[Federal Register Volume 83, Number 108 (Tuesday, June 5, 2018)]
[Rules and Regulations]
[Pages 25922-25936]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-11597]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R01-OAR-2017-0083; FRL-9978-27--Region 1]


Air Plan Approval; New Hampshire; Nonattainment Plan for the 
Central New Hampshire Sulfur Dioxide Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is approving the 
State Implementation Plan (SIP) revision that the State of New 
Hampshire submitted to EPA on January 31, 2017, for attaining the 1-
hour sulfur dioxide (SO2) primary national ambient air 
quality standard (NAAQS) for the Central New Hampshire Nonattainment 
Area. This plan (herein called a ``nonattainment plan'') includes New 
Hampshire's attainment demonstration and other elements required under 
the Clean Air Act (CAA). In addition to an attainment demonstration, 
the nonattainment plan addresses the requirements for meeting 
reasonable further progress (RFP) toward attainment of the NAAQS, 
implementation of reasonably available control measures and reasonably 
available control technology (RACM/RACT), base-year and projection-year 
emission inventories, enforceable emissions limitations and control 
measures, and contingency measures. EPA concludes that New Hampshire 
has appropriately demonstrated that the nonattainment plan provisions 
provide for attainment of the 2010 1-hour primary SO2 NAAQS 
in the Central New Hampshire Nonattainment Area by the applicable 
attainment date and that the nonattainment plan meets the other 
applicable requirements under the CAA. This action is being taken in 
accordance with the CAA.

DATES: This rule is effective on July 5, 2018.

ADDRESSES: EPA has established a docket for this action under Docket 
Identification No. EPA-R01-OAR-2017-0083. All documents in the docket 
are listed on the www.regulations.gov website. Although listed in the 
index, some information is not publicly available, i.e., CBI or other 
information whose disclosure is restricted by statute. Certain other 
material, such as copyrighted material, is not placed on the internet 
and will be publicly available only in hard copy form. Publicly 
available docket materials are available at www.regulations.gov or at 
the U.S. Environmental Protection Agency, EPA New England Regional 
Office, Office of Ecosystem Protection, Air Permits Toxics and Indoor 
Programs Unit, 5 Post Office Square--Suite 100, Boston, MA. EPA 
requests that if at all possible, you contact the contact listed in the 
FOR FURTHER INFORMATION CONTACT section to schedule your inspection. 
The Regional Office's official hours of business are Monday through 
Friday, 8:30 a.m. to 4:30 p.m., excluding legal holidays.

FOR FURTHER INFORMATION CONTACT: Leiran Biton, Air Permits, Toxics, and 
Indoor Programs Unit, U.S. Environmental Protection Agency, EPA New 
England Regional Office, 5 Post Office Square--Suite 100, (Mail code 
OEP05-2), Boston, MA 02109-3912, tel. (617) 918-1267, email 
[email protected].

SUPPLEMENTARY INFORMATION: Throughout this document whenever ``we,'' 
``us,'' or ``our'' is used, we mean EPA.

Table of Contents

I. Background and Purpose
II. Response to Comments
III. Final Action
IV. Incorporation by Reference
V. Statutory and Executive Order Reviews

I. Background and Purpose

    On June 22, 2010, EPA promulgated a new 1-hour primary 
SO2 NAAQS of 75 parts per billion (ppb), which is met at an 
ambient air quality monitoring site when the 3-year average of the 
annual 99th percentile of daily maximum 1-hour concentrations does not 
exceed 75 ppb, as determined in accordance with appendix T of 40 CFR 
part 50. See 75 FR 35520, codified at 40 CFR 50.17(a) and (b). On 
August 5, 2013, EPA designated a first set of 29 areas of the country 
as nonattainment for the 2010 SO2 NAAQS, including the 
Central New Hampshire Nonattainment Area within the State of New 
Hampshire. See 78 FR 47191, codified at 40 CFR part 81, subpart C. 
These ``round one'' area designations were effective October 4, 2013. 
Section 191(a) of the CAA directs states to submit SIPs for areas 
designated as nonattainment for the SO2 NAAQS to EPA within 
18 months of the effective date of the designation, i.e., by no later 
than April 4, 2015 in this case. These SIPs are required to demonstrate 
that their respective areas will attain the NAAQS as expeditiously as 
practicable, but no later than 5 years from the effective date of 
designation, which is October 4, 2018, in accordance with CAA sections 
191-192.
    Section 192(a) requires that such plans shall provide for NAAQS 
attainment as expeditiously as practicable, but no later than 5 years 
from the effective date of the nonattainment designation. Section 
172(c) of part D of the CAA lists the required components of a 
nonattainment plan submittal. The base year emissions inventory 
(section 172(c)(3)) is required to show a ``comprehensive, accurate, 
current inventory'' of all relevant pollutants in the nonattainment 
area. The nonattainment plan must identify and quantify any expected 
emissions from the construction of new sources to account for emissions 
in the area that might affect reasonable further progress (RFP) toward 
attainment, or that might interfere with attainment and

[[Page 25923]]

maintenance of the NAAQS, and it must provide for a nonattainment new 
source review (NNSR) program (section 172(c)(5)). The attainment 
demonstration must include a modeling analysis showing that the 
enforceable emissions limitations and other control measures taken by 
the state will provide for RFP and expeditious attainment of the NAAQS 
(section 172(c)(2), (4), (6), and (7)). The nonattainment plan must 
include an analysis and provide for implementation of the RACM 
considered, including RACT (section 172(c)(1)). Finally, the 
nonattainment plan must provide for contingency measures (section 
172(c)(9)) to be implemented either in the case that RFP toward 
attainment is not made, or in the case that the area fails to attain 
the NAAQS by the attainment date.
    On April 23, 2014, EPA issued a guidance document entitled, 
``Guidance for 1-Hour SO2 Nonattainment Area SIP 
Submissions.'' This guidance provides recommendations for the 
development of SO2 nonattainment SIPs to satisfy CAA 
requirements (see, e.g., sections 172, 191, and 192). An attainment 
demonstration must also meet the requirements of 40 CFR part 51, 
subparts F and G, and 40 CFR part 51, appendix W (the Guideline on Air 
Quality Models; ``the Guideline''), and include inventory data, 
modeling results, and emissions reduction analyses on which the state 
has based its projected attainment. The guidance also discusses 
criteria EPA expects to use in assessing whether emission limits with 
longer averaging times of up to 30 days ensure attainment of the 
SO2 NAAQS.
    For a number of areas, including the Central New Hampshire 
Nonattainment Area, EPA published a document on March 18, 2016, that 
pertinent states had failed to submit the required SO2 
nonattainment plan by the submittal deadline. See 81 FR 14736. This 
finding initiated a deadline under CAA section 179(a) for the potential 
imposition of new source review and highway funding sanctions, and for 
EPA to promulgate a federal implementation plan (FIP) under section 
110(c) of the CAA. In response to the requirement for SO2 
nonattainment plan submittals, New Hampshire submitted a nonattainment 
plan for the Central New Hampshire Nonattainment Area on January 31, 
2017. Pursuant to New Hampshire's January 31, 2017 submittal and EPA's 
subsequent completeness determination letter dated March 20, 2017, 
these sanctions under section 179(a) will not be imposed as a result of 
New Hampshire's having missed the April 4, 2015 submission deadline. 
Furthermore, with this current action issuing final approval of New 
Hampshire's SIP submittal, EPA's FIP obligation no longer applies, and 
no FIP will be imposed as a result of New Hampshire's missing the 
deadline.
    On November 29, 2017, EPA received a letter from New Hampshire 
correcting a misstatement in its January 2017 submittal to EPA. The 
State had earlier intended to modify its January 2017 submittal to EPA 
in response to a public comment on its draft nonattainment area plan, 
but inadvertently neglected to make the correction. Specifically, the 
State enclosed in its January 2017 submittal to EPA all comments and 
responses to comments relating to its draft nonattainment area plan, 
and among those was a set of comments submitted by Sierra Club to the 
State on January 5, 2017. Among other comments, Sierra Club asserted 
that the draft nonattainment area plan ``incorrectly suggests that an 
attainment demonstration can be made based on monitor readings alone,'' 
counter to EPA's April 2014 guidance, and stated that the plan should 
be revised to remove this inconsistency. In its response to that 
comment, New Hampshire indicated that it would remove the language per 
Sierra Club's comment, but inadvertently included the erroneous 
language nonetheless in its January 2017 submittal to EPA. New 
Hampshire's November 29, 2017 correction modifies the State's original 
submittal to exclude the erroneous language identified by Sierra Club, 
consistent with the State's response to comments. Hereafter, references 
to the State's January 31, 2017 SIP submittal are intended to include 
the November 29, 2017 correction.
    On September 28, 2017 (82 FR 45242), EPA proposed to approve New 
Hampshire's January 31, 2017 nonattainment plan submittal and 
SO2 attainment demonstration. The State's submittal and 
attainment demonstration included all the specific attainment elements 
mentioned above, including new SO2 emission limits found to 
be comparably stringent to the 1-hour form of the primary 
SO2 NAAQS and associated control technology efficiency 
requirements for the electric generating source Merrimack Station, 
currently owned and operated by GSP Merrimack LLC and formerly by 
Public Service of New Hampshire (PSNH) d/b/a Eversource Energy, 
impacting the Central New Hampshire Nonattainment Area. Merrimack 
Station's new SO2 emission limits were developed in 
accordance with EPA's April 2014 guidance. Comments on EPA's proposed 
rulemaking were due on or before October 30, 2017. EPA received a 
single set of comments on the proposed approval of New Hampshire's 
nonattainment area plan for the Central New Hampshire Nonattainment 
Area. The comments are available in the docket for this final 
rulemaking action. EPA's summary of the comments and EPA's responses 
are provided below. For a comprehensive discussion of New Hampshire's 
SIP submittal and EPA's analysis and rationale for approval of the 
State's submittal and attainment demonstration for this area, please 
refer to EPA's September 28, 2017 notice of proposed rulemaking.
    The remainder of this preamble summarizes EPA's final approval of 
New Hampshire's SIP submittal and attainment demonstration for the 
Central New Hampshire Nonattainment Area and contains EPA's response to 
public comments.

II. Response to Comments

    The single set of comments addressing the proposed approval of the 
SIP revision for the Central New Hampshire Nonattainment Area was 
received from Sierra Club on October 30, 2017. The Sierra Club's 
October 30, 2017 comments explicitly incorporated a July 15, 2016 
comment letter with supporting attachments submitted to New Hampshire 
by Sierra Club on behalf of both Sierra Club and Conservation Law 
Foundation (CLF) regarding the State's proposed permit for Merrimack 
Station. Because the October 30, 2017 Sierra Club comments on EPA's 
proposal are nearly identical to the prior July 15, 2016 comments, 
except where the October 30, 2017 comments provide updated information, 
EPA's responses to the October 30, 2017 Sierra Club comments also serve 
to respond to issues raised in the July 15, 2016 comments to the State, 
except where EPA identifies discussion as specifically applying only to 
comments from July 15, 2016. In the following discussion, EPA will 
refer to the Sierra Club or Sierra Club/CLF as ``the Commenter.'' To 
review the complete set of comments received, refer to the docket for 
this rulemaking as identified above. A summary of the comments received 
and EPA's responses are provided below.
    Comment 1: The commenter asserted that the proposed 7-day average 
limit on emissions from Merrimack Station is insufficient to protect 
the 1-hour NAAQS. The commenter indicated that short-term exposure to 
SO2 for as little as five minutes has significant health 
impacts and causes decrement in lung function, aggravation of asthma, 
chest tightness, and respiratory and

[[Page 25924]]

cardiovascular morbidity. The commenter stated that such short-term 
exposure is especially risky for children with asthma. To support these 
statements regarding health effects, the commenter cited several EPA 
documents related to the final SO2 NAAQS and air quality 
trends. The commenter stated that EPA changed the NAAQS from 140 ppb 
averaged over 24 hours to 75 ppb averaged over one hour in order to 
address these health impacts. The commenter stated that as a result of 
the form of the standard, which is evaluated through reference to the 
fourth-highest daily maximum hourly-average concentrations in each 
year, emission limits with an averaging period longer than one hour are 
highly unlikely to be able to protect the 1-hour NAAQS. The commenter 
indicated that the form of the NAAQS means that ambient air quality can 
be evaluated as unsafe with as few as four hours of elevated emissions 
over the course of a year. The commenter stated that even if the 7-day 
limit is complied with, possible short-term emission ``spikes'' that 
may coincide with startup, shutdown, or control system malfunction 
events, for example, could nevertheless cause ambient 1-hour 
SO2 concentrations sufficient to violate the NAAQS. In 
support of this point, the commenter provided language making similar 
points excerpted from two EPA letters that had been included in the 
attachments to the commenter's July 15, 2016 comments to New Hampshire, 
specifically an August 12, 2010 comment letter from EPA Region 7 to 
Kansas regarding the Sunflower Holcomb Station Expansion Project, and a 
February 1, 2012 comment letter from EPA Region 5 to Michigan regarding 
a draft construction permit for the Detroit Edison Monroe Power Plant. 
The commenter concluded that the 7-day limit proposed for inclusion in 
the State's SIP has an averaging period that is 168 times longer than 
that of the 1-hour NAAQS and should be revised to adequately protect 
the NAAQS. The commenter added that hourly emissions limits are not 
unreasonable, and cited several examples of permits that impose such 
limits. Therefore, the commenter concluded that a 1-hour emissions 
limit should be imposed.
    Response 1: EPA appreciates the commenter's concerns about the 
appropriateness of approving nonattainment plans with emission 
limitations that apply over a longer time period than the 1-hour form 
of the 2010 SO2 NAAQS. We discussed similar issues in EPA's 
April 2014 guidance. In this case, EPA has concluded that the approach 
employed by New Hampshire to develop the emission limitations for 
Merrimack Station and included in the State's SIP submittal is 
consistent with recommendations discussed in EPA's April 2014 guidance 
and adequately protects against violation of the 1-hour SO2 
NAAQS. EPA's rationale for this conclusion is explained in further 
detail below.
    The health effects information provided by the commenter is not in 
dispute in this rulemaking. This rulemaking instead addresses whether 
New Hampshire's plan is adequate to meet the previously established 
NAAQS.
    As mentioned above, CAA section 172(c) directs states with areas 
designated as nonattainment to demonstrate that the submitted 
nonattainment plan provides for attainment of the NAAQS. EPA's rules at 
40 CFR part 51, subpart G further delineate the control strategy 
requirements that SIPs must meet, and EPA has long required that all 
control strategies in nonattainment plans reflect four fundamental 
principles of quantification, enforceability, replicability, and 
accountability. See ``State Implementation Plans; General Preamble for 
the Implementation of Title I of the Clean Air Act Amendments of 1990; 
Proposed Rule,'' 57 FR 13498 (April 16, 1992) (General Preamble), at 
13567-68. Additional guidance is provided in EPA's April 2014 guidance. 
For SO2, there are generally two components needed to 
support an attainment demonstration submitted under section 172(c): (1) 
Emission limitations and other control measures that assure 
implementation of permanent, enforceable, and necessary emission 
controls; and (2) a modeling analysis that meets the requirements of 40 
CFR part 51, appendix W and demonstrates that these emission 
limitations and control measures provide for timely attainment of the 
primary SO2 NAAQS as expeditiously as practicable, but by no 
later than the applicable attainment date for the affected area. In all 
cases, the emission limitations and control measures must be 
accompanied by appropriate methods and conditions to determine 
compliance with the respective emission limitations and control 
measures. Furthermore, in all cases, the emission limitations and 
control measures must be: Quantifiable (i.e., a specific amount of 
emission reduction can be ascribed to the measures), fully enforceable 
(specifying clear, unambiguous, and measurable requirements for which 
compliance can be practicably determined), replicable (the procedures 
for determining compliance are sufficiently specific and non-subjective 
such that two independent entities applying the procedures would obtain 
the same result), and accountable (source specific limitations must be 
permanent and must reflect the assumptions used in the SIP 
demonstrations).
    In our April 2014 guidance, EPA notes that past Agency guidance has 
recommended that averaging times in SO2 SIP emissions 
limitations should not exceed the averaging time of the applicable 
NAAQS that the limit is intended to help attain (e.g., addressing 
emissions averaged over one or three hours). EPA's April 2014 guidance 
also discusses the possibility of utilizing emission limitations with 
longer averaging times of up to 30 days, so long as the state meets 
various suggested criteria to show that the longer-term limits are 
comparably stringent to the 1-hour critical emission value that is 
needed to meet the NAAQS. See EPA's April 2014 guidance, pp. 22 to 39. 
The guidance recommends that--should states elect to use longer 
averaging times--the longer-term average limit should be set at an 
adjusted level to reflect a stringency comparable to the 1-hour average 
critical emission value shown to provide for attainment through a 
modeling analysis that the plan otherwise would have set as an emission 
limit.
    At the outset, EPA notes that the specific examples of earlier EPA 
statements cited by the commenter (i.e., those contained in Exhibits 1, 
2, 3, and 4 to Appendix A of the comment submission) all pre-date the 
release of EPA's April 2014 guidance. As such these examples only 
reflect the Agency's development of its policy for implementing the 
2010 SO2 NAAQS as of the dates of their own issuance. At the 
time of their issuance, EPA had not yet addressed the specific question 
of whether it might be possible to devise an emission limit with an 
averaging period longer than 1-hour, with appropriate adjustments that 
would make it comparably stringent to an emission limit shown to attain 
1-hour emission level, that could adequately ensure attainment of the 
SO2 NAAQS. None of the pre-2014 EPA documents cited by the 
commenter address this question; consequently, it is not reasonable to 
read any of them as rejecting that possibility. However, EPA's April 
2014 guidance specifically addressed this issue as it pertains to 
requirements for SIPs for SO2 nonattainment areas under the 
2010 NAAQS, especially with regard to the use of appropriately set 
comparably stringent limitations based on averaging

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times as long as 30 days (see p. 2). EPA developed this guidance 
pursuant to a lengthy stakeholder outreach process regarding 
implementation strategies for the 2010 NAAQS, which had not yet 
concluded (or in some cases even begun) when the documents cited by the 
commenter were issued. As such, EPA's April 2014 guidance was the first 
instance in which the Agency provided recommended guidance for that 
component of this action. Consequently, EPA does not view those prior 
EPA statements as conflicting with the Agency's guidance addressing 
this specific question of how to devise a longer-term limit that is 
comparably stringent to a 1-hour critical emission value that has been 
modeled to attain the NAAQS. Moreover, EPA notes that the commenter has 
not raised specific objections to the general policy and technical 
rationale EPA provided in its proposed approval or in EPA's April 2014 
guidance for why such longer-term averaging-based limits may in 
specific cases be adequate to ensure NAAQS attainment, which we again 
summarize below.
    EPA's April 2014 guidance provides an extensive discussion of EPA's 
rationale for positing that an appropriately-set, comparably stringent 
limitation based on an averaging time as long as 30 days can, based on 
a situation's specific facts, be found to provide for attainment of the 
2010 primary SO2 NAAQS, provided it is shown to be 
comparably stringent to a 1-hour critical emission value that is 
demonstrated through modeling to attain the NAAQS. Essentially, to 
achieve such comparable stringency, rather than simply convert an 
attaining 1-hour emission rate to a longer term limit at the same 
level, it is expected that an adjustment would be needed to lower the 
emission rate as the averaging time is increased. It is first necessary 
to identify a modeled 1-hour emission value that attains the NAAQS 
before deriving a comparably stringent longer-term emission limit, 
i.e., an emission limit that has been appropriately adjusted downward. 
In evaluating this option, EPA considered in the April 2014 guidance 
the nature of the standard, conducted detailed analyses of the impact 
of the use of 30-day average limits on the prospects for attaining the 
standard, and carefully reviewed how best to achieve an appropriate 
balance among the various factors that warrant consideration in judging 
whether a state's nonattainment plan provides for attainment. Id. at 
pp. 22 to 39. See also id. at appendices B, C, and D.
    As specified in 40 CFR 50.17(b), the 1-hour primary SO2 
NAAQS is met at an ambient air quality monitoring site when the 3-year 
average of the annual 99th percentile of daily maximum 1-hour 
concentrations is less than or equal to 75 ppb. In a year with 365 days 
of valid monitoring data, the 99th percentile would be the fourth 
highest daily maximum 1-hour value. The 2010 SO2 NAAQS, 
including this form of determining compliance with the standard, was 
upheld by the U.S. Court of Appeals for the District of Columbia 
Circuit in Nat'l Envt'l Dev. Ass'n's Clean Air Project v. EPA, 686 F.3d 
803 (D.C. Cir. 2012). Because the standard has this form, a single 
exceedance of the numerical limit of 75 ppb does not constitute a 
violation of the standard. Instead, at issue is whether a source 
operating in compliance with a properly set longer-term average could 
cause exceedances, and if so the resulting frequency and magnitude of 
such exceedances. In particular, what matters is whether EPA can have 
reasonable confidence that a properly set longer-term average limit 
will provide that the 3-year average of annual fourth highest daily 
maximum values will be at or below 75 ppb. A synopsis of EPA's review 
of how to judge whether such plans ``provide for attainment,'' based on 
modeling of projected allowable emissions and in light of the form for 
determining attainment of the NAAQS at monitoring sites, follows.
    For SO2 nonattainment plans based on 1-hour emission 
limits, the standard approach is to conduct modeling using fixed 
emission rates. The maximum emission rate that would be modeled to 
result in attainment (i.e., in an ``average year'' \1\ shows fewer than 
four days with maximum hourly levels exceeding 75 ppb) is labeled the 
``critical emission value.'' The modeling process for identifying this 
critical emission value inherently considers the numerous variables 
that affect ambient concentrations of SO2, such as 
meteorological data, background concentrations, and terrain. In the 
standard approach, the state would then provide for attainment by 
setting a continuously applicable 1-hour emission limitation at this 
critical emission value.
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    \1\ An ``average year'' is used to mean a year with average air 
quality. While 40 CFR part 50, appendix T provides for averaging 
three years of 99th percentile daily maximum values (e.g., the 
fourth highest maximum daily concentration in a year with 365 days 
with valid data), this discussion and an example used later in EPA's 
response to Comment 1 uses a single ``average year'' in order to 
simplify the illustration of relevant principles.
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    EPA recognizes that some sources may have highly variable 
emissions, for example due to variations in fuel sulfur content and 
operating rate, that can make it extremely difficult, even with a well-
designed control strategy, to ensure in practice that emissions for any 
given hour do not exceed the critical emission value. EPA also 
acknowledges the concern that longer-term emission limits can allow 
short periods with emissions above the critical emission value, which, 
if coincident with meteorological conditions conducive to high 
SO2 concentrations, could create the possibility of a NAAQS 
exceedance occurring on a day when an exceedance would not have 
occurred if emissions were continuously controlled at the level 
corresponding to the 1-hour critical emission value. However, for 
several reasons, EPA finds that the approach recommended in its April 
2014 guidance document suitably addresses this concern, and that in 
this case, New Hampshire has devised a longer-term limit that is 
comparably stringent to the 1-hour critical emission value that 
suitably provides for meeting the NAAQS.
    First, from a practical perspective, EPA expects the actual 
emission profile of a source subject to an appropriately set longer-
term average limit to be similar to the emission profile of a source 
subject to an analogous 1-hour average limit. EPA expects this 
similarity because it has recommended that the longer-term average 
limit be set at a level that is comparably stringent to the otherwise 
applicable 1-hour limit (reflecting a downward adjustment from the 
critical emission value) and that takes the source's emissions profile 
into account. As a general matter, EPA would expect that any emission 
limit with an averaging time longer than 1 hour would need to reflect a 
downward adjustment to compensate for the loss of stringency inherent 
in applying a longer term average limit. This expectation is based on 
the idea that a limit based on the 30-day average of emissions, for 
example, at a particular level is likely to be a less stringent limit 
than a 1-hour limit at the same level, since the control level needed 
to meet a 1-hour limit every hour is likely to be greater than the 
control level needed to achieve the same limit on a 30-day average 
basis. EPA's approach for downward adjustment is to account for the 
expected variability in emissions over the time period up to 30 days to 
achieve comparable stringency to the emissions and expected air quality 
impacts for a 1-hour period. As a result, EPA expects

[[Page 25926]]

either form of emission limit to yield comparable air quality.
    Second, from a more theoretical perspective, EPA has compared the 
likely air quality with a source having maximum allowable emissions 
under an appropriately set longer-term limit, as compared to the likely 
air quality with the source having maximum allowable emissions under 
the comparable 1-hour limit. In this comparison, in the 1-hour average 
limit scenario, the source is presumed at all times to emit at the 
critical emission value, and in the longer-term average limit scenario, 
the source is presumed occasionally to emit more than the critical 
emission value but on average, and presumably at most times, to emit 
well below the critical emission value. In an ``average year,'' 
compliance with the 1-hour limit is expected to result in three 
exceedance days (i.e., three days with maximum hourly values above 75 
ppb) and a fourth day with a maximum hourly value at 75 ppb. By 
comparison, with the source complying with a longer-term limit, it is 
possible that additional exceedances would occur that would not occur 
in the 1-hour limit scenario (if emissions exceed the critical emission 
value at times when meteorology is conducive to poor air quality). 
However, this comparison must also factor in the likelihood that 
exceedances that would be expected in the 1-hour limit scenario would 
not occur in the longer-term limit scenario. This result arises because 
the longer-term limit requires lower emissions most of the time 
(because the limit is set below the critical emission value), so a 
source complying with an appropriately set longer-term limit is likely 
to have lower emissions at critical times than would be the case if the 
source were emitting as allowed with a 1-hour limit.
    As a hypothetical example to illustrate these points, suppose a 
source that always emits 1,000 pounds of SO2 per hour, which 
results in air quality exactly at the level of the NAAQS (i.e., results 
in a design value of 75 ppb). Suppose further that in an ``average 
year,'' these emissions cause the five highest maximum daily average 1-
hour concentrations to be 100 ppb, 90 ppb, 80 ppb, 75 ppb, and 70 ppb. 
Then suppose that the source becomes subject to a 30-day average 
emission limit of 700 pounds per hour, i.e., at a level adjusted 
downward from 1,000 pounds per hour by 30%. It is theoretically 
possible for a source meeting this limit to have emissions that 
occasionally exceed 1,000 pounds per hour, but with a typical emissions 
profile emissions would much more commonly be between 600 and 800 
pounds per hour. In this simplified example, assume a zero background 
concentration, which allows one to assume a linear relationship between 
emissions and air quality. (A nonzero background concentration would 
make the mathematics more difficult but would give similar results.) 
Air quality will depend on how much emissions occur on which critical 
hours, but suppose that emissions at the relevant times on these five 
days are 800 pounds per hour, 1,100 pounds per hour, 500 pounds per 
hour, 900 pounds per hour, and 1,200 pounds per hour, respectively. 
(This is a conservative example because the average of these emissions, 
900 pounds per hour, is well over the 30-day average emission limit of 
700 pounds per hour.) These emissions would result in daily maximum 1-
hour concentrations of 80 ppb, 99 ppb, 40 ppb, 67.5 ppb, and 84 ppb. In 
this example, the fifth day would have an exceedance that would not 
otherwise have occurred, but the third and fourth days would not have 
exceedances that otherwise would have occurred. In this example, the 
fourth highest maximum daily concentration under the 30-day average 
would be 67.5 ppb.
    This simplified example illustrates the findings of a more 
complicated statistical analysis that EPA conducted using a range of 
scenarios using actual plant data. As described in appendix B of EPA's 
April 2014 guidance, EPA found that the requirement for lower average 
emissions is highly likely to yield better air quality than is required 
with a comparably stringent 1-hour limit. Based on analyses described 
in appendix B, EPA expects that an emission profile with maximum 
allowable emissions under an appropriately set comparably stringent 30-
day average limit is likely to have the net effect of having a lower 
number of exceedances and better air quality than an emission profile 
with maximum allowable emissions under a 1-hour emission limit at the 
critical emission value. This result provides a compelling rationale 
for allowing the use of a longer averaging period, in appropriate 
circumstances where the facts indicate that this result can be expected 
to occur.
    The question then becomes whether this approach--which is likely to 
produce a lower number of overall exceedances even though it may 
produce some unexpected exceedances above the 1-hour critical emission 
value--meets the requirement in sections 110(a) and 172(c) for state 
implementation plans to ``provide for attainment'' of the NAAQS. For 
SO2, as for other pollutants, it is generally impossible to 
design a nonattainment plan in the present that will guarantee that 
attainment will occur in the future. A variety of factors can cause a 
well-designed nonattainment plan to fail and unexpectedly not result in 
attainment, for example if meteorology occurs that is more conducive to 
poor air quality than was anticipated in the plan. Therefore, in 
determining whether a plan meets the requirement to provide for 
attainment, EPA's task is commonly to judge not whether the plan 
provides absolute certainty that attainment will in fact occur, but 
rather whether the plan provides an adequate level of confidence of 
prospective NAAQS attainment. From this perspective, in evaluating use 
of a longer-term limit up to 30-days, EPA must weigh the likely net 
effect on air quality. Such an evaluation must consider the risk that 
occasions with meteorology conducive to high concentrations will have 
elevated emissions leading to exceedances that would not otherwise have 
occurred, and must also weigh the likelihood that the requirement for 
lower emissions on average will result in days not having exceedances 
that would have been expected with emissions at the critical emission 
value. Additional policy considerations, such as in this case the 
desirability of accommodating real world emissions variability without 
significant risk of violations, are also appropriate factors for EPA to 
weigh in judging whether a plan provides a reasonable degree of 
confidence that the plan will lead to attainment. Based on these 
considerations, especially given the high likelihood that a 
continuously enforceable limit, averaged over as long as 30 days, 
determined in accordance with EPA's April 2014 guidance, will result in 
attainment, EPA posits as a general matter that such limits, if 
appropriately determined, can reasonably be considered to provide for 
attainment of the 2010 SO2 NAAQS. Furthermore, as discussed 
below, EPA concludes that in this case, New Hampshire has demonstrated 
that its longer-term limit was appropriately determined and provides 
for NAAQS attainment.
    As stated by the commenter, the limit included in the State's SIP 
submittal is for a period of 7 days, or 168 hours. As stated above, EPA 
posits that limits based on periods of as long as 30 days (720 hours), 
determined in accordance with our April 2014 guidance, can, in many 
cases, be reasonably considered to provide for attainment of the 2010 
SO2 NAAQS. In EPA's April 2014 guidance, EPA supplied an 
analysis of the impact of emissions variability on air quality

[[Page 25927]]

and explained that it may be possible in some specific cases to develop 
control strategies that account for variability in 1-hour emissions 
rates through emissions limits with averaging times as long as 30 days 
and still provide for attainment of the 2010 SO2 NAAQS. 
Since seven days (168 hours) are well within the period of 30 days (720 
hours), EPA has concluded that a limit for Merrimack Station based on a 
period of 7 days and determined in accordance with EPA's April 2014 
guidance can be reasonably considered to provide for attainment.
    EPA's April 2014 guidance offers specific recommendations for 
determining an appropriate longer-term average limit. The recommended 
method starts with determination of the 1-hour emission limit that 
would provide for attainment (i.e., the 1-hour critical emission 
value), and applies an adjustment factor to determine the (lower) level 
of the longer term average emission limit that would be estimated to 
have a stringency comparable to the otherwise necessary 1-hour emission 
limit. This method uses a database of continuous emission data 
reflecting the type of control that the source will be using to comply 
with the SIP emission limits, which (if compliance requires new 
controls) may require use of a different emission database, e.g., from 
a different but comparable facility using similar emissions control 
equipment. The recommended method involves using these data to compute 
a complete set of emission averages, computed according to the 
averaging time and averaging procedures of the prospective emission 
limitation. In this recommended method, the ratio of the 99th 
percentile among these longer-term averages to the 99th percentile of 
the 1-hour values represents an adjustment factor that may be 
multiplied by the candidate 1-hour emission limit (i.e., the critical 
emission value) to determine a longer-term average emission limit that 
may be considered comparably stringent.\2\ The guidance also addresses 
a variety of related topics, such as the potential utility of setting 
supplemental emission limits, such as mass-based limits, to reduce the 
likelihood and/or magnitude of elevated emission levels that might 
occur under the longer-term emission rate limit.
---------------------------------------------------------------------------

    \2\ For example, if the critical emission value is 1,000 pounds 
of SO2 per hour, and a suitable adjustment factor is 
determined to be 0.70 (i.e., 70%), the recommended longer term 
average limit would be 700 pounds per hour.
---------------------------------------------------------------------------

    Preferred air quality models for use in regulatory applications are 
described in appendix A of the Guideline (40 CFR part 51, appendix 
W).\3\ In 2005, EPA promulgated AERMOD as the Agency's preferred near-
field dispersion modeling for a wide range of regulatory applications 
addressing stationary sources (for example in estimating SO2 
concentrations) in all types of terrain based on extensive 
developmental and performance evaluation. Supplemental guidance on 
modeling for purposes of demonstrating attainment of the SO2 
standard is provided in appendix A to EPA's April 2014 guidance. 
Appendix A provides extensive guidance on the modeling domain, the 
source inputs, assorted types of meteorological data, and background 
concentrations. Consistency with the recommendations in this guidance 
is generally necessary for the attainment demonstration to offer 
adequately reliable assurance that the plan provides for attainment.
---------------------------------------------------------------------------

    \3\ The most recent version of the Guideline was published on 
January 17, 2017 (see 82 FR 5182) and became effective on May 22, 
2017.
---------------------------------------------------------------------------

    As stated previously, attainment demonstrations for the 2010 1-hour 
primary SO2 NAAQS must demonstrate future attainment and 
maintenance of the NAAQS in the entire area designated as nonattainment 
(i.e., not just at the violating monitor) by using air quality 
dispersion modeling (see appendix W to 40 CFR part 51) to show that the 
mix of sources and enforceable control measures and emission rates in 
an identified area will not lead to a violation of the SO2 
NAAQS. For a short-term (i.e., 1-hour) standard, EPA asserts that 
dispersion modeling, using allowable emissions and addressing 
stationary sources in the affected area (and in some cases those 
sources located outside the nonattainment area which may affect 
attainment in the area) is technically appropriate, efficient, and 
effective in demonstrating attainment in nonattainment areas because it 
takes into consideration combinations of meteorological and emission 
source operating conditions that may contribute to peak ground-level 
concentrations of SO2.
    Regarding the commenter's position that only hourly SO2 
emissions limits are reasonable, citing the examples supplied in the 
commenter's submission, EPA agrees that 1-hour limits can be reasonable 
and protective so long as they are adequately supported by an 
attainment demonstration establishing those limits as meeting the 
NAAQS. In this action, EPA is not changing its position regarding the 
sufficiency in meeting the NAAQS with 1-hour emissions limitations to 
which other facilities, as cited by the commenter, are subject. The 
fact that New Hampshire could reasonably have chosen to establish 1-
hour limits does not mean that EPA should disapprove limits with 
comparable stringency using longer averaging times. In this instance, 
the State's emission limit for Merrimack Station utilizes a 7-day 
average, and New Hampshire has shown it to be comparably stringent to a 
1-hour limit at the critical emission level, which the State 
demonstrated to suitably provide for attainment of the NAAQS.
    Based on EPA's review of the State's submittal, EPA finds that the 
7-day average limit of 0.39 pounds (lb) per million British thermal 
units (MMBtu) established for Merrimack Station provides for a suitable 
alternative to establishing a 1-hour average emission limit for this 
source. New Hampshire used a suitable data profile in an appropriate 
manner and has thereby applied an appropriate adjustment, yielding 
emission limits that have comparable stringency to the 1-hour average 
limit that the State determined would otherwise have been necessary to 
provide for attainment. While the longer-term averaging limit allows 
occasions in which emissions may be higher than the level that would be 
allowed with the 1-hour limit, the State's limits compensate by 
requiring average emissions to be adequately lower than the level that 
would otherwise have been required by a 1-hour average limit. The 
September 28, 2017 notice of proposed rulemaking provided a detailed 
description of EPA's rationale for the proposed finding that the 7-day 
average limit for Merrimack Station is adequate to provide for 
attainment, and the commenter has not raised any concerns about this 
approach that we have not already addressed.
    Comment 2: The commenter states that the 7-day average approach 
would mask significant hours in which emissions are above safe levels. 
The commenter then presents information regarding historic hourly 
emissions from Merrimack Station after the flue gas desulfurization 
(FGD) scrubber system was installed. Specifically, using data from 
EPA's Air Markets Program Data (AMPD), the commenter identified over 
224 individual hours on 62 separate days in the period between January 
1, 2012, through September 30, 2017, during which emissions were above 
the 1-hour critical emission rate of 0.54 lb/MMBtu,\4\ i.e., the 
maximum

[[Page 25928]]

hourly emission rate determined to be protective of the NAAQS. The 
commenter indicated that during the same period, there do not appear to 
have been any 7-day periods in which average emissions exceeded the 
0.39 lb/MMBtu limit in the SIP revision. The commenter asserts that 
this disparity, i.e., the fact that emissions during over 224 hours on 
62 separate days exceeded the 1-hour critical emission rate of 0.54 lb/
MMBtu while the 7-day limit was not exceeded during the time period 
from January 2012 through September 2017, indicates that the downwardly 
adjusted 0.39 lb/MMBtu 7-day limit is inadequate to protect the NAAQS.
---------------------------------------------------------------------------

    \4\ In multiple instances, the Commenter appears to inaccurately 
assume the critical emission rate is 0.53 lb/MMBtu. The mass-based 
critical emission value, as calculated by the State's modeling, is 
2,544 lb/hour, which is equivalent to the critical emission rate of 
0.54 lb/MMBtu at the maximum rated capacity of Merrimack's two coal-
fired electric generating units, MK1 and MK2.
---------------------------------------------------------------------------

    Response 2: The commenter implies that occasions of emissions above 
the 1-hour critical emission rate, notwithstanding compliance with a 7-
day limit, create an unacceptable risk of additional exceedances that 
would result in violation of the standard. EPA does not agree with this 
notion, and the commenter has not supplied evidence to support it. 
Furthermore, in making this claim, the commenter is relying on an 
emissions dataset that, for the reasons enumerated below, is not 
appropriate for assessing the prospective likelihood of Merrimack 
Station emitting more than the critical emission value, which may 
result in unsafe air quality. First, the dataset includes emissions 
from periods during which Merrimack Station was not subject to State 
permit conditions on the operation of its FGD scrubber system, and is 
therefore not representative of current and expected future emissions. 
Second, the dataset includes some emission values that are 
unrealistically high because they are calculated or substitute data 
used for purposes of determining compliance with EPA's Acid Rain 
Program rather than measured data used for determining emissions for 
compliance with the 7-day limit. Third, emission data for Merrimack 
Station show that the facility has rarely emitted above the critical 
emission rate of 0.54 lb/MMBtu since September 1, 2016, when the 
State's permit TP-0189 became applicable and enforceable. Fourth, the 
State's rate-based emission limit is designed to ensure consistent 
control at all load levels during operation, so an exceedance of the 
critical emission rate (in lb/MMBtu) does not necessarily mean that 
emissions are higher than the critical emission value (in lb/hour). 
Fifth and finally, if actual measured emissions from Merrimack Station 
had occurred at the levels indicated by the commenter, the facility 
would have violated the current 7-day emission limit, had it been in 
place at the time, and therefore these data are not evidence that 
compliance with the 7-day limit would result in a higher risk of NAAQS 
violations. Each of these points is discussed in greater detail below.
    By reviewing the AMPD emissions data using EPA's Field Audit 
Checklist Tool (FACT) \5\ for the period between January 1, 2012, and 
March 31, 2018, EPA found 227 hours with emissions above 0.54 lb/MMBtu, 
a number that is consistent with the ``over 224 hours'' identified by 
the commenter. In the following discussion, EPA identifies the number 
of hours of those 227 hours that are not appropriate to use in the 
analysis of the adequacy of the 7-day emission limit. EPA has included 
a spreadsheet in the docket of this action which contains the relevant 
data used in EPA's analysis.
---------------------------------------------------------------------------

    \5\ Field Audit Checklist Tool (FACT) version 1.2.0.1, available 
for download at: www.epa.gov/airmarkets/field-audit-checklist-tool-fact. FACT provides users with metadata, including ``method of 
determination codes'' (MODC), beyond the information available using 
the AMPD website referenced by the Commenter.
---------------------------------------------------------------------------

    (1) The FGD at Merrimack Station first became operational on 
September 28, 2011. Under the conditions established in the State's 
permit TP-0008, Merrimack Station was not permitted to operate MK2, one 
of its two utility boilers, unless the FGD was in operation. Merrimack 
Station's other utility boiler, MK1, was permitted to bypass the FGD 
system for no more than 840 hours per consecutive 12-month period. Both 
of these permit conditions became applicable and enforceable as of July 
1, 2013. (This emission bypass provision is no longer permitted under 
the September 1, 2016 TP-0189 permit.) Prior to July 1, 2013, the 
facility was not subject to enforceable permit conditions requiring 
operation of the FGD. During 2012, Merrimack Station bypassed the FGD 
for emissions from MK1 on several occasions, the last of which occurred 
on November 7, 2012. As such, EPA does not view emissions occurring at 
Merrimack Station prior to July 1, 2013 as being representative of 
current or expected future emissions because prior to this date the 
relevant, enforceable permit provisions that required operation of the 
emission control system at Merrimack Station, as contained in permit 
number TP-0008, were not effective. Of the 227 hours with emissions 
above 0.54 lb/MMBtu, there were 188 hours that occurred prior to July 
1, 2013, leaving 39 hours for further analysis.
    (2) Merrimack Station is subject to emission monitoring and 
reporting requirements under the Acid Rain Program (40 CFR part 75). 
Under the Acid Rain Program, Merrimack Station must hold sufficient 
emission allowances to account for its SO2 emissions. For 
hours in which direct, quality-assured measurements from the continuous 
monitoring systems (CEMS) are not available, EPA's Acid Rain Program 
regulations require that high emission values are calculated or 
substituted for the emissions that are not monitored in order to ensure 
that the source holds sufficient allowances to account conservatively 
for its emissions. See 40 CFR part 75 subpart D. As described in New 
Hampshire's response to comments for its nonattainment area plan, the 
CEMS at Merrimack Station was certified on November 21, 2011 using only 
the low range of a dual range analyzer to measure from 0 to 300 parts 
per million (ppm) SO2 of in-stack exhaust gas. When the low 
range was exceeded, i.e., in-stack exhaust gas exceeded 300 ppm 
SO2, a calculated value of 200% of the maximum potential or 
uncontrolled concentration was reported to ensure that under reporting 
did not occur for purposes of the Acid Rain Program. As part of a 
periodic reassessment of the appropriate analyzer ranges, Merrimack 
Station retained a low range configuration and adjusted it to measure 
from 0 to 150 ppm on January 28, 2013. See section 2.1.1.5 of appendix 
A to 40 CFR part 75. On February 4, 2015, Merrimack Station began 
calibrating and quality-assuring the high range of the dual range 
analyzer from 150 to 2,600 ppm, while the lower range continued to be 
quality assured to measure between 0 and 150 ppm. In accordance with 
Acid Rain Program requirements, Merrimack Station was required to 
report calculated emissions at 200% of the maximum potential or 
uncontrolled concentration during the period from November 21, 2013 to 
February 4, 2015 when concentrations exceeded the lower range, i.e., 
in-stack exhaust gas exceeded 300 ppm. See section 2.1.1.4(f) of 
Appendix A to 40 CFR part 75. These hours are marked as SO2 
Method Of Determination Code (MODC) 19 in the FACT database and were 
reported as such in the hourly electronic emissions records. Additional 
CEMS outage hours that used substitute data calculated as the average 
of the hour before and after, reported as SO2 MODC 06, are 
not measured emissions data but rather are substitute data hours. EPA 
concludes from the CEMS data that data points flagged as calculated or 
substitute data

[[Page 25929]]

with SO2 MODC 06 or 19 are not appropriate for use in 
assessing NAAQS compliance in this case because these values do not 
represent actual measured emissions during those hours.
    Data points flagged as SO2 MODC 06 or 19 account for 32 
hours of the remaining 39 emissions data points over 0.54 lb/MMBtu, 
leaving seven hours for further analysis.
    (3) The emission profile for Merrimack Station, since the issuance 
of the September 2016 permit containing the 7-day average 
SO2 emissions limit, shows that exceedances of the critical 
emission rate, i.e., 0.54 lb/MMBtu, are infrequent. In the period from 
September 1, 2016, when the State's permit TP-0189 became applicable 
and enforceable, to March 31, 2018, Merrimack Station has emitted at a 
level higher than the 0.54 lb/MMBtu on three hours out of 3,109 
operating hours with measured emissions data, or less than 0.1%. In 
addition to the SO2 emission limit, the September 1, 2016 
permit TP-0189 included a more stringent limit for the SO2 
removal efficiency of the scrubber than was included in the TP-0008 
permit. In addition, TP-0189 prohibits the use of the emergency stack 
to bypass emissions controls except as necessary to prevent severe 
damage to equipment or potential injury to facility personnel. The 
infrequency of emissions above 0.54 lb/MMBtu since September 1, 2016 
indicates that the multiple SO2 emission control provisions 
contained in TP-0189, as described above, have been successful in 
consistently reducing emissions from Merrimack Station. Based on this 
evidence, EPA expects that future instances of emissions from Merrimack 
Station above 0.54 lb/MMBtu will continue to be extremely rare.
    (4) While emissions exceeded 0.54 lb/MMBtu during each of the seven 
hours since July 1, 2013 (of which only three hours exceeded 0.54 lb/
MMBtu since September 1, 2016, as described above), for six of these 
hours the total mass-based emission rate, measured in lb/hour, did not 
exceed the critical emission value of 2,544 lb/hour. Of those six 
hours, the highest emission level was 1,386.6 pounds of SO2, 
well below the critical emission value, and the other emission values 
range from 1.1 to 843.5 pounds SO2. Based on the State's 
attainment modeling demonstration, these lower emission values would 
not be expected to result in exceedances of the NAAQS. That is, New 
Hampshire's modeling indicates that Merrimack Station could emit 
constantly at the mass-based emission value for each of those six hours 
and the area would attain the standard.
    Only one hour had emissions above the critical emission value of 
2,544 lb/hour. Specifically, Merrimack emitted 2,578.6 pounds of 
SO2 on December 1, 2015 during the 7 a.m. hour.
    EPA does not regard the single hour on December 1, 2015 at 7 a.m., 
during which Merrimack Station had emissions over the critical emission 
value, by itself as representing a serious risk for causing a violation 
of the NAAQS. EPA has previously acknowledged that there could possibly 
be hourly emission levels above the critical emission value from a 
source complying with a longer-term average emission limit, e.g., a 7-
day limit. As stated in the proposal, an hour where emissions are above 
the critical emission value does not necessarily mean that a NAAQS 
exceedance is occurring in that hour. Similarly, an individual hour 
where emissions are above the level of the comparably stringent 7-day 
limit (0.39 lb/MMBtu in this instance) does not mean that an exceedance 
of the NAAQS is occurring in that hour, especially if the level of 
emissions is below the critical emission value. This notion also does 
not take into account the possible exceedances that would be expected 
with emissions always at the critical emission value that would 
otherwise be avoided because emissions are generally required to be 
lower (in this case, on average 27% lower). Based on this reasoning, 
EPA concludes that the risk of an exceedance for the one hour with 
emissions above the critical emission value of 2,544 lb/hour during 
4.75 years of emissions from Merrimack Station (from July 1, 2013 to 
March 31, 2018) does not suggest that a violation of the NAAQS is 
likely to have occurred.
    (5) Notwithstanding the explanations above regarding the 
appropriateness of omitting certain data points from considering NAAQS 
compliance, such emissions data, if they had actually been 
representative of real emissions, would have caused a violation of the 
permit conditions for Merrimack Station, if the 7-day permit limit had 
been in place at the time. EPA has evaluated the Merrimack Station 
emissions data for the period January 1, 2012 through March 31, 2017 in 
accordance with the 7-day average emission rate limit, both with and 
without the omission of data points flagged as calculated or substitute 
data.
    This evaluation found 27 periods during which the associated 7-day 
emission average would have violated the terms of the permit 
conditions, had those terms been in place at the time and assuming that 
all data points flagged as calculated or substitute data are actual 
emissions. Of the 27 7-day periods, 26 occurred in 2012, while the 
facility was still permitted to bypass the FGD system, a practice that 
is not permitted under the conditions of the September 2016 permit TP-
0189. Even by omitting data points flagged as calculated or substitute 
data, none of the 7-day emission averages associated with these 26 7-
day periods in 2012 would have met the 7-day emission limit, had it 
been in place at the time.
    The one remaining 7-day period ended on December 11, 2014, and the 
associated 7-day emission average of 0.419 lb/MMBtu would have exceeded 
the emission limit of 0.39 lb/MMBtu, if data points flagged as 
calculated or substitute data were treated as actual emissions. By 
omitting the calculated or substitute data from this time period, the 
7-day emission average ending on December 11, 2014 would have been 0.20 
lb/MMBtu, which would comply with the 7-day limit of 0.39 lb/MMBtu, had 
it been in place at the time.
    This finding contradicts the commenter's assertion that the ``over 
224'' individual hours with emissions purportedly higher than the 
critical emission rate would not have resulted in an exceedance of the 
7-day average limit. On the contrary, even if the emissions with 
reported emissions above the critical emission value did represent 
actual emissions, which EPA argues in the previous sections is 
incorrect, Merrimack Station would have been out of compliance with the 
7-day limit permit had it been in effect at the time.
    Therefore, based on the reasoning supplied in the sections above, 
EPA disagrees with the commenter that emissions data from Merrimack 
Station demonstrate the inadequacy of the 7-day emission limit imposed 
by the State. Rather, the data most representative of Merrimack 
Station's current and expected future emissions indicate that the 
facility, when complying with the applicable permit restrictions, is 
extremely unlikely to cause a violation of the SO2 NAAQS. 
The emissions data presented by the commenter are not representative of 
Merrimack Station's current and expected future emissions, and are 
therefore not appropriate for use in assessing NAAQS compliance in this 
case.
    EPA offers the following additional discussion to further respond 
directly regarding the sufficiency of an appropriately-calculated, 
longer-term average limit, up to 30-days, with comparable stringency to 
a 1-hour critical emission value, to provide for attainment of the 1-
hour NAAQS. EPA has conducted analyses to evaluate the extent to which 
longer-term average

[[Page 25930]]

limits that have been adjusted to have comparable stringency to 1-hour 
limits at the critical emission value provide for attainment. In brief, 
while a longer-term average limit as approved in this action will allow 
occasions when emissions exceed the critical emission value, the use of 
a lower limit (i.e., as adjusted downward) compensates by requiring 
most values to be lower than they are required to be with a 1-hour 
limit at the critical emission value. EPA expects that the net result 
for this action will be that the comparably stringent limit will 
provide a sufficient constraint on the frequency and magnitude of 
occurrences of elevated emissions such that this control strategy based 
on the comparably stringent limit will reasonably provide for 
attainment.
    As stated in appendix B of EPA's April 2014 guidance, the Agency 
acknowledges that even with an adjustment to provide comparable 
stringency, a source complying with a longer term average emission 
limit could possibly have hourly emissions which occasionally exceed 
the critical emission value. It is important to recognize that an hour 
where emissions are above the critical value does not necessarily mean 
that a NAAQS exceedance is occurring in that hour. EPA's April 2014 
guidance states that ``if periods of hourly emissions above the 
critical emission value are a rare occurrence at a source, these 
periods would be unlikely to have a significant impact on air quality, 
insofar as they would be very unlikely to occur repeatedly at the times 
when the meteorology is conducive for high ambient concentrations of 
SO2'' (p. 24).
    Exceedances of the SO2 NAAQS occur when emissions from 
relevant sources are sufficiently high on occasions when the 
meteorology is conducive for those emissions to cause elevated 
SO2 concentrations. An illustrative example would be a case 
in which a single source has a dominant impact on area concentrations, 
and the source only causes an exceedance at a particular location with 
light southwest winds with limited dispersion. In this example, the 
likelihood of an exceedance at that location will be a function of the 
likelihood of elevated emissions occurring during times of light 
southwest winds with limited dispersion. Stated more generally, the 
likelihood of an exceedance is a function of the likelihood of 
emissions being high when the meteorology is conducive for the source 
to cause an exceedance. By extension, the likelihood of a violation is 
a function of the likelihood of emissions being high on a sufficient 
number of times with meteorology conducive to having exceedances to 
have the average of the 99th percentile daily maximum values exceed the 
NAAQS. Viewed another way, the occasions when the meteorology is 
conducive for the source to cause an exceedance at a particular 
location are likely to be infrequent, and high concentrations are 
contingent on both emissions being sufficiently high and the 
meteorology being sufficiently conducive. The NAAQS itself is based on 
relatively rare occurrences, being based on the 99th percentile of 
daily maximum concentrations. Nevertheless, the point here is that the 
occurrence of high emissions will not cause an exceedance if it does 
not occur when meteorology is conducive to having an exceedance. 
Furthermore, a source with rare occurrences of high emissions and with 
much more frequent occurrences of moderate emissions is more likely to 
have moderate emissions on those occasions with meteorology conducive 
for exceedances, and the design value for the source may be more prone 
to reflect the moderate emissions than the high emissions.
    Thus, for a source complying with a limit using an averaging period 
of up to 30 days reflecting the downward adjustment generally 
recommended in EPA's April 2014 guidance, at issue is the likelihood 
that the source would have sufficiently high emissions on a sufficient 
fraction of the potential exceedance days to cause an SO2 
NAAQS violation. Although results will differ according to individual 
circumstances, EPA has presented illustrative analyses (see appendix B 
of EPA's April 2014 guidance) that indicate that suitably adjusted 
longer-term average limits can generally be expected to provide 
adequate confidence that the attainment plan will provide for 
attainment.
    Therefore, based on the reasoning presented above, EPA disagrees 
with the commenter about the over 224 hours with emissions purported to 
be higher than the critical emission rate, and concludes that the 
longer-term limit for Merrimack Station is not expected to lead to a 
greater risk of a future violation of the NAAQS.
    Comment 3: The commenter stated that New Hampshire's approach to 
develop a longer-term averaging period using an ``adjustment ratio'' is 
problematic.\6\ Specifically, the commenter posits that the period of 
time selected by the State (i.e., July 4, 2013 through March 30, 2015) 
is not representative of current or expected future operations at 
Merrimack Station. The commenter stated that the State did not disclose 
the nature of data corrections provided by the Merrimack Station's 
owner at the time PSNH in documentation accompanying the proposed 
permit for the facility. The commenter indicated that the nondisclosure 
regarding the nature of the corrections raises concerns about the 
accuracy of the State's analysis. For future operations, the commenter 
points to New Hampshire's projection of Merrimack Station's annual 
emissions for 2018 of 1,907 tons SO2, which is nearly double 
the annual emissions total of 1,044 tons SO2 for the 
facility in 2014. The commenter asserts that the time period selected 
for developing the adjustment factor is arbitrary and not 
representative of expected future operations, and that therefore the 
State should have selected a different time period. The commenter 
identified ``significant spikes'' in hourly emissions in the months 
before or after the time period selected by the State that are not 
included in the State's emissions database. The commenter suggested 
that these emission ``spikes'' are inappropriately excluded, and as a 
result the State's results are likely to be skewed. The commenter 
provides several alternative adjustment factors based on different time 
periods that include periods with emission ``spikes,'' including an 
adjustment factor for each year from 2012 through 2015; the period of 
July 4, 2013 through March 30, 2015, used by the State in its analysis; 
and the 25-month period from March 1, 2013 through March 30, 2015. The 
alternative adjustment factors for these periods vary from 0.34 to 
0.90, which would result in associated 7-day limits of between 0.19 to 
0.48 lb/MMBtu. The commenter states that selecting the wrong time 
period for analysis can result in a more than doubling of the resulting 
emission rate. The commenter concludes that the methodology New 
Hampshire used for developing a 7-day emission rate is inadequate 
because the adjustment factor depends greatly on which temporal series 
of emissions data is examined.
---------------------------------------------------------------------------

    \6\ EPA terms these ratio values ``adjustment factors.''
---------------------------------------------------------------------------

    Response 3: EPA analyzed the commenter's assertion regarding 
variability in adjustment factors based on the time period selected. An 
adjustment factor is a value multiplied by the 1-hour critical emission 
value (i.e., the maximum 1-hour emission value established to be 
protective of the NAAQS) to determine a downwardly adjusted longer-term 
average limit for an emission unit at a level that EPA would expect to 
be comparably stringent to a

[[Page 25931]]

1-hour limit set at the critical emission value.
    As stated in EPA's April 2014 guidance, we expect that establishing 
an appropriate longer-term average limit will involve assessing a 
downward adjustment in the level of the limit that would provide for 
comparable stringency. This assessment should generally be conducted 
using data obtained by CEMS, in order to have sufficient data to obtain 
a robust and reliable assessment of the anticipated relationship 
between longer-term average emissions and 1-hour emission values. This 
is necessary to have a suitable assessment of the warranted degree of 
adjustment of the longer-term average limit in order to provide 
comparable stringency to the 1-hour emission rate that is determined to 
provide for attainment. EPA generally expects that datasets reflecting 
hourly data for at least 3 to 5 years of stable operation (i.e., 
without changes that significantly alter emissions variability) would 
be needed to conduct a suitably reliable analysis.
    For Merrimack Station, at the time that New Hampshire had conducted 
its analysis, only approximately 21 months of emissions data were 
available that were consistent with anticipated current and future 
operations. Specifically, the emissions units at Merrimack Station 
became subject to certain enforceable conditions contained in permit 
number TP-0008 beginning on July 1, 2013. Thus, emissions from 
Merrimack Station prior to July 1, 2013 are not expected to have an 
emissions profile consistent with the current and anticipated future 
emissions profile for those units. March 2015 was selected by the State 
as the end point of the emissions dataset because it was the last month 
in which data were available through AMPD at the time it conducted the 
analysis. During the period assessed by the State, the combined 
emissions from Merrimack Station's units MK1 and MK2 were always 
controlled by FGD and the dataset includes emissions representative of 
current and expected future typical operations, including startup and 
shutdown events. Because the dataset includes only data from Merrimack 
Station while using the control technology, it is appropriate for use 
in developing adjustment factors for emission limits at this facility. 
EPA has concluded that New Hampshire used data from an appropriate time 
period.
    Prior to deriving the adjustment factor, the State removed several 
data points from the AMPD dataset based on information provided by the 
facility. A justification for removal of these data points was included 
in the State's response to comments document to permit TP-0189 
(included in New Hampshire's Finding of Fact document), which was also 
included in the State's SIP submittal. Specifically, New Hampshire 
justified the removal of several data points because of quality 
assurance issues. The State indicated in its response to comments 
document that substitute data was included within the AMPD dataset for 
hours with emissions at levels the CEMS had not been appropriately 
maintained and quality assured to measure. The State indicated and EPA 
agrees that these substitute emission data are not representative of 
actual emissions. According to the State's SIP submittal, the 
SO2 dual span analyzer in the CEMS was adjusted as of 
February 4, 2015, to better characterize both lower- and higher-end 
emissions. In its response to comments, the State provided an hour-by-
hour listing of the omitted data points, and a detailed discussion of 
the reasoning for these omissions. The State's Findings of Fact 
document is included in the docket for this action. As such, EPA notes 
that New Hampshire sufficiently provided its rationale and approach for 
removing certain data points from the AMPD dataset in the State's 
response to comments document. Therefore, EPA concludes that the State 
has appropriately disclosed the nature of the data corrections in the 
State's SIP submittal, and that the public has had adequate notice and 
opportunity to comment on the State's justification for data removal in 
the current rulemaking process. EPA has placed the raw data that New 
Hampshire used in the docket for this action, but EPA asserts that the 
information provided by the State and by EPA in its proposal was 
adequate to clarify EPA's rationale for concurring with the State's 
analysis of the data.
    Regarding the omission of calculated or substitute data, the 
calculated or substitute data points are not reliable indicators of 
emissions during those hours and are not appropriate for inclusion in 
the calculation of the adjustment factor. Based on this reasoning, EPA 
considers the State's omission of these values in the calculation of 
the adjustment factor to be appropriate.
    The adjustment factor was calculated as the ratio of the 99th 
percentile of mass emissions for the 7-day average period to the 99th 
percentile of 1-hour mass emissions. For the rolling 7-day averaging 
period, the adjustment factor was 0.73. That is, using EPA's 
recommended approach for determining comparably stringent limits, the 
7-day mass emission rate limit would need to be 0.73 times (or 27% 
lower than) the critical emission value to have stringency comparable 
to a 1-hour limit at the critical emission value. The State multiplied 
its adjustment factor of 0.73 to the critical emission rate of 0.54 lb/
MMBtu to derive a comparably stringent emission rate of 0.39 lb/MMBtu. 
EPA has confirmed that the State appropriately implemented the 
recommended methodology for developing an adjustment factor based on 
the State's supplied dataset. EPA notes that this emission database 
does include hours representative of startup and shutdown conditions, 
as well as hours with elevated emissions or ``spikes.''
    There were five individual alternative adjustment factors for 
Merrimack Station presented by the commenter as evidence that EPA's 
methodology (including adjustment factors) is not appropriate for 
developing emissions limitations based on averaging times for periods 
up to 30 days. Four of the five alternative adjustment factors 
presented by the commenter are based upon only one year of emissions 
data for each of the annual periods of 2012 through 2015. One of the 
periods presented includes emissions over a period of 25 months, 
specifically for the period from March 2013 through March 2015 
resulting in an alternative adjustment factor of 0.47, compared to the 
State's adjustment factor of 0.73 based on the 21-month time period of 
July 2013 through March 2015. None of the alternative adjustment 
factors provided by the commenter were calculated in accordance with 
the recommendations contained in EPA's April 2014 guidance. 
Specifically, EPA stated in its April 2014 guidance ``that data sets 
reflecting hourly data for at least 3 to 5 years of stable operation 
(i.e., without changes that significantly alter emissions variability) 
would be needed to obtain a suitably reliable analysis'' (p. 30). 
Furthermore, the alternative adjustment factors for March 2013 through 
March 2015 and the annual periods for 2012 and 2013 as presented by the 
commenter include periods of time (i.e., those prior to July 1, 2013 
when FGD use was not an enforceable State permit condition) during 
which operations are not representative of current and expected future 
operations at Merrimack Station, as discussed in greater detail in our 
response to Comment 2 of the notice. The remaining alternative 
adjustment factors that do not contain periods of time prior to July 1, 
2013, i.e., the annual periods for 2014 and 2015, are 0.90 and 0.70, 
respectively, which are reasonably consistent with the State's finding 
based

[[Page 25932]]

on a larger dataset. However, the commenter's results illustrate a 
point that EPA considered in formulating its guidance, which is that 
using insufficient data, e.g., using only one year's data, is prone to 
yield results that vary unduly by data period and may not be a 
sufficiently robust basis for determining a reliable adjustment factor. 
The variability of these annual values demonstrates the insufficiency 
of the annual time period for use in development of such an adjustment 
factor, but does not demonstrate the insufficiency of the method 
contained within EPA's April 2014 guidance had it been appropriately 
applied, nor does it demonstrate that New Hampshire's adjustment factor 
is inappropriate.
    EPA recognizes that the State used 21 months in its emissions 
variability analysis instead of the 3 to 5 years recommended for use in 
EPA's April 2014 guidance. As such, EPA has evaluated whether the 
period used by the State results in an appropriate adjustment factor. 
Specifically, EPA compared the State's adjustment factor to EPA's 
average 30-day adjustment factor for comparable sources. Merrimack 
Station's FGD system employs a wet scrubber, and so EPA compared New 
Hampshire's adjustment factor to the average adjustment factors listed 
in appendix D of the April 2014 guidance for sources with wet scrubbers 
(derived from a database of 210 sources). For this set of sources, EPA 
calculated an average adjustment factor for 30-day average limits of 
0.71 and an average adjustment factor for 24-hour limits of 0.89. The 
comparison of New Hampshire's adjustment factor of 0.73 for a 7-day 
limit for Merrimack Station suggests that the 21 months of data at 
Merrimack Station have variability that is quite similar to that of 
other similar facilities in the United States. Based on this 
comparison, EPA concludes that the State's adjustment factor is 
reasonable and will result in an appropriate downward adjustment from 
the critical emission value.
    Based on the State's SIP submittal, New Hampshire's future 
projection of SO2 emissions at Merrimack Station to 2018 
indicates an increase of nearly 85% compared to 2014 emissions for the 
facility. Specifically, Tables 5-1B and 5-2B of the State's SIP 
submittal indicate that Merrimack Station's SO2 emissions 
were 1,044 tons in 2014 and are projected to be 1,927 tons in 2018. The 
emission projection for 2018 includes the caveat from the State that it 
relies on an assumed control efficiency for the FGD of 90%, which is 
less efficient than the updated control efficiency of 94% for the FGD 
included in the State's SIP submittal. Nevertheless, this projected 
increase in annual emissions does not, however, indicate a different 
emissions profile. That is, based on available information, EPA does 
not expect an increase in the variability of hourly emissions due to an 
increase in annual emissions. In fact, the attainment demonstration 
included in New Hampshire's SIP submittal indicates that annual 
SO2 emissions at the critical emission value, equivalent to 
annual emissions of 11,144 tons, is anticipated to be protective of the 
2010 SO2 NAAQS. The State's comparably stringent 7-day 
average limit of 0.39 lb/MMBtu equates to total annual SO2 
emissions of 8,047 tons. Both values are above the State's 2018 
projected emissions of 1,927 tons. Because New Hampshire's attainment 
demonstration shows that the critical emission value is protective of 
the NAAQS, and the State's 7-day limit is comparably stringent to the 
1-hour critical emission value, EPA concludes that the State's 
projected 85% increase in annual SO2 emissions from 2014 to 
2018 would not result in a violation of the NAAQS.
    Therefore, based on the reasoning presented above, EPA has 
concluded that the commenter has not demonstrated that the State 
developed its adjustment factor for Merrimack Station inappropriately, 
or that the State's 7-day limit for Merrimack Station derived using the 
adjustment factor is inadequate.
    Comment 4: The commenter indicates that the polar receptor grid 
used by the State in its modeling analysis is inadequate because of the 
small overall number of receptors and lack of coverage over large areas 
of land. The commenter states that the polar grid ensures that the 
model will underpredict concentrations due to these ``blind spots,'' 
areas where there are no receptors and which the model will overlook 
when the wind is blowing in their direction across the sources. Because 
the model is ultimately the basis for the development of the emissions 
limit for Merrimack Station, the commenter posits that the polar 
receptor grid with contiguous radial coverage gaps is improper.
    Response 4: EPA agrees with the commenter that simple polar grids 
alone may not be appropriate for use without refinement in refined 
modeling analyses, though inclusion of a polar receptor grid does not 
in and of itself disqualify an attainment demonstration.
    Receptors are points that represent physical locations at which the 
air dispersion models will predict ambient pollutant concentrations. 
Groups of Cartesian or polar receptors usually are defined as a 
receptor grid network or grid. The primary purpose of this network or 
grid is to locate the maximum impact of concern per pollutant and 
averaging period. Deciding which type to use is largely a function of 
the type of modeling being performed (screening or refined), the size 
and number of emission sources, or the site location (including 
topography), and should be selected to provide the best ``coverage'' 
for the facility being modeled. Two types of receptors are generally 
employed: (1) A Cartesian receptor grid, which consists of receptors 
identified by their x (east-west) and y (north-south) coordinates; and 
(2) a polar receptor grid that consists of receptors identified by 
their distance and direction (angle) from a user defined origin (e.g., 
main boiler stack). Discrete receptors are used to identify specific 
locations of interest (e.g., school, community building). A modeling 
receptor grid may consist of any combination of discrete, polar, or 
Cartesian receptors, but must provide sufficient detail and resolution 
to identify the maximum impact.
    On October 30, 2015, the State submitted preliminary modeling to 
EPA for the attainment demonstration for the Central New Hampshire 
Nonattainment Area. EPA responded on January 6, 2016, to the State's 
preliminary modeling submittal. In EPA's response, the Agency indicated 
that section 4.2.1.2(b) of the Guideline \7\ describes the process for 
performing screening modeling in areas with complex terrain. As stated 
in our letter, in areas with complex terrain, ``even relatively small 
changes in a receptor's location may substantially affect the predicted 
concentration.'' The Guideline recommended a dense array of receptors 
in those situations, and suggests two modeling runs: the first with ``a 
moderate number of receptors carefully located over the area of 
interest,'' and a second with ``a more dense array of receptors in 
areas showing potential for high concentrations, as indicated by the 
results of the first model run.'' This process is also consistent with 
section 7.2.2 (Critical Receptor Sites) of the Guideline, which states 
that ``selection of receptor sites should be a case-by-case 
determination taking into consideration the topography, the 
climatology, monitor sites, and the results of the initial screening 
procedure.'' In our letter to New

[[Page 25933]]

Hampshire, EPA noted that the preliminary modeling results (i.e., those 
presented to the Agency on October 30, 2015) showed maximum 
concentrations resulting from Merrimack Station's SO2 
emissions in areas of complex terrain between 9 to 13 kilometers from 
Merrimack Station. EPA stated that the polar receptor grid at those 
distances from the source were insufficiently dense to properly 
characterize the extent of the impacts at locations with complex 
terrain. For example, at 13 kilometers from the source, the lateral 
distance between receptors is greater than 2 kilometers. EPA also 
indicated that other locations with similar terrain characteristics in 
the same general distance (i.e., 9-13 kilometers) from Merrimack 
Station did not have adequate receptor coverage. To address this issue, 
EPA suggested in its January 6, 2016 letter, that New Hampshire perform 
refined modeling consistent with its existing protocol, but with a 
denser array of receptors in the areas shown in the preliminary 
modeling to have the potential for high concentrations. Specifically, 
areas of complex terrain at distances within 15 kilometers of Merrimack 
Station, and particularly such areas to the northeast, were suggested 
by EPA to be modeled with high resolution receptor grids. EPA listed 
these areas and provided a map of these areas to the State. EPA 
indicated that these terrain features have the potential to be highly 
impacted by Merrimack Station because of their geographic 
characteristics and locations, but were not well characterized by the 
preliminary modeling due to the sparseness of the polar grid at 
distances beyond around 5 kilometers.
---------------------------------------------------------------------------

    \7\ At the time of EPA's January 6, 2016 letter to New 
Hampshire, the update to the Guideline had not yet been finalized 
and was not in effect. Therefore, the applicable Guideline was the 
version published on November 9, 2005 (see 70 FR 68218).
---------------------------------------------------------------------------

    In response to EPA's January 2016, letter, the State included 
additional receptors in these areas for its refined modeling conducted 
in February 2016. Specifically, New Hampshire included 2,308 additional 
receptors in dense Cartesian arrays with 100-meter spatial resolution 
over the areas of expected maximum predicted concentrations based on 
preliminary modeling, including over the areas suggested by EPA within 
5-15 kilometers from Merrimack Station. After reviewing the receptor 
grid included by the State in its refined modeling, EPA concludes that 
areas of complex terrain within 15 kilometers have adequate coverage to 
identify potential impacts in those areas. This conclusion is 
consistent with the statement in section 4 (Models for Carbon Monoxide, 
Lead, Sulfur Dioxide, Nitrogen Dioxide and Primary Particulate Matter) 
of the Guideline (specifically section 4.2(a)) that ``[i]n most cases, 
maximum source impacts of inert pollutants will occur within the first 
10 to 20 km from the source.'' Furthermore, EPA's review of both the 
preliminary and refined modeling indicate that these areas of complex 
terrain are likely to include the highest impact area. Therefore, EPA 
finds that the modeling domain and receptor network are sufficient to 
identify maximum impacts from Merrimack Station, and are therefore 
adequate for characterizing the nonattainment area.
    Comment 5: The commenter pointed out an error in Table 3-1 of the 
State's draft SIP submittal. Specifically, the commenter indicated that 
Table 3-1 incorrectly showed areas that are undesignated in New 
Hampshire as being designated Unclassifiable. The commenter indicated 
that those areas should instead be identified as undesignated.
    Response 5: EPA agrees with the commenter that all areas in New 
Hampshire other than the Central New Hampshire Nonattainment Area were 
undesignated as of the date of New Hampshire's submittal (i.e., January 
31, 2017). In its response to this identical comment on its proposed 
SIP submittal, the State indicated that Table 3-1 had been corrected. 
EPA has verified that the State did indeed correct the table. EPA notes 
that revised recommendations from New Hampshire other than those listed 
in Table 3-1 were received by EPA in December 2016, specifically for 
attainment at the New Hampshire Seacoast area and attainment/
unclassifiable for all other previously undesignated areas. 
Furthermore, on January 9, 2018, EPA published a document of a final 
rule that designated all areas in New Hampshire other than the Central 
New Hampshire Nonattainment Area as attainment/unclassifiable (see 83 
FR 1098, 1143, to be codified at 40 CFR 81.330). These inconsistencies 
in Table 3-1 with subsequent occurrences have to do with the timing of 
the SIP submittal along with the December 2016 update to the State's 
recommendations and EPA's January 9, 2018 final designations. These 
inconsistencies do not affect EPA's view of whether New Hampshire has 
satisfied applicable nonattainment planning requirements.
    Comment 6: The commenter states that the State's SIP submittal 
incorrectly indicates that an attainment demonstration can be made 
based on monitor readings alone. This idea is contrary to other 
statements in the State's SIP submittal, and also to EPA's April 2014 
guidance, which states that monitor data alone is insufficient for an 
attainment demonstration, and that modeling analyses are also required. 
The commenter asserts that the statement should be removed from the 
State's SIP submittal.
    Response 6: The State indicated in its response to an identical 
comment on its draft SIP submittal that it planned to remove the phrase 
``and thus may be able to demonstrate attainment for the SO2 
NAAQS'' from Section 3.1.1 on page 9 of its SIP submittal. In doing so, 
the State would be satisfying the request made by the commenter. 
However, the erroneous phrase still appeared in the State's January 31, 
2017 SIP submittal to EPA. EPA agrees with the commenter that the 
phrase is incorrect and ought not to be in the plan. EPA communicated 
with the State to confirm that it had intended to remove the phrase as 
indicated by the State's response to comments on its draft SIP 
submittal, and to suggest a clarification. On November 29, 2017, New 
Hampshire sent EPA a letter indicating that the language had been 
erroneously included in its January 31, 2017 submittal, and providing a 
corrected page 9 of the State's SIP submittal. EPA considers this 
amended version (i.e., the January 31, 2017, submittal as amended by 
the November 29, 2017, correction on page 9) to be consistent with the 
State's record, as included in its response to comments.
    Comment 7: The commenter identifies an error in Table 5-1B of the 
State's draft SIP submittal. Specifically, the commenter indicates that 
the table erroneously states that the total estimated emissions for the 
Central New Hampshire Nonattainment Area for 2014 was 22,947 tons of 
SO2. The commenter further states that the proper total for 
2014 emissions should be 1,480 tons of SO2. The commenter 
indicates that the figure is assumed to be an error that should be 
corrected.
    Response 7: EPA agrees with the commenter that the total 2014 
emissions within the Central New Hampshire Nonattainment Area should be 
1,480 tons SO2. The commenter had supplied an identical 
comment on New Hampshire's draft SIP submittal, and the State's 
response to comment document included in its final SIP submittal stated 
that the error would be corrected. As indicated by the State in its 
response to comments, Table 5-1B shows the corrected value. As such, 
EPA considers this comment to have been already addressed by the State.
    Comment 8: In the incorporated comments dated July 15, 2016, the 
commenter states that New Hampshire is long overdue for finalizing a 
plan to ensure attainment and maintenance of the SO2 NAAQS. 
The commenter goes

[[Page 25934]]

on to state that the (then) proposed permit is apparently only a step 
towards developing such a SIP. The commenter concludes by urging the 
State to swiftly address the issues identified in its comments on the 
proposed permit for Merrimack Station.
    Response 8: There are two plausible interpretations of this 
comment. The first interpretation is procedural. Interpreted in this 
fashion, the commenter would be requesting that the permitting 
authority expedite the permitting for Merrimack Station, which would be 
a critical component of the anticipated attainment plan for the area 
around Merrimack Station. Interpreted this first way, the comment is 
addressed through the current action, which is the final step in the 
procedure for approving an attainment plan for the area. A second 
interpretation implies technical insufficiency. Interpreted in this 
fashion, the commenter would be indicating that the proposed permit, 
when finalized, would be just one of multiple required actions 
necessary to ensure attainment in the nonattainment area. Interpreted 
this second way, the comment rests on the previous arguments provided 
by the commenter suggesting that the State's proposed plan does not 
ensure attainment of the NAAQS. On these grounds, EPA disagrees with 
the commenter that the proposed nonattainment area plan may be 
insufficient to ensure attainment. EPA has provided ample discussion 
and evidence, in both the current response to comments and the 
September 28, 2017 proposal, for why the State's nonattainment plan and 
SO2 attainment demonstration are sufficient.

III. Final Action

    EPA has determined that New Hampshire's SO2 
nonattainment plan meets the applicable requirements of sections 110, 
172, 191, and 192 of the CAA. EPA is approving New Hampshire's January 
31, 2017 SIP submission, as amended by the State on November 29, 2017, 
for attaining the 2010 primary 1-hour SO2 NAAQS for the 
Central New Hampshire Nonattainment Area and for meeting other 
nonattainment area planning requirements. This SO2 
nonattainment plan includes New Hampshire's attainment demonstration 
for the SO2 nonattainment area. The nonattainment area plan 
also addresses requirements for RFP, RACT/RACM, enforceable emission 
limits and control measures, base-year and projection-year emission 
inventories, and contingency measures.
    In New Hampshire's SIP submittal to EPA, New Hampshire included the 
applicable monitoring, testing, recordkeeping, and reporting 
requirements contained in Merrimack Station's permit, TP-0189, to 
demonstrate how compliance with Merrimack Station's SO2 
emission limit will be achieved and determined. EPA is approving into 
the New Hampshire SIP the provisions of Merrimack Station's permit, TP-
0189, that constitute the SO2 operating and emission limits 
and their associated monitoring, testing, recordkeeping, and reporting 
requirements. EPA is approving these provisions into the State's SIP 
through incorporation by reference, as described in section IV., below.
    EPA is not removing the portion of the New Hampshire SIP entitled 
``EPA-approved State Source specific requirements'' as it pertains to 
Merrimack Station's July 2011 permit, TP-0008, because EPA did not 
receive a request from the State to do so. See 40 CFR 52.1520(d). 
However, EPA considers those provisions to be superseded by the 
conditions of TP-0189, which are more stringent, and which are being 
incorporated into the SIP in this final action. Specifically, two of 
the provisions, items 6 and 8 from Table 4, relate to SO2 
emissions limits that have been superseded by Merrimack Station's 
September 2016 permit, TP-0189. Item 10 from Table 4 has also been 
superseded by Merrimack Station's September 2016 permit, TP-0189, in 
that the existing SIP provision allowed operation of one of Merrimack 
Station's two boilers, MK1, for up to 840 hours in any consecutive 12-
month period through the emergency bypass stack, i.e., not through the 
FGD system. Each of the corresponding provisions of Merrimack Station's 
September 2016 permit, TP-0189, are more stringent than those existing 
SIP provisions. The limits EPA is approving into New Hampshire's SIP in 
this action do not exempt any hours from being subject to the limit.

IV. Incorporation by Reference

    In this rule, EPA is finalizing regulatory text that includes 
incorporation by reference. In accordance with requirements of 1 CFR 
51.5, EPA is finalizing the incorporation by reference of certain 
federally enforceable provisions of Merrimack Station's permit, TP-
0189, effective on September 1, 2016, described in the amendments to 40 
CFR part 52 set forth below. Specifically, the following provisions of 
that permit are incorporated by reference: Items 1, 2, and 3 in Table 4 
(``Operating and Emission Limits''); items 1 and 2 in Table 5 
(``Monitoring and Testing Requirements''); items 1 and 2 in Table 6 
(``Recordkeeping Requirements''); and items 1 and 2 in Table 7 
(``Reporting Requirements''). EPA has made, and will continue to make, 
relevant documents, including the portions of TP-0189 being 
incorporated by reference, generally available through 
www.regulations.gov.

V. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Act and 
applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, EPA's role is to approve state 
choices, provided that they meet the criteria of the Clean Air Act. 
Accordingly, this action merely approves state law as meeting Federal 
requirements and does not impose additional requirements beyond those 
imposed by state law. For that reason, this action:

     Is not a significant regulatory action subject to review 
by the Office of Management and Budget under Executive Orders 12866 (58 
FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 2011);
     does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     does not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     is not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     does not provide EPA with the discretionary authority to 
address, as appropriate, disproportionate human health or environmental 
effects, using

[[Page 25935]]

practicable and legally permissible methods, under Executive Order 
12898 (59 FR 7629, February 16, 1994).
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the rule does not have tribal implications and will not impose 
substantial direct costs on tribal governments or preempt tribal law as 
specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. EPA will submit a report containing this action and 
other required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal Register. A major rule cannot 
take effect until 60 days after it is published in the Federal 
Register. This action is not a ``major rule'' as defined by 5 U.S.C. 
804(2).
    Under section 307(b)(1) of the Clean Air Act, petitions for 
judicial review of this action must be filed in the United States Court 
of Appeals for the appropriate circuit by August 6, 2018. Filing a 
petition for reconsideration by the Administrator of this final rule 
does not affect the finality of this action for the purposes of 
judicial review nor does it extend the time within which a petition for 
judicial review may be filed, and shall not postpone the effectiveness 
of such rule or action. This action may not be challenged later in 
proceedings to enforce its requirements. (See section 307(b)(2).)

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Reporting and recordkeeping 
requirements, Sulfur oxides.

    Dated: May 23, 2018.
Alexandra Dunn,
Regional Administrator, EPA New England.

    Part 52 of chapter I, title 40 of the Code of Federal Regulations 
is amended as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

Subpart EE--New Hampshire

0
2. Section 52.1520 is amended:
0
 a. In the table in paragraph (d) by:
0
 i. Revising the entry for ``PSNH Merrimack Station''; and
0
 ii. Adding the entry for ``PSNH d/b/a Eversource Energy Merrimack 
Station,'' at the end of the table; and
0
b. In the table in paragraph (e), by adding an entry for ``Central New 
Hampshire Nonattainment Area Plan for the 2010 Primary 1-Hour Sulfur 
Dioxide NAAQS'' at the end of the table.
    The revision and additions read as follows:


Sec.  52.1520   Identification of plan.

* * * * *
    (d) * * *

                             EPA-Approved New Hampshire Source Specific Requirements
----------------------------------------------------------------------------------------------------------------
                                                         State
          Name of source               Permit No.      effective    EPA approval date   Additional explanations/
                                                          date             \2\           Sec.   52.1535 citation
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
PSNH Merrimack Station...........  TP-0008..........     7/8/2011  8/22/2012, 77 FR     Flue Gas Desulfurization
                                                                    50602.               System. Portions of
                                                                                         this permit have been
                                                                                         superseded by TP-0189
                                                                                         for PSNH d/b/a
                                                                                         Eversource Energy
                                                                                         Merrimack Station.
 
                                                  * * * * * * *
PSNH d/b/a Eversource Energy       TP-0189..........     9/1/2016  6/5/2018, [Insert    Items 1, 2, and 3 in
 Merrimack Station.                                                 Federal Register     Table 4 ``Operating and
                                                                    citation].           Emission Limits'';
                                                                                         items 1 and 2 in Table
                                                                                         5 ``Monitoring and
                                                                                         Testing Requirements'';
                                                                                         items 1 and 2 in Table
                                                                                         6 ``Recordkeeping
                                                                                         Requirements''; items 1
                                                                                         and 2 in Table 7
                                                                                         ``Reporting
                                                                                         Requirements''.
----------------------------------------------------------------------------------------------------------------
\2\ In order to determine the EPA effective date for a specific provision listed in this table, consult the
  Federal Register notice cited in this column for the particular provision.

    (e) * * *

                                           New Hampshire Nonregulatory
----------------------------------------------------------------------------------------------------------------
                                  Applicable
  Name of  nonregulatory SIP     geographic or    State submittal     EPA approved
          provision              nonattainment     date/effective       date \ 3\            Explanations
                                     area               date
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Central New Hampshire          Central New               1/31/2017  6/5/2018 [Insert  ..........................
 Nonattainment Area Plan for    Hampshire SO2                        Federal
 the 2010 Primary 1-Hour        Nonattainment                        Register
 Sulfur Dioxide NAAQS.          Area.                                citation].
----------------------------------------------------------------------------------------------------------------
\3\ In order to determine the EPA effective date for a specific provision listed in this table, consult the
  Federal Register notice cited in this column for the particular provision.


[[Page 25936]]

[FR Doc. 2018-11597 Filed 6-4-18; 8:45 am]
BILLING CODE 6560-50-P