Clean Air Act Promulgation of Extension of Attainment Dates for PM10

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

EPA is proposing to grant a one-year extension of the attainment date for the Salt Lake County, Utah nonattainment area for particulate matter with an aerodynamic diameter less than or equal to a nominal 10 micrometers (PM₁₀). EPA is also proposing to grant two one-year extensions of the attainment date for the Utah County, Utah PM₁₀ nonattainment area. Salt Lake and Utah Counties failed to attain the National Ambient Air Quality Standards (NAAQS) for PM₁₀ by the applicable attainment date of December 31, 1994. The action is based on EPA's evaluation of air quality monitoring data and extension requests submitted by the State of Utah. EPA is also making the determination that Salt Lake County, Utah attained the PM₁₀ NAAQS as of December 31, 1995 and Utah County, Utah attained the PM₁₀ NAAQS as of December 31, 1996. Both areas are continuing to attain the PM₁₀ NAAQS. The intended effect of this action is to approve requests from the Governor of Utah in accordance with section 188(d) of the Clean Air Act (CAA).

DATES:

Written comments must be received on or before October 23, 2000.

ADDRESSES:

Written comments may be mailed to Richard R. Long, Director, Air and Radiation Program, Mailcode 8P-AR, Environmental Protection Agency (EPA), Region VIII, 999 18th Street, Suite 300, Denver, Colorado, 80202. Copies of the documents relevant to this action are available for public inspection during normal business hours at the Air and Radiation Program, Environmental Protection Agency, Region VIII, 999 18th Street, Suite 300, Denver, Colorado, 80202 and copies of the Incorporation by Reference material are available at the Air and Radiation Docket and Information Center, Environmental Protection Agency, 401 M Street, SW, Washington, DC 20460. Copies of the state documents relevant to this action are available for public inspection at the Utah Department of Environmental Quality, Division of Air Quality, 150 North 1950 West, Salt Lake City, Utah 84114-4820.

FOR FURTHER INFORMATION CONTACT:

Cindy Rosenberg, EPA, Region VIII, (303) 312-6436.

SUPPLEMENTARY INFORMATION:

Throughout this document, wherever “we,” “us,” or “our” are used, we mean the Environmental Protection Agency (EPA).

Table of Contents

I. Background

A. Designation and Classification of PM₁₀ Nonattainment Areas.

B. How Does EPA Make Attainment Determinations?

C. What are the CAA Requirements for an Attainment Date Extension that Apply to Utah?

II. EPA's Proposed Action

A. What Is EPA Proposing To Approve?

B. What is the History Behind this Proposal?

III. Basis for EPA's Proposed Action

A. Salt Lake County

1. Explanation of the Attainment Date Extension for the Salt Lake County PM₁₀ Nonattainment Area.

2. Determination that the Salt Lake County PM₁₀ Nonattainment Are Attained the PM₁₀ NAAQS as of December 31, 1995.

B. Utah County

1. Explanation of the Attainment Date Extension for the Utah County PM₁₀ Nonattainment Area.

2. Determination that the Utah County PM₁₀ Nonattainment Area Attained the PM₁₀ NAAQS as of December 31, 1996.

IV. Administrative Requirements

I. Background

A. Designation and Classification of PM₁₀ Nonattainment Areas

Areas meeting the requirements of section 107(d)(4)(B) of the CAA were designated nonattainment for PM₁₀ by operation of law and classified “moderate” upon enactment of the 1990 Clean Air Act Amendments. See generally, 42 U.S.C. 7407(d)(4)(B). These areas included all former Group I PM₁₀ planning areas identified in 52 FR 29383 (August 7, 1987) as further clarified in 55 FR 45799 (October 31, 1990), and any other areas violating the national ambient air quality standards (NAAQS) for PM₁₀ prior to January 1, 1989. A Federal Register notice announcing the areas designated nonattainment for PM₁₀ upon enactment of the 1990 Amendments, known as “initial” PM₁₀ nonattainment areas, was published on March 15, 1991 (56 FR 11101) and a subsequent Federal Register document correcting the description of some of these areas was published on August 8, 1991 (56 FR 37654). See 40 CFR 81.345 (codified air quality designations and classifications for Utah).

All initial moderate PM₁₀ nonattainment areas had the same applicable attainment date of December 31, 1994. Section 188(d) provides the Administrator the authority to grant up to two one-year extensions to the attainment date provided certain requirements are met as described below. States containing initial moderate PM₁₀ nonattainment areas were required to develop and submit to EPA by November 15, 1991, a SIP revision providing for, among other things, implementation of reasonably available control measures (RACM), including reasonably available control technology (RACT), and a demonstration of whether attainment of the PM₁₀ NAAQS by the December 31, 1994 attainment date was practicable. See section 189(a).

B. How Does EPA Make Attainment Determinations?

All PM₁₀ nonattainment areas are initially classified “moderate” by operation of law when they are designated nonattainment. See section 188(a). Pursuant to sections 179(c) and 188(b)(2) of the Act, we have the responsibility of determining within six months of the applicable attainment date whether, based on air quality data, PM₁₀ nonattainment areas attained the NAAQS by that date. Determinations under section 179(c)(1) of the Act are to be based upon an area's “air quality as of the attainment date.” Section 188(b)(2) is consistent with this requirement.

Generally, we will determine whether an area's air quality is meeting the PM₁₀ NAAQS for purposes of section 179(c)(1) and 188(b)(2) based upon data gathered at established state and local air monitoring stations (SLAMS) and national air monitoring sites (NAMS) in the nonattainment area and entered into the Aerometric Information Retrieval System (AIRS). Data entered into the AIRS has been determined to meet federal monitoring requirements (see 40 CFR 50.6, 40 CFR part 50, appendix J, 40 CFR part 53, 40 CFR part 58, appendix A & B) and may be used to determine the attainment status of areas. We will also consider air quality data from other air monitoring stations in the nonattainment area provided that the stations meet the federal monitoring requirements for SLAMS. All data are reviewed to determine the area's air quality status in accordance with our guidance at 40 CFR part 50, appendix K.

Attainment of the annual PM₁₀ standard is achieved when the annual arithmetic mean PM₁₀ concentration over a three year period (for example, 1993, 1994, 1995 for areas with a December 31, 1995 attainment date) is equal to or less than 50 micrograms per cubic meter (μg/m³). Attainment of the 24-hour standard is determined by calculating the expected number of days in a year with PM₁₀ concentrations greater than 150 μg/m³. The 24-hour standard is attained when the expected number of days with levels above 150 μg/m³ (averaged over a three year period) is less than or equal to one. Three consecutive years of air quality data is generally necessary to show attainment of the 24-hour and annual standard for PM₁₀. See 40 CFR part 50 and appendix K.

C. What Are the CAA Requirements for an Attainment Date Extension That Apply to Utah?

The Act provides the Administrator the discretion to grant up to two one-year extensions of the attainment date for a moderate PM₁₀ nonattainment area provided certain criteria are met. The CAA sets forth two criteria that a moderate nonattainment area must satisfy in order to obtain an extension: (1) The State has complied with all the requirements and commitments pertaining to the area in the applicable implementation plan; and (2) The area has no more than one exceedance of the 24-hour PM₁₀ standard in the year preceding the extension year, and the annual mean concentration of PM₁₀ in the area for the year preceding the extension year is less than or equal to the standard. See section 188(d).

The authority delegated to the Administrator to extend attainment dates for moderate PM₁₀ nonattainment areas is discretionary. Section 188(d) of the Act provides that the Administrator “may” extend the attainment date for areas that meet the minimum requirements specified above. The provision doesn't dictate or compel that we grant extensions to such areas.

We have stated in guidance that in exercising this discretionary authority for PM₁₀ nonattainment areas, we will examine the air quality planning progress made in the moderate area. We will be disinclined to grant an attainment date extension unless a State has, in substantial part, addressed its moderate PM₁₀ nonattainment area planning obligations. In order to determine whether the State has substantially met these planning requirements we will review the State's application for the attainment date extension to determine whether the State has: (1) Adopted and substantially implemented control measures that represent RACM/RACT in the moderate nonattainment area; and (2) Demonstrated that the area has made emission reductions amounting to RFP toward attainment of the PM₁₀ NAAQS as defined in section 171(1) of the Act. RFP for PM₁₀ nonattainment areas is defined in section 171(1) of the Act as annual incremental emission reductions to ensure attainment of the applicable NAAQS (PM₁₀) by the attainment date.

If the State doesn't have the requisite number of years of clean air quality data to show attainment and doesn't apply or qualify for an attainment date extension, the area will be reclassified to serious by operation of law under section 188(b)(2) of the Act. If an extension to the attainment date is granted, at the end of the extension year we will again determine whether the area has attained the PM₁₀ NAAQS. If the requisite three consecutive years of clean air quality data needed to determine attainment are not met for the area, the State may apply for a second one-year extension of the attainment date. In order to qualify for the second one-year extension of the attainment date, the State must satisfy the same requirements listed above for the first extension. We will also consider the State's PM₁₀ planning progress for the area in the year for which the first extension was granted. If a second extension is granted and the area doesn't have the requisite three consecutive years of clean air quality data needed to demonstrate attainment at the end of the second extension, no further extensions of the attainment date can be granted. Once a final determination to this effect is made by us through the Federal Register, the area will be reclassified as serious by operation of law. See section 188(d).

II. EPA's Proposed Action

A. What Is EPA Proposing To Approve?

In response to requests from the Governor of Utah, we are proposing to grant a one-year attainment date extension for the Salt Lake County, Utah PM₁₀ nonattainment area and two one-year attainment date extensions for the Utah County, Utah PM₁₀ nonattainment area in order to address CAA requirements. The effect of these actions would be to extend the attainment date for the Salt Lake County, Utah PM₁₀ nonattainment area from December 31, 1994 to December 31, 1995 and the attainment date for the Utah County, Utah PM₁₀ nonattainment area from December 31, 1994 to December 31, 1995 and from December 31, 1995 to December 31, 1996. The proposed action to extend the attainment date for Salt Lake County is based on monitored air quality data for the national ambient air quality standard (NAAQS) for PM₁₀ from the years 1992-94 and the action for Utah County is based on data from the years 1992-94 and 1993-1995. In addition, based on quality-assured data meeting the requirements of 40 CFR part 50, appendix K, we are proposing to find that, as of December 31, 1995, Salt Lake County attained the PM₁₀ NAAQS, and that, as of December 31, 1996, Utah County attained the PM₁₀ NAAQS. Both areas are continuing to attain the PM₁₀ NAAQS. If we finalize this proposal, consistent with CAA section 188, the areas will remain moderate PM₁₀ nonattainment areas and avoid the additional planning requirements that apply to serious PM₁₀ nonattainment areas.

This action should not be confused with a redesignation to attainment under CAA section 107(d) because Utah hasn't submitted a maintenance plan as required under section 175(A) of the CAA or met the other CAA requirements for redesignation. The designation status in 40 CFR part 81 will remain moderate nonattainment for both areas until such time as Utah meets the CAA requirements for redesignations to attainment.

We are soliciting public comments on the issues discussed in this document or on other relevant matters. These comments will be considered before taking final action. Interested parties may participate in the Federal rulemaking procedure by submitting written comments to the EPA Regional office listed in the ADDRESSES section of this document.

B. What is The History Behind this Proposal?

As initial moderate PM₁₀ nonattainment areas, both Salt Lake and Utah Counties were required by CAA section 188 to attain the PM₁₀ NAAQS by December 31, 1994. As noted above, section 188 of the CAA requires EPA to determine whether such moderate areas have attained the NAAQS or not within six months of the attainment date. In the event an area doesn't attain the NAAQS by the attainment date, section 188 also allows States to request and EPA to approve attainment date extensions if certain criteria are met. On May 11, 1995, the State of Utah requested a one-year extension of the attainment date for both Salt Lake and Utah Counties. On October 18, 1995, we indicated that we were granting the requested one-year extensions. We also indicated in a letter dated January 25, 1996 that we would publish a rulemaking action on the extension requests “in the very near future,” but we didn't do so. Nor did we publish determinations in the Federal Register that the areas had not attained the NAAQS as of December 31, 1994. On March 27, 1996, the State of Utah requested a second one-year extension of the attainment date for Utah County. We didn't publish a determination in the Federal Register that Utah County had not attained the NAAQS as of December 31, 1995.

EPA is now proposing to extend the attainment date from December 31, 1994 to December 31, 1995 for the Salt Lake County PM₁₀ nonattainment area and the Utah County PM₁₀ nonattainment area. EPA is also proposing to extend the attainment date for the Utah County PM₁₀ nonattainment area for an additional year—until December 31, 1996. As we explain more fully below, we believe these extensions are warranted under CAA section 188(d). In addition, we are finding that the Salt Lake County PM₁₀ nonattainment area attained the PM₁₀ NAAQS as of December 31, 1995 and the Utah County PM₁₀ nonattainment area attained the PM₁₀ NAAQS as of December 31, 1996.

III. Basis for EPA's Proposed Action

A. Salt Lake County

1. Explanation of the Attainment Date Extension for the Salt Lake County PM₁₀ Nonattainment Area

a. Air Quality Data. We are using data from calendar year 1994 to determine whether the area met the air quality criteria for granting a one-year extension to the attainment date under section 188(d) of the CAA.

The Salt Lake County PM₁₀ nonattainment area includes the entire county. In 1994, Utah's Department of Air Quality (UDAQ or Utah) operated six PM₁₀ monitors, which were SLAMS and NAMS, in Salt Lake County. We deemed the data from these sites valid and the data were submitted by Utah to be included in AIRS.

In 1994, there were eight exceedances of the 24-hour PM₁₀ NAAQS at one monitor (North Salt Lake Site) and one exceedance of the 24-hour NAAQS at another monitor (AMC Site). Based on nearby construction activity, Utah requested that the eight exceedances recorded at the North Salt Lake Site in 1994 be excluded under our “Guideline on the Identification and Use of Air Quality Data Affected By Exceptional Events,” (EPA-450/4-86-007). We determined that the North Salt Lake monitor was influenced by highly localized, fugitive dust events caused by the construction activity occurring in the immediate area. The Guideline allows consideration of the influence of certain events, such as construction, near air monitoring stations in determining if data should be used for regulatory purposes. Because of those impacts from localized construction near the North Salt Lake site, all data from June 8 to November 23, 1994 were excluded from the data set used in calculations for attainment/nonattainment purposes.

With the exclusion of the above-mentioned block of data, there was only one exceedance recorded at one other monitor (AMC site). Therefore, with only one exceedance of the PM₁₀ NAAQS recorded in 1994, the area met one of the requirements to qualify for an attainment date extension under section 188(d).

b. Compliance with the Applicable SIP. The State of Utah submitted the PM₁₀ SIP for Salt Lake County on November 14, 1991. On December 18, 1992 (57 FR 60149), EPA proposed to approve the plan as satisfying those moderate PM₁₀ nonattainment area requirements that were due November 15, 1991. On July 8, 1994 (59 FR 35036), EPA took final action approving the Salt Lake County PM₁₀ SIP. The SIP control strategies consist of controls for stationary sources and area sources (including controls for woodburning, mobile sources, and road salting and sanding) of primary PM₁₀ emissions as well as sulfur oxide (SO_X) and nitrogen oxide (NO_X) emissions, which are secondary sources of particulate emissions.

Based on information the State submitted in 1995, we believe that Utah was in compliance with the requirements and commitments in the applicable implementation plan that pertained to the Salt Lake County PM₁₀ nonattainment area when the State submitted its extension request. The milestone report indicates that Utah had implemented most of its adopted control measures, and therefore we believe Utah substantially implemented its RACM/RACT requirements.

c. Emission Reduction Progress. With its May 11, 1995, request for a one-year attainment date extension for Salt Lake County, the State of Utah also submitted a milestone report as required by section 189(c)(2) of the Act to demonstrate annual incremental emission reductions and reasonable further progress (RFP). On September 29, 1995, Utah submitted a revised version of the milestone report. The revised 1995 milestone report estimated current emissions from all source categories covered by the SIP and compared those estimates to 1988 actual emissions. These estimates of current emissions indicated that total emissions of PM₁₀, SO₂, and NO_X had been reduced by approximately 60,752 tons per year, from a 1988 value of 150,292 tons per year to a current value of 89,540 tons per year.

The effect of these emission reductions appears to be reflected in ambient measurements at the monitoring sites. Data from these sites show no violations of either the annual or the 24-hour PM₁₀ standard since the 1992-1994 period. Furthermore, in 1994 there was only one exceedance of the 24-hour standard and the highest monitored annual standard at any monitor was 47μ/m³. This is evidence that the State's implementation of PM₁₀ SIP control measures resulted in emission reductions amounting to reasonable further progress in the Salt Lake County PM₁₀ nonattainment area.

2. Determination that the Salt Lake County PM₁₀ Nonattainment Area Attained the PM₁₀ NAAQS as of December 31, 1995

Whether an area has attained the PM₁₀ NAAQS is based exclusively upon measured air quality levels over the most recent and complete three calendar year period. See 40 CFR part 50 and 40 CFR part 50, appendix K. If we finalize this action, the extended attainment date for Salt Lake County will be December 31, 1995, and the three year period will cover calendar years 1993, 1994, and 1995.

The PM₁₀ concentrations reported at six different monitoring sites showed one measured exceedance of the 24-hour PM₁₀ NAAQS between 1993 and 1995. Because data collection was less than 100% at these monitoring sites, the expected exceedance rate for 1994 was 1.03. For 1993 and 1995, it was 0.0. Thus, the three-year average was less than 1.0, which indicates Salt Lake County attained the 24-hour PM₁₀ NAAQS as of December 31, 1995.

Review of the annual standard for calendar years 1993, 1994 and 1995 reveals that Utah also attained the annual PM₁₀ NAAQS by December 31, 1995. There was no violation of the annual standard for the three year period from 1993 through 1995.

B. Utah County

1. Explanation of the Attainment Date Extension for the Utah County PM₁₀ Nonattainment Area

a. Air Quality Data. The Utah County PM₁₀ nonattainment area includes the entire county. In 1994 and 1995, UDAQ operated four PM₁₀ monitoring sites, which were either SLAMS or NAMS, in Utah County. We deemed the data from these sites valid and the data was submitted by Utah to be included in AIRS.

We are using data from calendar year 1994 to determine whether the area met the air quality criteria for granting a one-year extension of the attainment date, from December 31, 1994 to December 31, 1995, under section 188(d) of the CAA. We are using calendar year 1995 data to determine whether the Utah County area met the air quality criteria for granting an extension of the attainment date from December 31, 1995 to December 31, 1996.

In 1994, there were no exceedances of the 24-hour or annual PM₁₀ NAAQS in Utah County. Since no exceedances of the PM₁₀ NAAQS were recorded in 1994, the area met one of the requirements to qualify for a one-year attainment date extension under section 188(d). In 1995, there were no exceedances of the 24-hour or annual PM₁₀ NAAQS in Utah County. Since no exceedances of the PM₁₀ NAAQS were recorded in 1995, the area met one of the requirements to qualify for a second one-year attainment date extension under section 188(d).

b. Compliance with the Applicable SIP. The State of Utah submitted the PM₁₀ SIP for Utah County on November 14, 1991. On December 18, 1992 (57 FR 60149), EPA proposed to approve the plan as satisfying those moderate PM₁₀ nonattainment area requirements due November 15, 1991. On July 8, 1994 (59 FR 35036), EPA took final action approving the Utah County PM₁₀ SIP. The SIP control strategies consist of controls for stationary sources and area sources (including controls for woodburning, mobile sources, and road salting and sanding) of primary PM₁₀ emissions as well as sulfur oxide (SO_X) and nitrogen oxide (NO_X) emissions, which are secondary sources of particulate emissions.

Based on information the State submitted in 1995, we believe that Utah was in compliance with the requirements and commitments in the applicable implementation plan that pertained to the Utah County PM₁₀ nonattainment area when Utah submitted its first extension request. The milestone report indicates that Utah County had implemented most of its adopted control measures, and therefore we believe Utah substantially implemented its RACM/RACT requirements. Based on information the State submitted in 1996, we believe that Utah was in compliance with the requirements and commitments in the applicable implementation plan that pertained to the Utah County PM₁₀ nonattainment area when the State submitted its second extension request. The milestone report indicates that the State continued to implement its adopted control measures, and therefore we believe Utah substantially implemented its RACM/RACT requirements.

c. Emission Reduction Progress. With its May 11, 1995, request for a one-year attainment date extension for Utah County, the State of Utah also submitted a milestone report as required by section 189(c)(2) of the Act to demonstrate annual incremental emission reductions and RFP. On September 29, 1995, Utah submitted a revised version of the milestone report. The revised 1995 milestone report estimated current emissions from all source categories covered by the SIP and compared those estimates to 1988 actual emissions. These estimates of current emissions indicated that total emissions of PM₁₀, SO₂, and NO_X had been reduced by approximately 3,129 tons per year, from a 1988 value of 25,920 tons per year to a then current value of 22,791 tons per year.

With its March 27, 1996 request for an additional one-year attainment date extension for Utah County, the State of Utah submitted another milestone report. Utah submitted a revised version of this milestone report on May 17, 1996. The March 27, 1996 milestone report estimated current emissions from all source categories covered by the SIP and compared those estimates to 1988 actual emissions. These estimates of current emissions indicated that total emissions of PM₁₀, SO₂, and NO_X had been reduced from the 1988 total by approximately 8,391 tons per year.

The effect of these emission reductions appears to be reflected in ambient measurements at the monitoring sites. Data from these sites show no exceedances of either the annual or the 24-hour PM₁₀ standard in 1994 or 1995. The vast majority of monitored values were well below the 24-hour standard. The highest annual value recorded at any monitor during 1994 and 1995 was 39μ/m3. This is evidence that the State's implementation of PM₁₀ SIP control measures resulted in emission reductions amounting to RFP in the Utah County PM₁₀ nonattainment area.

2. Determination that the Utah County PM₁₀ Nonattainment Area Attained the PM₁₀ NAAQS as of December 31, 1996.

Whether an area has attained the PM₁₀ NAAQS is based exclusively upon measured air quality levels over the most recent and complete three calendar year period. See 40 CFR part 50 and 40 CFR part 50, appendix K. If we finalize this action, the extended attainment date for Utah County will be December 31, 1996, and the three year period will cover calendar years 1994, 1995, and 1996.

The PM₁₀ concentrations reported at four different monitoring sites showed no measured exceedances of the 24-hour PM₁₀ NAAQS between 1994 and 1996, which indicates Utah County attained the 24-hour PM₁₀ NAAQS as of December 31, 1996.

Review of the annual standard for calendar years 1994, 1995 and 1996 reveals that Utah also attained the annual PM₁₀ NAAQS by December 31, 1996. No monitoring sites showed a violation of the annual standard in the three year period from 1994 through 1996.

IV. Administrative Requirements

Under Executive Order 12866 (58 FR 51735, October 4, 1993), this proposed action is not a “significant regulatory action” and therefore is not subject to review by the Office of Management and Budget. This proposed action merely approves a state request as meeting federal requirements and imposes no requirements. Accordingly, the Administrator certifies that this proposed rule will not have a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.). Because this proposed rule would not impose any enforceable duty, it does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Public Law 104-4). For the same reason, this proposed rule also does not significantly or uniquely affect the communities of tribal governments, as specified by Executive Order 13084 (63 FR 27655, May 10, 1998). This proposed rule will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government, as specified in Executive Order 13132 (64 FR 43255, August 10, 1999), because it merely approves a state request for an attainment date extension, and does not alter the relationship or the distribution of power and responsibilities established in the Clean Air Act. This proposed rule also is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997), because it is not economically significant.

As required by section 3 of Executive Order 12988 (61 FR 4729, February 7, 1996), in issuing this proposed rule, EPA has taken the necessary steps to eliminate drafting errors and ambiguity, minimize potential litigation, and provide a clear legal standard for affected conduct. EPA has complied with Executive Order 12630 (53 FR 8859, March 15, 1988) by examining the takings implications of the rule in accordance with the “Attorney General's Supplemental Guidelines for the Evaluation of Risk and Avoidance of Unanticipated Takings” issued under the executive order. This rule does not impose an information collection burden under the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).

List of Subjects in 40 CFR Part 52

• Environmental protection
• Air pollution control
• Intergovernmental relations
• Particulate matter
• Reporting and recordkeeping requirements