Teresa Clemons To: Edmond_ Toy@ omb. eop. gov, afraas@ omb. eop. gov 02/ 06/ 04 04: 56 PM cc: Jeff Holmstead/ DC/ USEPA/ US@ EPA, Bill Wehrum/ DC/ USEPA/ US@ EPA, Alexander Cristofaro/ DC/ USEPA/ US@ EPA, Patricia Embrey/ DC/ USEPA/ US@ EPA, Mike Thrift/ DC/ USEPA/ US@ EPA, Keith Mason/ DC/ USEPA/ US@ EPA, ( bcc: Mary Kissell/ RTP/ USEPA/ US) Subject: Advance Copy of Risk Information  Plywood and Composite Wood Products Attached are advanced copies of the risk information for the Plywood and Composite Wood Products. We are still drafting sections and revising text for the risk portion of the MACT, so these files are not yet complete. Please call Mary Tom Kissell at 919 541 4516 if you have any questions.

( See attached file: pcwp_ appB 06feb04. wpd)( See attached file: plywood risk preamble. wpd)

THANKS! Teresa Clemons Emission Standards Division 919 541 0252 919 541 0072 ( Fax) 1 02/ 05/ 04 revised draft § 63.2231 Does this subpart apply to me?

This subpart applies to you if you meet the criteria in paragraphs ( a) and ( b) of this section ( a) You own or operate a plywood and composite wood products ( PCWP) manufacturing facility. A PCWP manufacturing facility is a facility that manufactures plywood and/ or composite wood products by bonding wood material ( fibers, particles,

strands, veneers, etc.) or agricultural fiber, generally with resin under heat and pressure, to form a structural panel or engineered wood product. Plywood and composite wood products manufacturing facilities also include facilities that manufacture dry veneer and lumber kilns located at any facility. Plywood and composite wood products include ( but are not limited to) plywood,

veneer, particleboard, oriented strandboard, hardboard,

fiberboard, medium density fiberboard, laminated strand lumber,

laminated veneer lumber, wood I joists, kiln dried lumber, and glue laminated beams.

( b) The PCWP manufacturing facility is located at a major source of HAP emissions. A major source of HAP emissions is any stationary source or group of stationary sources within a 2 contiguous area and under common control that emits or has the potential to emit any single HAP at a rate of 9.07 megagrams ( 10 tons) or more per year or any combination of HAP at a rate of 22.68 megagrams ( 25 tons) or more per year. 3 Appendix B to Subpart DDDD   Methodology and Criteria for Demonstrating That An Affected Source is Part of the Low risk Subcategory of Plywood and Composite Wood Products Manufacturing Facilities 1. Purpose This appendix provides the methodology and criteria for demonstrating that your affected source is part of the low risk subcategory of plywood and composite wood products ( PCWP)

manufacturing facilities. You must determine if your facility is part of the low risk subcategory using either a look up table analysis ( based on the look up tables included in this appendix)

or using a site specific risk assessment performed according to the criteria specified in this appendix. This appendix also specifies how and when you must obtain approval of the low risk demonstrations for your affected source and how to ensure that your affected source remains in the low risk subcategory of PCWP facilities.

2. Who is eligible to demonstrate that they are part of the lowrisk subcategory of PCWP facilities?

Each new, reconstructed, or existing affected source at a PCWP manufacturing facility may demonstrate that they are part of the low risk subcategory of PCWP facilities. Section § 63.2232 of 4 subpart DDDD defines the affected source and explains which affected sources are new, existing, or reconstructed.

3. What parts of my facility have to be included in the low risk demonstration?

Every process unit that is part of the PCWP affected source ( as defined in § 63.2292 of subpart DDDD) and that emits one or more HAP listed in Table 1 of this appendix must be included in the low risk demonstration. You are not required to include process units outside of the affected source in the low risk demonstration.

4. What are the criteria for determining if my facility is low risk?

( a) Determine the individual HAP emission rates from each process unit within the affected source using the procedures specified in section 5 of this appendix.

( b) Perform chronic and acute risk assessments using the dose response values found at http:// www. epa. gov/ ttn/ atw/ toxsource/ summary. html, as specified in paragraphs ( b)( 1) and ( 2) of this section.

( 1) For a look up table analysis or site specific chronic inhalation risk assessment, you should use the cancer and 5 noncancer dose response values listed on the EPA Air Toxics website ( http:// www. epa. gov/ ttn/ atw/ toxsource/ summary. html) to estimate carcinogenic and non carcinogenic chronic inhalation risk, respectively.

( 2) For site specific acute inhalation risk assessment, you must use the acute exposure guidance level ( AEGL 1) value for acrolein and the California EPA ( CalEPA) acute reference exposure level ( REL) value for formaldehyde for estimating acute inhalation risk.

( c) Determine if your facility is part of the low risk subcategory by estimating the maximum chronic and acute impacts of your facility using one of the methods described in either section 6 of this appendix ( look up table analysis) or section 7 of this appendix ( site specific risk assessment) and comparing the results to the low risk criteria. Your facility is low risk if the estimated maximum individual lifetime cancer risk is less than 1 in a million, the estimated maximum chronic hazard index values for respiratory effects and central nervous system ( CNS)

effects are less than 1, and the estimated maximum acute hazard quotient values for acrolein and formaldehyde are less than 1.

5. How do I determine HAP emissions from my affected source?

( a) You must conduct HAP emissions tests according to the 6 requirements in paragraphs ( b) through ( g) of this section and the methods specified in Table 2 of this appendix for every process unit within the affected source that emits one or more of the HAP listed in Table 1. You must test the process units at your facility to obtain the emission rates in pounds per hour ( lb/ hr) for each of the pollutants listed in Table 1.

( b) Periods when emissions tests must be conducted.

( 1) You must not conduct emissions tests during periods of startup, shutdown, or malfunction, as specified in § 63.7( e)( 1).

( 2) You must test under worst case operating conditions as defined in this appendix. You must describe your worst case operating conditions in your performance test report for the process and control systems ( if applicable) and explain why the conditions are worst case.

( c) Number of test runs. You must conduct three separate test runs for each test required in this section, as specified in § 63.7( e)( 3). Each test run must last at least 1 hour except for:

testing of a temporary total enclosure ( TTE) conducted using Methods 204A through 204F which require three separate test runs of at least 3 hours each; and testing of an enclosure conducted using the alternative tracer gas method in appendix A to subpart DDDD which requires a minimum of three separate runs of at least 7 20 minutes each.

( d) Sampling locations. Sampling sites must be located at the outlet of the control device, including wet control devices,

and prior to any releases to the atmosphere.

( e) Collection of monitoring data for HAP control devices.

During the emissions test, you must collect operating parameter monitoring system or continuous emissions monitoring system ( CEMS) data at least every 15 minutes during the entire emissions test and establish the site specific operating requirements ( including the parameter limits or total hydrocarbon ( THC)

concentration limit) in Table 2 of subpart DDDD using data from the monitoring system and the procedures specified in paragraphs ( k) through ( o) of § 63.2262 of subpart DDDD.

( f) Nondetect data. You may treat emissions of an individual HAP as zero if all of the test runs result in a nondetect measurement and the conditions in paragraphs ( 1) and ( 2) are met for the relevant test method. Otherwise nondetect data ( as defined in § 63.2292 of subpart DDDD) for individual HAP must be treated as one half of the method detection limit.

( 1) The method detection limit is less than or equal to 1 part per million by volume, dry ( ppmvd) for pollutant emissions 8 measured using Method 320 in appendix A to 40 CFR part 63; or the NCASI Method IM/ CAN/ WP 99.02; or ASTM D6348 03.

( 2) For pollutants measured using Method 29 in appendix A to 40 CFR part 60, you analyze samples using atomic absorption spectroscopy ( AAS).

( g) For purposes of your low risk demonstration, assume that 17 percent of your total chromium measured using EPA Method 29 in appendix A to 40 CFR part 60 is chromium ( VI). For purposes of your low risk demonstration, assume that 65 percent of your total nickel measured using EPA Method 29 in appendix A to 40 CFR part 60 is nickel subsulfide.

6. How do I conduct a look up table analysis?

Use the look up tables to determine if your facility is part of the low risk subcategory, following the procedures in paragraphs ( a) through ( d) of this section.

( a) Using the emission rate of each HAP required to be included in your low risk demonstration, determine your total toxicity weighted carcinogen and non carcinogen emission rates for each of your process units using Equations 1 and 2 of this appendix, respectively. 9 TWCER =

( ERi x UREi) Eqn. 1 TWCER = Toxicity weighted carcinogenic emission rate,

( lb/ hr)/( µ g/ m3)

ERi = Emission rate of pollutant i, pounds per hour ( lb/ hr)

UREi = Unit risk estimate for pollutant i, 1 per microgram per cubic meter ( µ g/ m3) 1 TWNER =

( ERi / RfCi) Eqn. 2 TWNER = Toxicity weighted non carcinogenic emission rate,

( lb/ hr)

ERi = Emission rate of pollutant i, pounds per hour ( lb/ hr)

RfCi = Reference concentration for pollutant i,

milligrams per cubic meter ( mg/ m3)

( b) Cancer risk. Determine the total toxicity weighted carcinogen emission rate for your affected source by summing the toxicity weighted carcinogen emission rates for each of your process units. Select the maximum allowable toxicity weighted 10 carcinogen emission rate from Table 3 of this appendix for your facility using the average stack height of your process units and the minimum distance between any HAP emission point at the facility and the closest boundary of the nearest residential, or residentially zoned, area. If one or both of these values do not match the values in the lookup tables then use the next lowest table value. Your facility is low risk for carcinogenic effects if your toxicity weighted carcinogen emission rate, determined using the methods specified in this appendix, does not exceed the values specified in Table 3 of this appendix.

( c) Non cancer risk. Determine the total CNS and respiratory target organ specific toxicity weighted noncarcinogen emission rate for your affected source by summing the toxicity weighted emission rates for each of your emission points. Select the maximum allowable toxicity weighted noncarcinogen emission rate from Table 4 of this appendix for your facility using the average stack height of your process units and the minimum distance between any HAP emission point at the facility and the closest boundary of the nearest residential, or residentially zoned, area. If one or both of these values do not match the values in the lookup tables then use the next lowest table value. Your facility is low risk for non carcinogenic effects if your toxicity weighted non carcinogen emission rate,

determined using the methods specified in this appendix, does not 11 exceed the values specified in Table 4 of this appendix.

( d) Low risk demonstration. Your facility is part of the low risk subcategory of PCWP sources if your affected source is determined to be low risk for both carcinogenic and noncarcinogenic effects using the look up table analysis described in this section and you meet the criteria specified in Section 11 of this appendix.

7. How do I conduct a site specific risk assessment?

Perform a site specific risk assessment following the procedures specified in this section. You may use any scientifically accepted peer reviewed assessment methodology for your site specific risk assessment. An example approach to performing a site specific risk assessment for air toxics is provided in the " Air Toxics Risk Assessment Guidance Reference Library". You may obtain a copy of the " Air Toxics Risk Assessment Reference Library" from EPA's air toxics website ( a) Your facility is low risk for carcinogenic chronic inhalation effects if your site specific risk assessment demonstrates that maximum off site individual lifetime cancer risk at a location where people can live is less than one in one million. 12 ( b) Your facility is low risk for non carcinogenic chronic inhalation effects if your site specific risk assessment demonstrates that every maximum off site target organ specific hazard index ( TOSHI) at a location where people can live is less than 1.

( c) Your facility is low risk for non carcinogenic acute inhalation effects if your site specific risk assessment demonstrates that the maximum off site acute hazard quotients for both acrolein and formaldehyde are less than 1.

( d) Your facility is part of the low risk subcategory of PCWP facilities if the affected source is determined to be low risk for all of the applicable effects listed in paragraphs ( a)

through ( c) of this section and you meet the criteria specified in section 11 of this appendix.

8. What information must I submit for the low risk demonstration?

( a) Your low risk demonstration must include the information specified in paragraphs ( a)( 1) through ( 5) of this section and the information specified in either paragraph ( b) or ( c) of this section.

( 1) Identification of each process unit at the affected source.

( 2) Stack parameters for each HAP emission point including, 13 but not limited to, the parameters listed in ( a)( 2)( i) through ( iv) below:

( i) Emission release type.

( ii) Stack height, stack area, stack gas temperature, and stack gas exit velocity.

( iii) Plot plan showing all HAP emission points, nearby residences, and fenceline.

( iv) Identification of any HAP control devices used to reduce emissions from each process unit.

( 3) Emission test reports for each process unit based on the test methods specified in Table 2 of this appendix, including a description of the process parameters identified as being worst case.

( 4) Identification of the dose response values used in your risk analysis ( look up table analysis or site specific risk assessment), according to section 5( b) of this appendix.

( 5) Identification of the controlling process factors ( including, but not limited to, production rate, annual emission rate, type of control devices, process parameters documented as worst case conditions during the emissions testing used for your low risk demonstration) that will become Federally enforceable permit conditions used to show that your facility remains in the low risk subcategory. 14 ( b) If you use the look up table analysis in section 6 of this appendix to demonstrate that your facility is low risk, your low risk demonstration must contain the information in paragraphs ( a) and ( b)( 1) through ( 4) of this section.

( 1) Identification of the process unit stack heights included in the calculation of average stack height.

( 2) Identification of the process unit with the nearest distance to a residential, or residentially zoned, area.

( 3) Calculations used to determine the toxicity weighted carcinogen and non carcinogen emission rates according to section 6( a) of this appendix.

( 4) Comparison of the values in the look up tables ( Tables 3 and 4 of this appendix) to your toxicity weighted emission rates for carcinogenic and non carcinogenic HAP.

( c) If you are using a site specific risk assessment as described in section 7 of this appendix to demonstrate that your facility is low risk ( for carcinogenic and non carcinogenic chronic inhalation and acute inhalation risks), your low risk demonstration must contain the information in paragraphs ( a) and ( c)( 1) through ( 8) of this section:

( 1) Identification of the risk assessment methodology used.

( 2) Documentation of the fate and transport model used.

( 3) Documentation of the fate and transport model inputs, 15 including the information described in paragraphs ( a)( 1) through ( 4) of this section converted to the dimensions required for the model and all of the following that apply: meteorological data;

building, land use, and terrain data; receptor locations and population data; and other facility specific parameters input into the model.

( 4) Documentation of the fate and transport model outputs.

( 5) Documentation of exposure assessment and risk characterization calculations.

( 6) Comparison of the carcinogenic inhalation risk to 1 in a million, as required in section 7( a) of this appendix.

( 7) Comparison of each chronic inhalation TOSHI ( for respiratory effects and CNS effects) to the limit of 1, as required in section 7( b) of this appendix.

( 8) Comparison of the acute inhalation HQ to the limit of 1,

as required in section 7( c) of this appendix.

9. Where do I send my low risk demonstration?

You must submit your low risk demonstration to EPA for review and approval. Send your low risk demonstration to U. S.

EPA, Risk and Exposure Assessment Group, Emission Standards Division ( C404 01), Attn: Dr. David Guinnup, Research Triangle Park, NC 27711. You are not part of the low risk subcategory 16 until you meet the requirements of section 11 of this appendix.

10. When do I submit my low risk demonstration?

( a) If you have an existing affected source, you must complete and submit for approval your low risk demonstration no later than [ INSERT 14 MONTHS AFTER DATE OF PUBLICATION].

( b) If you have a new or reconstructed affected source that starts up before the effective date of subpart DDDD, or an affected source that is an area source that increases its emissions or its potential to emit such that it becomes a major source of HAP before [ INSERT 2 MONTHS AFTER PUBLICATION], then you must comply with the requirements of subpart DDDD until you meet the criteria in section 11 of this appendix.

( c) If you have a new or reconstructed affected source that starts up after [ INSERT 2 MONTHS AFTER PUBLICATION], or an affected source that is an area source that increases its emissions or its potential to emit such that it becomes a major source of HAP after [ INSERT 2 MONTHS AFTER PUBLICATION], then you must follow the schedule in paragraphs ( 1) and ( 2) of this section.

( 1) You must complete and submit for approval a preliminary 17 low risk demonstration based on the information ( e. g., equipment types, estimated emission rates, etc.) used to obtain your title V permit. You must base your preliminary low risk demonstration on the maximum emissions allowed under your title V permit. If EPA concludes that your affected source appears to be part of the low risk subcategory based on this preliminary low risk demonstration, then your may start up your affected source without complying with the compliance options, operating requirements, and work practice requirements in subpart DDDD.

( 2) You must conduct the emission tests specified in section 4 of this appendix upon initial startup and use the results of these emissions tests to complete and submit your low risk demonstration within 180 days following your initial startup date. To be included in the low risk subcategory, you must meet the criteria in section 11 of this appendix within 18 months following initial startup of your affected source.

11. How does my facility become part of the low risk subcategory?

To be included in the low risk subcategory, you must meet the criteria in paragraphs ( a) and ( b) of this section. If you do not meet these criteria, then your affected source is subject to the applicable compliance options, operating requirements, and 18 work practice requirements in Subpart DDDD.

( a) Your demonstration of low risk must be approved by EPA.

( b) The parameters that defined your affected source as part of the low risk subcategory ( including, but not limited to,

production rate, annual emission rate, type of control devices,

process parameters documented as worst case conditions during the emissions testing used for your low risk demonstration) must be incorporated as Federally enforceable limits into your title V permit.

12. What must I do to ensure my facility remains a low risk facility?

( a) You must meet the requirements in Table 2 of subpart DDDD for each HAP control device used at the time when you completed your low risk demonstration. You must monitor and collect data according to § 63.2270 of subpart DDDD to show continuous compliance with your control device operating requirements. You must demonstrate continuous compliance with the control device operating requirements that apply to you by collecting and recording the monitoring system data listed in Table 2 of this subpart for the process unit according to § § 63.2269( a), ( b), and ( d) of subpart DDDD; AND reducing the monitoring system data to the specified averages in units of the 19 applicable requirement according to calculations in § 63.2270 of subpart DDDD; AND maintaining the average operating parameter at or above the minimum, at or below the maximum, or within the range ( whichever applies) established according to section 4( e)

of this appendix.

13. What happens if the critera used in the risk determination change?

( a) You must certify with each Title V permit renewal that the basis for your facility's low risk determination has not changed. You must submit this certification to the permitting authority. You must consider the following:

( 1) Process changes that increases HAP emissions, including,

but not limited to, production rate increase, annual emission rate increase, change in type of control device, changes in process parameters documented as worst case conditions during the emissions testing used for your approved low risk demonstration.

( 2) Population shifts.

( 3) Unit risk estimate increases.

( 4) Reference concentration decreases.

( 5) Dose response values ( URE, RfC, CSF, and RfD) on the EPA website ( http:// www. epa. gov/ ttn/ atw/ toxsource/ summary. html). 20 ( b) At any time a change occurs that was not a permit condition, including the changes listed in paragraphs ( a)( 1)

through ( 5), you must notify the permitting authority immediately.

( 1) If the change does not change the risk designation of the facility, you must explain the change and why the facility is still low risk. You must also certify that the facility is still low risk and part of the low risk subcategory.

( 2) If the change results in the facility no longer being low risk, then the facility is no longer part of the low risk subcategory and is subject to all the applicable requirements of subpart DDDD.

( 3) If your facility is no longer low risk, you may update your low risk demonstration and resubmit it to EPA. You must submit your revised low risk demonstration to EPA prior to revising your permit to incorporate the process change. If you use the same approach/ risk assessment model, you may . . . [ text needed if possible to expedite reveiw   REAG] time 14. What records must I keep?

( a) You must keep records of the information used in developing the low risk demonstration for your affected source,

including all of the information specified in section 8 of this appendix. 21 ( b) You must keep the records required in section 12( d) of this appendix to show continuous compliance with the operating requirements for control devices.

( c) For each THC CEMS, you must keep the records specified in § 63.2282( c) of subpart DDDD.

15. Definitions.

The definitions in § 63.2292 of subpart DDDD apply to this appendix. Additional definitions applicable for this appendix are as follows:

Direct fired process unit means a process unit that is heated by the passing of combustion exhaust directly through the process unit such that the process material is contacted by the combustion exhaust.

Hazard Index ( HI) means the sum of more than one hazard quotient for multiple substances and/ or multiple exposure pathways.

Hazard Quotient ( HQ) means the ratio of the predicted media concentration of a pollutant to the media concentration at which no adverse effects are expected. For inhalation exposures, the 22 HQ is calculated as the air concentration divided by the RfC.

Look up table analysis means a risk screening analysis based on comparing the toxicity weighted HAP emission rate from the affected source to the maximum allowable toxicity weighted HAP emission rates specified in Tables 3 and 4 of this appendix.

Reference Concentration ( RfC) means an estimate ( with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population ( including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from various types of human or animal data, with uncertainty factors generally applied to reflect limitations of the data used.

Target organ specific hazard index ( TOSHI) means the sum of hazard quotients for individual chemicals that affect the same organ or organ system ( e. g., respiratory system, central nervous system).

Unit Risk Estimate ( URE) means the upper bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µ g/ m3 in air. 23 Worst case operating conditions means operation of a process unit during emissions testing under the conditions that result in the highest HAP emissions or that result in the emissions stream composition ( including HAP and non HAP) that is most challenging for the control device if a control device is used. For example,

worst case conditions could include operation of the process unit at maximum throughput, at its highest temperature, with the wood species mix likely to produce the most HAP, and/ or with the resin formulation containing the greatest HAP. 24 Table 1 to Appendix B of Subpart DDDD. HAP that must be included in the demonstration of eligibility for the low risk PCWP subcategory.

For your analysis of the following effects... You must include the following HAP...

( 1) Chronic inhalation cancer acetaldehyde, benzene, arsenic, beryllium, cadmium, chromium, lead, nickel, formaldehyde.

( 2) Chronic inhalation noncancer respiratory acetaldehyde, acrolein, formaldehyde, .

( 3) Chronic inhalation noncancer CNS manganese, phenol.

( 4) Acute inhalation acrolein, formaldehyde. 25 Table 2 to Appendix B of Subpart DDDD. Emission Test Methods.

For... You must... Using...

( 1) each process unit select sampling ports' location and the number of traverse points Method 1 or 1A of 40 CFR part 60, appendix A ( as appropriate).

( 2) each process unit determine velocity and volumetric flow rate; Method 2 in addition to Method 2A, 2C, 2D, 2F, or 2G in appendix A to 40 CFR part 60 ( as appropriate).

( 3) each process unit conduct gas molecular weight analysis Method 3, 3A, or 3B in appendix A to 40 CFR part 60 ( as appropriate).

( 4) each process unit measure moisture content of the stack gas Method 4 in appendix A to 40 CFR part 60.

( 5) each process unit measure emissions of the following HAP: acetaldehyde, acrolein, formaldehyde, and phenol NCASI Method IM/ CAN/ WP 99.02; OR Method 320 in appendix A to 40 CFR part 63; OR ASTM D6348 03 provided that % R as determined in Annex A5 of ASTM D6348 03 is equal or greater than 70% and less than or equal to 130%.

( 6) each process unit measure emissions of benzene Method 320 in appendix A to 40 CFR part 63; OR ASTM D6348 03 provided that % R as determined in Annex A5 of ASTM D6348 03 is equal or greater than 70% and less than or equal to 130%.

( 7) each press that processes board containing methylene diphenyl diisocyanate ( MDI) resin measure emissions of MDI Method 320 in appendix A to 40 CFR part 63; OR Conditional Test Method ( CTM) 031 which is posted on http:// www. epa. gov/ ttn/ emc / ctm. html ( 8) each direct fired process unit measure emissions of the following HAP metals: arsenic, beryllium, cadmium, chromium, lead, manganese, and nickel. Method 29 in appendix A to 40 CFR part 60. You must analyze samples using atomic absorption spectroscopy ( AAS).

( 9) any process unit that is known to emit HAP not otherwise listed in this table measure emissions of the HAP emitted the methods specified in this table ( as appropriate) or petition the Administrator for approval of an alternative test method. 26 ( 11) each reconstituted wood product press or reconstituted wood product board cooler with a HAP control device meet the design specifications included in the definition of wood products enclosure in § 63.2292 of subpart DDDD OR determine the percent capture efficiency of the enclosure directing emissions to an add on control device Methods 204 and 204A through 204F of 40 CFR part 51, appendix M to determine capture efficiency ( except for wood products enclosures as defined in § 63.2292). Enclosures that meet the definition of wood products enclosure or that meet Method 204 requirements for a PTE are assumed to have a capture efficiency of 100%. Enclosures that do not meet either the PTE requirements or design criteria for a wood products enclosure must determine the capture efficiency by constructing a TTE according to the requirements of Method 204 and applying Methods 204A through 204F ( as appropriate). As an alternative to Methods 204 and 204A through 204F, you may use the tracer gas method contained in appendix A to this subpart.

( 12) each reconstituted wood product press or reconstituted wood product board cooler determine the percent capture efficiency a TTE and Methods 204 and 204A through 204F ( as appropriate) of 40 CFR part 51, appendix M. As an alternative to installing a TTE and using Methods 204 and 204A through 204F, you may use the tracer gas method contained in appendix A to this subpart.

( 13) each process unit with a HAP control device establish the sitespecific operating requirements ( including the parameter limits or THC concentration limits) in Table 2 of subpart DDDD data from the parameter monitoring system or THC CEMS and the applicable performance test method( s). 27 Table 3 to Appendix B of Subpart DDDD. Maximum allowable toxicity weighted carcinogen emission rate ( lb/ hr)/( µ g/ m3)

Fenceline ( m)

Stack height ( m) 0 50 100 150 200 250 500 1000 1500 2000 3000 5000 5 8.72E 07 8.72E 07 8.72E 07 9.63E 07 1.25E 06 1.52E 06 1.25E 06 4.25E 06 4.39E 06 4.39E 06 4.39E 06 5.00E 06 10 2.47E 06 2.47E 06 2.47E 06 2.47E 06 2.47E 06 2.61E 06 3.58E 06 5.03E 06 5.89E 06 5.89E 06 5.89E 06 6.16E 06 20 5.81E 06 5.81E 06 5.81E 06 5.81E 06 5.81E 06 5.81E 06 5.90E 06 7.39E 06 8.90E 06 9.97E 06 9.97E 06 1.12E 05 30 7.74E 06 7.74E 06 7.74E 06 7.74E 06 7.74E 06 7.74E 06 8.28E 06 9.49E 06 1.17E 05 1.35E 05 1.55E 05 1.61E 05 40 9.20E 06 9.20E 06 9.20E 06 9.20E 06 9.20E 06 9.20E 06 9.24E 06 1.17E 05 1.34E 05 1.51E 05 1.98E 05 2.22E 05 50 1.02E 05 1.02E 05 1.02E 05 1.02E 05 1.02E 05 1.02E 05 1.02E 05 1.36E 05 1.53E 05 1.66E 05 2.37E 05 2.95E 05 60 1.13E 05 1.13E 05 1.13E 05 1.13E 05 1.13E 05 1.13E 05 1.13E 05 1.53E 05 1.76E 05 1.85E 05 2.51E 05 3.45E 05 70 1.23E 05 1.23E 05 1.23E 05 1.23E 05 1.23E 05 1.23E 05 1.23E 05 1.72E 05 2.04E 05 2.06E 05 2.66E 05 4.07E 05 80 1.34E 05 1.34E 05 1.34E 05 1.34E 05 1.34E 05 1.34E 05 1.34E 05 1.92E 05 2.15E 05 2.31E 05 2.82E 05 4.34E 05 100 1.52E 05 1.52E 05 1.52E 05 1.52E 05 1.52E 05 1.52E 05 1.52E 05 1.97E 05 2.40E 05 2.79E 05 3.17E 05 4.49E 05 200 1.76E 05 1.76E 05 1.76E 05 1.76E 05 1.76E 05 1.76E 05 1.76E 05 2.06E 05 2.94E 05 3.24E 05 4.03E 05 5.04E 05 MIR= 1E 06 Emission rates in table expressed as equivalents normalized to theoretical HAP with URE = 1( µ g/ m3) 1 28 Table 4 to Appendix B of Subpart DDDD. Maximum allowable toxicity weighted non carcinogen emission rate ( lb/ hr)

Fenceline ( m)

Stack height ( m) 0 50 100 150 200 250 500 1000 1500 2000 3000 5000 5 2.51E 01 2.51E 01 3.16E 01 3.16E 01 3.16E 01 3.16E 01 3.16E 01 3.46E 01 4.66E 01 6.21E 01 9.82E 01 1.80E+ 00 10 5.62E 01 5.62E 01 5.62E 01 5.62E 01 5.62E 01 5.62E 01 5.62E 01 5.70E 01 6.33E 01 7.71E 01 1.13E+ 00 1.97E+ 00 20 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.43E+ 00 1.68E+ 00 1.83E+ 00 2.26E+ 00 3.51E+ 00 30 2.36E+ 00 2.36E+ 00 2.36E+ 00 2.36E+ 00 2.36E+ 00 2.36E+ 00 2.53E+ 00 3.04E+ 00 3.04E+ 00 3.33E+ 00 4.45E+ 00 5.81E+ 00 40 3.11E+ 00 3.11E+ 00 3.11E+ 00 3.11E+ 00 3.11E+ 00 3.11E+ 00 3.42E+ 00 4.04E+ 00 5.07E+ 00 5.51E+ 00 6.39E+ 00 9.63E+ 00 50 3.93E+ 00 3.93E+ 00 3.93E+ 00 3.93E+ 00 3.93E+ 00 3.93E+ 00 4.49E+ 00 4.92E+ 00 6.95E+ 00 7.35E+ 00 8.99E+ 00 1.25E+ 01 60 4.83E+ 00 4.83E+ 00 4.83E+ 00 4.83E+ 00 4.83E+ 00 4.83E+ 00 5.56E+ 00 6.13E+ 00 7.80E+ 00 1.01E+ 01 1.10E+ 01 1.63E+ 01 70 5.77E+ 00 5.77E+ 00 5.77E+ 00 5.77E+ 00 5.77E+ 00 5.77E+ 00 6.45E+ 00 7.71E+ 00 8.83E+ 00 1.18E+ 01 1.36E+ 01 1.86E+ 01 80 6.74E+ 00 6.74E+ 00 6.74E+ 00 6.74E+ 00 6.74E+ 00 6.74E+ 00 7.12E+ 00 9.50E+ 00 1.01E+ 01 1.29E+ 01 1.72E+ 01 2.13E+ 01 100 8.87E+ 00 8.87E+ 00 8.87E+ 00 8.87E+ 00 8.87E+ 00 8.87E+ 00 8.88E+ 00 1.19E+ 01 1.37E+ 01 1.55E+ 01 2.38E+ 01 2.89E+ 01 200 1.70E+ 01 1.70E+ 01 1.70E+ 01 1.70E+ 01 1.70E+ 01 1.70E+ 01 1.70E+ 01 2.05E+ 01 2.93E+ 01 3.06E+ 01 4.02E+ 01 4.93E+ 01 HI= 1 Emission rates in table expressed in lbs/ hr as equivalents normalized to theoretical HAP with RfC = 1.0 IV. Summary of Responses to Major Comments and Changes to the Plywood and Composite Wood Products NESHAP K. Risk based approaches 1. General comments a. Risk based approaches Comment: Numerous commenters encouraged EPA to exercise all of the flexibility within its authority and offer the widest possible array of options so that facilities that pose no significant risk to public health or the environment would not be forced to add expensive and unproductive control equipment which would weaken them financially or cause them to close. Commenters specifically recommended that EPA incorporate risk based options similar to all three industry " white papers," which would exclude facilities that pose no significant risk to public health or the environment. ( As an alternative, one commenter recommended that EPA at least incorporate the concentration based de minimis applicability exemption.)

Commenters stated that inclusion of risk provisions has the potential to achieve overall environmentally superior results in a cost effective manner, particularly in cases where criteria pollutants from control devices ( i. e., incinerators) may result in greater impacts that the HAP emissions that they control.

According to a life cycle analysis conducted by one commenter,

incinerators used to limit HAP emissions from low risk wood products facilities would create more harm than good through their consumption of electricity and natural gas. The commenter 2 noted that incinerators emit carbon monoxide ( CO2) and criteria pollutants, which could affect a State's ability to meet the National Ambient Air Quality Standards ( NAAQS) attainment requirements under the CAA. In particular, the commenter referred to EPA's projection that adoption of MACT floor level controls would result in increased emissions of NOx, a precursor to ozone and PM. According to the commenter, the draft rule ( without risk provisions) would work against the industry's voluntary commitment, in response to President Bush's initiative,

to reduce the emissions of greenhouse gases by 12 percent over the next 10 years. The commenter noted that the costly mandatory controls proposed, coupled with stiff foreign competition and regulatory mandates under other MACT rules, would also create significant financial hardship across all sectors of the industry and jeopardize the commercial viability of numerous facilities,

many of which are the principal employer in the small, rural towns in which they are located. The projected costs for the proposed rule are enormous amounts of money for an industry already operating at the margin in a depressed economic climate.

Noting EPA's prediction that the draft rule would avert 0.07 cases of cancer per year, or one case every 14 years, the commenter stated that this would yield a cost effectiveness of $ 2.4 billion per cancer case averted. The commenter compared the cost per premature death averted for several rules and found the PCWP rule to be one of the more costly. The commenter concluded 3 that, in its current form, the draft rule would impose hundreds of millions of dollars of additional cost with virtually no gain to either the environment or the health. The commenter stated that the draft rule would be one of the most cost ineffective rules ever promulgated by EPA. According to the commenter, the overwhelming advantage of the risk based approach is that it avoids imposing high costs on low risk facilities, where there is little or no benefit to be gained for either the environment or the public interest. The commenter stated that the wood products industry as a whole poses a small to insignificant risk to human health and the environment.

The commenter stated that the final rule should include reasonable risk based mechanisms to allow facilities posing no significant risk to limit their emissions below levels of concern without having to install incinerator controls. The commenter stated that facilities wishing to take advantage of the risk based compliance option would take a federally enforceable permit limit that would guarantee that their emissions remain below the risk based emission standard. This would constitute an " emission limitation," within the statutory definition of the term, and it would allow facilities to forego the installation of incinerators where they are not warranted by public health and environmental considerations.

Commenters argued that the risk based options are legally justified, protective of human health and the environment, and 4 economically sensible. Commenters stated that the risk based options are supported under the CAA, through EPA's authority under sections 112( d)( 4) and 112( c)( 9) to set emission standards other than MACT for certain low risk facilities and delist technology defined low risk subcategories, respectively, and through EPA's inherent de minimis authority to avoid undertaking regulatory action in the absence of meaningful risk. One commenter pointed out that, by meeting the stringent health benchmarks necessary to qualify for the risk based compliance approaches, facilities already would have satisfied the residual risk provisions 8 years ahead of the statutory requirements set forth in section 112( f) of the CAA.

Two commenters believed that the risk based approach would particularly benefit small mills located in rural areas with timber dependent economies. One commenter stated that, by offering manufacturers an opportunity to apply for subcategorization on a site specific basis, facilities that are remotely located, or which were originally planned and sited with thorough consideration of airshed impacts, would not be unduly burdened with MACT requirements which yield little or no public health benefits.

Commenters argued that such low risk facilities should not be burdened with the requirements of MACT. One commenter noted that the regulatory framework exists within their State to implement a risk based approach. Another commenter agreed with 5 the concept of a risk bsed approach but stated that it would not be appropriate for State and local programs to determine which facilities should be exempted from MACT. Another commenter suggested that exemptions be provided on a case by case basis to individual facilities that are able to demonstrate that they pose no significant risk to public health or the environment.

Several commenters opposed the risk based exemptions. Two commenters stated that the use of risk based concepts to evade MACT applicability is contrary to the intent of the CAA and is based on a flawed interpretation of section 112( d)( 4) written by an industry subject to regulation. One commenter added that the CAA requires a technology based floor level of control and does not provide exclusions for risk or secondary impacts in applying the MACT floor. The other commenter was particularly concerned about industry's unprecedented proposal to include " de minimis exemptions" and " cost" in the MACT standard process. The commenter stated that including case by case risk based exemptions would jeopardize the effectiveness of the national air toxics program to adequately protect public health and the environment and to establish a level playing field. A third commenter noted that subcategorization and source category deletions under section 112( c) have been implemented several times since the MACT program began.

Commenters pointed out that they have not been able to comment on the technical merit of the risk analysis employed by 6 the EPA. They argued that, until the residual risk analysis procedures have been implemented via the section 112( f) process,

risk analysis should not be used in making MACT determinations pursuant to section 112( d)( 4). Also, risk analysis could never be used to establish a MACT floor.

One commenter pointed out that, in separate rulemakings and lawsuits, EPA adopted legal positions and policies that refute and contradict the very risk based and cost based approaches contained in the proposal. In these other arenas, EPA properly rejected risk assessment to alter the establishment of MACT standards. The EPA also properly rejected cost in determining MACT floors and in denying a basis for avoiding the MACT floor.

( See Brief for Respondent Environmental Protection Agency, Sierra Club v. EPA; Brief for Respondent Environmental Protection Agency, Cement Kiln Recycling Coalition v. EPA, No. 99 1457 and consolidated cases, ( D. C. Cir.) ( Jan. 18, 2001); Brief for Respondent Environmental Protection Agency, National Lime Ass'n v. EPA, 233 F. 3D 625 ( D. C. Cir. 2000) ( July 14, 2000).)

Response: We believe that the assertions by one commenter about the negative environmental disbenefits of the PCWP rule are overstated. We disagree that the PCWP industry as a whole poses a small to insignificant risk to human health and the environment. However, we acknowledge that there are some PCWP facilities that pose little risk to human health and the environment. Consequently, we have included an option in today's 7 final PCWP rule that would allow individual facilities to be delisted ( as part of a low risk subcategory) if they demonstrate that they do not pose a significant risk to human health or the environment. The low risk subcategory delisting in today's final PCWP rule is based on our authority under CAA sections 112( c)( 1)

and ( 9). This statute requires that categories or subcategories meet specific risk criteria, and to determine this, risk analyses may be used. We disagree with the commenter that we must wait for implementation of CAA section 112( f) before utilizing risk analysis in this manner. Section 112( d)( 1) of the CAA gives us the authority to distinguish among classes, types, and sizes of sources within a category. We believe these provisions of the CAA allow us to define a subcategory of sources in terms of risk.

Thus, the low risk subcategory of PCWP facilities is defined in terms of risk, not cost. We are not subcategorizing or determining MACT floors based on cost. Furthermore, as discussed elsewhere in this section, the MACT level of emissions reduction required by today's final rule is not affected by facilities becoming part of the low risk subcategory.

For many of the reasons provided by the commenters, we are not pursuing the risk based exemptions based on section 112( d)( 4). We do not believe that a risk based approach based on section 112( d)( 4) is appropriate for the PCWP industry because PCWP facilities emit HAP for which no health thresholds have been established and because the legislative history of the 1990 8 Amendments to the CAA indicates that Congress considered and rejected allowing us to grant such source specific exemptions from the MACT floor. We also are not relying on de minimis authority. Legal issues associated with the risk based provisions are addressed elsewhere in this section.

In today's final PCWP rule, we are identifying the criteria we will use to identify low risk PCWP facilities and requesting that any candidate facilities submit information to us based on those criteria so that we can evaluate whether they might be low risk. Today's final PCWP rule also establishes a low risk PCWP subcategory based on the criteria and delists the subcategory based on our finding that no source that would be eligible to be included in the subcategory based on our adopted criteria emits HAP at levels that exceed the thresholds specified in section 112( c)( 9)( B) of the CAA. To be found eligible to be included in the delisted source category, facilities will have to demonstrate to us that they meet the criteria established by today's final PCWP rule and assume federally enforceable limitations that ensure their HAP emissions do not subsequently increase to exceed levels reflected in their eligibility demonstrations.

The criteria defining the low risk subcategory of PCWP facilities are included in Appendix B to Subpart DDDD. The criteria in the appendix were developed for and apply only to the PCWP industry and are not applicable to other industries. 9 Today's final PCWP rule provides two ways that a facility may demonstrate that they are part of the low risk subcategory of PCWP facilities. First, look up tables allow facilities to determine, using a limited number of site specific input parameters, whether emissions from their sources might cause an HI limit for non carcinogens or a cancer benchmark of one in a million to be exceeded. Second, a tiered modeling approach ( each tier less conservative and more complex than the previous) can be used by those facilities that cannot demonstrate that they are part of the low risk subcategory using the look up tables.

The low risk subcategory delisting that is included in today's final PCWP rule is intended to avoid imposing unnecessary controls on facilities that do not pose a significant risk to human health or the environment. Facilities will have to select controls or other methods of limiting risk and then demonstrate,

using Appendix B to Subpart DDDD and/ or the " Air Toxics Risk Assessment Reference Library," that their emissions qualify them to be included in the low risk subcategory, and, therefore, are not subject to the compliance options included in today's final PCWP rule.

Comment: Several commenters objected to EPA using the preambles of individual rule proposals as the forum for introducing significant changes in the way that MACT standards are established. One commenter stated that, for many years, they have coordinated with EPA on development of MACT standards for 10 the national air toxics program, and there has been no indication of any kind regarding inclusion of risk based exemptions in the first phase of the MACT program. The commenter thought it was unprecedented and alarming that EPA was proposing such a radical change at the end of Phase 1 of the MACT standard process. The commenter believed that allowing risk based exemptions requires changes to existing law and that such a debate should take place within the democratic legislative process and not in the MACT standard process. Another commenter stated that precedentsetting change of the magnitude that EPA has raised should be discussed openly and carefully with all affected parties instead of being buried in the preambles of individual standards. A third commenter expressed concern that other parties may miss commenting on the risk based exemptions because they are contained within six separate proposals. The commenter added that to give the issue full consideration, the risk provisions should not be adopted within any of the final rules but should be addressed in one place, such as in revisions to the General Provisions of 40 CFR Part 63, Subpart A.

Response: The discussion of risk based provisions in MACT was included in individual proposals for several reasons. First,

we recognize that such provisions are only appropriate for certain source categories, and our decision making process required source category specific input from stakeholders.

Second, the 10 year MACT standards, which are now being 11 completed, are the last group of MACT standards currently planned for development, and for any risk provisions to be useful, the provisions must be finalized in a timely manner ( i. e., not later than the promulgation of the MACT standards). Third, these final MACT source categories were included in the " 10 year bin" because they were considered to be the lowest risk source categories.

Finally, the risk based provisions are not available for standards that have already been implemented, and any decisions regarding risk must, therefore, be applied on a source categoryspecific basis. We do not agree that changes to existing law are necessary because of the discretion provided to the Administrator under section 112( d)( 1) to distinguish among classes, types, and sizes of sources within a category. We consider low risk facilities to be a class of sources within the PCWP source category.

Comment: Several commenters stated that the risk based exemption proposal removes the " level playing field" that would result from the proper implementation of technology based MACT standards. According to the commenters, establishing a baseline level of control is essential to prevent industry from moving to areas of the country that have the least stringent air toxics programs, which was one of the primary goals of developing a uniform national air toxics program under section 112 of the 1990 CAA amendments. The commenters argued that risk based approaches 12 would jeopardize future reductions of HAP in a uniform and consistent manner across the nation. One commenter stated that National Air Toxics Assessment ( NATA) data show that virtually no area of the country has escaped measurable concentrations of toxic air pollution. The NATA information indicates that exposure to air toxics is high in both densely populated and remote rural areas.

One commenter disagreed with the assertion that the level playing field would be removed. The commenter pointed out that the argument that EPA should impose unnecessary and potentially environmentally damaging controls for the sole purpose of equalizing control costs across facilities would be at odds with the stated purpose of the CAA. According to the commenter, the claim that the risk based approach would favor facilities located away from population centers is incorrect. As contemplated, the risk based approaches to the NESHAP would be keyed to the comparison of health benchmarks with potential maximum exposure,

regardless of whether actual receptors are present at the exposure location. According to the commenter, the presence or absence of human populations would have no effect on whether facilities would qualify.

Response: We agree that one of the primary goals of developing a uniform national air toxics program under section 112 of the 1990 CAA amendments was to establish a level playing field. We do not believe that defining a low risk subcategory in 13 today's final PCWP rule does anything to remove the level playing field for PCWP facilities. Today's final PCWP rule and its criteria for demonstrating eligibility for the delisted low risk subcategory apply uniformly to all PCWP facilities across the nation. Today's final PCWP rule establishes a baseline level of emission reduction or a baseline level of risk ( for the low risk subcategory). All PCWP facilities are subject to these same baseline levels, and all facilities have the same opportunity to demonstrate that they are part of the delisted low risk subcategory. The criteria for the low risk subcategory are not dependent on local air toxics programs. Therefore, concerns regarding facilities moving to areas of the country with lessstringent air toxics programs should be alleviated.

Although NATA may show measurable concentrations of toxic air pollution across the country, these data do not suggest that facilities that do not contribute to the high exposures and risk should be included in regulations. A discussion is provided elsewhere in this section regarding how background concentrations are accounted for by facilities demonstrating eligibility for the delisted low risk subcategory.

Comment: One commenter stated that the dockets for the MACT proposals that contain the risk approaches make it clear that the White House Office of Management and Budget ( OMB) and industry were the driving forces behind the appearance of these unlawful approaches in EPA's proposals. The commenter cited internal e 14 mails between the White House OMB and EPA that reveal OMB officials exerting pressure on EPA to " take ownership" of the deregulatory approaches developed by industry. The commenter noted that comparison of the proposal language for the Brick and Structural Clay Products ( BSCP) rule and PCWP rule makes it clear that EPA capitulated to OMB pressure to remove references to the risk based exemptions in the PCWP proposal preamble as being " industry's suggested approaches." The commenter cited preamble edits from OMB that the commenter believes reveals an OMB agenda to dictate EPA adoption of industry's risk based approaches, and to signal these plans in the rulemaking proposals, even before public comment has been taken. The commenter also noted that OMB urged support of a dangerous and technically unfounded HI of 10.0. The commenter condemned the industry driven agenda that is being promoted by the White House OMB.

A second commenter stated that the accusations that EPA succumbed to industry lobbying and internal pressures are entirely unfounded. The commenter stated that risk based approaches are warranted because EPA's NESHAP program has now turned to the low risk source categories that Congress instructed EPA to address last. The commenter pointed out that 80 source categories have already been addressed with MACT standards.

According to the commenter, the remaining source categories are lower priority and include a large number of facilities that pose negligible risk to public health and environment. The commenter 15 stated that EPA purposefully saved those categories for last in accordance with Congress' explicit, risk based priority setting mandate expressed in section 112( e)( 2). The commenter concluded that EPA has now reached the point where regulation by MACT would result in more environmental harm than good.

Response: The first commenter is correct in stating that industry representatives and OMB support the inclusion of riskbased approaches in today's final PCWP rule as a method of reducing costs. We are required by Executive Order 12866 to submit to OMB for review all proposed and final rulemaking packages that would have an annual effect on the economy of $ 100 million or more. The comments we received from OMB reflect their position.

b. Effects on MACT program Comment: Several commenters expressed concern about the impact of a risk based approach on the MACT program. Some commenters stated that the proposal to include risk based exemptions is contrary to the 1990 CAA Amendments, which calls for MACT standards based on technology rather than risk as a first step. The commenters pointed out that Congress incorporated the residual risk program under section 112( f) to follow the MACT standards, not to replace them. One commenter added that risk based approaches would be used separately to augment and improve technology based standards that do not adequately provide protection to the public. 16 Another commenter believed that section 112( b)( 4) and the regulatory precedent established in over 80 MACT standards reject the inclusion of risk in the first phase of the MACT standards process. The commenter argued that the use of risk assessment at this stage of the MACT program is, in fact, directly opposed to Title III of the CAA.

Response: We disagree that inclusion of a low risk subcategory in today's final PCWP rule is contrary to the 1990 CAA Amendments. The PCWP rule is a technology based standard developed using the procedures dictated by section 112 of the CAA. The only difference between today's final PCWP rule and other MACT rules is that we used our discretion under CAA sections 112( c)( 1) and ( 9) to subcategorize low risk facilities.

The CAA requires that categories or subcategories meet specific risk criteria, and to determine this, risk analyses may be used.

We disagree with the commenter that we must wait for implementation of CAA section 112( f) before utilizing risk analysis in this manner. We believe that today's final PCWP rule is particularly well suited for a risk based option because of the specific pollutants that are emitted. For many facilities,

the pollutants are emitted in amounts that do not pose a significant risk to the surrounding population. However, the cost of controlling these pollutants is high, and may not be justified by environmental benefits for these low risk facilities. Only those PCWP facilities that demonstrate that 17 they are low risk are eligible for inclusion in the delisted lowrisk subcategory. The criteria included in today's final PCWP rule defining the delisted low risk subcategory are based on sufficient information to develop health protective estimates of risk and will provide ample protection of human health and the environment.

Inclusion of a low risk subcategory in today's final PCWP rule does not alter the MACT program or affect the schedule for promulgation of the remaining MACT standards. We recognize that such provisions are only appropriate for certain source categories, and our decision making process required source category specific input from stakeholders. The 10 year MACT standards, which are now being completed, are the last group of MACT standards currently planned for development, and for any risk provisions to be useful, the provisions must be finalized in a timely manner ( i. e., not later than the promulgation of the MACT standards). These final MACT source categories were included in the " 10 year bin" because they were considered to be the lowest risk source categories.

Comment: Several commenters stated that the inclusion of a risk based approach would delay the MACT program and/ or promulgation of the PCWP MACT standard. Commenters stated that the proposal to allow risk based exemptions would divert back to the time consuming NESHAP development process that existed prior 18 to the 1990 CAA Amendments. Under this process, which began with a risk assessment step, only eight NESHAP were promulgated during a 20 year period. If the proposed approaches are inserted into upcoming standards, the commenters feared the MACT program ( which is already far behind schedule) would be further delayed.

One commenter stated that they were strongly opposed to returning to the morass of risk based analysis in an attempt to preempt the application of technology based MACT standards and exempt facilities. The commenter stated that designing a riskbased analysis procedure would also take significant resources,

as evidenced by the fact that it took five plus pages in the Federal Register to discuss just the basic issues to be considered in the analysis. The commenter indicated that the demand on government resources could cause a delay in the application of MACT nationwide. The commenter stated that EPA should also consider the issue of fairness since the rest of the industrial sector whose NESHAP have already been promulgated did not have a risk based option.

Another commenter stated that it is evident that the proposed risk based exemptions would require extensive debate and review in order to launch, which would further delay promulgation of the remaining MACT standards. The commenter stated that delays could be exacerbated by litigation following legal challenges to the rules, and such delays would trigger the section 112( j) MACT hammer provision, which would unnecessarily 19 burden the State and local agencies and the industries. The commenter concluded that, obviously, further delay is unacceptable. Another commenter agreed, stating that it is imperative that EPA meet the new deadlines for promulgating the final MACT standards.

Two commenters stated that EPA's proposal to improperly incorporate risk assessment into the technology based standard process would cripple a MACT program already in disarray. The commenters argued that the risk based approach could exacerbate the delay in HAP emissions reductions required by section 112.

One commenter noted that EPA's Office of Inspector General recently found that EPA is nearly 2 years behind in fulfilling its statutory responsibilities for implementing Phase 1 MACT standards. According to the commenter, this delay potentially harms the public and environment. The inclusion of risk based exemptions in 10 year MACT standards would only further delay this process. The other commenter noted that EPA lacks adequate emissions and exposure data, source characterization data, and health and ecological effects information to conduct this process anyway. This commenter believed that the air toxics program is flawed and failing to protect public health and the environment and argued that it was irresponsible for EPA to pursue a deregulatory agenda that would further weaken the effectiveness of the air toxics program. The commenter noted that EPA acknowledged the complexity and delays associated with the 20 proposed risk based approaches in deciding not to adopt the approaches in the final BSCP rule.

Response: We disagree that identification and delisting of a low risk subcategory in today's final PCWP rule will alter the MACT program or affect the schedule for promulgation of the remaining MACT standards. We do not anticipate any further delays in completing the remaining MACT standards. The delisting of a low risk subcategory in today's final PCWP rule affects only the PCWP rule, and not all other MACT standards that have yet to be promulgated.

We believe that the PCWP rule is particularly well suited for a risk based option because of the specific pollutants that are emitted. For many facilities, the pollutants are emitted in amounts that do not pose a significant risk to the surrounding population. However, the cost of controlling these pollutants is high and may not be justified by environmental benefits for these low risk facilities. Only those PCWP facilities that demonstrate that they are low risk are eligible for inclusion in the delisted low risk subcategory. The criteria defining the delisted lowrisk subcategory are based on sufficient information to develop health protective estimates of risk and will provide ample protection of human health and the environment.

Delisting of a low risk subcategory of PCWP facilities does not mean that we will provide risk based options for other industries. Furthermore, we have no intentions of reopening 21 previously promulgated NESHAP in light of decisions made specific to the PCWP source category. The PCWP NESHAP is being promulgated by the February 2004 court ordered deadline. Any delays in implementation of the PCWP NESHAP caused by legal challenges are beyond our control.

2. Legal authority a. Section 112( d)( 4)

Comment: We received multiple comments stating that section 112( d)( 4) provides EPA with authority to exclude sources that emit threshold pollutants from regulation. The commenters cited the language in section 112( d)( 4) and CAA legislative history.

The commenters pointed out that EPA exercised its section 112( d)( 4) authority previously in choosing not to impose control requirements on hydrogen chloride ( HCl) emissions from chemical recovery furnaces at pulp mills ( 40 CFR Part 63, Subpart MM, See 63 FR 18754, 18765 ( April 15, 1998)).

We also received multiple comments disagreeing that section 112( d)( 4) can be interpreted to allow exemptions for individual sources. The commenters argued that section 112( d)( 4) applies only to categories or subcategories of sources and not to individual sources. These commenters also cited the language of section 112( d)( 4) and CAA legislative history. The commenters interpreted section 112( d)( 4) to state that health based thresholds can be considered when establishing the degree of the 22 MACT floor requirements, but they should not be used in lieu of the requirements established pursuant to section 112( d)( 3). One commenter also argued that the third scenario suggested by EPA   application of section 112( d)( 4) exemption to emission points within a facility   is unlawful because there is no statutory provision within the CAA to authorize emission point by point exemption.

Several commenters supported the use of section 112( d)( 4)

applicability cutoffs for both threshold and non threshold pollutants and believe that a health threshold of one in a million cancer risk is appropriate for non threshold pollutants.

The commenters interpreted the language in section 112( d)( 4) to mean EPA may issue standards for any pollutant for which a threshold may be established. The commenters believe that EPA could use its section 112( d)( 4) authority to establish a " threshold" risk of one in a million for non threshold carcinogens. The commenters also believe that section 112( d)( 4)

may be properly applied to carcinogenic HAP that EPA determines have a threshold of safe exposure. The commenters noted that the current health science for formaldehyde and aceteladehyde shows that these two HAP are threshold carcinogens that are emitted from wood products facilities at levels that will not pose a significant risk to human health.

Multiple other commenters stated that section 112( d)( 4) does not apply for source categories that emit carcinogens. The 23 commenters argued that EPA may only use the section 112( d)( 4)

authority for pollutants with a well established health threshold. The commenters stated that section 112( d)( 4) only allows EPA to substitute a health threshold for a MACT standard when the threshold " has been established." The commenters contended that Congress did not intend for EPA to spend time determining if a threshold exists and that it was Congress'

intent that EPA have a high degree of scientific certainty before using its section 112( d)( 4) authority. The commenters cited legislative history. ( See S. Rep. 101 228 at 171.) The commenters also stated that Congress specified that EPA must have direct evidence of no effects, i. e., use of a no observable effects level ( NOEL), before invoking section 112( d)( 4); thus,

EPA must be sure that there are no effects from exposure at the level chosen for the emission standard. The commenters further argued that all carcinogens must be treated as non threshold pollutants and noted that the history of the 1990 CAA Amendments shows that Congress legislated with an understanding that carcinogens do not have a safe threshold.

Response: We acknowledge the commenters' arguments regarding our discussion in the PCWP proposal preamble regarding potential applicability cutoffs for threshold pollutants under the authority of section 112( d)( 4) of the CAA. We believe that section 112( d)( 4) does not give us the authority to exempt facilities or emission points from MACT limitations on non 24 threshold pollutant emissions. All PCWP facilities emit carcinogens ( e. g., formaldehyde), which are currently considered non threshold pollutants. Therefore, we are not using section 112( d)( 4) authority to create risk based options for PCWP. We do not expect to further explore the use of section 112( d)( 4) of the CAA to exempt PCWP facilities from the MACT floor on a case by case basis or to set alternative standards, because PCWP facilities emit HAP for which no health thresholds have been established and because the legislative history to the 1990 Amendments to the CAA indicates that Congress considered and rejected allowing us to grant such source specific exemptions from the MACT floor. ( See, e. g., 1 Legis. Hist. at 866, 877; 2 Legis. Hist. at 2141 42, 3939.) As discussed below, we are establishing and delisting a subcategory of low risk PCWP facilities using our authority under CAA sections 112( c)( 1) and ( 9).

We are establishing criteria in today's final PCWP rule that define a low risk subcategory of PCWP facilities, which requires demonstration that a facility warrants being included in this subcategory. The criteria are not included in the rule as " emission standards" or " emission limits" but are included in an appendix to the rule that specifies how facilities must make their low risk demonstrations and the steps that facilities must take to ensure that they remain in the low risk subcategory. We are not setting a risk based emission limit, but, rather, we are 25 using our section 112( c)( 9) authority to delist facilities that demonstrate they meet the risk and hazard criteria for being included in this low risk subcategory.

b. De minimis Comment: Some commenters attempted to identify a source of authority for risk based approaches that was not discussed in the preamble to the proposed rule. The commenters stated that a risk based compliance option for both threshold and non threshold HAP is well within EPA's authority under the CAA and the de minimis doctrine articulated by appellate courts. The commenters cited appellate case law which they believe makes it clear that EPA may lawfully exempt de minimis sources of risk from MACT level controls because the legislative mandate of section 112 is not " extraordinarily rigid" and the exemption is consistent with the CAA's health protective purpose. The commenters also noted that sections 112( c)( 9) and 112( f)( 2)

indicate that Congress considered a cancer risk below one in a million to be de minimis and therefore insufficient to justify regulation under section 112. The commenters stated that ( and cited examples where) EPA's exercise of de minimis authority has withstood judicial challenge, and that application of de minimis authority ( as well as its treatment by reviewing courts) is based on the degree of risk at issue, not on the mass of emissions to be regulated. The commenters stated that the D. C. Circuit has 26 invalidated EPA's de minimis authority only where it was applied under statutory designs that are " extraordinarily rigid." The commenters stated that section 112 provides clear indication of Congressional intent as to the degree of risk that properly is to be considered de minimis. A cancer risk of one in a million triggers further review under the " residual" risk provision of section 112( f), and a one in a million cancer risk is the threshold below which EPA is authorized under section 112( c)( 9)( B) to remove source categories from MACT regulation.

One commenter attached a paper they developed entitled " Legal and Policy Basis for EPA's Exercise of Its De minimis Authority Under Section 112 of the Clean Air Act in the Context of the Wood Products MACT."

Other commenters argued that de minimis authority does not exist to create MACT exemptions on a facility by facility or category wide basis. In addition, the commenters stated that EPA lacks de minimis authority to delist subcategories based on risk.

The commenters cited case law and stated that EPA may not rely on its narrow de minimis exemption authority to escape the highly prescriptive provisions in section 112. The commenters further noted that EPA has not revealed any administrative record justifying a de minimis exemption, to demonstrate in any way that compliance with MACT would " yield a gain of trivial or no value."

Response: We disagree with the commenters who claimed that the low risk approaches, especially the concentration based 27 exemption, can be justified by de minimis principles. Our de minimis authority exists to help avoid excessive regulation of tiny amounts of pollutants, where regulation would yield a result contrary to a primary legislative goal. It is unavailable " where the regulatory function does provide benefits, in the sense of furthering the regulatory objectives, but the agency concludes that the acknowledged benefits are exceeded by the costs." EDF v. EPA, 82 F. 3d 451, 466 ( D. C. Cir. 1996); Public Citizen v.

Young, 831 F. 2d 1108, 1112 13 ( D. C. Cir. 1987); Alabama Power v.

EPA, 636 F. 2d 323, 360 61 & n. 89 ( D. C. Cir. 1979). Accordingly,

a de minimis exemption to section 112( d)( 3) is unavailable in today's final PCWP rule because it would frustrate a primary legislative goal by preventing application of the MACT floor to tons of PCWP facilities' HAP emissions.

The U. S. Court of Appeals for the District of Columbia Circuit has already addressed the de minimis concept in the MACT context, in National Lime Ass'n v. EPA, 233 F. 3d 625, 640 ( D. C.

Cir. 2000) ( National Lime), in which the court rejected the industry petitioner's claim that, in light of both the high costs and low quantities of HAP at issue in that case, we should read a de minimis exception into the requirement that it regulate all HAP emitted by major sources. In that case, the Court found that " EPA reasonably rejected this argument on the ground that the statute ` does not provide for exceptions from emissions standards based on de minimis principles where a MACT floor exists.'" ( See 28 National Lime at 640.) We recently re affirmed our position on the unavailability of de minimis exemptions from the MACT floor in the final rule regulating organic liquids distribution. ( See 69 FR 5038 ( February 3, 2004).)

We see no reason to revisit this fundamental issue. Section 112 of the CAA is replete with careful definitions of volume or effect based limitation on regulation, indicating that Congress has already defined what amounts of HAP emissions are too small to warrant MACT standards or other controls under section 112.

The requirement to adopt MACT emission limitations, for example,

applies without exception to " each category or subcategory of major sources... of [ HAP]." ( See CAA section 112( d)( 1).) For sources below the major source threshold, however, we have discretion to require " generally available control technologies or management practices." ( See CAA section 112( d)( 5).) Congress has, thus, itself defined volumetrically which sources' emissions are small enough not to warrant mandatory MACT standards.

Congress likewise defined several MACT exceptions applicable where emissions have de minimis health effects. Section 112( d)( 4) of the CAA allows us to establish standards less stringent than MACT for HAP with an established health threshold,

so long as we set a standard below the health threshold with " an ample margin of safety." Section 112( b)( 3)( C) of the CAA directs us to delist HAP   precluding section 112( d) MACT standards   if we determine that " there is adequate data on the health and 29 environmental effects of the substance to determine that emissions, ambient concentrations, bioaccumulation or deposition of the substance may not reasonably be anticipated to cause any adverse effects to the [ sic] human health or adverse environmental effects." Section 112( c)( 9)( B)( i) of the CAA ( discussed further below) lets us delete source categories and subcategories from the category list   the consequence again being no MACT control   if we determine that, for emissions of carcinogenic HAP, " no source in the category... emits such [ HAP]

in quantities which may cause a lifetime risk of cancer greater than one in one million to the individual in the population who is most exposed to emissions of such pollutant from the source."

For noncarcinogens, we may delete source categories and subcategories if we determine that " emissions from no source in the category or subcategory... exceed a level which is adequate to protect public health with an ample margin of safety and no adverse environmental effect will result from emissions from any source." ( See CAA section 112( c)( 9)( B)( ii).) Moreover, in defining which source modifications trigger additional regulatory standards, CAA section 112( g)( 1)( A) mentions a " greater than de minimis increase in actual emission of a [ HAP]." This shows that Congress knew how to use the de minimis concept when it considered it appropriate in section 112, and the fact that Congress did not use it in section 112( d)( 3) supports our   and the D. C. Circuit's   conclusion that it is unavailable to support 30 an exception to a MACT floor that is not otherwise authorized under section 112.

We do not find persuasive the proposition that the overall purpose of section 112 is protecting human health and the environment, and that, therefore, as long as this general purpose is met, we may fashion de minimis exceptions from MACT beyond those allowed under section 112. First, this position appears to assume that the issue is to be drawn on a clean slate, while the D. C. Circuit has affirmed our view that section 112( d)( 3)

provides no discretion to use a de minimis rationale to avoid MACT. Second, the commenter appears to give prominence to an over arching statutory goal over the specific language of the statutory provisions themselves, in assessing whether those provisions are " extraordinarily rigid" regarding EPA's otherwiseinherent de minimis authority; the logical extension of such an approach would be to find that no single provision in the CAA could restrict our de minimis authority, in light of the CAA's over arching purpose " to promote the public health and welfare."

( See CAA section 101( b)( 1).) Third, the commenter does not present any persuasive statutory arguments to overcome those that we presented to the court   and which the court affirmed   in National Lime. Fourth, we are unable to discern the basis for the commenter's suggestion that we have in fact been relying on de minimis authority in the MACT program for several years in establishing applicability thresholds, and we are not aware of 31 any instance in which we have explicitly justified an exception from an applicable MACT floor based on a de minimis rationale that would be, like the commenter's requested exemption, in contravention of the Court's ruling in NLA. Finally, to the extent the commenters believe such a de minimis exemption is justified by the wish to reduce the costs of the PCWP rule, we are not free to grant a de minimis exemption to account for costs. Congress already took cost into account in section 112( d), relying on prior business judgments by the best performing sources to substitute for the judgment of the rest of the PCWP industry, therefore, denying us the leeway to consider costs as a factor to modify the MACT floor. Only in considering more stringent " beyond floor" standards may we consider costs in the MACT context. Therefore, we do not believe it is appropriate or necessary to revisit our and the D. C. Circuit's prior conclusions regarding the availability of the de minimis principle in today's final PCWP rule.

c. Section 112( c)( 9)

Comment: Two commenters opposed using subcategorization as a mechanism to exempt facilities. One of the commenters stated that subcategorization is a tool that should be used in the standard setting process, and using it to exempt facilities would have a detrimental effect on the stringency of the MACT floor and would generally degrade the standard. According to the commenter, the two step subcategorization proposal is 32 inconsistent with how subcategorization has been done in numerous previous NESHAP.

The other commenter argued that EPA's subcategorization theories are unlawful. According to the commenter, section 112( c)( 9) does not authorize EPA to separate identical pollution sources into subcategories that are regulated differently to weed out low risk facilities or reduce the scope/ cost of the standard.

The commenter stated that subcategories based solely on risk do not bear a reasonable relationship to Congress' technology based approach or the statutory structure and purposes of section 112,

and are not authorized by the CAA. According to the commenter,

categories and subcategories are required to be consistent with the categories of stationary sources in section 111. The commenter was not aware of any instance in which EPA has established categories or subcategories based on risk. The commenter stated that EPA routinely defines subcategories based on equipment characteristics ( e. g., technical differences in emissions characteristics, processes, control device applicability, or opportunities for pollution prevention).

According to the commenter, EPA has not offered any explaination for why reinterpreting the statute to ignore nearly 12 years of settled practices and expectations under the MACT program is reasonable, nor why reducing the applicability of HAP emission standards serves Congress's goals in enacting the 1990 CAA Amendments. 33 The commenter noted that EPA's discussion of the risk based exemptions was contained in a preamble section entitled, " Can We Achieve the Goals of the Proposed Rule in a Less Costly Manner,"

which strongly suggests that EPA's motivation for considering these risk based approaches is consideration of cost. The commenter cited prior EPA documentation and stated that EPA in the past has rejected the notion that cost should influence MACT determination, and this prior, consistently applied interpretation better serves the purposes of section 112. The commenter argued that subcategorizing to set a no control MACT floor is the same as refusing to set a MACT standard because the benefits would be negligible, which is unlawful.

The commenter also stated that section 112( c)( 9)( B)( i) does not authorize EPA to delist subcategories. According to the commenter, section 112( c)( 9)( B) contains two subsections:

subsection ( i) refers only to categories, and subsection ( ii)

refers to both categories and subcategories. The commenter argued that the absence of the term " subcategories" in section 112( c)( 9)( B)( i) indicates a Congressional choice not to permit the Administrator to delist subcategories of sources under section 112( c)( 9)( B). The commenter stated that this is consistent with Congress' decision to require a higher standard to delist categories that emit carcinogens. According to the commenter, the section 112( c)( 9)( B)( ii) requirement of less than one in a million lifetime cancer risk for the most exposed 34 individual is a higher and more specific standard than the standard for other HAP.

To the contrary, two commenters stated that EPA has ample authority under sections 112( c)( 1) and 112( c)( 9) to create and delist low risk categories or subcategories. According to the commenters, section 112( c)( 1) provides the Administrator with significant flexibility to create categories and subcategories as needed to implement section 112. One commenter stated that there is nothing in the statute that limits the criteria the Administrator can use in establishing categories and subcategories. The commenter added that there is also nothing in the history of EPA's interpretation of section 112( c) that precludes subcategorization based on risk. In addition, EPA has stated that emission characteristics are factors to be considered when defining categories.

The commenter stated that application of statutory authority to exclude sources from regulation under section 112( d)( 3) is also supported by relevant case law, e. g., in the Vinyl Chloride case. ( NRDC v. EPA, 824 F. 2D 1126 ( D. C. Cir. 1987)) According to the commenter, the court in that case established a range of acceptable level of risk in establishing limits under prior language in section 112, and the establishment of an acceptable level of risk could be used to create a low risk subcategory that could be delisted. The commenter stated that technological or operational differences among sources may also help discriminate 35 between low risk and high risk sources. The commenter stated that effective use of section 112( c)( 1) authority to create riskbased subcategories would significantly improve the costeffectiveness of the section 112 program without undermining its role in protecting public health and the environment.

Both commenters noted that section 112( c)( 9)( B) provides EPA with broad authority to remove from MACT applicability those categories and subcategories of facilities whose HAP emissions are sufficiently low as to demonstrate a cancer risk less than one in a million to the most exposed individual in the population ( for non threshold carcinogens) and no adverse environmental or public health effect ( for threshold HAP). ( The commenter asserted that Congress used the terms category and subcategory interchangeably, indicating that either one can be delisted.)

One commenter suggested that sources able to demonstrate a basis for inclusion in the delisted category on a case by case basis would then be exempted from the MACT, subject to possible federally enforceable conditions designed by EPA. The commenter stated that the new category could include the following: all low risk facilities, facilities producing wood products found to pose no expected risk to human health ( i. e., fiberboard, medium density fiberboard and plywood), facilities with acrolein emissions below a certain threshold, or facilities selected on the basis of some other risk criterion. The commenter suggested that the low risk category be included in the final rule and 36 delisted within 6 months following publication of the final rule.

The delisting notices would designate health benchmarks and facilities would be required to submit evidence ( e. g., tiered dispersion modeling) demonstrating that their emissions result in exposures that fall below the benchmarks. Following delisting of the category, an affected source could apply to EPA for a determination that it qualifies for inclusion in the low risk category. After evaluating the source's petition, EPA would issue a written determination of applicability based on the petition that would be binding on the permitting authority ( unless the petition was found to contain significant errors or omissions) and appealable by the affected source or interested parties. The EPA could require all facilities that qualify for inclusion in the delisted category to comply with federally enforceable conditions, similar to the conditions established in permits for " synthetic minor" sources ( e. g.,

limits on potential to emit, production limits).

The commenter also responded to objections regarding the subcategorization and delisting of low risk facilities. The commenter stated that the contrasting of the terms " category" and " subcategory" offered a distinction that in no way limited EPA's authority to delist low risk facilities. According to the commenter, the argument that EPA cannot create subcategories based on risk is contradicted by the statutory language, which expressly states that the categories and subcategories EPA 37 creates under section 112 need not match those created under section 111. Furthermore, prior EPA statements do nothing to detract from EPA's broad discretion to establish categories and subcategories. The subcategorization factors previously discussed by EPA justify subcategorization based on risk. The authority cited by one commenter does not establish that EPA's discretion to alter subcategorization is limited in any way, and even if it were, EPA is not bound by any prior position. The arguments that EPA may not delist subcategories for carcinogens ( or sources emitting carcinogens) rest on a formalistic distinction that EPA previously has rejected as meaningless, and that, at any rate, can be remedied with a simple recasting of a subcategory as a category. The commenter stated that doing so is undisputedly within EPA's authority.

Three commenters addressed the issue of subcategorizing PCWP facilities based on characteristics other than risk. One commenter stated that the only option that appears consistent with the CAA, does not create excessive work for State and local agencies, and may be able to be based on science, is the subcategorization and delisting approach. However, the commenter added that the subcategories should be based on equipment or fuel use, not risk. The commenter stated that a subcategory based on site specific risk creates a circular definition and does not make sense. The commenter also stated that subcategory delisting should occur before the compliance date so that facilities don't 38 put off compliance in the hope or anticipation of delisting.

The second commenter stated that EPA requested comment on the establishment of PCWP subcategories ostensibly based on physical and operational characteristics, but in reality based on risk. According to the commenter, this indirect approach is just a variation on the approach ( direct reliance on risk) that EPA itself notes would disrupt and weaken establishment of MACT floors, and is accordingly unlawful. The commenter stated that,

even if these approaches were lawful, to the extent that EPA's proposal could be read to suggest that facilities could be allowed to become part of the allegedly low risk subcategory in the future without additional EPA rulemaking, this too would be unlawful. According to the commenter, section 112( c)( 9) provides the EPA Administrator alone the authority to make delisting determinations, and such authority may not be delegated to other government authorities or private parties. The commenter stated that EPA's proposal suggests an approach entirely backward from the statute   allowing sources to demonstrate after the fact that they belong in a subcategory that has been delisted under section 112( c)( 9), when the statute requires that EPA determine that no source in the category emits cancer causing HAP above specified levels, or that no source in the category or subcategory emit non carcinogenic HAP above specified levels, by the time EPA establishes the standard. The commenter stated that EPA has provided no explanation of how the suggested approaches would be 39 lawful or workable.

The third commenter indicated that low risk is an adequate and appropriate criterion for categorization. The commenter disagreed that EPA should create and delist categories on a technology basis when the intent is delisting of low risk facilities. The commenter believed that seeking a technology based surrogate for risk is unnecessary within the statutory framework. The commenter noted that the Congressional intent was " to avoid regulatory costs which would be without public health benefit." ( S. Rep. No. 228, 101st Cong., 1st.

Sess. 175 6 ( 1990)) Nevertheless, the commenter described some technology based criteria that they believed could be used to develop low risk groups of PCWP facilities.

Four commenters addressed the impact that creation of a lowrisk subcategory under CAA section 112( c)( 9) could have on the establishment of MACT floors for the PCWP category. Two commenters argued that such subcategorization would have a negative effect. One commenter stated that this situation provided a valid reason for EPA not to mix risk based and technology based standards development. The commenter added that EPA also did not address how the " once in, always in" policy would apply in such a situation. The other commenter stated that this situation was another compelling reason why the suggested section 112( c)( 9) subcategorization approach was unlawful and arbitrary. The commenter stated that the flaw was so obvious, 40 inherent, and contrary to the MACT floor provisions of section 112 and its legislative history, that it proves the undoing of the suggested section 112( c)( 9) exemption. According to the commenter, EPA cannot simultaneously exercise its source category delisting authority consistent with section 112( c)( 9), establish appropriate MACT floors under section 112( d), and establish subcategory exemptions in the manner suggested by EPA, because the latter approach contravenes both section 112( c)( 9) and the section 112( d) floor setting process. The commenter stated that section 112' s major source thresholds and statutory deadlines make clear that sources meeting MACT by the time EPA is required to issue MACT standards must install MACT controls and may not subsequently throw them off or be relieved from meeting the MACT level standards. While the section 112( f) residual risk process allows EPA to establish more stringent emissions standards, there is nothing in the CAA that suggests EPA possesses authority to relax promulgated MACT standards.

The third commenter indicated that dilution of the MACT floor would not occur if low risk category delisting occurred as follows: ( 1) propose low risk category with final PCWP rule, ( 2)

promulgate low risk category 6 months after proposal, and ( 3)

delist facilities prior to MACT compliance deadline. If EPA issued the final PCWP rule   thereby setting the MACT floor   before it allowed affected sources to apply for inclusion in the low risk category to be delisted, then every affected source 41 would be considered in the establishment of the MACT floor.

Thus, as a result of this timing, the MACT floor could not be diluted because no sources would be exempted from MACT before the MACT floor is set.

The fourth commenter believed that a MACT floor reevaluation would be appropriate and would further ensure that only facilities posing significant risk are required to install expensive controls.

Response: We believe that establishing a " low risk" PCWP subcategory under CAA section 112( c)( 1) and deleting that subcategory under CAA section 112( c)( 9) best balances Congress'

dual concerns that categories and subcategories of major sources of HAP be subject to technology based ( and possible future riskbased emission standards, but that undue burdens not be placed on groups of sources within the PCWP source category whose HAP emissions are demonstrated to present little risk to public health and the environment. We do not contend that the CAA specifically directs us to establish categories and subcategories of HAP sources based on risk, and we recognize that, at the time of the 1990 CAA Amendments, Congress may have assumed that we would generally base categories and subcategories on the traditional technological, process, output, and product factors that had been considered under CAA section 111. However, when properly considered, it becomes apparent that Congress did not intend the unduly restrictive   and consequently over 42 regulatory   reading of the CAA that some commenters urge regarding low risk PCWP facilities.

Numerous CAA section 112 provisions evidence Congress'

intent that we be able to find that sources, such as those in the PCWP category whose HAP emissions are below identified risk levels, should not necessarily be subject to MACT. These provisions, together with other indications of Congressional intent regarding the goals of section 112, must all be considered in determining whether we may base a PCWP subcategory on risk and delist that group of sources, without requiring additional HAP regulation that would be redundant for purposes of meeting Congress' risk based goals.

While it is true that CAA section 112( c)( 1) provides that "[ t] o the extent practicable, the categories and subcategories listed under this subsection shall be consistent with the list of source categories established pursuant to section 111 and part C[,]" the provision also states that "[ n] othing in the preceding sentence limits the Administrator's authority to establish subcategories under this section, as appropriate." Therefore, by its plain terms, section 112( c)( 1) does not preclude basing subcategories on criteria other than those traditionally used under section 111 before 1990, or those used after 1990 for sections 111 and 112. Moreover, while after 1990 we have principally used the traditional criteria to define categories and subcategories, such use in general does not restrict how we 43 may define a subcategory in a specific case, " as appropriate,"

since each HAP emitting industry presents its own unique situation and factors to be considered. ( See, e. g., Sierra Club v. EPA, D. C. Cir. No. 02 1253, 2004 U. S. App. LEXIS 348 ( decided Jan. 13, 2004).)

Even assuming for argument that the language of section 112( c)( 1) may initially appear to restrict our authority to define subcategories, section 112( c)( 1) cannot be read in isolation. A broad review of the entire text, structure, and purpose of the statute, as well as Congressional intent shows that, applied within the context of CAA section 112( c)( 9), our approach of defining a low risk subcategory of PCWP facilities is reasonable, at the very least as a way to reconcile the possible tension between the arguably restrictive language of section 112( c)( 1) and the Congressional intent behind section 112( c)( 9).

( See, e. g., Virginia v. Browner, 80 F. 3d 869, 879 ( 4th Cir.

1996).) Alternatively, even if the language is clear on its face in restricting our ability to define subcategories, we believe that, as a matter of historical fact, Congress could not have meant what the commenter asserts it appears to have said, and that as a matter of logic and statutory structure, it almost surely could not have meant it. ( See, e. g., Engine Mfrs. Ass'n 44 v. EPA, 88 F. 3d 1075, 1089 ( D. C. Cir. 1996).)

Our interpretation of the CAA is a reasonable accommodation of the statutory language and Congressional intent regarding the relationship of the statutory categorization and subcategorization, delisting, MACT and residual risk provisions that apply to the PCWP category. This becomes clear in light of the issue addressed by commenters, which is whether we may delist a subcategory of low risk PCWP facilities only if such a group of sources is defined by criteria we have traditionally used to define categories and subcategories for regulatory, rather than delisting purposes. Our approach implements Congressional intent to avoid the over regulatory result that flows from an overly rigid reading of the CAA. When the CAA is read as a whole, it is apparent that Congress   which in 1990 likely did not fully anticipate the policy considerations that come into play in regulating HAP emissions from PCWP facilities   has not spoken clearly on the precise issue. Our interpretation is necessary to fill this statutory " gap" and prevent the thwarting of Congressional intent not to unnecessarily burden low risk PCWP facilities by forcing them to meet stringent MACT controls when they already meet the risk based goals of section 112. Our interpretation thus lends symmetry and coherence to the statutory scheme.

While we do not believe section 112( c)( 1) actually restricts our authority to establish a low risk PCWP subcategory, even if 45 the language is so restrictive, it must be read within the context of Congress' purpose in allowing us to delist categories and subcategories of low risk sources that are defined according to the traditional criteria under section 111. It is beyond dispute that Congress determined that certain identifiable groups or sets of sources may be delisted if, as a group and without a single constituent source's exception, they are below the enumerated eligibility criteria of section 112( c)( 9). There is no apparent reason why such a group or set of sources must be limited to those defined by traditional categorization or subcategorization criteria. This is because, first, Congress in section 112( c)( 1) clearly did not absolutely prohibit us from basing categories and subcategories on other criteria generally;

and, second, the underlying characteristic of an eligible set or group of sources under section 112( c)( 9)   that no source in the set or group presents risks above the enumerated levels   can be applied under several approaches to defining categories and subcategories and is not dependent upon such set or group being traditionally defined in order to implement the purpose of section 112( c)( 9). Put another way, there is nothing apparent in the statute that precludes us from delisting a discernible set of low risk PCWP facilities just because that set cannot also be defined according to other traditional criteria that have nothing to do with the question of whether each of the constituent PCWP facilities is low risk. As a matter of logic and statutory 46 structure, Congress almost surely could not have meant to require that every identifiable group of low risk PCWP facilities, no matter how large in number or in percentage with respect to higher risk facilities in the PCWP category, must remain subject to section 112, simply because that group could not be subcategorized as separate from the higher risk PCWP facilities by application of traditional subcategorization criteria.

Where Congress squarely confronted the issue, it explicitly provided relief for categories and subcategories, defined by traditional criteria, that also happen to present little risk.

( See CAA sections 112( d)( 4), 112( c)( 9), and 112( f)( 2).) These CAA provisions addressing risk based relief from, or thresholds for, HAP emissions regulation evidence Congressional concern that the effects of such pollution be taken into account, where appropriate, in determining whether regulation under section 112 is necessary. At the time of the 1990 Amendments, Congress did not consider it necessary to provide express relief for additional groups such as low risk PCWP facilities, beyond those defined by traditional category and subcategory criteria, because it assumed we could implement a comprehensive regulatory scheme for air toxics that would both address situations where technology based standards were needed to reduce source HAP emissions to levels closer to the risk based goals of section 112, and avoid unnecessary imposition of technology based requirements on groups of sources that were already meeting those 47 goals. Congress enacted or revised various CAA air toxics provisions   including sections 112( c), ( d) and ( f)   to that end. Had events unfolded in that anticipated fashion, in the case of each industrial category and subcategory, there would have been a perfect correlation between the traditional criteria for defining categories and subcategories and the facts showing whether those groups are either high or low risk HAP sources.

This context turned out to be more complex than Congress anticipated, and in the case of PCWP facilities there is no clear differentiation between high versus low risk sources that corresponds to our traditional approach for identifying source categories and subcategories. Nevertheless, as in the case of a low risk source group defined by traditional category or subcategory criteria, for the PCWP industry, we are able to identify a significant group of sources whose HAP emissions pose little risk to public health and the environment, applying the same section 112( c)( 9) delisting criteria that would apply to any traditionally defined source group. We believe it is reasonable to conclude that Congress would not have intended to overregulate the low risk PCWP facilities due to the inability to define such a group by traditional criteria and thereby frustrate the coherent scheme Congress set forth of ensuring that HAP sources ultimately meet common risk based goals under section 112.

The commenter's assertion that we are inappropriately 48 altering our interpretation of the applicable statutory provisions and departing from the traditional categorization and subcategorization criteria in addressing low risk PCWP facilities is thus unfounded. As explained above, the complexity of the air toxics problem and the relationship between the traditional criteria and what might be groups of low risk sources, a context not fully understood by either Congress or EPA at the time of the 1990 Amendments, provides adequate justification for any unique applications of the our approach for low risk PCWP facilities.

Our approach does not equate to one that Congress considered and rejected that would have allowed source by source exemptions from MACT based on individualized demonstrations that such sources are low risk. This is because, contrary to that approach, we rely upon the application of specific eligibility criteria that are defined in advance of any source's application to be included in the low risk PCWP subcategory, in much the same way as any other applicability determination process works.

Moreover, in response to the assertion that our approach nevertheless conflicts with legislative history rejecting a similar ( but not identical) approach Congress considered under section 112, this legislative history is not substantive legislative history demonstrating that Congress voted against relief from MACT in this situation   there is no such history. The commenters point to a provision in the House bill that was not enacted but that would have provided in certain situations for 49 case by case exemptions for low risk sources. There is no evidence that this provision was ever debated, considered, or voted upon, so its not being enacted is not probative of congressional intent concerning our ability to identify and delist a group of low risk PCWP facilities. Instead, it is reasonable to assume that, had Congress been aware in 1990 of the possibility that an identifiable group of PCWP facilities is lowrisk while that group does not correspond to traditional criteria differentiating categories and subcategories, Congress would have expressly, rather than implicitly, authorized our action here.

Moreover, the commenters are unable to cite any provision in CAA section 112 that would prevent us from being able to add individual or additional groups of low risk PCWP facilities to the group we initially identify in our final delisting action, as those additional low risk PCWP facilities prove their eligibility for inclusion in the delisted group over time. In fact, the approach we are taking for identifying additional low risk PCWP facilities is fully consistent with the approach we have long taken in identifying, on a case by case basis and subject to appropriate review, whether individual sources are members of a category or subcategory subject to standards adopted under CAA sections 111 and 112.

Regarding the comment that Congress did not expressly provide relief for carcinogen emitting low risk groups of sources 50 within the PCWP category other than as an entire category, we construe the provisions of section 112( c)( 9) to apply to listed subcategories as well as to categories. This construction is logical in the context of the general regulatory scheme established by the statute, and it is the most reasonable one because section 112( c)( 9)( B)( ii) expressly refers to subcategories. Under a literal reading of section 112( c)( 9)( B),

no subcategory could ever be delisted, notwithstanding the explicit reference to subcategories, since the introductory language of section 112( c)( 9)( B) provides explicit authority to only delist categories. Such a reading makes no sense, at the very least because Congress plainly assumed we might also delist another collection of sources besides either categories or subcategories, even in the case of sources of carcinogens. Both sections 112( c)( 9)( B)( i) and ( ii) refer additionally to " groups of sources in the case of area sources" as being eligible for delisting, even though only a " category" of sources is specifically identified as eligible for delisting in the introductory language of section 112( c)( 9)( B). In light of the broader congressional purpose behind the delisting authority, we interpret the absence of explicit references to subcategories in this introductory language and in section 112( c)( 9)( B)( i) as representing nothing more than a drafting error.

Regarding the comments about establishing PCWP subcategories based on characteristics other than risk, the criteria for the 51 low risk subcategory we are proposing to delist are based solely on risk and not on technological differences in equipment or emissions. We performed an analysis to determine which major source PCWP facilities may be low risk facilities. Whether facilities are low risk or not depends on the facility HAP emissions; and facility HAP emissions are a function of the type and amount of product( s) produced, the type of process units ( e. g., direct fired versus indirect fired dryers) used to produce the product, and the emission control systems in place. Our analysis indicates that the facilities which show low risk include facilities producing particleboard, molded particleboard,

medium density fiberboard, softwood plywood, softwood veneer,

fiberboard, engineered wood products, hardboard, and oriented strandboard.

However, there are also major sources that produce these products that are not low risk, and therefore,

product type cannot be used to define the low risk subcategory.

There is no correlation between production rate and low risk facilities ( e. g., when facilities are sorted by production rate for their product, the low risk facilities are not always at the lower end of the production rate range), so production rate cannot be used as criteria for defining the low risk subcategory.

The low risk facilities use a variety of process equipment ( e. g.,

veneer dryers at softwood plywood plants and tube dryer at MDF 52 plants). This same equipment is used at PCWP plants that are not low risk, and therefore, there is no process unit type distinction that can be used to define the low risk subcategory.

The pollutant that drives the risk estimate can vary from facility to facility because of the different types of process units at each facility. There is no clear distinction among lowrisk and non low risk facilities when ranked by emissions of individual pollutants because of other factors that contribute to facility risk such as presence of a co located PCWP facility or variability in the pollutants emitted. Thus, there is no emissions distinction that can be used to define the low risk subcategory. There is no technological basis for creating a subcategory of PCWP facilities that are low risk. The commonality between all of the low risk PCWP facilities is that they are low risk, and, therefore, we have established the lowrisk subcategory based on risk.

We do not agree with the commenters' assertions that our approach for the low risk PCWP subcategory undermines our ability to identify the MACT floor for the larger PCWP category, either in today's final PCWP rule or in any future consideration of technological development under section 112( d)( 6). This is because, while low risk PCWP facilities will literally be part of a separate subcategory, there is nothing in the CAA that prevents us from including them in any consideration of what represents the " best controlled similar source" in the new source MACT floor 53 context, and because it is not unprecedented for us to look outside the relevant category or subcategory in identifying the " average emission limitation achieved" by the best controlled existing sources if doing so enables us to best estimate what the relevant existing sources have achieved. In fact, EPA has taken this very approach in the Industrial Boilers MACT rulemaking, in order to identify the MACT floor for mercury emissions.

Moreover, the unique issues presented by the low risk PCWP subcategory show that it would be unreasonable to exclude any better performing low risk PCWP sources from the MACT floor pool for the larger PCWP category. Traditionally, EPA has based categories and subcategories partly on determinations of what pollution control measures can be applied to the relevant groups of sources in order to effectively and achievably reduce HAP. In other words, EPA has identified subcategories for purposes of identifying the MACT floor in a way that accounts for the differences of sources types in their abilities to control HAP emissions. But whether a PCWP source is a low risk source does not necessarily turn on such a distinction   two sources might have identical abilities to control HAP emissions, but the unique circumstances of one source regarding the impacts of its HAP emissions will determine whether or not it is a low risk PCWP source. ( In fact, it is theoretically possible that between two sources the better performing source will be a high risk source,

and the worse performing source will be a low risk source, based 54 on circumstances that are unrelated to the question of what abilities the sources have to control HAP emissions through application of MACT, such as the sources' locations vis a vis exposed human populations.) Therefore, EPA believes that not only is it appropriate to include any better performing low risk PCWP sources in the MACT floor determinations for the larger PCWP category, but that excluding such sources simply based on the unique facts of the impacts of their emissions, with there being no difference in the abilities of high risk and low risk sources to apply HAP emission control measures, would be an unlawful weakening of the MACT floor for the larger PCWP category. To that end, the MACT floors established for PCWP process units today are in no way affected by our establishment of the low risk PCWP subcategory.

Finally, we disagree with the argument by one commenter that the low risk PCWP subcategory approach represents an impermissible cost based exemption from MACT or factor in determining MACT. Certainly it is true that costs may not be considered in setting the MACT floor. However, there is nothing in the CAA that prevents us from noting the cost impacts,

beneficial or adverse, of our actions in setting MACT floors,

assessing possible beyond the floor measures, or conducting riskbased actions under section 112. In fact, we routinely evaluate the costs of our regulatory actions, even when cost factors may not be used to influence the regulatory decision itself, in order 55 to comply with applicable Executive Order and statutory administrative review requirements. Simply because there is a cost benefit to some members of the PCWP category in our establishing a low risk PCWP subcategory does not make that action impermissible, provided that our subcategorization and delisting are otherwise properly based on the appropriate riskbased criteria under section 112( c)( 9). Section 112 by its own terms does not forbid the goal of achieving environmental protection in a less costly manner. Similarly, it is appropriate for EPA to note the beneficial air pollution related impacts of not requiring low risk PCWP sources to, for example, install criteria pollutant emission producing RTOs. While it is true that such air quality related impacts could not constitute "

nonair quality health and environmental impacts" that EPA must consider when setting MACT under CAA section 112( d)( 2), nothing in the CAA prevents EPA from taking account of such impacts in developing its policy regarding whether it is appropriate to delist a subcategory under section 112( c)( 9) when that subcategory otherwise meets the statutory criteria for de listing.

Therefore, EPA does not agree with commenters who claim that its approach to delisting the low risk PCWP subcategory conflicts with how it has argued issues regarding either de minimis authority, cost based exemptions from MACT, or the treatment of non air quality impacts and the consideration of risk in setting the actual MACT standard before the U. S. Court of Appeals for the 56 D. C. Circuit. Nor does our approach contravene any of that Court's rulings on these issues.

3. Criteria for demonstrating low risk a. Dose response values Comment: Two commenters suggested that EPA incorporate into the PCWP rule the findings of the nationwide wood products risk assessment, which demonstrates that the vast majority of wood products sources cause no meaningful risk to human health or the environment at current emission levels. The commenters stated that the risk assessment used existing air dispersion modeling studies of 34 wood products facilities throughout the U. S. to estimate the maximum annual off site HAP concentrations at wood products facilities nationwide. According to the commenters, the risk assessment indicates that large subgroups of facilities that are affected sources under the PCWP rule ( i. e., fiberboard,

medium density fiberboard, and plywood facilities) generally are expected to pose insignificant risks to human health, based on a comparison of predicted off site concentrations with applicable health benchmarks. One of the commenters stated that many of the facilities with low off site concentrations will likely be smaller plants that would not be able to justify installation of ( additional) emission controls and may face closure without a risk based compliance option. The other commenter stated that a comparison of off site concentrations of formaldehyde and 57 acetaldehyde with benchmarks reflecting the latest toxicological evidence indicates that exposures to those HAP are well below levels of concern. Acrolein was the only HAP with potential exposures at some facilities ( i. e., subset of fiberboard, medium density fiberboard and plywood facilities) that exceeded the health benchmark. However, the commenter stated that the acrolein findings may not represent an actual risk to human health because exceedences of the benchmark may be attributable to EPA averaging a large number of non detects at one half the detection limit, thereby artificially increasing predicted acrolein emissions. Based on these overall findings, the commenter concluded that the wood products risk assessment indicates that incinerator control is not warranted on the basis of human health concerns for a large number of facilities.

Response: We acknowledge receipt of the industry sponsored nationwide wood products MACT risk assessment submitted by the commenter. However, we conducted our own risk analysis to evaluate the merits of including a low risk subcategory in today's final PCWP rule. The methodology used in our risk analysis differed widely from the methodology used in industry's risk assessment. For example, industry's risk assessment was based on previously conducted air dispersion modeling studies for 34 PCWP facilities, while our analysis used emission estimates developed for each PCWP facility believed to be a major source of HAP. We used different ( generally more protective) human health 58 benchmarks in our risk assessment than were used in industry's risk assessment. We also considered all HAP ( including metal HAP) in our risk analysis, whereas industry's risk assessment considered only methanol, formaldehyde, acetaldehyde, acrolein,

phenol, and propionaldehyde.

Based on our risk analysis, we conclude that HAP emissions from some PCWP facilities pose little risk to human health and the environment. Therefore, we have included a subcategory of low risk PCWP facilities in today's final PCWP rule. Appendix B to Subpart DDDD includes procedures that facilities may use to demonstrate that they are part of the low risk subcategory, and,

therefore, are not subject to the compliance options included in today's final PCWP rule. To demonstrate eligibility for the lowrisk subcategory, facilities must first conduct emissions testing for up to 13 pollutants ( 5 organic HAP from all process units, 7 metal HAP from direct fired process units, and MDI from presses processing product containing MDI resin). The rationale for selection of these 13 pollutants is described elsewhere in this section. Facilities must use the results from emissions testing to determine if they are part of the low risk subcategory using either a look up table analysis ( based on the look up tables included in Appendix B to Subpart DDDD) or site specific risk assessment methodology ( described in Appendix B to Subpart DDDD and the " Air Toxics Risk Assessment Reference Library") and risk benchmarks ( described in Appendix B to Subpart DDDD). 59 Regarding acrolein, the commenter is correct in that, when developing AP 42 emission factors, we used a value of one half the detection limit for all non detect sample runs if acrolein was detected in any sample runs from the applicable source category. Acrolein has been detected in process unit emissions from all sectors of the PCWP industry, except for hardwood plywood manufacturing. When using emission factors to estimate emissions from PCWP facilities, we did not estimate emissions of a pollutant when all of the emissions test runs were non detect.

However, we did use emission factors that included a mixture of detectable values and values based on one half of the method detection limit ( MDL) when acrolein was detected at least once for a particular type of process unit. We maintain that this approach to handling non detects is appropriate for the purposes that we used the emissions data. Facilities will conduct emissions tests instead of using emission factors to demonstrate eligibility for the low risk subcategory. To prevent facilities from including HAP that are not detected in their low risk demonstrations, Appendix B to Subpart DDDD states that facilities may use zero for non detects when all of the emission test runs are below the MDL, provided that certain criteria to ensure that emissions testing and analysis procedures are adequate to detect low concentrations of HAP.

Comment: One commenter stated that section 112( d)( 4) is 60 particularly ill suited to the PCWP and industrial boiler source categories. The commenter stated that, even if EPA had authority to create individualized MACT exemptions based on health thresholds, it could not do so if there is insufficient evidence on the pollutants emitted to establish a NOEL. According to the commenter, section 112( d)( 4) does not apply for chemicals that do not have a well defined threshold based on reliable science. The commenter stated that available evidence does not establish a noeffect threshold for acetaldehyde, acrolein, benzene, carbon tetrachloride, chloroform, formaldehyde, manganese, methylene chloride, and phenol. As rationale, the commenter presented a summary of the available health effects data for each of these pollutants.

Response: As stated elsewhere in this preamble, we are not pursuing establishment of a threshold emission rate for the PCWP source category under section 112( d)( 4) because PCWP facilities emit non threshold pollutants. Therefore, this comment is irrelevant in the context of the PCWP rule. Comments pertaining to the Industrial/ Commercial/ Institutional Boilers and Process Heaters NESHAP are addressed in the comment response document for that rule. ( See Docket ID No. OAR 2002 0058.)

Comment: Two commenters expressed concern about the health benchmark data sources that EPA used. The first commenter argued that the proposal inappropriately used draft guidelines and toxicity profiles that had not been subject to public review 61 and/ or were not publicly available. The commenter was particularly concerned with the use of non linear carcinogenic risk values and toxicity profiles ( for HAP) that have not been finalized and are not available for review by the public.

The second commenter argued that EPA should not rely solely on the health benchmarks in its Integrated Risk Information System ( IRIS) database. The commenter stated that IRIS, while useful for obtaining information about the health effects of chemicals, is far from definitive, as EPA resource constraints have resulted in many chemical summaries that are significantly outdated and do not reflect the most recent scientific developments. Moreover, the commenter stated that the IRIS database is a non statutory, in house EPA activity, and IRIS entries are not subject to formal notice and comment. The commenter noted that EPA management has repeatedly emphasized in directives that other information must be considered, in addition to the IRIS database, when evaluating the health effects of chemicals in a regulatory context. The commenter concluded that EPA must use a scientifically appropriate health benchmark based on a consideration of all relevant information to ensure that the health benchmark is up to date and scientifically credible, even if that means departing from the value in IRIS.

A third commenter agreed with EPA's choice to derive their data from IRIS, California EPA ( CalEPA), and Agency for Toxic Substances and Disease Registry ( ATSDR) for its documentation for 62 1U. S. Environmental Protection Agency. 1999. Residual Risk Report to Congress. Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711, March 1999, EPA 453/ R 99 001; available at http:// www. epa. gov/ ttn/ oarpg/ t3/ meta/ m8690. html. ( EPA 1999) establishing risk based threshold and non threshold values. The commenter added that almost all HAP are being reviewed and reevaluated on a regular basis, and it would be inappropriate to single out formaldehyde and acetaldehyde at this time. The commenter stated that EPA can only rely on what is currently published and has underdone either peer review or EPA review.

According to the commenter, the issue of changing health based guideline values will always be a concern once health based regulations are promulgated.

Response: We agree with the first two commenters that we should use the best available sources of health effects information for risk or hazard determinations. As we have stated previously, we will not be relying exclusively on IRIS values,