to access the orifice plate

for recalibration. Also, the EPA requests comments on whether the ASME

PTC adequately addresses the need for calibrating the signal from the

flow meter.

Additionally, the EPA requests comments on the use of boiler feed

water flow as an alternative method for continuously monitoring load

for steam-generating MWC's.

Furthermore, the EPA is considering allowing the use of the

continuous flue gas volumetric flow rate to measure maximum capacity

for both steam-generating MWC's, as well as those MWC's that do not

generate steam. These types of monitors are based on ultrasonic,

thermal, or differential pressure methods, and are now being required

as part of the EPA's Acid Rain Program (40 CFR part 75). The EPA

requests comments on whether continuous flue gas volumetric flow rate

monitors are adequately demonstrated and accurate methods for

determining compliance with the load level requirements, and if they

should be allowed as an alternative to the use of the ASME PTC.

Under the guidelines, MWC's would establish a site-specific maximum

flue gas temperature at the final PM control device inlet demonstrated

during their most recent dioxin/furan compliance test. Similar to the

provisions for establishing a maximum load level measurement, the

maximum demonstrated PM control device inlet temperature is established

as the maximum 4-hour block average temperature measured during the

most recent dioxin/furan compliance test. The MWC must then be operated

so that the temperature at the final PM control device inlet does not

exceed this level by more than 17 deg.C (30 deg.F) (4-hour block

average basis).

5. Operator Certification and Training

The proposed emission guidelines would require full certification

of all MWC shift supervisors and MWC chief facility operators by the

ASME or a State program. The proposed guidelines would also require

that at least one of the following persons be on duty at the MWC at all

times during which the MWC is combusting waste: A fully certified MWC

chief facility operator, a fully certified shift supervisor, or a

provisionally certified control room operator. A provisionally

certified control room operator would be allowed to ``stand in'' during

times that a fully certified chief facility operator or shift

supervisor is offsite.

In addition, the proposed emission guidelines would require each

owner or operator of an MWC with an aggregate capacity greater than 35

Mg/day to develop and maintain a site-specific training manual and to

review it with all employees associated with the operation of the MWC

(including MWC maintenance personnel, crane/load operators, and ash

handlers). The manual and training would be updated annually.

Section 129 of the Act of 1990 requires the EPA to develop and

promote a model State program for the training and certification of MWC

operators. Section 129 specifies that ``any person with control over

processes affecting emissions from a unit'' must successfully complete

an acceptable training program. Consistent with section 129, today's

proposed emission guidelines would require all MWC chief facility

operators, shift supervisors, and control room operators at MWC plants

with capacities above 35 Mg/day to complete the MWC operator training

course developed by the EPA or a State program. The EPA has developed a

model training program and has distributed it to State air pollution

control agencies, EPA regional offices, and MWC industry groups. This

model training program could be used to fulfill this requirement and

prepare for the ASME certification.

6. Nitrogen Oxides Emissions

The proposed emission guidelines would require MWC's at large

plants, except refractory MWC's, to control NOX emissions to a

level of 180 ppmv (corrected to 7 percent O2, dry basis, on a 24-

hour daily average basis). A ``no control'' NOX emission guideline

level for MWC's at small plants and refractory MWC's at large plants is

proposed and discussed in section VIII of this preamble.

7. Fly Ash or Bottom Ash Fugitive Emissions

The proposed guidelines for fly ash/bottom ash fugitive dust

emissions would establish a guideline of no visible emissions for fly

ash or bottom ash emissions from an MWC facility.

The visible emissions guidelines would apply to buildings and

external ash handling or transfer activities (e.g., loading), and any

other area at the designated facility that is a potential source of fly

ash or bottom ash fugitive emissions.

E. Comparison of the 1991 Guidelines and Today's Proposal

The subpart Ca emission guidelines promulgated on February 11, 1991

and today's proposed subpart Cb emission guidelines both contain

guideline emission levels for dioxins/furans, PM, SO2, and HCl at

large MWC's; however, today's proposed guidelines for most of these

pollutants are more stringent than the guidelines promulgated on

February 11, 1991. The February 11, 1991 guidelines did not address Cd,

Pb, Hg, NOX, or fly ash/bottom ash fugitive emissions, but each of

these is included in today's proposal. Also, today's proposal covers

all MWC units at plants with aggregate capacities above 35 Mg/day,

whereas the February 11, 1991 guidelines only covered MWC units with

unit capacities above 225 Mg/day. A comparison of the 1991 guidelines

and proposed guideline emission levels is provided in table 2.

Table 2.--Comparison of The Proposed Guidelines (Subpart Cb) and The 1991 Guidelines (Subpart Ca)

----------------------------------------------------------------------------------------------------------------

Guideline emission levela

----------------------------------------------------------------------------------------

Proposed subpart Cb 1991 guidelines (subpart Ca)

Pollutant guidelinesb ----------------------------------------------------------

------------------------------ MWC's > 225 Mg/day but 225 Mg/dayc 1000 Mg/dayc MWC's > 1000 Mg/dayc

----------------------------------------------------------------------------------------------------------------

Dioxins/furans......... 0.5 ng/dscm toxic 125 ng/dscm, total mass 60 ng/dscm, total mass

equivalence or 30 ng/dscm (equivalent to 2.0 ng/dscm (equivalent to 1.0 ng/dscm

total mass. toxic equivalence). toxic equivalence).

SO2.................... 35 ppmv or 75-percent 30 ppmv or 50-percent 30 ppmv or 70-percent

reductiond. reductiond. reductiond.

HCl.................... 35 ppmv or 95-percent 25 ppmv or 50-percent 25 ppmv or 90-percent

reductiond. reductiond. reductiond.

PM..................... 27 mg/dscm.................. 69 mg/dscm.................. 34 mg/dscm.

Opacity................ 10 percent.................. 10 percent.................. 10 percent.

Cd..................... 0.040 mg/dscm............... None........................ None.

Pb..................... 0.50 mg/dscm................ None........................ None.

Hg..................... 0.080 mg/dscm (or 85-percent None........................ None.

reduction)d.

NOX.................... 180 ppmv.................... None........................ None.

Fly ash/bottom ash No visible emissions from None........................ None.

fugitive emissions. buildings, ash transfer

points, or ash handling

areas.

----------------------------------------------------------------------------------------------------------------

a All emission levels are corrected to 7 percent O2, dry basis.

b Separate guideline levels are also proposed for MWC plants with aggregate plant capacities between 35 and 225

Mg/day.

c The February 11, 1991 guidelines were based on MWC unit capacity, and today's proposed guidelines are based on

aggregate plant capacity.

d Whichever is less stringent.

The MWC operating guidelines (GCP) included in today's proposal are

the same as those in the February 11, 1991 guidelines. The training and

certification requirements have changed somewhat. The February 11, 1991

guidelines required only provisional certification of MWC chief

facility operators and shift supervisors, but today's proposed

guidelines would require both provisional and then full certification.

This change is being proposed because the full operator certification

program is now widely available. In 1991, the program was not widely

available.

Today's proposal also adds a provision to allow provisionally

certified MWC control room operators to stand in for the MWC chief

facility operators or shift supervisors in their temporary absence from

the MWC. Additionally, today's proposal would require all MWC chief

facility operators, shift supervisors, and control room operators to

complete the EPA or a State MWC training course. This training course

requirement was not included in the February 11, 1991 guidelines.

F. Performance Testing and Monitoring Requirements

Information related to the performance testing and monitoring

requirements for MWC acid gases (SO2 and HCl), MWC organics

(dioxins/furans), PM, and MWC operating practices was published in the

February 11 and 13, 1991 Federal Register notices (56 FR 5514 and 56 FR

5758). These same requirements would be adopted by today's proposed

guidelines and would be extended to apply to all MWC's at plants with

aggregate capacities above 35 Mg/day. Because the proposed guidelines

allow compliance with either a dioxin/furan limit in terms of TEQ or a

dioxin/furan limit on a total mass basis, procedures are being proposed

for determining dioxin/furan emissions on a TEQ basis. The mass of each

tetra- through octa- chlorinated dibenzo-p-dioxin and dibenzofuran

congener would be measured by EPA Reference Method 23. Each congener

mass would then be adjusted by the corresponding toxic equivalency

factor (TEF; the 1989 NATO international TEF's). Finally, the adjusted

congener masses would be added together to determine dioxins/furans in

ng/dscm TEQ. Furthermore, today's proposal would require both large and

small MWC facilities to conduct annual opacity tests using EPA

Reference Method 9. This testing would be in addition to the continuous

monitoring of opacity levels. Also, today's proposal allows small MWC

facilities to conduct less frequent testing for dioxin/furan, HCl, and

PM emissions if the small facility consistently demonstrates

compliance. More specifically, under today's proposed emission

guidelines, if three consecutive annual compliance tests for an MWC at

a small MWC plant indicate compliance with the emission guideline for a

pollutant (i.e., PM, HCl, or dioxins/furans), the MWC would be allowed

to wait 3 years before retesting for the pollutant. If the next test

conducted in the third year shows compliance with the emission

guideline for that pollutant, then the facility could again wait 3

years to test for the pollutant. If noncompliance with the emission

guideline for the pollutant occurs, corrective actions would be

required to be undertaken and annual testing would be required to be

conducted until 3 consecutive years of compliance with the emission

guideline is established. At a minimum, performance tests for dioxins/

furans, HCl, and PM would be required to be performed for each MWC at a

small MWC plant every 3 years. This provision is included to minimize

costs for small MWC plants, while still retaining periodic testing to

ensure compliance. All large MWC plants would continue to be required

to conduct annual compliance tests.

Annual performance tests to determine compliance with the Cd, Pb,

and Hg emission guidelines would be based on EPA Reference Method 29.

The average emission rates of three or more test runs using this

methodology would be used to determine compliance. The EPA considered

the use of EPA Reference Method 101A for Hg testing; however, based on

available data, the EPA has concluded that Method 29 is a better

measure of Cd, Pb, and Hg emissions than Method 101A and has therefore

proposed Method 29 for testing MWC's. Also, as discussed above for

dioxins/furans, PM, and HCl, if small plants demonstrate compliance

with the Cd, Pb, and Hg emission guidelines for 3 consecutive years,

they would be allowed to begin testing for these three pollutants every

third year.

The EPA Reference Method 29 is proposed in a separate part of

today's Federal Register. Method 29 is very similar to the method that

has been used by the EPA's Office of Solid Waste to measure metal

emissions from boilers cofiring hazardous waste, commonly referred to

as the EPA multimetals method. The proposed Method 29 is discussed in

section IV.H of this preamble.

The proposed emission guidelines for NOX would require

continuous monitoring of NOX emissions for MWC's at large plants,

except refractory units for which a ``no control'' emission guideline

is proposed. Compliance with the NOX emission guideline level for

nonrefractory MWC's at large plants would be determined by calculating

the arithmetic average of the hourly emission rates, as measured by the

continuous emission monitoring system (CEMS), for a 24-hour period that

the MWC operates, using EPA Reference Method 19. Quality assurance

would be maintained in accordance with appendix F of 40 CFR part 60.

Annual performance tests to determine compliance with proposed fly

ash/bottom ash visible emissions guidelines would be based on EPA

Reference Method 22 (3-hour continuous visual observation). The limits

would apply at all times, and tests would be conducted during periods

of time when fly ash/bottom ash is transferred from the combustor or

from the air pollution control device to the ash loading area, and when

ash is loaded for transportation or is being transported onsite.

The data availability requirement for CEMS (SO2, NOX, CO,

and O2 (or CO2)) has been changed from the 1991 NSPS.

Today's proposal would require that valid paired CEMS hourly

averages (i.e., SO2 and O2 (or CO2), NOX and

O2 (or CO2), and CO and O2 (or CO2)) be obtained

for 75 percent of the hours per day for 90 percent of the days per

calendar quarter that the designated facility is operated and

combusting MSW.

G. Reporting, Recordkeeping, and Compliance Schedule Guidelines

The MWC emission guidelines promulgated on February 11, 1991 for

MWC's with unit capacities above 225 Mg/day established reporting and

recordkeeping requirements for MWC organics (dioxins/furans), MWC

metals (PM and opacity), MWC acid gases (SO2 and HCl), and

operating practices (CO, load, flue gas temperature, and operator

training/certification). These reporting and recordkeeping requirements

are discussed in the February 11, 1991 Federal Register notice (56 FR

5514). These same reporting and recordkeeping requirements would be

adopted under the proposed guidelines, except that dioxin/furan

emissions would be recorded and reported on either a total mass basis

or a TEQ basis. Furthermore, if small MWC's meet the criteria in

today's proposal allowing them to conduct performance tests for

dioxins/furans, HCl, and PM every third year, they would submit a

simplified annual report for years in which a full compliance test was

not required.

Today's proposal also would add reporting and recordkeeping

requirements for Cd, Pb, Hg, and NOX. The proposed emission

guidelines would require that initial and annual compliance reports be

submitted for Cd, Pb, and Hg for MWC's at plants with capacities above

35 Mg/day. If small MWC's meet the criteria allowing them to conduct

performance tests for Cd, Pb, or Hg every third year, they would be

allowed to submit a simplified annual report for years when a full

compliance test was not required. The proposed guidelines would also

require that the amount of activated carbon injected for Hg control at

small and large plants be recorded during MWC operation.

The NSPS for MWC's promulgated on February 11, 1991 (56 FR 5488)

establishes reporting and recordkeeping requirements for NOX for

new MWC's; however, no NOX requirements were established for

existing MWC's. These NSPS reporting and recordkeeping requirements

would now apply to MWC's only at large plants under today's proposed

emission guidelines. Submittal of initial and quarterly reports for all

CEMS data and accuracy determinations for NOX emissions would be

required. Quality assurance would be required in accordance with

appendix F in 40 CFR part 60.

Initial and annual compliance reports for fly ash/bottom ash

visible emissions testing would be required under today's proposal for

both small and large plants.

The proposed emission guidelines include revised compliance

scheduling requirements. The proposed guidelines require State plans to

require both small and large MWC plants to meet one of the following

two compliance schedules: (1) Full compliance with the State plan

within 1 year after approval of the State plan, or (2) full compliance

with the State plan within 3 years following issuance of a revised

construction or operation permit, if a permit modification is required,

or within 3 years following approval of the State plan, if a permit

modification is not required, provided the State plan includes

measurable and enforceable incremental steps of progress toward

compliance with the State plan (see section IV.I of this preamble for

further discussion of this requirement).

The proposed emission guidelines also include an accelerated

compliance schedule for compliance with the proposed dioxin/furan and

Hg emission limits for certain MWC's. Under the accelerated schedule,

MWC units for which construction commenced after June 26, 1987 and that

are located at large MWC plants would be required to be in compliance

with the proposed dioxin/furan and Hg emission guidelines within 1 year

following issuance of a revised construction or operation permit, if a

permit modification is required, or within 1 year following approval of

the State plan, if a permit modification is not required (these units

are already equipped with acid gas/PM control systems). The rationale

for requiring this accelerated schedule is provided in section IV.I of

this preamble.

Additionally, the proposal requires compliance with both the

operator training and certification requirements by 1 year after the

date of promulgation of the emission guidelines.

Records of all data, including results of emission tests and

compliance reports would be maintained for 5 years following the date

of submission of the data.

III. Impacts of the Proposed Emission Guidelines

This section describes the impacts (i.e., air, water, solid waste,

energy, control cost, and economic impacts) of the proposed emission

guidelines for small and large MWC facilities. The impacts are

summarized in table 3. Table 3 presents: (1) The impact of these

proposed subpart Cb guidelines over a pre-1989 baseline (i.e., baseline

prior to the effective date of the subpart Ca guidelines); and (2) the

incremental impact of these proposed subpart Cb guidelines over the

subpart Ca guidelines. The following discussion focuses only on the

impacts of today's proposal based on a pre-1989 baseline, since the

emission guidelines promulgated in 1991 have not been implemented. For

further information on the impacts of the proposed emission guidelines,

refer to the document entitled ``Economic Impact Analysis for Proposed

Emission Standards and Guidelines for Municipal Waste Combustors'' that

is included in the list of items under Supplementary Information at the

beginning of this preamble.

Table 3.--Impacts of the 1991 Subpart Ca and Proposed Subpart Cb

Guidelines

------------------------------------------------------------------------

Increment

of proposed

Proposed 1994

1991 1994 subpart Cb

Parameter subpart Ca subpart Cb guidelines

guidelinesa guidelinesa over the

1991

subpart Ca

guidelinesb

------------------------------------------------------------------------

Characteristics of Existing

MWC's:

Combustion capacity (106 Mg/yr) 35.9 39.0 3.1

Number of MWC plants........... 158 179 21

Cost (1990 Dollars):

Capital cost ($106)............ 888 2,100 1,212

Annualized cost ($106/yr)...... 168 445 277

Average cost increase ($/Mg MSW

combusted).................... 6.40 13.60 7.20

Annual Emissions Reduction (Mg/

yr):

SO2............................ 25,000 43,000 18,000

HCl............................ 36,000 56,000 20,000

PM............................. 1,100 3,100 2,000

Cd............................. 2 5 3

Pb............................. 30 83 53

Hg............................. 11 47 36

NOX............................ 0 19,000 19,000

Total dioxins/furans (kg/yr)c.. 117 157 40

Dioxin/furan TEQ (g/yr)d....... 1,950 2,620 670

------------------------------------------------------------------------

a The impacts are based on a pre-1989 baseline (i.e., a baseline prior

to the effective date of the subpart Ca guidelines).

b The impacts are calculated by subtracting the impacts of the 1991

subpart Ca guidelines from the impacts of the proposed 1994 subpart Cb

guidelines (based on a pre-1989 baseline).

c kg/yr = kilograms per year.

d g/yr = grams per year.

A. Air Impacts

The air emission reductions discussed below, as well as all other

impacts discussed in today's proposal, are nationwide impacts that

would result from full implementation of the guidelines and are

relative to the current baseline MWC population, considering in-place

air pollution control devices. These are not incremental impacts

relative to the February 11, 1991 emission guidelines. The total

impacts are presented because the February 11, 1991 guidelines have not

been implemented and are being significantly altered by today's

proposal.

Under today's proposed emission guidelines, nationwide emissions of

total dioxins/furans would be reduced by about 157 kilograms per year

(kg/yr) compared with emissions in the absence of nationwide

guidelines. Emissions of dioxins/furans on a TEQ basis would be reduced

by about 2,620 grams per year (g/yr). This represents a nationwide

reduction of about 99 percent compared to baseline levels in the

absence of the guidelines. Remaining nationwide dioxin/furan emissions

would be about 42 g/yr TEQ.

Nationwide emissions of PM would be decreased by about 3,100

megagrams per year (Mg/yr) compared with levels in the absence of

emission guidelines. This represents a reduction of just under 50

percent compared to baseline levels in the absence of nationwide

guidelines. In combination with baseline control, this would represent

greater than 99-percent PM control. Emissions of Cd would be reduced by

about 6 Mg/yr, Pb would be reduced by about 91 Mg/yr, and Hg would be

reduced by about 48 Mg/yr. These emission reductions represent

decreases of about 70 to 80 percent for each of these three metals. In

combination with baseline control, this would represent greater than

99-percent control for Cd and Pb and greater than 80-percent control

for Hg.

Nationwide emissions of SO2 and HCl would be decreased by

43,000 Mg/yr and 56,000 Mg/yr, respectively, relative to current

baseline levels. This represents about 87-percent control of acid gases

compared to baseline levels in the absence of emission guidelines. In

combination with baseline control, this would represent about 95-

percent control of these acid gases.

The proposed emission guidelines would reduce nationwide emissions

of NOX by 19,000 Mg/yr, representing an overall nationwide

emission reduction of over 30 percent compared to baseline levels that

would be emitted without the proposed guidelines.

B. Water and Solid Waste Impacts

Water and solid waste impacts that would result from today's

proposal were determined not to be significant. No water pollution

impacts are projected because the control technologies considered would

not produce a wastewater stream.

The EPA believes that MWC ash disposal is adequately addressed by

current waste management standards, so that considerations of ash

quality need not play a role in this rulemaking.

C. Energy Impacts

The energy impacts of applying add-on pollutant emission controls

required as part of today's proposal would not result in significant

energy impacts. Today's proposal for MWC acid gases, MWC organics, MWC

metals, and NOX would affect an estimated 179 MWC plants and would

result in energy requirements of 400 to 500 gigawatt-hours per year

(GW-hr/yr) of electricity to operate the air pollution control devices,

and about 780 terajoules per year (TJ/yr) of natural gas to maintain

combustor operating conditions that reflect GCP.

Most of the MWC's that would be affected by the proposed guidelines

generate electricity for sale. For example, a large mass burn/waterwall

MWC plant would generate about 500 GW-hr/yr of electricity. The energy

to operate its air pollution control equipment would represent only

about 4 percent of generation. Additionally, natural gas that is fired

for GCP requirements represents less than 0.2 percent of the annual

heat input to MWC's. Considering that a large percentage of new power

plant capacity to be constructed in the next 10 years will fire natural

gas, the firing of small amounts of natural gas for GCP (while

generating electricity) actually reallocates natural gas use rather

than just increasing consumption.

D. Cost and Economic Impacts

1. National Overview

The EPA projects that about 33 million Mg of MSW will be combusted

in the year 2000 in existing MWC plants subject to the guidelines being

proposed today. The EPA estimates that there would be 179 existing MWC

plants in operation that would be subject to the subpart Cb guidelines:

60 in the 35- to 225-Mg/day capacity range and 119 in the larger than

225-Mg/day capacity range. The typical plant has two or three MWC

units.

The cost estimates given below are in 1990 dollars and are for

emission control and compliance testing. The estimates do not include

costs for such things as permitting and enforcement. To estimate the

costs of the guidelines being proposed today, the EPA has taken into

account all existing control equipment. Cost estimates are incremental

over costs associated with the control equipment in current use and

include retrofit premiums. Cost estimates are total costs for the

revised MWC guidelines and are not incremental to the February 11, 1991

guidelines.

The nationwide annual cost of the guidelines including testing,

reporting, and recordkeeping for acid gas, PM, Hg, and NOX control

would be about $445 million. The national average annual cost of the

guidelines per unit of MSW combusted would be about $14/Mg.

The above costs for the guidelines are overall national costs

spread over the entire existing MWC population. However, about one half

of the affected waste flow from existing MWC's larger than 225 Mg/day

already is combusted in facilities equipped with spray dryer/

electrostatic precipitator (SD/ESP) or spray dryer/fabric filter (SD/

FF) systems, and these MWC's would incur only a minor compliance cost

(about $3/Mg) as a result of the proposed guidelines. The average

annual cost of acid gas, PM, and Hg control per unit of MSW combusted

at large plants that do not already have SD/ESP or SD/FF systems would

be about $20/Mg.

The average annual cost per unit of MSW combusted at small plants

using dry sorbent injection/electrostatic precipitator (DSI/ESP)

systems and Hg control would be about $36/Mg.

The guidelines will have a wide range of impacts on the price of

combustion services. To study these potential impacts, the EPA first

applied a cost accounting procedure that approximates the one that

would be used by an individual publicly owned MWC. Then, using a 1993

average tipping fee of $57/Mg of MSW combusted (1990 dollars) of waste

combusted and assuming the full cost of meeting acid gas, PM, Hg, and

NOX requirements is passed directly to MWC customers, the EPA

found that the lowest and highest tipping fee increases for the model

plants used in the EPA's economic analysis would be $9 and $56,

respectively, per megagram of MSW combusted. The majority of tipping

fee increases would be in the $17 to $28/Mg range. (These estimates

apply only to MWC's at small plants that do not already have DSI/ESP,

SD/ESP, or SD/FF systems or large plants that do not currently have SD/

ESP or SD/FF systems.)

The EPA projects that, regardless of how the regulatory costs are

financed, most of the burden will find its way directly or indirectly

to households served by MWC's. Costs that are directly assessed to

households are likely to be in the form of increased collection fees

and/or increased taxes. Indirect household costs are price increases

charged by businesses that similarly are faced with increases in

collection fees and/or taxes. For the guidelines being proposed today,

the EPA projects an increase in the average annual household cost of

waste disposal of about $25 for communities that have MWC's. The actual

cost per household will depend on local conditions, including the

extent to which recycling and landfilling are also used within the

affected community. Approximately 62 percent of the total average

household cost is a direct cost, thus the annual direct household cost

would be approximately $15. The EPA estimates that the average annual

household cost breaks down to $26 per year for communities over 250,000

in population; $24 for communities with populations between 100,000 and

250,000; $24 for communities with populations between 50,000 and

100,000; and $22 for communities with populations under 50,000. This

range represents less than 1 percent of household income. The actual

cost per household will depend on local conditions.

The EPA identified 39 private firms each of which owns one or more

MWC's. Detailed financial data are published for only 17 of the firms

projected to incur costs, none of which is small (under $6 million in

annual sales). (Firms for which annual sales data are not available are

assumed to be small.) The total annual cost of the guidelines as a

percentage of sales averages less than 1 percent and ranges from less

than 1 percent to about 80 percent for these 17 firms. Potential

tipping fee increases, based on an assumed full cost pass-through

(i.e., passing all control costs to consumers via the tipping fee) and

an average tipping fee of $57/Mg, are about 18 percent for MWC's owned

by small firms and about 14 percent for MWC's owned by large firms.

Some of the benefits of the emission guidelines have been

quantified. The absence of sufficient exposure-response and valuation

information precludes a comprehensive benefits analysis for many of the

MWC pollutants. The EPA expects partial benefits for reduction of PM

and SO2, including benefits from reductions in morbidity and

mortality, to total about $106 million annually. The total benefits

would be higher if benefits from reductions of other pollutants were

valuated. In addition, recent evidence suggests the mortality reduction

benefits of particulate mater controls may be higher than is assumed in

this analysis.

2. Control Costs for Typical MWC Plants

The previous section presented costs of the proposal on a national

basis. This section presents examples of typical retrofit costs that

would be experienced at both a large MWC plant and a small MWC plant.

These are typical costs. Lower costs will be experienced at MWC plants

that have already installed the air pollution control components

required by the proposal. Higher costs will be experienced for MWC

plants with more difficult retrofit applications.

The costing data presented in this section are provided in the

following formats: capital cost, annualized cost, and cost per Mg of

municipal waste combusted. The costing information is subcategorized by

air pollution control components (i.e., GCP upgrade, acid gas scrubber,

activated carbon injection application, and NOX control). For

perspective, the estimated cost of combustion units is also displayed.

Since the actual MWC unit cost for an existing combustion unit is

sensitive to past funding practices, the EPA could not provide this

cost. Instead, the EPA has provided the cost of combustion units for a

new MWC plant for reference. This costing information has been derived

from 1989 background information documents that were used in developing

the 1991 NSPS and emission guidelines (see SUPPLEMENTARY INFORMATION

for more information about these documents), and is presented in 1987

dollars (the escalation factor for converting to mid-1990 dollars is

1.111).

From table 3A, it can be noted that the capital cost for retrofit

at a large existing MWC plant (980 Mg/day capacity) would be about

$16.8 million of which $13.6 million would be for the acid gas control,

2.9 million for NOX control, and less than one million for

activated carbon injection and GCP. On an annualized basis, the cost

would be about $5.1 million/yr or about $16/Mg of waste combusted. This

would increase baseline combustor cost from about $60/Mg combusted

(based on the baseline combustor cost for a new large MWC plant

presented in table 3B) to about $76/Mg combusted. Large MWC plants

represent about 94 percent of the existing MWC combustion capacity.

Table 3A.--Capital and Annualized Costs of Air Pollution Control for Typical Existing Large and Small MWC

Plantsa

----------------------------------------------------------------------------------------------------------------

Air pollution control device costa

Baseline ------------------------------------------------ Total

Parameter combustor GCPb Acid gas/ Total APCD combustor and

PM CIc NOX costd APCD cost

----------------------------------------------------------------------------------------------------------------

Existing large MWC

plant (980 Mg/day MB/

WW retrofitted with

GCP, SD/ESP, CI, and

SNCR)e,f,g,h:

Capital cost NAi 0.086 13.6 0.279 2.9 16.8 NA

($10\6\).

Annualized cost NA 0.148 3.8 0.498 0.844 5.14 NA

($10\6\/yr).

Average cost NA 0.45 11.7 1.52 2.53 15.7 NA

increase ($/Mg

MSW combusted).

Existing small MWC

plant (135 Mg/day MOD/

SA retrofitted with

GCP, DSI/ESP and

CI)j,k,l:

Capital cost NA 0.27 2.5 0.055 0 2.55 NA

($10\6\).

Annualized cost NA 0.182 0.726 0.041 0 0.77 NA

($10\6\/yr).

Average cost NA 4.01 16.0 0.90 0 16.9 NA

increase ($/Mg

MSW combusted).

----------------------------------------------------------------------------------------------------------------

aThe costs presented are in 1987 dollars. To calculate mid-1990 dollars, multiply 1987 dollars by a factor of

1.111. Total cost values may not add due to rounding.

bGCP = good combustion practices.

cCI = activated carbon injection.

dAPCD = air pollution control device.

eMB/WW = mass burn waterwall combustor.

fSNCR = selective noncatalytic reduction.

gSD/ESP = spray dryer and electrostatic precipitator.

hThe costs presented are based on the assumption that an existing ESP was upgraded and retrofitted with a spray

dryer system.

iNA = not available. Because the capital cost of the existing combustor was not available, the total costs could

not be calculated. Refer to the baseline combustor cost in table 3B for new facilities, which is similar to

the cost for existing facilities.

jMOD/SA = modular starved-air combustor.

kDSI/ESP = dry sorbent injection and electrostatic precipitator.

lThe costs presented are based on the assumption that an existing ESP was upgraded and retrofitted with a dry

sorbent injection system.

Table 3B.--Capital and Annualized Costs of Air Pollution Control for Typical New Large and Small MWC Plantsa

----------------------------------------------------------------------------------------------------------------

Air pollution control device costa Total

Baseline ------------------------------------------------ combustor

Parameter combustor GCPb Acid gas/ Total APCD and APCD

PM CIc NOX costd cost

----------------------------------------------------------------------------------------------------------------

New large MWC plant (730 Mg/

day MB/WW with SD/FF, CI,

and SNCR)e,f,g:

Capital cost ($106)...... 50 0 12 0.150 2.0 14.2 64.2

Percent of total capital

cost (%)h............... 78 0 19 0.2 3 22 100

Annualized cost ($106/yr) 14.4 0 3.56 0.091 0.582 4.23 18.6

Average cost increase ($/

Mg MSW combusted)....... 59.5 0 14.8 0.37 2.39 17.5 77.05

New small MWC plant (90 Mg/

day MOD/SA with SD/FF and

CI)i:

Capital cost ($106)...... 5.5 0 3.1 0.043 0 3.14 8.64

Percent of total capital

cost (%)h............... 64 0 36 0.5 0 36 100

Annualized cost ($106/yr) 1.83 0 0.91 0.014 0 0.92 2.76

Average cost increase ($/

Mg MSW combusted)....... 60.5 0 30.2 0.46 0 30.7 91.2

----------------------------------------------------------------------------------------------------------------

AaThe costs presented are in 1987 dollars. To calculate mid-1990 dollars, multiply 1987 dollars by a factor of

1.111. Total cost values may not add due to rounding.

AbGCP = good combustion practices. Costs for GCP are included in combustor design (no cost).

AcCI = activated carbon injection.

AdAPCD = air pollution control device.

AeMB/WW = mass burn waterwall combustor.

AfSD/FF = spray dryer and fabric filter.

AgSNCR = selective noncatalytic reduction.

AhDoes not add to 100 percent due to rounding.

AiMOD/SA = modular starved-air combustor.

For a small existing MWC plant (135 Mg/day capacity), table 3A

shows a capital cost for retrofit of about $2.6 million of which $2.5

million would be for the acid gas control system and the remaining for

activated carbon injection and GCP. On an annualized basis, the cost

would be about $770,000/yr or about $17/Mg of waste combusted. This

would increase baseline combustor cost from about $61/Mg combusted

(based on the baseline combustor cost for a new small MWC plant

presented in table 3B) to about $78/Mg combusted. Small MWC plants

represent about 6 percent of the existing MWC combustion capacity.

IV. Rationale for the Proposed Guidelines for MWC Emissions

This section addresses the legal, technical, and economic basis for

the proposed emission guidelines. The basis for regulating MWC's, for

regulating the specified pollutants, and for regulating MWC's according

to the specified size categories are discussed. The section also

presents the EPA's approach in establishing the MACT floor and

selecting MACT. Additionally, the section discusses the selected format

of the proposed guidelines, the proposed performance testing and

monitoring requirements, and the proposed reporting and recordkeeping

requirements.

A. Background

On November 15, 1990, the Act was amended. The Act of 1990 includes

a new section 129 that applies to a range of solid waste incinerators

including MWC's, medical waste incinerators (MWI's), infectious waste

incinerators, and industrial waste incinerators.

Under authority of sections 111 and 129 of the Act of 1990, the EPA

was directed to promulgate MACT-based guidelines for MWC's. However,

section 129 also includes a clause directing the EPA to issue emission

guidelines based on BDT under the terms imposed in the consent decree

issued from State of New York et al. v. Reilly (No. 89-1729 D.D.C.),

but limiting applicability of those emission guidelines to MWC's with

unit capacities greater than 225 Mg/day. Emission guidelines that were

signed by the Administrator on January 11, 1991 and published in the

Federal Register on February 11, 1991 (56 FR 5514) complied with this

component of the section 129 requirements.

Regarding the MACT-based guidelines, section 129 directs the EPA to

promulgate MACT-based guidelines for MWC units located at plants with

capacities greater than 225 Mg/day and at plants with capacities less

than 225 Mg/day. The MACT-based guidelines are to include numerical

emission limits for Cd, Pb, Hg, and NOX, and are to address

operator training requirements.

Today's proposal complies with all requirements of section 129

described above. This has been done by: (1) Proposing MACT-based

guidelines that cover MWC units at plants with capacities above 35 Mg/

day; (2) proposing numerical emission limits for Cd, Pb, Hg, and

NOX; (3) proposing operator training requirements; and (4)

proposing opacity limits for air curtain incinerators firing specific

``clean'' fuels.

The subpart Eb NSPS that is proposed in a separate notice in

today's Federal Register would apply to new facilities constructed

after September 20, 1994. However, the February 11, 1991 subpart Ea

NSPS will remain in effect. Therefore, those existing facilities

subject to the February 11, 1991 NSPS that were constructed on or prior

to September 20, 1994 would be subject to both the subpart Ea NSPS and

the proposed subpart Cb emission guidelines.

B. Selection of Source Category

The MWC guidelines adopted on February 11, 1991 provided the

rationale for the selection of MWC's as a source category to be

regulated (56 FR 5514). Moreover, section 129 of the Act directs the

EPA to issue guidelines for this source category, and thereby confirms

the EPA's earlier decision.

Today's proposed emission guidelines (subpart Cb) would apply to

existing MWC's, defined as those MWC's for which construction,

modification, or reconstruction commenced on or before September 20,

1994. Municipal waste combustors for which construction, modification,

or reconstruction commenced after September 20, 1994 would be covered

by the subpart Eb NSPS proposed in a separate notice in today's Federal

Register.

Also, as required by section 129 of the Act, today's proposed

guidelines would establish opacity limits for certain existing air

curtain incinerators, for which construction, modification, or

reconstruction commenced on or before September 20, 1994. Under the

proposed guidelines, air curtain incinerators that burn only yard

wastes, tree trimmings, and clean untreated lumber would be required to

meet an opacity limit, and no other requirements would apply. The

proposed guidelines for these air curtain incinerators are presented in

section VI of this preamble.

C. Modification or Reconstruction of Existing MWC's

The subpart Ea NSPS proposal published in the Federal Register on

December 20, 1989 (54 FR 52251) provided a discussion of the terms and

conditions associated with construction, modification, and

reconstruction for MWC's. One change is being proposed. Previously, the

terms ``modification'' and ``reconstruction'' were defined under

sections 60.14 and 60.15 of subpart A of part 60. Section 129 of the

Act has specified a new definition of ``modified solid waste

incineration unit'' that combines and revises the previous definitions

of ``modification'' and ``reconstruction.'' Specifically, ``modified

solid waste incineration unit'' refers to: (1) Modifications for which

the

* * * cumulative costs of the modifications, over the life of

the unit, exceed 50 per centum of the original cost of the

construction and installation of the unit (not including the cost of

any land purchased in connection with such construction or

installation) updated to current costs. * * *

or (2) modifications involving

* * * a physical change in or change in the method of operation

of the unit which increases the amount of any air pollutant emitted

by the unit for which standards have been established under [section

129] or section 111 * * *.

D. Selection of Designated Pollutants

A complete discussion of the rationale for selecting ``MWC

emissions'' as the designated pollutants under sections 111(b) and

111(d) of the Act is provided in the December 20, 1989 proposal

preamble for the 1991 emission guidelines (54 FR 52209). Additionally,

section 129 of the Act specifies that emission guidelines be developed

for PM, opacity, SO2, HCl, NOX, CO, Cd, Pb, Hg, and dioxins/

furans. Emission guidelines for all but four of these pollutants (Cd,

Pb, Hg, and NOX) were established in the February 11, 1991

emission guidelines (56 FR 5514). Section 129 specifies that emission

limits be set for each of the metals (Cd, Pb, and Hg).

Emission guidelines for fugitive MWC fly ash/bottom ash emissions

are proposed today because these emissions also contain PM, Cd, Pb, Hg,

and dioxins/furans.

E. Selection of Designated Facilities

For the proposed emission guidelines, the designated facility, an

MWC unit, is defined as any setting or equipment chamber or pit used to

burn MSW (including RDF) and extends to and includes MWC fly ash/bottom

ash emission points, including ash storage areas, conveyor transfer

points, and ash loading areas for hauling trucks at the MWC site. This

does not extend to ash handling outside of the MWC property boundary or

at ash fill sites.

Municipal waste combustion includes the burning (or pyrolysis) of

MSW in any type of equipment, chamber, or pit including equipment with

and without heat recovery. Municipal solid waste is defined as either a

mixture or a single-item stream of household, commercial, and/or

institutional discards. This would include discards such as paper,

wood, yard wastes, tree trimmings, plastics, leather, rubber, glass,

metals, and other combustible and noncombustible materials. The MSW

definition includes household discards as well as discards from

institutional and commercial sources, but does not include industrial

process or manufacturing discards. The MSW definition also includes

RDF, which is a type of MSW that is shredded (or pelletized) and

classified by size before combustion. Municipal solid waste does not

include wastes that are solely segregated medical wastes. However, any

mixtures of medical waste with nonmedical hospital waste or with

household, commercial, or institutional waste is considered to be MSW.

Minor editing has been done to the definition of MSW to clarify this

point.

Cofired combustors are those that fire MSW with non-MSW fuel such

as coal. Cofired combustors that combust a fuel feed stream comprised,

in aggregate, of equal to or less than 30 percent MSW or RDF (by

weight, based on a 24-hour average), would not be subject to the

emission guidelines and would be required only to submit reports of the

amount of MSW and other fuels combusted. The exclusion of cofired

combustors from the guidelines is consistent with the Act of 1990. This

exclusion is unchanged from the February 11, 1991 guidelines.

Waste-fuel power generation facilities that combust a single-item

waste stream of tires, fuel derived solely from tires, or used oil

would be subject only to an initial report and to no other provisions

in today's proposal or to the emission guidelines that were promulgated

on February 11, 1991 (56 FR 5514). This exclusion is unchanged from the

February 11, 1991 guidelines.

Air curtain incinerators with unit capacities to combust greater

than 35 Mg/day of MSW are subject to the proposal; however, air curtain

incinerators that combust only tree trimmings, yard wastes, and clean

untreated lumber (these are a subset of MSW) would be subject to an

opacity standard and its associated testing, recordkeeping, and

reporting included in today's proposal, but would not be subject to

other parts of today's proposal. This exclusion does not apply to air

curtain incinerators that combust other MSW materials.

Today's proposed guidelines for MWC's would apply to MWC units at

plants with capacities above 35 Mg/day. The lower size cutoff of 35 Mg/

day aggregate plant capacity for controlling MWC emissions under the

proposed emission guidelines was selected after reviewing the

population distributions of MWI's and MWC's. Most incinerators at

medical waste facilities are smaller incinerators that fire segregated

medical waste with general hospital discards (MSW), and these

incinerators would have the potential to be covered by today's

proposal. The population distribution of MWI's is distinctly different

from the population distribution of traditional MWC plants that are the

target of today's proposal. The existing distribution of MWC's is

composed of about 372 units (about 179 plants), with an average plant

size of about 600 Mg/day combustion capacity, with two or three MWC

units at each plant. The potential nationwide combustion capacity of

existing MWC's is about 107,000 Mg/day, assuming continuous operation.

The MWI distribution is quite different and includes about 7,000

combustors with a single combustion unit per facility and an average

unit size of less than 3 Mg/day combustion capacity. The total U.S.

capacity of MWI's is about 20,000 Mg/day. This population is being

addressed under a separate rulemaking. Clearly, the MWC population

represents a smaller number of comparatively larger units, and MWI's

represent a much larger number of smaller units. The lower size cutoff

of 35 Mg/day aggregate plant capacity that is included in today's

proposed emission guidelines would exclude less than 1 percent of the

total nationwide combustion capacity of MWC's and would result in over

99 percent of total MWC capacity being covered by this proposal. The

same lower size cutoff would prevent significant dual coverage under

this proposal by excluding more than 99 percent of MWI units and about

97 percent of nationwide MWI capacity from today's proposed revisions.

As mentioned above, the proposed emission guidelines with a 35 Mg/

day cutoff would cover the great majority of MWC's, and may also cover

a few of the largest MWI's (nine units at three sites are known to

cofire medical waste with MSW and are above the 35 Mg/day of MSW total

plant capacity cutoff). Section 129 of the Act requires that

regulations for MWI's be developed in a separate rulemaking. For these

reasons, it is appropriate that today's proposed guidelines focus on

MWC's and that a separate regulation focus on MWI's. The NSPS and

guidelines for MWI's are scheduled to be proposed in 1995.

Municipal waste combustor plants with aggregate capacities below 35

Mg/day would not be subject to the emission limits under today's

proposed emission guidelines. However, those facilities with aggregate

plant capacities between 25 and 35 Mg/day would be required to report

(one time) their location, startup date, and aggregate plant capacity.

They would also be required to provide supporting information,

including calculations used to determine plant capacity. This one-time

report would allow the EPA or State agency to enforce the lower size

cutoff for applicability to the proposed guidelines. Plants with

aggregate capacities of 25 Mg/day or below would not be subject to any

provisions under this proposal.

The proposed emission guidelines for MWC's are subdivided into two

subcategories of air emissions requirements: The first for MWC's

located at MWC plants with aggregate capacities to combust more than 35

Mg/day but less than or equal to 225 Mg/day of MSW (referred to as

small MWC plants), and the second for MWC's located at MWC plants with

aggregate capacities to combust greater than 225 Mg/day of MSW

(referred to as large MWC plants). The 225 Mg/day dividing point was

established because this size break represents a transition point

between field-erected waterwall MWC's and modular MWC's.

In the subcategory of existing plants with capacities greater than

225 Mg/day, there are about 119 MWC plants with 235 MWC units. In the

subcategory of existing plants with capacities greater than 35 Mg/day

but equal to or less than 225 Mg/day, there are about 60 plants with

137 units. The large plant subcategory accounts for about 94 percent of

the total combustion capacity whereas the smaller subcategory accounts

for about 5 percent of total capacity.

F. Selection of Maximum Achievable Control Technology

The following discussion addresses the EPA's selection of MACT. The

existing technologies for controlling emissions of the designated

pollutants from MWC's are reviewed, followed by a summary of the EPA's

approach for establishing the MACT floor. Finally, the discussion

presents the EPA's selection of MACT for MWC's at small and large MWC

plants.

1. Summary of MWC Control Technologies

The following discussion reviews the existing technologies for

controlling emissions of acid gases, dioxins/furans, PM, Cd, Pb, Hg,

and NOx from MWC's.

a. Acid Gas/PM Control Technologies. Municipal waste combustor acid

gas/PM control is a general term that refers to a group of MWC air

pollution control technology combinations. These combinations control a

wide range of pollutants, such as acid gases (including SO2 and

HCl), organics (including dioxins/furans), and PM and metals (including

Cd, Pb, and a number of other metals except Hg). The three acid gas/PM

controls most commonly used in the United States for existing MWC's

are: (1) GCP plus DSI followed by an ESP; (2) GCP plus an SD followed

by an ESP; and (3) GCP plus an SD followed by an FF. Discussions of

each of these control systems were presented in the December 20, 1989

proposal preamble for the acid gas and PM emission guidelines in

subpart Ca (54 FR 52209). Control of Cd, Pb, and Hg were not discussed

in detail in the 1989 preamble.

Since 1991, the performance of the acid gas/PM control systems for

removal of Cd, Pb, and Hg has been investigated in more depth. Cadmium

and Pb are both volatile at temperatures present in combustion systems,

but condense onto PM in the flue gas at temperatures associated with

the operation of most PM control systems. As a result, the control of

Cd and Pb is generally related to the control of PM emissions. Much of

the PM in the flue gas from an MWC is fine PM; from 20 to 70 percent of

the PM in the flue gas from an MWC has an aerodynamic diameter of less

than 1 micrometer (1 micron). Because of the potential for adsorption

of Cd and Pb onto fine PM that is less readily collected by control

devices than larger PM, the control of fine PM is especially important

in controlling these metals.

Both FF-equipped systems (i.e., DSI/FF's and SD/FF's) and

electrostatic precipitator (ESP)-equipped systems (e.g., ESP's, DSI/

ESP's, and SD/ESP's) can achieve efficient control of PM, and the

efficiency of total PM and fine PM control achieved by these systems

depends on their design. However, FF-equipped systems are generally

more effective in capturing fine PM than ESP-equipped systems.

Therefore, the control of Cd and Pb achieved by FF-equipped systems is

typically better than that of ESP-equipped systems.

For DSI/FF and SD/FF systems, data for controlled Cd emissions

range from 0.001 to 0.0100 mg/dscm. Emissions of Pb from MWC's with

these systems are less than 0.10 mg/dscm. For SD/ESP systems, the data

for Cd and Pb emissions are variable, showing emission levels from

0.005 to 0.040 mg/dscm for Cd, and levels of less than 0.10 to 0.50 mg/

dscm for Pb. For DSI/ESP and ESP-only systems, there is no indication

of a difference in the level of Cd and Pb control between these control

systems. For both of these systems, Cd emission levels range up to 0.10

mg/dscm, and Pb emission levels range up to 1.6 mg/dscm.

Although the above combinations of acid gas/PM controls are

effective at removing Cd, Pb, and other metals, they do not

consistently remove Hg without integrating some other form of Hg

control. A discussion of Hg control is presented below.

b. Mercury Control Technologies. The EPA estimates that typical

uncontrolled Hg levels for MWC's in the United States range from 0.20

to 1.4 mg/dscm at 7 percent O2. Unlike other metals, Hg has a high

vapor pressure at typical operating temperatures of air pollution

control devices. As a result, collection of Hg by the PM control device

is highly variable. The EPA collected test data from more than 30 MWC's

with various air pollution controls that indicate a wide range of Hg

control. High-efficiency PM control, lower flue gas temperatures in the

air pollution control system, and a sufficient level of carbon in the

fly ash facilitate Hg control. Higher levels of carbon in the fly ash

and reduced flue gas temperatures enhance Hg adsorption onto the

carbon, which is removed by the PM control device. To promote Hg

adsorption, it is important to operate the control systems at

temperatures less than about 150 to 200 deg.C. Low flue gas

temperature is inherent to acid gas control.

Municipal waste combustors having high combustion efficiency will

have effective carbon burnout and, therefore, will have low fly ash

carbon content. These units may achieve little or no Hg control even

when equipped with acid gas/PM control systems, and the control may be

highly variable even at the same site.

Three techniques for Hg control are currently being used at MWC's:

Activated carbon injection, sodium sulfide (Na2S) injection, and

wet scrubbing. Activated carbon injection and Na2S injection are

used in conjunction with an existing acid gas control device. Brief

discussions of these three Hg control technologies and their

capabilities are presented below.

Injection of powdered activated carbon into the flue gas prior to

the acid gas/PM control device has been tested at U.S. MWC's. The

removal mechanism is not fully understood, but it is believed that

activated carbon is a catalyst for the oxidation of elemental Hg to

mercuric oxide and mercuric chloride, which can more readily be

captured in the air pollution control device. This technology has been

applied commercially to MWC's in Europe equipped with SD/ESP's and

during test programs in Europe and Canada to MWC's with SD/FF's and

DSI/FF's. The EPA also tested activated carbon injection at the

Stanislaus County MWC in California and the Camden County MWC in New

Jersey. The Stanislaus County MWC is equipped with an SD/FF, and the

Camden County MWC is equipped with an SD/ESP. Test results show Hg

reductions greater than 85 percent when injecting activated carbon.

A second Hg control technology is Na2S injection. Sodium

sulfide is a crystalline solid that dissolves in water. The resulting

Na2S solution is sprayed into the flue gas prior to the acid gas/

PM control device. The reaction of Na2S and Hg precipitates solid

mercuric sulfide (HgS) that is collected in the PM control device.

Three MWC's in Sweden, two in Germany, and one in Canada have used

Na2S injection to control Hg emissions. All of these facilities

use DSI/FF systems for acid gas/PM control, and injection of Na2S

occurs prior to the DSI/FF system at flue gas temperatures of 130 to

250 deg.C. In addition, Hg emission tests were conducted at the

Stanislaus County MWC in California while using Na2S injection.

Results from tests at European, Canadian, and U.S. MWC's have shown Hg

removal efficiencies of 40 to 90 percent when using Na2S

injection.

Wet scrubbing is a form of acid gas control that also controls Hg

without use of an add-on Hg control system. It has been used primarily

in Europe and Japan. Typically, the flue gas is first directed through

an ESP to reduce PM, followed by wet scrubbing, which involves passing

the flue gas through a one- or two-stage absorber system where the gas

stream is saturated with an alkaline solution. During this process,

flue gas temperatures are reduced to as low as 55 deg.C. The low

absorber operating temperature promotes Hg condensation, resulting in

an Hg reduction of 80 percent or better. The alkaline solution used in

the wet scrubbing process, typically containing calcium hydroxide,

reacts with the acid gas to form salts, which are generally insoluble

and may be removed by sequential clarifying, thickening, and vacuum

filtering. The dewatered salts or sludges are then sent to a landfill.

The disadvantages of wet scrubbing include the quantity of water

required, potential difficulties with waste handling, and undefined

performance at MWC units firing domestic (U.S.) MSW streams.

c. Nitrogen Oxides Control Technologies. During the combustion

process, NOX are formed through two mechanisms: (1) Oxidation of

fuel-bound nitrogen (N2) contained in MSW to NOX; and (2)

fixation and oxidation of atmospheric N2. In MWC's, the conversion

of fuel-bound N2 accounts for most (75 to 80 percent) of the

NOX production.

Controlling NOX emissions from MWC's can be accomplished

through: (1) Combustion modifications to reduce NOX formation; (2)

postcombustion control, which reduces NOX in the flue gas to

elemental N2; or (3) use of ``low-NOX'' combustors to reduce

NOX formation. Combustion modifications include staged combustion,

low excess air, and flue gas recirculation. Combustion modification

retrofit at existing MWC's has had limited application and its retrofit

potential must be evaluated on a case-by-case basis.

Postcombustion NOX control using selective noncatalytic

reduction (SNCR) is more flexible and has been more commonly used for

MWC NOX control. The SNCR control technology reduces NOX to

N2 without the use of catalysts. Techniques include Thermal

DeNOXTM, which injects ammonia into the combustor as a

reducing agent; the NOXOUTTM process, which injects urea with

chemical additives; and a two-stage urea/methanol injection process. A

discussion of SNCR NOX control was presented in the December 20,

1989 proposal preamble (54 FR 52251) for the 1991 NSPS for new MWC's.

The use of SNCR at existing MWC's results in NOX emission

reductions of about 45 percent.

However, for existing mass burn/refractory MWC's, SNCR retrofit

problems exist. Mass burn/refractory MWC's are generally older and

operate with greater fluctuations in combustor flue gas temperature

profiles than is typical for other types of MWC's. The fluctuating

temperature profiles create SNCR applicability and performance

problems. The SNCR control has not been used nor is expected to be used

at mass burn/refractory MWC's or other specialized combustors.

The SNCR technology has also never been applied to a modular

combustor, and the performance of such a system on a modular combustor

is questionable. Performance questions arise because of the potential

for temperature fluctuations resulting from batch-feed operations along

with the inability of the refractory-lined furnace to dampen

temperature spikes. The EPA requests comment on the applicability of

SNCR and other NOX control techniques to MWC's at small plants.

The EPA requests that comments address the cost, technical performance,

and reliability of application of SNCR or other NOX control

techniques specifically to modular starved-air MWC's and modular

excess-air MWC's. Based on the comments and information received, the

EPA will reconsider requiring NOX control on MWC's at small

plants.

Three types of MWC's, mass burn/rotary combustors, fluidized-bed

combustors, and modular/excess-air combustors, are considered ``low

NOX'' combustors. Available data show that these types of MWC's

consistently show NOX levels below 150 ppmv without the use of

SNCR.

2. MACT Floor and MACT Requirements of the Act

Section 129 of the Act, as amended in 1990, directs the EPA to

review and revise the February 11, 1991 guidelines to reflect MACT.

Section 129 also establishes a minimum ``floor'' for the guidelines, in

terms of their stringency; specifically:

* * * emission standards for existing units * * * shall not be

less stringent than the average emission limitation achieved by the

best performing 12 percent of units in the category * * *.

The intent of this MACT floor is to ensure that the guidelines

reflect the performance of the best emission control technologies

currently operating at existing MWC units. A large portion of the

existing MWC population is represented by relatively new and relatively

well-controlled MWC units (the average age of an MWC unit is less than

10 years). This results in a large percentage of existing MWC units

being operated with the best emission control technologies. This subset

constitutes about 45 percent of existing MWC units at large MWC plants,

and, based on EPA's current information, these units are all well

maintained and operated. Based on the examination and analysis of the

emission data available from these units, the EPA has not found a basis

for separating the top 12 percent of these units from the remaining

units in the subset of those units that are well-equipped, maintained,

and operated. Consequently, to determine the MACT floor, the EPA

utilized emission limitations included in Federal/State permits.

Emission limitations for existing MWC units at large plants were

determined by examining the air quality permits for those units

obtained from the EPA Regional Offices and by examining responses to

section 114 information requests, which included a section regarding

permitted emission limits. Emission limitations for MWC units at small

plants were determined only by examining the responses to section 114

information requests.

The emission limitations for each pollutant were then converted to

common units so that they could be compared. The emission limitations

for each pollutant were ranked separately for the small and large

categories of MWC plants. From those rankings, the average of the top

12 percent of emission limitations (i.e., the average of the most

stringent limitations) for each pollutant in the small and large plant

categories were calculated to determine the MACT floors.

The MACT floor defines the minimum level of emission control that

may be considered in defining MACT, regardless of cost or other

considerations. In considering control alternatives beyond the MACT

floor, the EPA must consider the cost of achieving such emission

reductions and any nonair quality health and environmental impacts and

energy requirements. Therefore, the level of control that represents

MACT may be more stringent than the MACT floor.

In the proposed regulations, subcategorization of existing MWC

units was limited only to size (units at large and small MWC plants).

Since the MACT floors may be sensitive to subcategorization, it is

possible that further or alternative means of subcategorization may

affect the determination of the MACT floor (i.e., the minimum level of

control requirements under section 129). The Act provides that ``the

Administrator may distinguish among classes, types (including mass-

burn, refuse-derived fuel, modular, and other types of units), and

sizes of units within a category'' in establishing MACT standards. In

examining various ways of subcategorization, the EPA found that

subcategorization uniformly across all emission standards could result

in more stringent standards for one pollutant and somewhat less

stringent standards for other pollutants. For example,

subcategorization by MWC technology generally results in a less

stringent MACT floor for NOX and a more stringent floor for PM.

Depending upon the approach used for subcategorization, the NOX

MACT floor for some units could be considerably higher than the 215

ppmv floor in the proposed rule. For example, the NOX MACT floor

for mass burn/waterwall units could be 230 ppmv, and the NOX MACT

floor for refuse-derived fuel units could be 275 ppmv.

The EPA is soliciting comments on whether subcategorization (beyond

size) should be used in the final rule and on the basis that one would

support for such further subcategorization (e.g., the inapplicability

of SNCR for mass burn/refractory combustors, and the inherently ``low-

NOX'' emission characteristics of mass burn/rotary combustors,

fluidized bed combustors, and modular/excess-air combustors.) In

addition, the EPA is seeking comment on the appropriateness of using

different subcategorization approaches for different pollutants. For

example, in setting standards under section 111 of the Act for

industrial boilers, the EPA established different emission standards

based on different fuel type inputs.

The following section presents the EPA's rationale for establishing

the MACT floor and MACT for MWC's.

3. MACT Floor and MACT for Large MWC Plants

This section summarizes the MACT floor and presents the EPA's

rationale for establishing MACT for each pollutant for MWC's at large

MWC facilities.

a. Summary of MACT Floor for Large MWC Plants. This proposal

determines the MACT floor for existing MWC's based on permit limits.

The population of MWC's at large plants consists of about 235 combustor

units. Therefore, the top 29 combustor units with the most stringent

permit limitations would represent the top 12 percent of emission

limitations for determining the MACT floor. An average of the top 29

permit limits was calculated to determine the floor for each pollutant.

The MACT floor emission levels for each pollutant for large MWC plants

is shown in table 4.

Table 4.--Mact Floor Emission Levels for Existing MWC's at Large MWC

Plants

------------------------------------------------------------------------

Pollutant MACT floor emission levela,b

------------------------------------------------------------------------

SO2................................ 35 ppmv.

HCl................................ 35 ppmv.

PM................................. 27 mg/dscm.

Cd................................. 0.25 mg/dscm.

Pb................................. 0.53 mg/dscm.

Hg................................. 0.36 mg/dscm.

Dioxins/furans..................... 100 ng/dscm total mass or about 1.7

ng/dscm TEQ.

NOX................................ 215 ppmv.

------------------------------------------------------------------------

aAll emission levels are corrected to 7 percent O2, dry basis.

bMost of the MACT floor requirements for large MWC plants are more

stringent than the 1991 subpart Ca guidelines. See table 2.

The top 12 percent MACT floor for the emission guidelines could be

constructed in a number of different ways including a permit basis

(this proposal), a technology basis, or an emissions data basis. Under

a technology basis, MWC's would be ranked by their control technology

to determine the technology used by the average or median of the top 12

percent of the MWC population, and the floor would be based on the

performance of that technology. Under an emission data basis, data on

the best top 12 percent of available test runs would be averaged to

calculate the floor. Other approaches are also possible. The different

approaches would result in noticeably different MACT floor performance

levels. The EPA specifically requests comments on what approach is most

appropriate and the rationale for that approach. Based on the EPA's

review of comments received on this issue, as well as reanalysis of any

data submitted, the MACT floor for the promulgated guidelines may be

noticeably higher or lower than the floor included in the proposal.

b. Discussion of the Selection of MACT for Large MWC Plants. After

establishing the MACT floor for each pollutant based on permit limits,

the EPA considered the cost, health and environmental impacts, and

energy requirements of selecting MACT for each pollutant at a control

level more stringent than the MACT floor. In selecting MACT for each

pollutant for large plants, the EPA used principally the data base

created for establishing the emission guidelines for MWC's proposed in

1989 and promulgated in 1991 under subpart Ca. For a few pollutants in

this proposal, the EPA utilized more recent test data to supplement the

1989 data base. Because most of the test data used for this proposal

are more than 4 years old, and in consideration of the fact that most

MWC's retest at least once per year, the EPA requests submittal of the

most recent MWC emissions test data.

The EPA requests comment on which MWC emissions test data would be

the most appropriate to use for establishing MACT for existing MWC's.

For example, if the EPA has multiple emission tests for a given MWC

over its operating history (which is common), should the EPA utilize

the data from all of the emission tests performed for the unit or from

only the most recent emission test, in determining the performance of

the unit? Additionally, the EPA requests comment on suggestions of

analytical methods to use for analyzing the data (e.g., analytical

methods that could be used to address emissions variability, including

methods for analyzing variable test data for one MWC collected over

multiple years and methods of adjusting the best 12 percent of the

emissions data to account for variability). The appropriate treatment

of variability will be related to the format chosen for the standards

(see discussion of alternative formats below).

Based on the new data submitted and on the final choice of which

test data and what analysis methods to use, the EPA may promulgate

final emission guidelines that are more or less stringent than those

proposed today. The following sections IV.F.3.c through IV.F.3.j

present the EPA's rationale for selecting MACT for each pollutant for

MWC's at large MWC facilities.

c. MACT for Sulfur Dioxide for Large MWC Plants. Uncontrolled

levels of SO2 for MWC's are typically about 160 ppmv. The MACT

floor for SO2 at large plants is 35 ppmv. Therefore, acid gas

control would be needed to achieve the MACT floor level of control.

Both SD/ESP's and SD/FF's can meet the MACT floor level of control.

Tests of many SD/FF's have demonstrated SO2 control to levels

below 35 ppmv.

Although SD/FF systems can generally achieve slightly better

SO2 control than SD/ESP systems, the cost of requiring existing

SD/ESP systems to retrofit an SD/FF to meet SO2 control levels

more stringent than the MACT floor would be prohibitively expensive and

is considered unreasonable. For example, at a typical 1,400 Mg/day MWC

plant already equipped with an SD/ESP, the capital cost to remove the

ESP and retrofit a new FF (as part of an SD/FF system) would be about

$14 million. This cost would be in addition to paying the remaining

debt for the relatively new ESP (about $5 million including interest

payments) and would result in a relatively small increase in control

device efficiency. The incremental cost of control for requiring a

retrofit from an SD/ESP to an SD/FF would be greater than $10,000/Mg of

acid gas reduction and would increase SO2 removal efficiency by

only about 6 percent. Therefore, the EPA is proposing that the MACT

guideline level for SO2 remain at the MACT floor level of 35 ppmv.

Additionally, the EPA is proposing an alternative SO2 guideline

level of 75-percent reduction to address SO2 emissions

variability. Therefore, the proposed MACT floor guideline level for

SO2 is either 35 ppmv or 75-percent reduction (24-hour averaging

period), whichever is less stringent.

d. MACT for Hydrogen Chloride for Large MWC Plants. Acid gas

control would also be needed for large MWC's to reduce HCl emissions

from uncontrolled levels of about 500 ppmv to the HCl MACT floor level

of 35 ppmv. The same types of acid gas control systems needed to

achieve the MACT control level for SO2 will also meet the MACT

floor levels of HCl. While it is expected that SD/FF systems could

achieve slightly lower HCl levels than SD/ESP systems, it has not been

demonstrated that existing SD/FF or SD/ESP systems can consistently

meet HCl levels below the MACT floor. Therefore, the EPA is proposing

that the MACT guideline level for HCl remain at the MACT floor level of

35 ppmv. Additionally, the EPA is proposing an alternative HCl

guideline level of 95-percent reduction to address HCl emissions

variability. Therefore, the proposed MACT floor guideline level for HCl

is either 35 ppmv or 95-percent reduction, whichever is less stringent.

e. MACT for Particulate Matter for Large MWC Plants. On average,

uncontrolled levels of PM from MWC's are about 3,700 mg/dscm. The MACT

floor for PM at large MWC plants is 27 mg/dscm. The MACT floor will

require greater than a 99-percent reduction in PM emissions. The EPA's

analysis of data from existing MWC's showed that both SD/FF and SD/ESP

systems can meet MACT floor PM levels. Although the newest SD/FF

systems can meet levels of less than 15 mg/dscm, SD/ESP systems and

many existing SD/FF systems cannot achieve such levels. Therefore, the

proposed MACT for PM at large MWC's is the MACT floor level of 27 mg/

dscm.

f. MACT for Cadmium for Large MWC Plants. Average uncontrolled

levels of Cd are about 1.2 mg/dscm from MWC's. The MACT floor for Cd

for large MWC plants is 0.25 mg/dscm. Therefore, the MACT floor will

require about 80-percent Cd reduction. As with Pb, Cd control is

associated with PM control. The EPA's analysis of Cd control showed

that SD/FF systems can generally achieve Cd levels of less than 0.010

mg/dscm and that SD/ESP systems can achieve less than 0.040 mg/dscm.

The Cd removal efficiency achievable with an SD/FF is only about 1.2

percent better than an SD/ESP (99.5-percent reduction versus 98.3-

percent reduction, respectively). Again, the high cost of retrofit to

an SD/FF is considered unreasonable for such a small incremental

reduction in emissions. Because a level of 0.040 mg/dscm is achievable

with both SD/ESP and SD/FF systems, and these technologies would

already be needed to meet MACT for acid gas control, the proposed MACT

for Cd is more stringent than the MACT floor, at a level of 0.040 mg/

dscm.

g. MACT for Lead for Large MWC Plants. Uncontrolled Pb emissions

from MWC's are about 25 mg/dscm, and the MACT floor for large MWC's is

0.53 mg/dscm. A reduction of about 98 percent would be needed to

achieve the MACT floor. The SD/ESP or SD/FF systems needed to meet MACT

for acid gases will also meet the MACT floor for Pb. The EPA's analysis

of Pb control showed that SD/FF systems can meet Pb levels of 0.20 mg/

dscm, and SD/ESP systems can meet Pb levels of 0.50 mg/dscm. The Pb

removal efficiency achievable with an SD/FF is only about 0.8 percent

better than an SD/ESP (reductions of about 99.8 versus 99.0 percent,

respectively). As explained above, the cost of replacing an SD/ESP with

an SD/FF would be unreasonable considering the small difference in

control efficiency. Because both SD/FF and SD/ESP systems can achieve

Pb levels of 0.50 mg/dscm, the proposed MACT for Pb is more stringent

than the MACT floor, at a level of 0.50 mg/dscm.

h. MACT for Mercury for Large MWC Plants. Uncontrolled levels of Hg

from MWC's are about 0.65 mg/dscm on average. The MACT floor for Hg for

large plants is 0.36 mg/dscm. The MACT floor, therefore, will require

about 40-percent reduction in Hg emissions. As described in section

IV.F.1.b of this preamble, Hg control can be achieved by using

activated carbon injection in combination with an acid gas/PM control

system (and the associated low flue gas temperatures). Recent tests at

the MWC's at Camden County, New Jersey (SD/ESP), and Stanislaus County,

California (SD/FF), demonstrate that both SD/ESP and SD/FF systems with

activated carbon injection can achieve an 85-percent emission reduction

in Hg emissions or an Hg emission level of 0.080 mg/dscm, corrected to

7 percent O2. Data from individual test runs show occasional

spikes of high inlet Hg emissions due to the variability in the waste

feed composition. In cases where Hg levels are temporarily elevated, a

0.080 mg/dscm level may not be consistently achievable; however,

activated carbon injection could achieve an 85-percent reduction during

such episodes. Based on the data from MWC's using activated carbon

injection, Hg control to these levels is achievable by properly

operated systems on all types of MWC's.

Although the MACT floor requires Hg control, the control levels

achievable using SD/ESP or SD/FF systems and activated carbon injection

are more stringent than the MACT floor. The incremental cost of

reducing Hg emissions from the MACT floor level of 0.36 mg/dscm to the

demonstrated level of 0.080 is less than about $1.00/Mg of MSW

combusted. This incremental cost is considered reasonable given the

toxicity and bioaccumulation potential of Hg. Therefore, the proposed

MACT guidelines for Hg are 0.080 mg/dscm or an 85-percent reduction,

whichever is least stringent.

The EPA has selected activated carbon injection as the basis for

achieving MACT for Hg, although facilities may use any technology

capable of meeting the proposed guideline. Of the three Hg control

technologies discussed in section IV.F.1.b of this preamble, the EPA

has determined that activated carbon injection is the most widely

tested of the three Hg control technologies in the United States.

i. MACT for Dioxins/Furans for Large MWC Plants. The average level

of dioxins/furans from an uncontrolled MWC is about 1,000 ng/dscm total

mass. The MACT floor for total dioxins/furans of 100 ng/dscm would

require about a 90-percent reduction.

Dioxins/furans are controlled by GCP and acid gas/PM control. Good

combustion practices alone can achieve total dioxin/furan levels of

about 500 ng/dscm. In combination with GCP, SD/FF systems can achieve

total dioxin/furan levels less than 30 ng/dscm, and SD/ESP systems can

achieve total dioxin/furan levels of less than 60 ng/dscm. Therefore,

the MACT floor (i.e., 100 ng/dscm) can be achieved with either SD/ESP

or SD/FF systems, and these systems would already be the basis for

meeting MACT for acid gas and PM emissions.

As discussed above, the MACT for Hg would be based on activated

carbon injection. Recent tests at the Camden County, New Jersey, MWC

showed that the injection of activated carbon into the flue gas of an

SD/ESP system provides further removal of dioxins/furans (greater than

50-percent reduction over levels achieved by the SD/ESP systems). The

greater than 50-percent reduction of the 60 ng/dscm level achieved by

an SD/ESP would equate to total dioxin/furan emission levels below 30

ng/dscm (0.5 ng/dscm dioxin/furan TEQ) for SD/ESP systems with

activated carbon injection.

As noted, SD/ESP or SD/FF systems with activated carbon injection

would already be needed to achieve MACT for acid gas, PM, and Hg.

Because both of these control systems in combination with activated

carbon injection can achieve a dioxin/furan emission level of 30 ng/

dscm or less, and because of the high cost for retrofitting an SD/FF,

the proposed guideline for dioxin/furan at large MWC's is based on GCP

and SD/ESP systems plus activated carbon injection. The EPA is

proposing MACT for dioxins/furans on both a TEQ and a total mass basis.

The 30 ng/dscm of total dioxins/furans is equivalent to 0.50 ng/dscm of

dioxin/furan TEQ; therefore, the proposed guideline level for large MWC

plants is 30 ng/dscm total dioxins/furans or 0.50 ng/dscm of dioxin/

furan TEQ. Comments are requested on whether lower dioxin/furan

guideline levels, which would require SD/FF's, should be incorporated

into the final guidelines.

j. MACT for Nitrogen Oxides for Large MWC Plants. The average level

of NOX emissions from MWC's without postcombustion NOX

control is about 225 ppmv. The MACT floor, however, is 215 ppmv.

Therefore, postcombustion NOX controls will be needed by most

existing MWC's at large plants to meet the MACT floor.

Selective noncatalytic reduction is currently used by 16 existing

MWC units at large plants. Tests conducted by the EPA at the Stanislaus

County, California, MWC showed that existing SNCR systems achieve

NOX levels of 180 ppmv on a 24-hour average basis.

Because postcombustion NOX control is required by the MACT

floor, and there is only a small incremental cost to operate an SNCR

system to achieve 180 ppmv versus the MACT floor level of 215 ppmv, the

proposed guideline level for NOX for large plants (excluding mass

burn/refractory MWC's) is 180 ppmv.

As discussed in section IV.F.1.c of this preamble, SNCR may not be

effective on mass burn/refractory MWC's. Therefore, postcombustion

NOX control is not being considered for this type of MWC. The MACT

guideline for NOX for mass burn/refractory MWC's at large MWC

plants is based on no control. Section VIII of this preamble discusses

``no control'' emission limits for NOX.

The EPA recognizes that costs associated with the proposed NOX

control requirements for large existing MWC plants are not

insignificant. Under the proposal, about 73 percent of current MWC

capacity would be expected to retrofit NOX control. On a national

basis, the retrofit of NOX controls to existing MWC plants would

cost about $56 million/yr and would represent about 13 percent of the

$445 million annual cost of the entire proposal.

As discussed above, the MACT floor for large MWC plants is 215 ppmv

and would require less than 20-percent NOX control (reduction).

This could be achieved by application of SNCR technology at a low

performance level or, perhaps, by using combustion modification (e.g.,

excess air) or materials management. The proposal, however, goes beyond

MACT floor requirements and would establish MACT at 180 ppmv or about

30- to 40-percent NOX reduction based on the full application of

SNCR at an MWC with average baseline emissions of 225 ppmv.

The EPA requests comment on the alternative of establishing

NOX standards at the level of the MACT floor (215 ppmv) based on

the above approach. The EPA also requests comment and data supporting

the achievability of a MACT floor level (24-hour arithmetic average,

corrected to 7 percent O2) without the use of an SNCR system.

Additionally, the EPA requests data and information on alternative

NOX control technologies including but not limited to the

application of combustion modification techniques to existing MWC's or

of other management measures (perhaps separation of yard waste) to

comply with either the proposed level or a floor level at a lower cost

than an SNCR system.

4. MACT Floor and MACT for Small MWC Plants

This section summarizes the MACT floor and presents the EPA's

rationale for establishing MACT for each pollutant for MWC's at small

MWC facilities.

a. Summary of MACT Floor for Small MWC Plants. The proposal

determines the MACT floor for existing MWC's based on permit limits.

The population of MWC units at small MWC plants consists of about 137

combustor units. Only 88 of the 137 units are facilities that have

federally enforceable permit limitations. Therefore, for determining

the MACT floor, the emission limitations achieved by the top 11 units

in the small MWC plant category represent the top 12 percent of units

with federally enforced permit limitations. Many of the smallest MWC's

with unit capabilities below 45 Mg/day (i.e., those MWC's not subject

to the 1971 subpart E NSPS) do not have federally enforceable permit

limitations. For some pollutants, less than 11 permits were identified

for the category of small MWC plants (i.e., many small plants with

permits have emission limits for only some of the pollutants covered by

the proposed guidelines.) In such cases, typical uncontrolled emission

levels for that pollutant were used for determining the average of the

top 12 percent of emission limitations. Table 5 provides a summary of

the MACT floor emission levels for each pollutant for small MWC plants.

Table 5.--MACT Floor Emission Levels for Existing MWC's at Small MWC

Plants

------------------------------------------------------------------------

Pollutant MACT floor emission levela

------------------------------------------------------------------------

SO2................................ 120 ppmv.

HCl................................ 660 ppmv.

PM................................. 85 mg/dscm.

Cd................................. 1.1 mg/dscm.

Pb................................. 15 mg/dscm.

Hg................................. 1.2 mg/dscm.

Dioxins/furans..................... 1,700 ng/dscm total mass or about

28 ng/dscm TEQ.

NOX................................ Uncontrolled.

------------------------------------------------------------------------

aAll emission levels are corrected to 7 percent O2, dry basis.

As discussed in Section IV.F.3.a. for large plants, the MACT floor

could be constructed in a number of different ways including a permit

basis (this proposal), a technology basis, or an emission data basis.

Comments are requested on what approach is most appropriate and the

rationalization for the approach. Based on the EPA's review of the

comments received and reanalysis of the data, the MACT floor for the

promulgated guidelines may be noticeably higher or lower than the floor

included in the proposal.

b. Discussion of the Selection of MACT for Small MWC Plants. After

establishing the MACT floor for each pollutant based on permit limits,

the EPA considered the cost, health and environmental impacts, and

energy requirements of selecting MACT for each pollutant at a control

level more stringent than the MACT floor. As discussed above for large

MWC plants in section IV.F.3.b, in selecting MACT for each pollutant

for small plants, the EPA used principally the data base created for

establishing the emission guidelines for MWC's proposed in 1989 and

promulgated in 1991 under subpart Ca. As discussed, the EPA

specifically requests submittal of the most recent MWC emissions test

data. Additionally, as discussed, the EPA requests comment on which MWC

emissions test data would be the most appropriate to use for

establishing MACT for existing MWC's (e.g., if the EPA has multiple

emission tests for a given MWC over its operating history, should the

EPA utilize the data from all of the emission tests performed for the

unit or from only the most recent emission test) and comment on

suggestions of analytical methods to use for analyzing the data (e.g.,

analytical methods that could be used to address emissions variability,

including methods for analyzing variable test data for one MWC

collected over multiple years and methods of adjusting the best 12

percent of the emissions data to account for variability). The

appropriate treatment of variability will be related to the format

chosen for the standards (see discussion of alternative formats below).

Based on the new data submitted and on the final choice of which

test data to utilize, the EPA may promulgate final emission guidelines

that are more or less stringent than those proposed today. The

following sections IV.F.4.c through IV.F.4.j present the EPA's

rationale for selecting MACT for each pollutant for MWC's at small MWC

facilities.

c. MACT for Sulfur Dioxide for Small MWC Plants. Uncontrolled

SO2 emissions from MWC's are typically about 160 ppmv, and the

MACT floor for SO2 for small MWC plants is 120 ppmv. Therefore,

MACT will require SO2 reduction of about 35 percent compared to

uncontrolled levels. Dry sorbent injection/ESP systems can achieve

greater than 50-percent reductions in SO2, and can satisfy the

MACT floor requirements. Retrofitting a new SD/FF system would achieve

greater acid gas control and small additional reductions in other MWC

pollutants, but the associated costs of such retrofits at small MWC's

would be prohibitively high (greater than $10,000/Mg of acid gas

reduction).

Although the MACT floor requires SO2 control to only 120 ppmv,

the incremental cost of operating a DSI/ESP system to achieve 80 ppmv

(about a 50-percent reduction) versus 120 ppmv is small and results in

improved cost effectiveness. Therefore, the MACT guideline proposed for

SO2 is more stringent than the MACT floor and is proposed at a

level of either 80 ppmv or 50-percent reduction (24-hour averaging

period), whichever is less stringent.

The EPA recognizes that costs associated with the proposed acid gas

control retrofit requirements for small MWC plants are not

insignificant. Small MWC plants represent about 10 percent of the

national MWC capacity to be retrofitted with acid gas control systems,

and their associated cost burden would be about 15 percent of the

national cost of the proposal. On a national basis, the retrofit of

acid gas controls to small MWC plants would cost about $60 million

annually and the retrofit of acid gas controls to large MWC plants

would be about $340 million annually.

As discussed above, the MACT floor for small MWC plants is 120 ppmv

and would require about 35-percent SO2 control (reduction). This

could be achieved by application of a DSI/ESP scrubbing system. The

proposal, however, goes beyond the MACT floor requirements and would

establish MACT at 80 ppmv or 50-percent SO2 reduction based on the

application of a DSI/ESP at its full optimal capability. Even at

optimal conditions, acid gas scrubbing on MWC units at small plants has

a higher control cost ($/Mg acid gas removed) than for MWC units at

large plants. In fact, acid gas control costs for small plants ($/Mg

acid gas removed) are more than twice those for large plants.

In the final regulations, the EPA is considering the alternative of

establishing acid gas control requirements for small MWC plants at the

level required by the MACT floor (120 ppmv or 35-percent reduction).

The EPA requests comment and data supporting the achievability of a 120

ppmv MACT floor level (24-hour geometric average, corrected to 7

percent O2) without the use of a scrubbing system. Additionally,

the EPA requests data and information on alternative acid gas control

technologies that could be applied to MWC units at small plants to

comply with a 120 ppmv floor level at a lower cost than a DSI/ESP

system.

Because some MWC units at small existing MWC plants are operated at

a low annual capacity factor and because the cost effectiveness of acid

gas control is sensitive to annual capacity factor, the EPA requests

comment on the appropriateness of subcategorizing MWC units at small

plants by annual capacity factor before determining the MACT floor. The

reanalysis after subcategorizing by annual capacity factor may conclude

that MACT for low capacity MWC units is less restrictive than MACT for

high capacity MWC units at small existing plants.

If the final guidelines establish different control requirements

for low capacity MWC units than high capacity MWC units, the guidelines

would include operational restrictions for low capacity units. That is,

each low capacity MWC unit located at a small MWC plant would be

required to have a federally enforceable operating permit that limits

the annual capacity factor of the unit to a specified capacity level,

and records would have to be maintained to document the amount of waste

fired in the unit on an annual basis. The annual capacity factor would

be calculated on a unit basis and not on a plant basis. This would

assure that obsolete and inoperable MWC units at an MWC site (i.e.,

with a 0-percent annual capacity factor) are not averaged together with

replacement high capacity units to calculate the annual capacity

factor, with the possible effect of circumvention of emission control

requirements for high capacity factor units. Additionally, if a

decision was made to switch a unit from a low capacity operational

designation to a high capacity designation, the unit would have to be

retrofitted with emission control equipment to comply with the emission

guideline requirements for high capacity MWC's.

d. MACT for Hydrogen Chloride for Small MWC Plants. The MACT floor

for HCl for small MWC plants is 660 ppmv, which is above the typical

uncontrolled level of about 500 ppmv. The MACT floor for HCl would not

require acid gas control, but MACT for SO2 would already require

acid gas control based on DSI/ESP systems. Dry sorbent injection/ESP

systems used for SO2 control can achieve greater than 50-percent

reductions in HCl emissions. As discussed above, the cost to retrofit

an SD/ESP or SD/FF system on a small MWC plant would be unreasonably

expensive.

Because a DSI/ESP system operating in a manner that achieves the

MACT for SO2 would also achieve a 50-percent reduction in HCl, the

proposed MACT guideline for HCl at small MWC plants is either 250 ppmv

or 50-percent reduction, whichever is less stringent.

The EPA recognizes that costs associated with the proposed acid gas

control retrofit requirements for small MWC plants are not

insignificant. The same acid gas control system used to control

SO2 emissions controls HCl emissions, and similar issues exist. As

discussed under the MACT SO2 section, small MWC plants represent

about 10 percent of the national MWC capacity to be retrofitted with

acid gas control systems, and the associated cost burden for this acid

gas retrofit would be about 15 percent of the national cost of the

proposal. On a national basis, the retrofit of SO2/HCl acid gas

control systems to small MWC plants would cost about $60 million/yr and

the retrofit of acid gas controls to large MWC plants would be about

$340 million/yr.

As discussed above, the HCl MACT floor for small MWC plants is 660

ppmv and would not require any HCl control. The proposal, however, goes

beyond the MACT floor requirement and would establish MACT at 250 ppmv

or 50-percent HCl reduction based on the DSI/ESP acid gas control

system installed for SO2 control. The EPA is soliciting comments

on the alternative of establishing HCl control requirements for small

MWC plants at the level required by the MACT floor (i.e., 660 ppmv,

which requires no control). The EPA requests comment and data

supporting the achievability of a 660 ppmv MACT floor level (24-hour

geometric average, corrected to 7 percent O2) without the use of a

scrubbing system.

e. MACT for Particulate Matter for Small MWC Plants. Average

uncontrolled PM emissions from MWC's are about 1,500 mg/dscm. The MACT

floor for PM is 85 mg/dscm, which would require about a 95-percent

reduction in PM over uncontrolled levels.

The MACT floor for PM can be achieved with the same DSI/ESP system

needed to meet MACT for the other pollutants. A DSI/ESP system can

achieve PM emissions of less than 69 mg/dscm. The cost to operate a

DSI/ESP system to achieve 69 mg/dscm versus the MACT floor level of 85

mg/dscm is negligible. Therefore, the proposed MACT guideline for PM

for small MWC plants is below the MACT floor at a level of 69 mg/dscm.

f. MACT for Cadmium for Small MWC Plants. Typical uncontrolled

levels of Cd from MWC's are about 1.2 mg/dscm. The MACT floor is also

1.1 mg/dscm, thus the MACT floor requires less than 10-percent Cd

control. However, the DSI/ESP systems that would already be needed to

achieve the MACT floor for SO2 can achieve Cd levels of 0.10 mg/

dscm. The proposed Cd MACT guideline, therefore, is 0.10 mg/dscm based

on DSI/ESP control.

g. MACT for Lead for Small MWC Plants. The average uncontrolled

emission level of Pb from MWC's is about 25 mg/dscm, and the MACT floor

for Pb for small plants is 15 mg/dscm. The MACT floor requires a 40-

percent reduction in Pb. The DSI/ESP systems needed to meet MACT for

acid gases can achieve Pb levels of 1.6 mg/dscm. The proposed MACT for

Pb is based on DSI/ESP control, and the proposed MACT guideline Pb

level is 1.6 mg/dscm.

h. MACT for Mercury for Small MWC Plants. The MACT floor for Hg for

small MWC plants is 1.2 mg/dscm, which is above typical uncontrolled Hg

emission levels for MWC's. Therefore, no Hg control is needed to meet

the MACT floor.

Because acid gas/PM control systems (DSI/ESP) will be needed at

small plants to meet other MACT requirements, activated carbon

injection could be added to the acid gas/PM control system to achieve

Hg control. The incremental cost to add activated carbon injection to

control Hg at small MWC plants already equipped with acid gas/PM

control is about $1.40/Mg of MSW combusted. The EPA believes that this

cost is reasonable given the concerns over the bioaccumulation of Hg in

the environment.

In addition to the EPA's test programs to study Hg removal using

SD-based scrubbing systems with activated carbon injection, the EPA has

also conducted Hg performance tests of DSI-based scrubbing systems with

activated carbon injection at small MWI's (Borgess, Michigan, MWI). The

use of activated carbon injection with either SD-based scrubbing

systems or DSI-based scrubbing systems has demonstrated greater than

85-percent Hg control.

In combination, DSI/ESP systems with activated carbon injection can

achieve Hg emission levels of 0.080 mg/dscm or an 85-percent reduction

in Hg emissions. Therefore, the proposed MACT guideline for Hg for

small MWC plants is 0.080 mg/dscm or an 85-percent reduction, whichever

is less stringent.

i. MACT for Dioxins/Furans for Small MWC Plants. The MACT floor for

total dioxins/furans is 1,700 ng/dscm, which is above typical

uncontrolled levels of about 1,000 ng/dscm. Although the MACT floor for

dioxins/furans would be based on no control, DSI/ESP is already needed

to meet MACT for other pollutants, and GCP are needed to meet MWC

operational and CO requirements. The combination of GCP and DSI/ESP can

achieve total dioxin/furan levels of less than 125 ng/dscm.

As discussed above, MACT for Hg for small plants would be based on

using activated carbon injection. Activated carbon injection provides

additional removal of dioxins/furans beyond that achieved by the acid

gas/PM control system, as discussed in the rationale for MACT for

dioxins/furans for large plants. Recent tests at small MWI's using DSI

systems with activated carbon injection have also shown that additional

dioxin/furan removal is achieved with activated carbon injection

(greater than a 50-percent reduction over levels achieved by the acid

gas/PM control system). Based on the use of activated carbon injection

with GCP and DSI/ESP systems, a level of 60 ng/dscm would be

achievable. The EPA is proposing MACT for dioxins/furans on both a TEQ

basis and a total mass basis. Based on EPA's analysis, a total dioxin/

furan level of 60 ng/dscm is equivalent to 1.0 ng/dscm of dioxin/furan

TEQ. Therefore, the proposed MACT guideline for MWC's at small plants

is 1.0 ng/dscm of dioxin/furan TEQ or 60 ng/dscm total mass dioxins/

furans.

j. MACT for Nitrogen Oxides for Small MWC Plants. Uncontrolled

NOX emissions from MWC's are about 225 ppmv on average. The MACT

floor is no control. The addition of SNCR postcombustion NOX

control has not been demonstrated on any modular starved-air MWC's, and

the performance of such a system on a modular starved-air MWC is in

question. Since NOX control is not required by the MACT floor and

SNCR has not been demonstrated on modular starved-air MWC's,

postcombustion NOX control is not being proposed for small MWC's.

The MACT guideline for NOX for MWC's at small MWC plants is based

on no control. Section VIII of this preamble discusses ``no control''

emission limits for NOX.

G. Selection of Format for the Proposed Guidelines

The February 11, 1991 emission guidelines described a format for

MWC acid gases (SO2 and HCl), MWC metals (PM and opacity), MWC

organics (dioxins/furans), and MWC operating practices (CO, load, and

flue gas temperature), and that same format is being adopted by today's

proposed guidelines, except for dioxins/furans. The selection of the

format for the emission guidelines for the above pollutants is

described in previous Federal Register notices (54 FR 52209, December

20, 1989 and 56 FR 5514, February 11, 1991). For dioxins/furans, the

proposed guidelines establish dioxin/furan guideline emission levels on

both a total mass dioxins/furans basis and a TEQ basis. The format for

the proposed emission guidelines for NOX is the same as the format

of the 1991 NSPS (56 FR 5488, February 11, 1991) and today's proposed

subpart Eb NSPS. The selection of the format for the 1991 NOX

standard is in previous Federal Register notices (54 FR 52251, December

20, 1989 and 56 FR 5488, February 11, 1991). The same format will apply

under the emission guidelines for NOX proposed today for MWC's at

large plants. The specific formats of the proposed emission guidelines

for Cd, Pb, and Hg are discussed below.

As required by section 129(a)(4) of the Act, the proposed emission

guidelines would establish numerical emission limitations for Cd, Pb,

and Hg. For the purpose of regulating Cd and Pb, the format selected in

the proposed emission guidelines for the numerical emission limitations

would be a numerical concentration limit (mg/dscm) corrected to 7

percent O2. For the purpose of regulating Hg, the format selected

in the proposed emissions guidelines would be both a numerical

concentration limit (mg/dscm) and an alternative percentage reduction

requirement. The numerical Hg emission limit reflects the emission

level that can be achieved based on activated carbon injection in

combination with acid gas/PM control. An alternative percentage

reduction requirement may be met instead of the numerical emission

level because emissions of Hg can be highly variable and dependent on

the Hg input level. Even at the same MWC, test data show occasional

spikes of high Hg emissions due to variability in the waste feed. In

cases where Hg levels are temporarily elevated, the 0.080 mg/dscm level

may not be consistently achievable. However, the control devices could

achieve an 85-percent reduction during such episodes. Therefore, a

combination of a concentration level and an optional percentage

reduction format best assures the maximum achievable Hg control while

accommodating potential spikes in Hg emission levels.

As discussed above, the proposed emission guidelines for SO2,

HCl, and Hg include two formats: (1) A percent reduction format, and

(2) an emission limit (concentration) format. The EPA requests comment

on and test data supporting the appropriateness of promulgating final

guidelines for SO2, HCl, and Hg which include only the emission

limit format. For each pollutant, the commenter should specify an

appropriate emission limit (without an associated alternative percent

reduction format) and provide rationale for the limit. Based on the

comments received, the EPA may promulgate final emission guidelines for

SO2, HCl, and Hg in the form of emission limits that are higher or

lower than the proposed emission limits.

The EPA has proposed emission guidelines that reflect the

performance levels achieved by MWC's equipped with properly designed,

constructed, and operated air pollution control systems. The proposed

emission guideline levels would apply during all periods of MWC

operation. To comply with the proposed guideline levels, the air

pollution control system would be designed and operated such that

actual emissions are less than the proposed guideline levels. Where

continuous monitoring systems are available, such as for SO2 and

NOX, the proposal would require their use to determine compliance

on a continuous basis. For other pollutants, an annual stack test would

be required. The EPA requests comment on whether continuous monitoring

methods exist for any additional pollutants.

The EPA also seeks comments on alternate formats of the guidelines

that would encourage optimal control system operation and optimal

performance, thus minimizing emissions. For example, the guidelines

could provide incentives, such as reduced testing and reporting, for

MWC's that operate well below the guideline emission levels. One

approach would be to structure the guideline such that, for an MWC with

three units, if all units demonstrated emissions at least 30 percent

less than the limit, then only one of the units would be tested each

year. The unit selected for testing would be rotated such that each

unit would be tested once every three years.

Another potential regulatory approach to assure optimal performance

would be to supplement the current emission guidelines (which must be

demonstrated by annual stack tests) with more stringent emission

guidelines calculated for each pollutant based on long-term average

emission levels. Compliance with this supplemental emission level would

be determined by continuous monitoring, where applicable, or by the

average of the annual tests from the current year and one or more

preceding years. The current guideline emission levels account for

variability from one emissions test to another, whereas the composite

average emission levels would reflect the mean performance level. This

may be a preferable measure of environmental performance for some of

the pollutants because it is their long term or cumulative emissions

that are of most concern. Other formats of the guidelines that

encourage optimal performance would also be possible. Comments and

suggestions are requested. Based on the information and comments

received, the EPA may change the form of the rule to include a long

term emissions average, and alternative compliance testing schedule, or

other alternative format to encourage optimal performance of the air

pollution control system.

Additionally, the EPA requests comment and suggestions on specific

work practice requirements or equipment requirements that would assure

optimal operation of the air pollution control system and minimize

emissions. Such operating practices or equipment practices would be

most beneficial for minimizing emissions of those pollutants for which

annual stack testing is the proposed compliance test method. Comments

are specifically requested on work practices or equipment requirements

that would minimize dioxin/furan, Hg, Cd, and PM emissions. Based on

the information received, the EPA may require specific work practices

or equipment to supplement the emission limits included in the final

guidelines.

H. Performance Test Methods and Monitoring Requirements

The emission guidelines promulgated on February 11, 1991 (56 FR

5514) for MWC's with unit capacities above 225 Mg/day established

performance testing and monitoring requirements for MWC acid gases

(SO2 and HCl), MWC metals (PM and opacity), MWC organics (dioxins/

furans), and MWC operating practices (CO, load, and flue gas

temperature). These same requirements would be adopted under today's

proposed emission guidelines, except that: (1) Procedures are being

proposed for determining dioxin/furan emissions on a TEQ basis; (2)

testing schedule provisions have been incorporated for annual

compliance testing for PM (opacity not included), HCl, and dioxins/

furans at small MWC plants; and (3) annual opac

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