Review of historic data supports identification of the Jones Ranch monitor as the monitoring location where the highest concentrations are recorded among the network of monitoring locations selected to measure the impact of smelterrelated emissions on ambient air quality. We note that the Jones Ranch monitoring site was determined to be the ``limiting site'' for the purposes of establishing emissions limits for the smelter. ADEQ closed its monitoring site at Jones Ranch in 1994, and while PhelpsDodge continues to operate an SO2 monitor at that site, the data is not recorded in AQS.\3\ In 1995, ADEQ began monitoring at the Ridgeline site, and no exceedances have ever been recorded there.
\3\ ADEQ has committed to working with PhelpsDodge to begin entering SO2 monitoring data collected at the Jones Ranch site to AQS beginning with the first quarter of 2008. See letter from Nancy C. Wrona, Director, Air Quality Division, ADEQ, to Deborah Jordan, Air Division Director, EPARegion IX, dated October 18, 2006.

Based on a review of the data from the Miami SO2 Maintenance Plan as well as tables 2 and 3 presented above, we find that the Miami nonattainment area has attained the SO2 NAAQS and thereby meets the first criterion for redesignation. Our conclusion is based on six basic interrelated facts:

Under CAA section 107(d)(3)(E)(ii), the SIP for the Miami area must be fully approved under CAA section 110(k) of the Act. We examined the applicable SIP for Arizona and also looked at the disapprovals listed in 40 CFR 52.125 and have determined that no disapprovals listed remain relevant to the applicable SIP. Arizona has a fully approved SIP with respect to SO2 in the Miami area.
C. The Improvement in Air Quality Must Be Due to Permanent and Enforceable Reductions in Emissions

CAA section 107(d)(3)(E)(iii) requires that EPA determine that the improvement in air quality is due to permanent and enforceable reductions in emissions resulting from implementation of the SIP and/or applicable federal measures. Figure 6.1 of the Miami SO2 Maintenance Plan (as amended in ADEQ's submittal dated June 30, 2004) illustrates the significant decline in emissions from the Miami smelter since the 1970's in inverse proportion to the level of control over smelter emissions sources.

Control over the smelter's SO2 emissions has been made permanent and enforceable through EPA approval of State rules limiting such emissions as a revision to the Arizona SIP (specifically, R182 715, R182715.01, R182715.02, and R182Appendix 8) and through ADEQ's issuance of a title V permit for the Miami smelter. Arizona's primary copper smelter rules and ADEQ's title V permit contain enforceable emission limitations that cap emissions at a level that has been shown to be protective of the NAAQS. Any relaxation to the SIP approved limits must be approved by EPA as a revision to the Arizona SIP, and EPA may not approve any such SIP revision without a demonstration that the relaxation in the limits would not interfere with attainment or maintenance of the NAAQS. See CAA section 110(l). Therefore, we find that the improvement in ambient SO2 concentrations in the Miami, AZ area is due to permanent and enforceable reductions in emissions resulting from implementation of the SIP.
D. The Area Must Have Met All Applicable Requirements Under Section 110 and Part D

Under CAA section 107(d)(3)(E)(v), we must determine whether the State of Arizona has met all requirements under section 110 and under part D (of title I) of the CAA applicable to the Miami SO2 nonattainment area.

1. Section 110 Requirements

CAA section 110 contains the general requirements for SIPs (enforceable emissions limits, ambient monitoring, permitting of new sources, adequate funding, etc.). EPA's guidance for implementing section 110 of the Act is discussed in the General Preamble to Title I (57 FR 13498, April 16, 1992). Over the years, we have approved Arizona's SIP as meeting these basic requirements. The SIP includes enforceable emission limitations; requires monitoring, compiling, and analyzing of ambient air quality data; requires preconstruction review of new
[[Page 3067]]
major stationary sources and major modifications to existing ones; provides for adequate funding, staff, and associated resources necessary to implement its requirements; and requires stationary source emission monitoring and reporting.

2. Part D Requirements

Before an area can be redesignated to attainment, it must have fulfilled the applicable requirements under part D (of title I). For this area, the relevant requirements are found in subparts 1 and 5 of part D. Subpart 1 of part D specifies the basic requirements applicable to all nonattainment areas. Subpart 5 sets out additional provisions for areas designated nonattainment for SO2. As discussed below, EPA finds that Arizona has met the requirements of subpart 1 of part D, specifically sections 172(c) and 176, and subpart 5 as applicable for the Miami SO2 nonattainment area. a. Section 172

CAA section 172 contains the general requirements for nonattainment SIPs. A thorough discussion of the requirements of 172(c) can be found in the General Preamble for the implementation of title I (57 FR 13498, April 16, 1992). Additional guidance can be found in the Calcagni memo.

EPA has interpreted the requirements of CAA sections 172(c)(2) (reasonable further progressRFP), 172(c)(6) (other measures), and 172(c)(9) (contingency measures) as not relevant to a redesignation request because they only have meaning for an area that is not attaining the standard (see the General Preamble and the Calcagni Memo), and as discussed above in section IV.A. of this notice, we find that the Miami area is attaining the SO2 standard. Furthermore, the State has not sought to exercise options that would trigger section 172(c)(4) (identification of certain emissions increases). Thus, this provision is also not relevant to this redesignation request. The other provisions under 172(c) are discussed below.

Reasonably available control measures. Under CAA section 172(c)(1), reasonably available control measures (RACM), which include requirements for reasonably available control technology (RACT), are required for existing sources in nonattainment areas. In 1983, we approved the State's submittal of Rule R93315, a predecessor to the State's current smelter rules codified at Arizona Administrative Code (AAC) R182715. See 48 FR 1717 (January 14, 1983). This rule limited stack emissions from primary copper smelters, including the smelter in the Miami area. We concluded, however, that the control strategy for SO2 in Arizona's six SO2 nonattainment areas was incomplete due to the failure to address fugitive emissions problems. See 48 FR 1717 (January 14, 1983) and 40 CFR 52.125(a)(1).

In 1998, 2003, and 2006, the State submitted amended rules (AAC R182715 (sections F, G, and H), R182715.01, R182715.02, and R18 2Appendix 8).\5\ These rules address both fugitive and stack emissions from smelters and, in approving the rules, we found that the amended rules met the RACT requirement under CAA sections 172(c)(1) and 191(b). See 69 FR 26789 at 26788 (May 14, 2004), 69 FR 63321 (November 2, 2004), and 71 FR 18624 at 18625 (April 12, 2006). Furthermore, because the area has attained the standard, no further demonstration that RACM has been implemented need be submitted by the State.
\5\ A more extensive summary of the regulatory history of copper smelters in Arizona is included in EPA's proposed action on these rules. See 69 FR 26786 (May 14, 2004).

Emissions inventory. The emissions inventory requirement of section 172(c)(3) is satisfied by the maintenance plan inventory requirements. The maintenance plan inventory is evaluated below, in section IV.E.1.

NSR permit program. Section 172(c)(5) requires new source review (NSR) permits for the construction and operation of new and modified major stationary sources located in nonattainment areas. ADEQ is the agency responsible for implementing the nonattainment area NSR permit program in the Miami area. Under ADEQ's rules, all new major sources and modifications to existing major sources are subject to the NSR requirements of these rules.

We have not yet fully approved the ADEQ NSR rules.\6\ We have, however, determined that an area being redesignated from nonattainment to attainment does not need to have an approved NSR program prior to redesignation, provided that the area demonstrates maintenance of the standard without nonattainment NSR in effect. See memorandum from Mary Nichols dated October 14, 1994 (``Part D New Source Review (part D NSR) Requirements for Areas Requesting Redesignation to Attainment.'') We have determined that the maintenance demonstration for Miami does not rely on nonattainment NSR.
\6\ ADEQ's NSR rules are included in the preconstruction review and permitting provisions of Arizona Administrative Code (AAC), Title 18, Chapter 2, Articles 3 and 4. EPA approved an earlier version of ADEQ's NSR requirements (AAC R93302) on May 5, 1982 (47 FR 19328) and August 10, 1988 (53 FR 30220).

Prevention of significant deterioration (PSD) is the permitting program that applies in attainment areas. PSD was established to preserve air quality in areas that are meeting the NAAQS. The PSD program requires new, modified, or reconstructed stationary sources to undergo preconstruction review and to apply best available control technology. In addition, sources are required to review PSD increment consumption and undertake preconstruction modeling. ADEQ has an EPA approved PSD permitting program (Arizona Air Pollution Rule R93304) for all criteria pollutants except respirable particulate matter (PM\10\). See 48 FR 19878 (May 3, 1983). The federal PSD program for PM\10\ was delegated to the State on March 12, 1999. ADEQ's partially approved, partially delegated PSD program will apply automatically to new major sources or major modifications to existing sources of SO2 in the Miami area once the area is redesignated to attainment.

Compliance with section 110(a)(2). Under section 172(c)(7), plan provisions submitted to satisfy part D must meet the applicable provisions of section 110(a)(2) of the CAA. As noted in section IV.B. above, the Miami portion of the Arizona SIP meets these requirements.

Equivalent techniques. Under section 172(c)(8), EPA may allow the use of equivalent modeling, emission inventory, and planning procedures, unless EPA determines that the proposed techniques are, in the aggregate, less effective than the methods specified by EPA. The Miami SO2 Maintenance Plan relies on an equivalent modeling technique referred to as Multipoint Rollback (MPR). MPR was used to derive emissions limits for the Miami smelter that provide for attainment and maintenance of the SO2 NAAQS. The State's rules containing MPRderived emission limits for the Miami smelter were approved by EPA on January 14, 1983 (48 FR 1717) and amended versions of the rules were approved by EPA on November 1, 2004 (69 FR 63321). b. Section 176

Section 176(c) of the CAA requires states to establish criteria and procedures to ensure that federally supported or funded projects conform to the air quality planning goals in the applicable SIP. The requirement to determine conformity applies to transportation plans, programs, and projects developed, funded or approved
[[Page 3068]]
under title 23 U.S.C. or the Federal Transit Laws (``transportation conformity'') as well as to all other federally supported or funded projects (``general conformity''). Because EPA does not consider SO2 a transportationrelated pollutant, only the requirements related to general conformity apply to the Miami SO2 area. The State of Arizona adopted general conformity criteria and procedures as a revision to the Arizona SIP. EPA approved Arizona's general conformity SIP on April 23, 1999 (64 FR 19916). Thus, the requirements of CAA section 176 have been satisfied.

c. Subpart 5

Subpart 5 of part D contains additional provisions for areas designated nonattainment for SO2. Under CAA section 191(b), States with existing nonattainment areas for the primary SO2 NAAQS where those areas lack fully approved SIPs, including part D plans, must submit implementation plans meeting the requirements of subpart 1 of part D. As discussed in section IV.D.2.a of this notice, the State of Arizona has met the requirements of subpart 1 of part D for the Miami area. Under CAA section 192(b), such areas were required to meet the primary SO2 NAAQS as expeditiously as possibly but no later than November 15, 1995. As discussed in section IV.A of this notice, the Miami SO2 nonattainment area met the primary SO2 standards well before the applicable attainment date of November 15, 1995 and has continued to attain since then. E. The Area Must Have a Fully Approved Maintenance Plan

Section 107(d)(3)(E)(iv) of the Act makes EPA approval of a maintenance plan meeting the requirements of section 175A another prerequisite to redesignation. Under section 175A, a maintenance plan must provide for maintenance of the NAAQS for at least 10 years after redesignation, and include any additional control measures as may be necessary to ensure such maintenance. In addition, maintenance plans are to contain such contingency provisions as EPA deems necessary to assure the prompt correction of a violation of the NAAQS that occurs after redesignation. The contingency measures must include, at a minimum, a requirement that the state will implement all control measures contained in the nonattainment SIP prior to redesignation.

The Calcagni Memo contains EPA guidance on the contents of maintenance plans submitted for the purposes of meeting section 175A. Generally, such plans should address the following five topics: the attainment emissions inventory, maintenance demonstration, monitoring network, verification of continued attainment, and a contingency plan.

Lastly, under CAA section 175A(b), states are required to submit a subsequent maintenance plan eight years after redesignation providing for maintenance of the NAAQS for an additional 10year period beyond the initial 10year maintenance period.

1. Attainment Inventory

The Miami SO2 Maintenance Plan includes an emissions inventory for point sources, area sources, and mobile sources for 1999 and 2000 as well as a projection of emissions to 2015. See table 4 below. As discussed in section IV.A of this notice, the Miami area has continued to attain the SO2 NAAQS since at least 1990 and thus 1999 and 2000 are acceptable as the basis upon which to develop an ``attainment emissions inventory'' for the purposes of a maintenance plan.

ADEQ developed the area and mobile source estimates shown in table 4 based on EPA's AIRData for Gila County. Point source estimates are based on ADEQ annual emissions inventory data. See section 4.0 and appendix B of the Miami SO2 Maintenance Plan. Sulfur dioxide emissions from the PhelpsDodge smelter copper smelter itself are based on continuous emission monitoring systems and the assumption that stack emissions represent 25 percent of the facility's total annual (i.e., stack plus fugitive) SO2 emissions. The actual percentage of total facility emissions emanating from the stacks varies from year to year (e.g., from 19 percent to 33 percent over the 1996 to 2000 period) but the 25 percent assumption is a reasonable average annual value based on material balance calculation methods.
Table 4.SO2 Emissions Inventories for 1999, 2000, and Projected Inventory for 2015 for the Miami Area (in TPY) Source type 1999 2000 2015 Area and Mobile................................................. 149 150 162 Point (excluding Miami smelter)................................. 7 4 9 Miami Smelter................................................... 7,819 6,810 8,000

Total....................................................... 7,975 6,964 8,171 Source: Miami SO2 Maintenance Plan, tables 4.4 and 4.6.

Based on our review of the submitted plan, we conclude that the emissions inventory is based on reasonable methods and assumptions and is comprehensive and accurate.

2. Maintenance Demonstration

EPA allows states to demonstrate maintenance of the NAAQS by either showing that future emissions of a pollutant or its precursors will not exceed the level of the attainment inventory, or by modeling to show that the future mix of sources and emission rates will not cause a violation of the NAAQS.\7\ In the case of the Miami nonattainment area, the demonstration of maintenance relies on both a projected emissions inventory for future years of 2005, 2010, and 2015 for sources in the Miami nonattainment area as well as SO2 emission limits for the Miami smelter that were developed using a variant of Multipoint Rollback (MPR) modeling and intended to minimize the probability of an exceedance of the SO2 NAAQS due to smelter emissions. \7\ See Calcagni Memo, at p. 9.

The inventory from the Miami SO2 Maintenance Plan shows that about 98% of the total SO2 emissions in the Miami nonattainment area are generated by the smelter.\8\ Projections for the Miami smelter itself anticipate a minor increase from those in 1999 [7,819 tons per year (tpy)] to 2005 and beyond (8,000 tpy). The remaining point sources in the nonattainment area have existing permits that limit their allowable emissions to less than 100 tpy. Projections for area and mobile sources
[[Page 3069]]
(increasing from 149 tpy \9\ to 162 tpy) are based on anticipated moderate increases in population and the assumption that SO2 emissions from such sources are proportionate to the population. Total projected actual emissions of point, area, and mobile sources are expected to remain relatively constant, with total SO2 emissions projected to be less than 24 tons on a daily basis and approximately 8,200 tons on annual basis by 2015.\10\ This represents an increase of only about 2 percent from 1999 levels. Thus, throughout the maintenance period, the Miami smelter is expected to continue to be the overwhelming source of SO2 emissions in the area. \8\ See appendix B of submitted plan.
\9\ The most recent quality assured inventory is from 1996. The 1999 SO2 inventory for area and mobile sources is based on economic growth activity.

\10\ See table 4.6 of submitted plan.

The emissions projections for the smelter (from 7,819 tpy) in 1999 to 8,000 tpy in 2005 and beyond are based on the expectation that, through 2015, the copper industry will not expand. While the expectation of continued low price pressures on copper may well have been reasonable in 2002 when the maintenance plan was adopted, changes in the copper market in fact have occurred over the past several years raising the price for copper thereby leading to a reasonable expectation of higher production levels at the Miami smelter than anticipated in the Miami SO2 Maintenance Plan.

Nonetheless, the demonstration of maintenance of the SO2 NAAQS in the Miami area does not rely solely on the emissions projections, but also on the SO2 emission limits established under SIP rule AAC R182715 (approved by EPA in 2004 and, as amended, in 2006) and incorporated into the title V operating permit for the PhelpsDodge Miami smelter. These limits cap stack emissions at 604 pounds per hour (lbs/hr) on an annual average basis and total facility (i.e., stacks plus fugitives) emissions at 2,420 lbs/hr on an annual basis. SIP rule AAC R182715 also establishes a cumulative occurrence table that caps the number of occurrences of 3hour average emissions above various levels with, for example, only two occurrences allowed per year of stack SO2 emissions greater than 5,900 lbs/hr, 3hour average. The total facility emissions cap (2,420 lbs/hr) corresponds to approximately 10,600 tpy assuming roundtheclock, year round operation (the permit however cites 10,400 tpy based on 357 work days in a given year).

As explained below, ADEQ has demonstrated that the new limits are protective of the SO2 NAAQS. In order to increase the smelter's emissions limits the State would have to submit a SIP revision that demonstrates that, consistent with CAA section 110(l), the revision does not interfere with maintenance of the SO2 NAAQS. Therefore, the emission limits for the smelter, supported by the emissions inventory projections that show that the smelter will remain the overwhelming source of SO2 emissions in the area for the foreseeable future, in essence provide the demonstration necessary to show that the Miami area will continue to attain the SO2 standard indefinitely, and thereby comply with CAA section 175A(a), which requires maintenance plans to provide for maintenance of the NAAQS for at least 10 years after redesignation.

Given the link then between the SO2 emission limits on the PhelpsDodge Miami smelter and the demonstration of maintenance, the Miami SO2 Maintenance Plan provides a detailed explanation of how the limits were derived and how they minimize the probability of exceedance of the SO2 NAAQS due to smelter operations. See chapter 5 of the submitted plan. First, it is important to note that ADEQ used a variant of the Multipoint Rollback (MPR) method to derive these emissions limits. In brief, MPR uses the ratio of monitored concentrations to the NAAQS to determine how much to scale the smelter's existing hourly distribution of emission rates so that they meet the NAAQS. Unlike simple rollback, which yields a single maximum emission rate never to be exceeded, MPR yields limitations on the number of times per year that the facility may exceed each of a series of emission rates. In the resulting cumulative occurrence table, the larger the emissions rate, the fewer number of occurrences are allowed per year. The emission rates are chosen so that the full hourly distribution results in attainment of the NAAQS on a probabilistic basis. This approach has been approved by EPA for use with smelters because of their highly variable emission rates.\11\ ADEQ used a variant of MPR, as explained further below, to show that the new limits are protective of the NAAQS.
\11\ See EPA Final Rule, ``Approval and Promulgation of Implementation Plans; Arizona Plan Revision: Sulfur Oxides Control Strategy and Regulations for Existing Nonferrous Smelters,'' 48 FR 1717 (January 14, 1983); and the SO2 Guideline Document, EPA452/R94008, February 1994, section 6.4.4.

ADEQ derived the original emissions limits for the smelter in the late 1970's using MPR, and adopted the original smelter SO2 emissions rule in 1979. To derive new, enforceable limits on the smelter stacks, it was necessary to distinguish stack emissions from total emissions, which include fugitives (those emissions not vented through the stack). The new emissions limits were derived by apportioning the old facility wide emission limits between the stack emissions and fugitive emissions. Using mass balance, the total amount of emissions can be calculated from the total mass of sulfur entering the plant in raw materials. Stack emissions are monitored, and account for about 25% of the total sulfur. The fugitive emissions were then determined by subtracting the monitored stack emissions from the calculated total emissions. Because the release height of the stack and fugitive emissions is similar, and their emissions are fairly wellmixed by the time they reach the monitor, the stack also accounts for 25% of the observed concentration at the monitor, on average. Thus, 25% of the existing facilitywide limits (2,420 lb/hr) are what the stack must be limited to (605 lb/hr; the SIP rule caps the emissions at 604 lb/hr, which is slightly more conservative) in order to meet the NAAQS.

This provides only an annual average emission rate. To derive MPR style limits on allowed occurrences of various emission rates (i.e., a cumulative occurrence table), ADEQ used the shape of the current hourly emission distribution \12\ and scaled it to match the required annual average emission rate. Since the new average limit is 1.75 times the current average actual emissions (604 lb/hr limit vs. 345 lb/hr current average), the current distribution and occurrence emission levels were scaled up by this factor. The result is new occurrence limits consistent with the new average limit of 604 lb/hr, the level needed to meet the NAAQS based upon the 1979 MPR analysis and the 25% stack fraction.
\12\ Emissions from each hour of 1999 were averaged with the corresponding hour in 2000, which represents a minor departure from how original MPR was carried out; i.e., using all data in a single distribution. EPA believes any resulting changes to the calculations are insignificant in the context of the Miami MPR analysis and finds this to be an acceptable approach.

However, scaling according to the 1979 limits assumes that the 1979 relationship between emissions and ambient concentrations has not changed. There have been substantial operational and emissions changes at the smelter since the 1979 average
[[Page 3070]]
emission limit and occurrence table were derived, which could have altered the shape of the emissions curve. If the current distribution shape has a broader peak than the 1979 one, then there will be relatively more instances of high ambient impacts, and so scaling of the average will not guarantee NAAQSprotective limits on shortterm emissions.

In order to address this, ADEQ carried out a second step in the submittal that is more consistent with the MPR procedure, in that it incorporated the ambient effect of the current emissions distribution, rather than relying on the 1979 relationship. ADEQ used monitoring data from 19962000, and emissions during that same period. The new emission limits, though a decrease from the old limits, represent an increase over the current actual emissions, and so should be shown to be consistent with the NAAQS. ADEQ assumed the smelter operated at the higher emissions rate allowed in the new limits, and applied the fractional emissions increase to ambient 3hour, 24hour, and annual SO2 concentrations. This uses the current relationship between emissions and ambient concentration to show that the scaledup emissions allowed in the new limits are consistent with the NAAQS. The result of this ``rollback'' scaling is shown in figure 5.4 of the Miami SO2 Maintenance Plan, and also in table 5 below. Table 5.Predicted Ambient SO2 Concentrations Based on Emissions Limits Predicted Percent of Averaging time level [mu]g/m3 NAAQS [mu]g/m3 NAAQS 3hour.......................................................... 1,180 1,300 91 24hour......................................................... 230 365 63 Annual.......................................................... 25 80 31 Note: The predicted 3hour and 24hour average concentrations represent secondhigh values in a given year. Predicted levels listed in this table are derived from figure 5.4 of the Miami SO2 Maintenance Plan.

With this second verification step, ADEQ used a procedure consistent with MPR, an EPAapproved method for smelter attainment demonstrations, to show that the new limits are protective of the NAAQS. We find that the protection of the NAAQS provided by the smelter's SO2 emissions limits, considered in the context of emissions projections that show that the smelter will remain the overwhelming source of SO2 emissions in the area for the foreseeable future, sufficient to demonstrate maintenance through the maintenance period and beyond.

3. Monitoring Network

Currently, there are three monitoring sites in the Miami nonattainment area: the Ridgeline monitor operated by ADEQ, and the Jones Ranch and Townsite monitors operated by PhelpsDodge. ADEQ and PhelpsDodge Miami commit to continue monitoring ambient SO2 concentrations at their respective sites for at least 10 years following the approval of the Miami SO2 Maintenance Plan. PhelpsDodge has the option of shutting down the monitors if the smelter has not operated for more than 2 years but commits to resume monitoring at the two sites three months prior to restarting of smelting operations. In addition, ADEQ commits to discussing changes to monitor locations with EPA and indicates that all ambient monitoring data will continue to be qualityassured in accordance with the requirements of 40 CFR part 58, Ambient Air Quality Surveillance. See section 7.2 of the submitted plan. We find that the Miami
SO2 Maintenance Plan adequately provides for continued monitoring of SO2 concentrations in the Miami area.

At the present time, only the SO2 monitoring data collected at ADEQ's Ridgeline site is certified and entered into AQS. However, because the Jones Ranch site has historically measured the highest SO2 concentrations in the area and because the data from Jones Ranch is used in connection with the contingency plan, EPA has requested that ADEQ commit to working with PhelpsDodge to ensure that SO2 monitoring data from the Jones Ranch site is entered into AQS. By letter to EPA dated October 18, 2006, ADEQ has agreed that entering SO2 monitoring data from the Jones Ranch site into AQS is appropriate and has committed to working with PhelpsDodge to accomplish this task no later than the first quarter of 2008. This commitment provides additional assurance that a suitable monitoring network will be maintained within the Miami area through the maintenance period and provides additional support for the contingency plan discussed below in section IV.E.5 of this action.

4. Verification of Continued Attainment

ADEQ intends to track the progress of the Miami SO2 Maintenance Plan through implementation and enforcement of the monitoring, reporting, and certification procedures to which permitted sources are subject under AAC R182306 and R182309. As a permitted source, the PhelpsDodge Miami smelter is subject to these State requirements. ADEQ also notes that it has authority pursuant to Arizona Revised Statutes section 49101 to monitor and ensure source compliance with all applicable rules and permit conditions. See section 7.3 of the submitted plan. Lastly, we note that ADEQ is required under 40 CFR part 51, subpart A, to report emissions data for large stationary sources, such as the PhelpsDodge Miami smelter, on an annual basis. Considered together, the submitted plan and relevant EPA regulations adequately provide for verification of continued attainment of the SO2 NAAQS in the Miami area.

5. Contingency Plan

Section 175A(d) of the CAA requires that maintenance plans include contingency provisions to promptly correct any violation of the NAAQS that occurs after redesignation of the area. The Calcagni memo provides additional guidance, noting that, although a state is not required to have fully adopted contingency measures that will take effect without further action by the state in order for the maintenance plan to be approved, the maintenance plan should ensure that the contingency measures are adopted expediently once they are triggered. Specifically, the maintenance plan should clearly identify the measures to be adopted, include a schedule and procedure for adoption and implementation of the measures, and contain a specific time limit for action by the state. In addition, the state should identify specific indicators, or triggers, that will be used to determine when the contingency measures need to be implemented.

Because the PhelpsDodge smelter is the overwhelming source of SO2 emissions in the Miami area, the
[[Page 3071]]
contingency plan contained in section 7.4 of the Miami SO2 Maintenance Plan focuses on ambient impacts and emissions attributable to it. The contingency plan uses monitored ambient concentrations of SO2 to trigger actions designed to ensure continued attainment of the SO2 NAAQS. The trigger levels and associated notification procedures and associated actions are described below.

Notification Procedure: If either of the PhelpsDodge monitors or the ADEQoperated monitor record ambient 3hour average SO2 levels between 0.425 ppm and 0.5 ppm (i.e., levels greater than 85%, but less than 100%, of the secondary SO2 NAAQS), \13\ the entity that operates the monitor is required to notify the other party. A second occurrence in a calendar year of ambient concentrations between 0.425 ppm and 0.5 ppm, or an exceedance of the secondary NAAQS is defined as the protective trigger level (PTL). The response required by a triggering of the PTL is divided into two action levels. \13\ See Table 5, above, which shows that the threehour SO2 NAAQS is ``limiting'' in the sense of being the most constraining on emissions, since this averaging time has the least room for additional emission increases. This is consistent with past findings that the threehour average requires the most stringent reduction in emissions. See 46 FR 58098 (November 30, 1981) at page 58102.

First Action Level: If the PTL is tripped, PhelpsDodge must undertake a series of inspections and a full calibration check of the ambient SO2 analyzers and recording systems in order to validate the data. If the data are determined to be valid, PhelpsDodge must perform any needed repairs or corrective actions and implement specified preventive measures. The source must also submit a report to ADEQ by the close of the second business day following an exceedance in which it describes the nature of the event, any corrective actions taken to resolve the event, and recommendations for future corrective actions to avoid recurrence of such an event.

Second Action Level: If the source is unable to correct the triggering of the PTL by implementing the actions required under the first action level, PhelpsDodge must undertake an analysis to identify additional control measures needed to ensure maintenance of the NAAQS. PhelpsDodge is required to submit recommendations to ADEQ

FOR FURTHER INFORMATION CONTACT Ginger Vagenas, Air Planning Office, (415) 9723964 or by email at vagenas.ginger@epa.gov.