than five years following date of the final action of this FIP.
iv. Colstrip
    As described in section V.C., Colstrip Units 1 and 2 were
determined to be subject to BART. As explained in section V.C., the
document titled ``Identification of BART Eligible Sources in the WRAP
Region'' dated April 4, 2005 provides more details on the specific
emission units at each facility. PPL Montana's (PPL) Colstrip Power
Plant (Colstrip), located in Colstrip, Montana, consists of a total of
four electric utility steam generating units. Of the four units, only
Units 1 and 2 are subject to BART. We previously provided in Section
V.C. our reasoning for proposing that these two units are BART-eligible
and why they are subject to BART. Units 1 and 2 boilers have a nominal
gross capacity of 333 MW each. The boilers began commercial operation
in 1975 (Unit 1) and 1976 (Unit 2) and are tangentially fired
pulverized coal boilers that burn Powder River Basin (PRB) sub-
bituminous coal as their exclusive fuel.

    Our analysis follows EPA's BART Guidelines. For Colstrip Units 1
and 2, the BART Guidelines are mandatory because the combined capacity
for all four units at Colstrip is greater than 750 MW.\112\
---------------------------------------------------------------------------

    \112\ Also, the BART Guidelines establish presumptive
NOX limits for coal-fired Electric Generating Units
(EGUs) located at greater than 750 MW power plants that are
operating without post-combustion controls. For the tangential-fired
boilers burning sub-bituminous coal at Colstrip, that limit is 0.15
lb/MMBtu. 70 FR 39172 (July 6, 2005), Table 1. The guidelines
provide that the five factor analysis may result in a limit that is
different than the presumptive limit.
---------------------------------------------------------------------------

    We requested a five factor BART analysis for Colstrip Units 1 and 2
from PPL and the Company submitted that analysis in August 2007 along
with updated information in June 2008 and September 2011. PPL's five
factor BART analysis information is contained in the docket for this
action and we have taken it into consideration in our proposed action.
(a) Colstrip Unit 1
NOX
    The Colstrip Unit 1 boiler is of tangential-fired design with low-
NOX burners and close-coupled overfire air (CCOFA).
Originally, the unit operated with a NOX emission limit of
0.7 lb/MMBtu. In 1997, EPA approved an early election plan under the
acid rain program (ARP) that included a 0.45 lb/MMBtu annual
NOX limit. The early reduction limit expired in 2007 and the
new annual limit of 0.40 lb/MMBtu under the ARP became effective in
2008. Normally, the unit operates with an actual annual average
NOX emission rate in the range of 0.30 to 0.35 lb/MMBtu,
accomplished with low NOX burners and CCOFA.\113\
---------------------------------------------------------------------------

    \113\ Baseline emissions were determined by averaging the annual
emissions from 2008 through 2010 as reported to the CAMD database
available at http://camddataandmaps.epa.gov/gdm/index.cfm?fuseaction=emissions.
---------------------------------------------------------------------------

Step 1: Identify All Available Technologies
    We identified that the following NOX control
technologies are available: separated overfire air (SOFA), advanced
separated overfire air (ASOFA), rotating opposed fire air (ROFA), rich
reagent injection (RRI), SNCR, and SCR.
    SOFA technology is similar to CCOFA but the air injection point for
SOFA is separated some distance above the main burners and can result
in improved NOX removal efficiencies. SOFA in combination
with LNB technology provides additional NOX control by
injecting air into the lower temperature combustion zone where
NOX is less likely to form. This allows complete combustion
of the fuel while reducing both thermal and chemical NOX
formation.
    ASOFA technology is similar to SOFA, but the amount of air staged
is in the range of 20 to 30%, and, in some cases, can result in even
further improved NOX removal efficiencies compared to SOFA.
    ROFA is a low NOX system that is somewhat similar to the
SOFA. ROFA uses more ports and a significantly bigger fan to accomplish
similar results of getting air into the upper portion of the boiler.
ROFA uses a rotating opposed fire air process, while the SOFA system
uses both horizontal (yaw) and vertical nozzle tip controls.
    RRI is similar to SNCR and achieves similar results.
    In SNCR systems, a reagent such as NH3 or urea is
injected into the flue gas at a suitable temperature zone, typically in
the range of 1,600 to 2,000[emsp14] [deg]F and at an appropriate ratio
of reagent to NOX.
    SCR uses either NH3 or urea in the presence of a metal
based catalyst to selectively reduce NOX emissions.
Step 2: Eliminate Technically Infeasible Options
    Based on our review, all the technologies identified in Step 1
appear to be technically feasible for Colstrip Unit 1. In particular,
both SCR and SNCR have been widely employed to control NOX
emissions from coal-fired power plants.\114,115,116\
---------------------------------------------------------------------------

    \114\ Institute of Clean Air Companies (ICAC) White Paper,
Selective Catalytic Reduction Controls of NOX Emissions
from Fossil Fuel-Fired Electric Power Plants, May 2009, pp. 7-8.
    \115\ Control Technologies to Reduce Conventional and Hazardous
Air Pollutants from Coal-Fired Power Plants Northeast States for
Coordinated Air Use Management (NESCAUM), March 31, 2011, p. 16.
    \116\ ICAC White Paper, Selective Non-Catalytic Reduction for
Controlling NOX Emissions, February 2008, pp. 6-7.
---------------------------------------------------------------------------

    However, in the BART Guidelines, EPA states that it may be
appropriate to eliminate from further consideration technologies that
provide similar control levels at higher cost. The guidelines say that,
``a possible outcome of the BART procedures discussed in these
guidelines is the evaluation of multiple control technology
alternatives which result in essentially equivalent emissions. It is
not our intent to encourage evaluation of unnecessarily large numbers
of control alternatives for every emissions unit. For example, if two
or more control techniques result in control levels that are
essentially identical, considering the uncertainties of emissions
factors and other parameters pertinent to estimating performance, you
may evaluate only the less costly of these options.'' 70 FR 39165 (July
6, 2005). As explained below, we have eliminated ASOFA, ROFA, and RRI
from further consideration for this reason. SOFA is the least costly of
these options.
    Since ASOFA would likely not achieve greater emissions reductions
compared to SOFA it is not considered further.
    Since ROFA would achieve very similar emissions reductions compared
to the SOFA system, ROFA is not considered further.
    Since RRI would not achieve greater emissions reductions compared
to SNCR, RRI is not considered further.
Step 3: Evaluate Control Effectiveness of Remaining Control Technology
    At tangentially fired boilers firing PRB coal, SOFA in combination
with CCOFA and LNB, can typically achieve emission rates below 0.15 lb/
MMBtu on an annual basis.\117\ However, due to certain issues unique to
Colstrip Unit 1, a rate of 0.20 lb/MMBtu is more realistic.
Specifically, these issues include: (1) that the furnace is sized
smaller than others and therefore runs hotter than similar units, and
(2) that the PRB coal used, classified as a borderline sub-bituminous B
coal, is less reactive (produces more NOX) than typical PRB
coals.\118\ The 0.20 lb/MMBtu rate represents a 34.9% reduction from
the current baseline (2008 through 2010) rate of 0.308 lb/MMbtu.
---------------------------------------------------------------------------

    \117\ Low NOX Firing Systems and PRB Fuel; Achieving
as Low as 0.12 LB NOX/MMBtu, Jennings, P., ICAC Forum,
Feb. 2002.
    \118\ June 2008 PPL Addendum, p. 5-1.
---------------------------------------------------------------------------

    The post-combustion control technologies, SNCR and SCR, have been
evaluated in combination with combustion controls. That is, the inlet
concentration to the post-combustion controls is assumed to be 0.20 lb/
MMBtu. This allows the equipment and operating and maintenance costs of
the post-combustion controls to be minimized based on the lower inlet
NOX concentration. Typically, SNCR reduces NOX an
additional 20 to 30% above LNB/combustion controls without excessive
NH3 slip.\119\ Assuming that a minimum 25% additional
emission reduction is achievable with SNCR, SOFA combined with SNCR can
achieve an overall control efficiency of 51.1%. SCR can achieve
performance emission rates as low as 0.04 to 0.07 lb/MMBtu

on an annual basis.\120\ Assuming that an annual emission rate of 0.05
lb/MMBtu is achievable with SCR, SOFA combined with SCR can achieve an
overall control efficiency of 83.8%. A summary of emissions projections
for the control options is provided in Table 65.
---------------------------------------------------------------------------

    \119\ White Paper, SNCR for Controlling NOX
Emissions, Institute of Clean of Clean Air Companies, pp. 4 and 9,
February 2008.
    \120\ Information available at: http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/NOx%20control%20Lani%20AWMA%200905.pdf.

                 Table 65--Summary of NOX BART Analysis Control Technologies for Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
                                               Control
             Control option                 effectiveness   Annual  emission      Emissions         Remaining
                                                 (%)        rate  (lb/MMBtu)  reduction  (tpy)  emissions  (tpy)
----------------------------------------------------------------------------------------------------------------
SOFA+SCR................................              83.5             0.050               425               678
SOFA+SNCR...............................              51.1             0.150             2,097             2,006
SOFA....................................              34.9             0.200             1,432             2,671
No Controls (Baseline) \1\..............  ................             0.308  ................             4,103
----------------------------------------------------------------------------------------------------------------
\1\ Baseline emissions were determined by averaging the annual emissions from 2008 to 2010 as reported to the
  CAMD database available at http://camddataandmaps.epa.gov/gdm/.

Step 4: Evaluate Impacts and Document Results
Factor 1: Costs of Compliance
    We relied on a number of resources to assess the cost of compliance
for the control technologies under consideration. In accordance with
the BART Guidelines (70 FR 39166 (July 6, 2005)), and in order to
maintain and improve consistency, in all cases we sought to align our
cost methodologies with the EPA's Control Cost Manual (CCM).\121\
However, to ensure that our methods also reflect the most recent cost
levels seen in the marketplace, we also relied on control costs
developed for the Integrated Planning Model (IPM) version 4.10.\122\
These IPM control costs are based on databases of actual control
project costs and account for project specifics such as coal type,
boiler type, and reduction efficiency. The IPM control costs reflect
the recent increase in costs in the five years proceeding 2009 that is
largely attributed to international competition. Finally, our costs
were also informed by cost analyses submitted by the sources, including
in some cases vendor data.
---------------------------------------------------------------------------

    \121\ EPA's CCM Sixth Edition, January 2002, EPA 452/B-02-001.
    \122\ Documentation for EPA Base Case v.4.10 Using the
Integrated Planning Model, August 2010, EPA 430R10010.
---------------------------------------------------------------------------

    Annualization of capital investments was achieved using the CRF as
described in the CCM.\123\ The CRF was computed using an economic
lifetime of 20 years and an annual interest rate of 7%.\124\ Unless
otherwise noted, all costs presented in this proposal for the PPL BART
units have been adjusted to 2010 dollars using the Chemical Engineering
Plant Cost Index (CEPCI).\125\ EPA's detailed control costs for
Colstrip can be found in the docket.
---------------------------------------------------------------------------

    \123\ Section 1, Chapter 2, p. 2-21.
    \124\ Office of Management and Budget, Circular A-4, Regulatory
Analysis, http://www.whitehouse.gov/omb/circulars_a004_a-4/.
    \125\ Chemical Engineering Magazine, p. 56, August 2011. (http://www.che.com).
---------------------------------------------------------------------------

SOFA
    We relied on estimates submitted by PPL in 2008 for capital costs
and direct annual costs for SOFA.\126\ The Capital Cost is listed in
Table 66. We then used the CEPCI to adjust capital costs to 2010
dollars. Annual costs were determined by summing the indirect annual
cost and the direct annual cost (see Table 67).
---------------------------------------------------------------------------

    \126\ Addendum to PPL Montana's Colstrip BART Report Prepared
for PPL Montana, LLC; Prepared by TRC, (``Colstrip Addendum''), June
2008, Table 5.1-1.

Table 66--Summary of NOX BART Capital Cost Analysis for SOFA on Colstrip
                                 Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment SOFA...........................       4,507,528
------------------------------------------------------------------------

 Table 67--Summary of NOX BART Annual Cost Analysis for SOFA on Colstrip
                                 Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Indirect Annual Cost..............................         425,511
Total Direct Annual Cost................................         664,884
                                                         ---------------
  Total Annual Cost.....................................       1,090,395
------------------------------------------------------------------------

                         Table 68--Summary of NOX BART Costs for SOFA on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions reductions     Average cost effectiveness
           (MM$)               Total annual cost  (MM$)              (tpy)                      ($/ton)
----------------------------------------------------------------------------------------------------------------
                4.508                        1.090                        1,432                         761
----------------------------------------------------------------------------------------------------------------

    SOFA+SNCR We relied on control costs developed for the IPM for
direct capital costs for SNCR.\127\ We then used methods provided by
the CCM for the remainder of the SOFA+SNCR analysis. Specifically, we
used the methods in the CCM to calculate total capital investment,
annual costs associated with operation and maintenance, to

annualize the total capital investment using the CRF, and to sum the
total annual costs.
---------------------------------------------------------------------------

    \127\ IPM, Chapter 5, Appendix 5-2B.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' reflecting an SNCR retrofit of
typical difficulty in the IPM control costs. As Colstrip Unit 1 burns
sub-bituminous PRB coal having a low sulfur content of 0.91 lb/MMBtu
(equating to a SO2 rate of 1.8 lb/MMBtu),\128\ it was not
necessary to make allowances in the cost calculations to account for
equipment modifications or additional maintenance associated with
fouling due to the formation of ammonium bisulfate. These are only
concerns when the SO2 rate is above 3 lb/MMBtu.\129\
Moreover, ammonium bisulfate formation can be minimized by preventing
excessive NH3 slip. Optimization of the SNCR system can
commonly limit NH3 slip to levels less than the 5 parts per
million (ppm) upstream of the pre-air heater.\130\ EPA's detailed cost
calculations for SOFA+SNCR can be found in the docket.
---------------------------------------------------------------------------

    \128\ Cost and Quality of Fuels for Electric Utility Plants 1999
Tables, Energy Information Administration, DOE/EIA-0191(99), June
2000, Table 24.
    \129\ IPM, Chapter 5, p. 5-9.
    \130\ ICAC, p. 8.
---------------------------------------------------------------------------

    We used a urea reagent cost estimate of $450 per ton taken from
PPL's September 2011 submittal.\131\ To estimate the average cost
effectiveness (dollars per ton of emissions reductions) we divided the
total annual cost by the estimated NOX emissions reductions.
We summarize the costs from our SOFA+SNCR cost analysis in Tables 69,
70, and 71.
---------------------------------------------------------------------------

    \131\ NOX Control Update to PPL Montana's Colstrip
Generating Station BART Report Prepared for PPL Montana, LLC, by
TRC, September 2011, p. 4-1.

  Table 69--Summary of NOX BART Capital Cost Analysis for SOFA+SNCR on
                             Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       4,507,528
Capital Investment SNCR.................................       8,873,145
                                                         ---------------
    Total Capital Investment SOFA+SNCR..................      13,380,673
------------------------------------------------------------------------

 Table 70--Summary of NOX BART Total Annual Cost Analysis for SOFA+SNCR
                           on Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................       1,090,395
Total Annual Cost SNCR..................................       2,188,569
                                                         ---------------
    Total Annual Cost SOFA+SNCR.........................       3,278,964
------------------------------------------------------------------------

                      Table 71--Summary of NOX BART Costs for SOFA+SNCR on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions reductions     Average cost effectiveness
           (MM$)               Total annual cost  (MM$)              (tpy)                      ($/ton)
----------------------------------------------------------------------------------------------------------------
               13.381                        3.279                        2,097                       1,564
----------------------------------------------------------------------------------------------------------------

SOFA+SCR
    We relied on control costs developed for the IPM for direct capital
costs for SCR.\132\ We then used methods in the CCM for the remainder
of the SOFA+SCR analysis. Specifically, we used the methods in the CCM
to calculate total capital investment, annual costs associated with
operation and maintenance, to annualize the total capital investment
using the CRF, and to sum the total annual costs.
---------------------------------------------------------------------------

    \132\ IPM, Chapter 5, Appendix 5-2A.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' in the IPM control costs, which
reflects an SCR retrofit of typical difficulty. We used an aqueous
ammonia (29%) cost of $240 per ton,\133\ and a catalyst cost of $6,000
per cubic meter.\134\ To estimate the average cost effectiveness
(dollars per ton of emissions reductions) we divided the total annual
cost by the estimated NOX emissions reductions. We summarize
the costs from our SOFA+SCR cost analysis in Tables 72, 73, and 74.
---------------------------------------------------------------------------

    \133\ Email communication with Fuel Tech, Inc., March 2, 2012.
    \134\ Cichanowicz 2010, p. 6-7.

   Table 72--Summary of NOX BART Capital Cost Analysis for SOFA+SCR on
                             Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       4,507,528
Capital Investment SCR..................................      78,264,060
                                                         ---------------
    Total Capital Investment SOFA+SCR...................      82,771,589
------------------------------------------------------------------------

Table 73--Summary of NOX BART Total Annual Cost Analysis for SOFA+SCR on
                             Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................       1,090,395

Total Annual Cost SCR...................................       9,852,395
                                                         ---------------
    Total Annual Cost SOFA+SCR..........................      10,942,766
------------------------------------------------------------------------

                       Table 74--Summary of NOX BART Costs for SOFA+SCR on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions reductions            Average cost
           (MM$)               Total annual cost  (MM$)              (tpy)              effectiveness  ($/ton)
----------------------------------------------------------------------------------------------------------------
               82.772                       10.942                        3,425                       3,195
----------------------------------------------------------------------------------------------------------------

Factor 2: Energy Impacts
    SNCR reduces the thermal efficiency of a boiler as the reduction
reaction uses thermal energy from the boiler.\135\ Therefore,
additional coal must be burned to make up for the decreases in power
generation. Using CCM calculations we determined the additional coal
needed for Unit 1 equates to 77,600 MMBtu/yr. For an SCR, the new
ductwork and the reactor's catalyst layers decrease the flue gas
pressure. As a result, additional fan power is necessary to maintain
the flue gas flow rate through the ductwork. SCR systems require
additional electric power to meet fan requirements equivalent to
approximately 0.3% of the plant's electric output.\136\ Both SCR and
SNCR require some minimal additional electricity to service
pretreatment and injection equipment, pumps, compressors, and control
systems. The additional energy requirements that would be involved in
installation and operation of the evaluated controls are not
significant enough to warrant eliminating any of the options evaluated.
Note that cost of the additional energy requirements has been included
in our calculations.
---------------------------------------------------------------------------

    \135\ CCM, Section 4.2, Chapter 1, p. 1-21.
    \136\ Id., Section 4.2, Chapter 2, p. 2-28.
---------------------------------------------------------------------------

Factor 3: Non-Air Quality Environmental Impacts
    SNCR and SCR will increase the quantity of ash that will need to be
disposed. Transporting this waste stream for disposal would use natural
resources for fuel and would have associated air quality impacts. The
disposal of the solid waste itself would be to a landfill and could
possibly result in groundwater or surface water contamination if a
landfill's engineering controls were to fail. Transporting the chemical
reagents and catalysts would use natural resources for fuel and would
have associated air quality impacts. The chemical reagents would be
stored on site and could result in spills to the environment while
being transferred between storage vessels or if containers were to fail
during storage or movement. The environmental impacts associated with
proper transportation, storage, and/or disposal should not be
significant. Therefore, the non-air quality environmental impacts do
not warrant eliminating either SNCR or SCR.
Factor 4: Remaining Useful Life
    EPA has determined that the default 20-year amortization period is
most appropriate to use as the remaining useful life of the facility.
Without commitments for an early shut down, EPA cannot consider a
shorter amortization period in our analysis. Thus, this factor does not
impact our BART determination because the annualized cost was
calculated over a 20 year period in accordance with the BART
Guidelines.
Factor 5: Evaluate visibility impacts
    We conducted modeling for Colstrip Unit 1 as described in section
V.C.3.a. Table 75 presents the visibility impacts of the 98th
percentile of daily maxima for each Class I area from 2006 through
2008. Table 76 presents the number of days with impacts greater than
0.5 deciviews for each Class I area from 2006 through 2008.

                    Table 75--Delta Deciview Improvement for NOX Controls on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
                                                                    Improvement     Improvement     Improvement
                                                     Baseline      from SOFA+SCR  from SOFA+SNCR     from SOFA
                  Class I area                     impact (delta      (delta          (delta          (delta
                                                     deciview)       deciview)       deciview)       deciview)
----------------------------------------------------------------------------------------------------------------
North Absaroka WA...............................           0.414           0.181           0.089           0.047
Theodore Roosevelt NP...........................           0.922           0.404           0.264           0.182
UL Bend WA......................................           0.895           0.378           0.249           0.164
Washakie WA.....................................           0.410           0.121           0.077           0.052
Yellowstone NP..................................           0.275           0.081           0.059           0.034
----------------------------------------------------------------------------------------------------------------

                  Table 76--Days Greater Than 0.5 Deciview for NOX Controls on Colstrip Unit 1
                                               [Three year total]
----------------------------------------------------------------------------------------------------------------
                                                     Baseline                          Using
                  Class I area                        (days)      Using SOFA+SCR     SOFA+SNCR      Using SOFA
----------------------------------------------------------------------------------------------------------------
North Absaroka WA...............................               7               5               5               7

Theodore Roosevelt NP...........................              52              17              27              33
UL Bend WA......................................              68              29              47              52
Washakie WA.....................................              12               5               9              10
Yellowstone NP..................................               4               2               2               2
----------------------------------------------------------------------------------------------------------------

Step 5: Select BART
    We propose to find that BART for NOX is SOFA+SNCR at
Colstrip Unit 1 with an emission limit of 0.15 lb/MMBtu (30-day rolling
average). Of the five BART factors, cost and visibility improvement
were the critical ones in our analysis of controls for this source.
    In our BART analysis for NOX at Colstrip Unit 1, we
considered SOFA, SOFA+SNCR, and SOFA+SCR. The comparison between our
SOFA, SOFA+SNCR, and SOFA+SCR analysis is provided in Table 77.

                                Table 77--Summary of NOX BART Analysis Comparison of Control Options for Colstrip Unit 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Visibility impacts \1\
                                                                          Average cost    Incremental cost ---------------------------------------------
          Control option              Total capital     Total annual    effectiveness ($/ effectiveness ($/       Visibility
                                    investment (MM$)     cost (MM$)           ton)              ton)          improvement (delta      Fewer days >0.5
                                                                                deciviews)              deciview
--------------------------------------------------------------------------------------------------------------------------------------------------------
SOFA+SCR..........................            82.772            10.942             3,195             5,770  0.404 TRNP...........  35 TRNP.
                                                                                0.378 UL Bend........  39 UL Bend.
SOFA+SNCR.........................            13.380             3.279             1,564             3,291  0.264 TRNP...........  25 TRNP.
                                                                                0.249 UL Bend........  21 UL Bend.
SOFA..............................             4.508             1.090               761               \2\  0.182 TRNP...........  19 TRNP.
                                                                                0.164 UL Bend........  16 UL Bend.
--------------------------------------------------------------------------------------------------------------------------------------------------------
TRNP--Theodore Roosevelt National Park.
UL Bend--UL Bend Wilderness Area.
\1\ The visibility improvement described in this table represents the change in the maximum 98th percentile impact over the modeled 3-year
  meteorological period (2006 through 2008) at the Class I areas in the table.
\2\ Incremental cost is not applicable to the option that has the lowest effectiveness.

    We have concluded that SOFA, SOFA+SNCR, and SOFA+SCR are all cost
effective control technologies. SOFA has a cost effectiveness value of
$761 per ton of NOX emissions reduced. SOFA+SNCR is more
expensive than SOFA, with a cost effectiveness value of $1,564 per ton
of NOX emissions reduced. SOFA+SCR is more expensive than
SOFA or SOFA+SNCR, having a cost effectiveness value of $3,195 per ton
of NOX emissions reduced. This is well within the range of
values we have considered reasonable for BART and that states have
considered reasonable for BART.
    We have weighed costs against the anticipated visibility impacts
for Colstrip Unit 1. Any of the control options would have a positive
impact on visibility; however, the cost of SOFA+SCR ($3,195/ton) is not
justified by the visibility improvement of 0.404 deciviews at TRNP and
0.378 deciviews at UL Bend. The lower cost of SOFA+SNCR ($1,564/ton) is
justified when the visibility improvement is considered. SOFA+SNCR
would have a visibility improvement of 0.264 deciviews at Theodore
Roosevelt NP and 0.249 deciviews at UL Bend WA and it would result in
25 fewer days above 0.5 deciviews at Theodore Roosevelt-NP and 21 fewer
days above 0.5 deciviews at UL Bend WA. In addition, application of
SOFA+SNCR at both Colstrip Units 1 and 2 would have a combined modeled
visibility improvement of 0.501 deciviews at Theodore Roosevelt NP and
0.451 deciviews at UL Bend WA. We consider these improvements to be
substantial, especially in light of the fact that Theodore Roosevelt NP
and UL Bend WA are not projected to meet the URP. We propose that the
NOX BART emission limit for Colstrip Unit 1 should be based
on what can be achieved with SOFA+SNCR.
    The proposed BART emission limit of 0.15 lb/MMBtu allows for a
sufficient margin of compliance for a 30-day rolling average limit that
would apply at all times, including startup, shutdown, and
malfunction.\137\ We are also proposing monitoring, recordkeeping, and
reporting requirements as described in our proposed regulatory text for
40 CFR 52.1395.
---------------------------------------------------------------------------

    \137\ As discussed in the BART Guidelines, section V (70 FR
39172, July 6, 2005), and Section 302(k) of the CAA, emissions
limits such as BART are required to be met on a continuous basis.
---------------------------------------------------------------------------

    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' We propose a compliance
deadline of five (5) years from the date our final FIP becomes
effective because of the equipment installation and potential
combustion modifications that will be required.
SO2
    Colstrip Unit 1 is already controlled by wet venturi scrubbers for
simultaneous particulate and SO2 control. The venturi
scrubbers utilize the alkalinity of the fly ash to achieve an estimated
SO2 removal efficiency of 75%.\138\ Based on emissions data
from the EPA Clean Air Markets Division (CAMD), for the baseline period
2008 through 2010, the average SO2 emission rate was 0.418
lb/MMBtu and the

average SO2 emissions were 5,548 tpy.\139\
---------------------------------------------------------------------------

    \138\ BART Assessment Colstrip Generating Station, prepared for
PPL Montana, LLC, by TRC (``Colstrip Initial Response''), August
2007, p. ES-3.
    \139\ Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm/.
---------------------------------------------------------------------------

Step 1: Identify All Available Technologies
    The Colstrip Unit 1 venturi scrubber currently achieves greater
than 50% removal of SO2. For units with preexisting post-
combustion SO2 controls achieving removal efficiencies of at
least 50%, the BART Guidelines state that upgrades to the system
designed to improve the system's overall removal efficiency should be
considered. 70 FR 39171 (July 6, 2005). For wet scrubbers, the BART
Guidelines recommend that the following upgrades be considered: (a)
Elimination of bypass reheat; (b) installation of liquid distribution
rings; (c) installation of perforated trays; (d) use of organic acid
additives; (e) improve or upgrade scrubber auxiliary equipment; and (f)
redesign spray header or nozzle configuration.
    In addition to the upgrades recommended by the BART Guidelines, two
other upgrades are available: lime injection and lime injection with an
additional scrubber vessel. Some of the upgrades recommended by the
BART Guidelines are inherent in lime injection; consequently, they are
available technologies only within that context. Specifically, these
include options (b), (e), and (f) as listed above.
    A venturi scrubber works by increasing the contact between the
pollutant-bearing gas stream and the scrubbing liquid. This is achieved
in the throat of the venturi scrubber where the gas stream is
accelerated, thereby atomizing the scrubber liquid and promoting
greater gas-liquid contact.\140\ Absorption of SO2 is
further enhanced by use of alkaline reagents. Currently, the venturi
scrubbers for Colstrip Unit 1 rely on the alkalinity of the coal ash to
reduce SO2. Adding lime to the water stream for these
scrubbers will increase SO2 removal. However, as the amount
of lime is increased, scaling of piping and equipment is also expected
to increase and this scaling will have to be removed. The scrubber
vessel would not be operational during the descaling process, resulting
in downtime. Greater removal efficiencies could be achieved if an
additional scrubber vessel is added to the system to reduce downtime
for descaling. Therefore, addition of a spare scrubber vessel is an
upgrade that can improve the overall SO2 removal efficiency
of the scrubber system by increasing the system's reliability and
decreasing its downtime. The additional scrubber vessel is an example
of equipment redundancy that will enhance the overall system
performance.
---------------------------------------------------------------------------

    \140\ EPA Air Pollution Control Technology Fact Sheet: Venturi
Scrubber, EPA-452/F-03-017.
---------------------------------------------------------------------------

Step 2: Eliminate Technically Infeasible Options
    Elimination of bypass reheat is not feasible option because
Colstrip Unit 1 is designed so that there is no bypass of flue gas.
Installation of perforated trays is not a feasible option because the
existing scrubber design already includes this technology in the form
of wash trays. Finally, the use of organic acid additives is not a
feasible option because the reactivity of the lime would neutralize the
acids, making the additives ineffective.
    Lime injection or lime injection with an additional scrubber vessel
are technically feasible control options because lime injection is
currently used to control SO2 emissions at Colstrip Units 3
and 4.
Step 3: Evaluate Control Effectiveness of Remaining Control Technology
    An annual emission rate of 0.015 lb/MMBtu can be achieved with lime
injection without an additional scrubber vessel. PPL stated that this
is the lowest emission rate that could be achieved without adding an
additional scrubber vessel.\141\ An annual emission rate of 0.08 to
0.09 lb/MMBtu can be achieved with lime injection with an additional
scrubber vessel. This is the emission rate that is being achieved at
Colstrip Units 3 and 4 according to emissions data from CAMD.\142\ The
control effectiveness of each of the control options was calculated
using the controlled emission rates that were provided by PPL.
---------------------------------------------------------------------------

    \141\ Colstrip Addendum, p. 4-1.
    \142\ Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm/.
---------------------------------------------------------------------------

    A summary of control efficiencies, emission rates, and resulting
emissions and emission reductions, is provided in Table 78. EPA's
detailed emissions calculations can be found in the docket.

               Table 78--Summary of BART Analysis Control Technologies for SO2 for Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
                                               Control      Annual  emission
             Control option                 effectiveness    rate (lb/MMBtu)      Emissions         Remaining
                                               (%) \1\             \2\         reduction (tpy)   emissions (tpy)
----------------------------------------------------------------------------------------------------------------
Lime Injection with Additional Scrubber               80.9             0.080             4,486             1,062
 Vessel.................................
Lime Injection..........................              64.1             0.150             3,557             1,991
Existing Controls (Baseline) \3\........  ................             0.418  ................             5,548
----------------------------------------------------------------------------------------------------------------
\1\ Control efficiency is provided relative to the emission rate with current controls.
\2\ Emission rates are provided on an annual basis.
\3\ Baseline emissions for 2008 through 2010 from Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm/.

Step 4: Evaluate Impacts and Document Results
Factor 1: Costs of Compliance
    We relied on capital costs and direct annual costs provided by PPL
when determining the cost of compliance for both lime injection and
lime injection with an additional scrubber vessel.\143,144\ All costs
presented here for the Colstrip Unit 1 SO2 control options
are in year 2007 dollars. EPA's cost calculations can be found in the
docket.
---------------------------------------------------------------------------

    \143\ Colstrip Initial Response, Table A4-6(c).
    \144\ Colstrip Addendum, Table 4.1-4.
---------------------------------------------------------------------------

Lime Injection
    We summarize our cost analysis for lime injection in Tables 79, 80,
and 81.

  Table 79--Summary of SO2 Capital Cost Analysis for Lime Injection on
                             Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment................................       3,000,000
------------------------------------------------------------------------

Table 80--Summary of SO2 BART Annual Cost Analysis for Lime Injection on
                             Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Direct Annual Cost................................       1,600,000
Indirect Annual Cost....................................         283,200
                                                         ---------------
    Total Annual Cost...................................       1,883,200
------------------------------------------------------------------------

                    Table 81--Summary of SO2 BART Costs for Lime Injection on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                                            Average cost effectiveness
           (MM$)               Total annual cost (MM$)    Emissions reductions (tpy)            ($/ton)
----------------------------------------------------------------------------------------------------------------
                3.000                        1.883                        3,557                        $529
----------------------------------------------------------------------------------------------------------------

Lime Injection With an Additional Scrubber Vessel
    We summarize our cost analysis for lime injection with an
additional scrubber vessel cost analysis in Tables 82, 83, and 84.

 Table 82--Summary of SO2 Capital Cost Analysis for Lime Injection With
            an Additional Scrubber Vessel on Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment, Lime Injection................       3,000,000
Capital Investment, Scrubber Vessel.....................      25,000,000
                                                         ---------------
    Total Capital Investment............................      28,000,000
------------------------------------------------------------------------

  Table 83--Summary of SO2 BART Annual Cost Analysis for Lime Injection
          With an Additional Scrubber Vessel on Colstrip Unit 1
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Direct Annual Cost................................       1,450,000
Indirect Annual Cost....................................       2,643,200
                                                         ---------------
    Total Annual Cost...................................       4,093,200
------------------------------------------------------------------------

 Table 84--Summary of SO2 BART Costs Analysis for Lime Injection With an Additional Scrubber Vessel on Colstrip
                                                     Unit 1
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                                            Average cost effectiveness
           (MM$)               Total annual cost (MM$)    Emissions reductions (tpy)            ($/ton)
----------------------------------------------------------------------------------------------------------------
              $28.000                       $4.100                        4,486                         912
----------------------------------------------------------------------------------------------------------------

Factor 2: Energy Impacts
    According to PPL, the pressure drop of the venturi scrubbers is
maintained in the range of 17 to 20 inches of water column. The
injection of lime will be accompanied by little to no increase in
pressure drop, but it will require a small increase in pump power
consumption. This is included in the cost analysis in the additional
operations and maintenance expenses of $125,000 per year.\145\ The
additional energy requirements are not significant enough to warrant
eliminating either lime injection or lime injection with an additional
scrubber vessel.
---------------------------------------------------------------------------

    \145\ Colstrip Initial Response, p. 4-16.
---------------------------------------------------------------------------

Factor 3: Non-Air Quality Environmental Impacts
    Adding lime to the scrubbers will require more frequent descaling
operations that would increase the quantity of solid waste from
descaling operations. Transporting this waste stream for disposal would
use natural resources for fuel and would have associated air quality
impacts. The disposal of the solid waste itself would

be to a landfill and could possibly result in groundwater or surface
water contamination if a landfill's engineering controls were to fail.
EPA's analysis indicates that the environmental impacts associated with
the proper transport and land disposal of the solid waste should not be
significant. Therefore, the non-air quality environmental impacts do
not warrant eliminating either lime injection addition or lime
injection addition with an additional scrubber vessel.
Factor 4: Remaining Useful Life
    EPA has determined that the default 20-year amortization period is
most appropriate to use as the remaining useful life of the facility.
Without commitments for an early shut down, EPA cannot consider a
shorter amortization period in our analysis. Because the remaining
useful life of the source is equal to that assumed for amortization of
control option capital investments, this factor does not impact our
BART determination.
Factor 5: Evaluate Visibility Impacts
    We conducted modeling for Colstrip Unit 1 as described in section
V.C.3.a. Table 85 presents the visibility impacts of the 98th
percentile of daily maxima for each Class I area from 2006 through
2008. Table 86 presents the number of days with impacts greater than
0.5 deciviews for each Class area from 2006 through 2008.

                    Table 85--Delta Deciview Improvement for SO2 Controls on Colstrip Unit 1
----------------------------------------------------------------------------------------------------------------
                                                                              Improvement from
                                                                               lime  injection  Improvement from
                       Class I area                          Baseline impact    + additional     lime  injection
                                                            (delta deciview)   scrubber vessel  (delta deciview)
                                                                              (delta deciview)
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.........................................             0.414             0.164             0.146
Theodore Roosevelt NP.....................................             0.922             0.350             0.284
UL Bend WA................................................             0.895             0.261             0.234
Washakie WA...............................................             0.410             0.154             0.145
Yellowstone NP............................................             0.275             0.115             0.090
----------------------------------------------------------------------------------------------------------------

                  Table 86--Days Greater Than 0.5 Deciview for SO2 Controls on Colstrip Unit 1
                                               [Three-year total]
----------------------------------------------------------------------------------------------------------------
                                                                                Using lime
                                                                                injection +       Using lime
                       Class I area                          Baseline (days)     additional         injection
                                                                               scrubber vessel
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.........................................                 7                 7                 7
Theodore Roosevelt NP.....................................                52                29                33
UL Bend WA................................................                68                31                41
Washakie WA...............................................                12                 6                 7
Yellowstone NP............................................                 4                 2                 2
----------------------------------------------------------------------------------------------------------------

Step 5: Select BART
    We propose to find that BART for SO2 is lime injection
with an additional scrubber vessel at Colstrip Unit 1 with an emission
limit of 0.08 lb/MMBtu (30-day rolling average). Of the five BART
factors, cost and visibility improvement were the critical ones in our
analysis of controls for this source.
    In our BART analysis for SO2 at Colstrip Unit 1, we
considered lime injection and lime injection with an additional
scrubber vessel. The comparison between our lime injection and lime
injection with an additional scrubber vessel analysis is provided in
Table 87.

    Table 87--Summary of EPA SO2 BART Analysis Comparison of Lime Injection and Lime Injection With an Additional Scrubber Vessel for Colstrip Unit 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Incremental                  Visibility impacts \1\
                                     Total capital   Total annual    Average cost        cost      -----------------------------------------------------
          Control option              investment      cost (MM$)     effectiveness   effectiveness    Visibility improvement
                                         (MM$)                          ($/ton)         ($/ton)         (delta deciviews)      Fewer days  >0.5 deciview
--------------------------------------------------------------------------------------------------------------------------------------------------------
Lime Injection with Additional              28.000           4.100             912           1,957  0.350 TRNP...............  23 TRNP.
 Scrubber Vessel.                                                                                0.261 UL Bend............  37 UL Bend.
Lime Injection....................           3.000           1.883             529             \2\  0.283 TRNP...............  19 TRNP.
                                                                                0.234 UL Bend............  27 UL Bend.
--------------------------------------------------------------------------------------------------------------------------------------------------------
TRNP--Theodore Roosevelt National Park.
UL Bend--UL Bend Wilderness Area.
\1\ The visibility improvement described in this table represents the change in the maximum 98th percentile impact over the modeled 3-year
  meteorological period (2006 through 2008) at the Class I areas in the table.
\2\ Incremental cost is not applicable to the option that has the lowest effectiveness.

    We have concluded that lime injection and lime injection with an
additional scrubber vessel are both cost effective control
technologies. Lime injection has a cost effectiveness value of $539 per
ton of SO2 emissions

reduced. Lime injection with an additional scrubber vessel is more
expensive than lime injection, with a cost effectiveness value of $912
per ton of SO2 emissions reduced. Both of these costs are
well within the range of values we have considered reasonable for BART
and that states have considered reasonable for BART.
    We have weighed costs against the anticipated visibility impacts
for Colstrip Unit 1. Either of the control options would have a
positive impact on visibility. We have concluded that the cost of lime
injection with an additional scrubber vessel ($912/ton) is justified by
the visibility improvement of 0.350 deciviews at Theodore Roosevelt NP
and 0.261 deciviews at UL Bend WA and it would result in 23 fewer days
above 0.5 deciviews at Theodore Roosevelt NP and 37 fewer days above
0.5 deciviews at UL Bend WA. In addition, the application of lime
injection with an additional scrubber vessel on both Colstrip Units 1
and 2 would result in a combined modeled visibility improvement of
0.592 deciviews at Theodore Roosevelt NP and 0.384 deciviews at UL Bend
WA. We consider these improvements to be substantial, especially in
light of the fact that Theodore Roosevelt NP and UL Bend WA are not
projected to meet the URP. We propose that the SO2 BART
emission limit for Colstrip Unit 1 should be based on what can be
achieved with lime injection with an additional scrubber vessel.
    The proposed BART emission limit of 0.08 lb/MMBtu allows for a
sufficient margin of compliance for a 30-day rolling average limit that
would apply at all times, including startup, shutdown, and
malfunction.\146\ We are also proposing monitoring, recordkeeping, and
reporting requirements as described in our proposed regulatory text for
40 CFR 52.1395.
---------------------------------------------------------------------------

    \146\ As discussed in the BART Guidelines, section V (70 FR
39172, July 6, 2005), and Section 302(k) of the CAA, emissions
limits such as BART are required to be met on a continuous basis.
---------------------------------------------------------------------------

    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' We propose a compliance
deadline of five (5) years from the date our final FIP becomes
effective because of the equipment installation that will be required.
PM
    Colstrip Unit 1 currently has wet venturi scrubbers designed to
control PM emissions. Venturi scrubbers use a liquid stream to remove
solid particles. In the venturi scrubber, gas laden with PM passes
through a short tube with flared ends and a constricted middle. This
constriction causes the gas stream to speed up when the pressure is
increased. A water spray is directed into the gas stream either prior
to or at the constriction in the tube. The difference in velocity and
pressure resulting from the constriction causes the particles and water
to mix and combine. The reduced velocity at the expanded section of the
throat allows the droplets of water containing the particles to drop
out of the gas stream. Venturi scrubbers are effective in removing
small particles, with removal efficiencies of up to 99%.\147\ The
venturi scrubbers at Unit 1 are designed to have at least 98% control
efficiency and have shown control efficiencies approximating
99.5%.\148\ The present filterable particulate emission rate is 0.047
lb/MMBtu.\149\
---------------------------------------------------------------------------

    \147\ EPA Air Pollution Control Online Course, description at:
http://www.epa.gov/apti/course422/ce6a3.html.
    \148\ Colstrip Addendum, p. 6-1
    \149\ Colstrip Initial Response, p. 4-8.
---------------------------------------------------------------------------

    Based on our modeling described in V.C.3.a., PM contribution to the
baseline visibility impairment is low. Table 88 shows the maximum
baseline visibility impact and percentage contribution to that impact
from coarse PM and fine PM.

    Table 88--Colstrip Unit 1 Visibility Impact Contribution From PM
------------------------------------------------------------------------
    Maximum baseline
   visibility impact      % Contribution coarse   % Contribution fine PM
       (deciview)                   PM
------------------------------------------------------------------------
                0.922                     0.73                     3.01
------------------------------------------------------------------------

    The PM contribution to the baseline visibility impact for Colstrip
Unit 1 is very small; therefore, any visibility improvement that could
be achieved with improvements to the existing PM controls would be
negligible.
    Colstrip Unit 1 must meet the filterable PM emission standard of
0.1 lb/MMBtu in accordance with their Final Title V Operating Permit
OP0513-06. This requirement appears in Permit Condition B.2.;
and was included in the permit pursuant to ARM 17.8.340 and 40 CFR part
60, subpart D.
    Taking into consideration the above factors we propose basing the
BART emission limit on what Colstrip Unit 1 is currently meeting. The
units are exceeding a PM control efficiency of 99%, and therefore we
are proposing that the current control technology and the emission
limit of 0.1lb/MMBtu for PM/PM10 as BART. We find that the
BART emission limit can be achieved through the operation of the
existing venturi scrubbers. Thus, as described in our BART Guidelines,
a full five-factor analysis for PM/PM10 is not needed for
Colstrip Unit 1.
    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' Since we propose a BART
emission limit that represents current operations and no installation
is necessary, we propose a compliance deadline of 30 days from the date
our final FIP becomes effective.
(b) Colstrip Unit 2
NOX
    The Colstrip Unit 2 boiler is of tangential-fired design with LNB
and OFA. Originally, the unit operated with a NOX emission
limit of 0.7 lb/MMBtu. In 1997, EPA approved an early election plan
under the ARP that included a 0.45 lb/MMBtu annual NOX
limit. The early reduction limit expired in 2007 and the new annual
limit under the ARP (0.40 lb/MMBtu) became effective in 2008. Normally,
the unit operates with an actual annual average NOX emission
rate in the range of 0.30 to 0.35 lb/MMBtu, accomplished with the low
NOX burners and CCOFA.\150\
---------------------------------------------------------------------------

    \150\ Baseline emissions were determined by averaging the annual
emissions from 2008 to 2010 as reported to the CAMD database
available at http://camddataandmaps.epa.gov/gdm/index.cfm?fuseaction=emissions.
---------------------------------------------------------------------------

Step 1: Identify All Available Technologies
    We identified that the same NOX control technologies for
Colstrip Unit 2

as for Colstrip Unit 1; see Step 1 above under Colstrip Unit 1 for a
list of proposed controls.
Step 2: Eliminate Technically Infeasible Options
    Our analysis for Colstrip Unit 1 explains our reasoning for
eliminating some of the technologies that were identified in Step 1. We
have retained SOFA, SOFA+SNCR, and SOFA+SCR for evaluation.
Step 3: Evaluate Control Effectiveness of Remaining Control Technology
    At tangentially fired boilers firing PRB coal, SOFA in combination
with CCOFA and LNB, can typically achieve emission rates below 0.15 lb/
MMBtu on an annual basis.\151\ However, due to certain issues unique to
Colstrip Unit 2, a rate of 0.20 lb/MMBtu is more realistic.
Specifically, these issues include: (1) That the furnace was sized too
small and therefore runs hotter than similar units, and (2) that the
PRB coal, classified as a borderline sub-bituminous B coal, is less
reactive (produces more NOX) than typical PRB coals.\152\
The 0.20 lb/MMBtu rate represents a 35.3% reduction from the current
baseline (2008 through 2010) rate of 0.309 lb/MMbtu.
---------------------------------------------------------------------------

    \151\ Low NOX Firing Systems and PRB Fuel; Achieving
as Low as 0.12 LB NOX/MMBtu, Jennings, P., ICAC Forum,
Feb. 2002.
    \152\ Colstrip Addendum, p. 5-1.
---------------------------------------------------------------------------

    The post-combustion control technologies, SNCR and SCR, have been
evaluated in combination with combustion controls. That is, the inlet
concentration to the post-combustion controls is assumed to be 0.20 lb/
MMBtu. This allows the equipment and operating and maintenance costs of
the post-combustion controls to be minimized based on the lower inlet
NOX concentration. Typically, SNCR reduces NOX an
additional 20 to 30% above LNB/combustion controls without excessive
NH3 slip.\153\ Assuming that a minimum 25% additional
emission reduction is achievable with SNCR, SOFA combined with SNCR can
achieve an overall control efficiency of 51.4%. SCR can achieve
performance emission rates as low as 0.04-0.07 lb/MMBtu on an annual
basis.\154\ Assuming that an annual emission rate of 0.05 lb/MMBtu is
achievable with SCR, SOFA combined with SCR can achieve an overall
control efficiency of 83.8%. A summary of emissions projections for the
control options is provided in Table 89.
---------------------------------------------------------------------------

    \153\ White Paper, SNCR for Controlling NOX
Emissions, Institute of Clean Air Companies, pp. 4 and 9, February
2008.
    \154\ http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/NOx%20control%20Lani%20AWMA%200905.pdf.

                 Table 89--Summary of NOX BART Analysis Control Technologies for Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
                                              Control        Annual emission      Emissions         Remaining
             Control option              effectiveness (%)   rate (lb/MMBtu)   reduction (tpy)   emissions (tpy)
----------------------------------------------------------------------------------------------------------------
SOFA+SCR...............................               83.8             0.050             3,376               652
SOFA+SNCR..............................               51.4             0.150             2,072             1,956
SOFA...................................               35.3             0.200             1,420             2,608
No Controls (Baseline) \1\.............                0               0.309  ................             4,028
----------------------------------------------------------------------------------------------------------------
\1\ Baseline emissions were determined by averaging the annual emissions from 2008 to 2010 as reported to the
  CAMD database available at http://camddataandmaps.epa.gov/gdm/index.cfm?fuseaction=emissions. A summary of
  this information can be found in our docket.

Step 4: Evaluate Impacts and Document Results
Factor 1: Costs of Compliance
    Refer to the Colstrip Unit 1 section above for general information
on how we evaluated the cost of compliance for NOX controls.
SOFA
    We relied on estimates submitted by PPL in 2008 for capital costs
and direct annual costs for SOFA.\155\ We then used the CEPCI to adjust
capital costs to 2010 dollars (see Table 90). Annual costs were
determined by summing the indirect annual cost and the direct annual
cost (see Table 91).
---------------------------------------------------------------------------

    \155\ Colstrip Addendum, Table 5.1-1.

Table 90--Summary of NOX BART Capital Cost Analysis for SOFA on Colstrip
                                 Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment SOFA...........................       4,507,528
------------------------------------------------------------------------

 Table 91--Summary of NOX BART Annual Cost Analysis for SOFA on Colstrip
                                 Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Indirect Annual Cost..............................         425,511
Total Direct Annual Cost................................         664,884
                                                         ---------------
    Total Annual Cost...................................       1,090,395
------------------------------------------------------------------------

                         Table 92--Summary of NOX BART Costs for SOFA on Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions  reductions           Average cost
           (MM$)               Total annual cost (MM$)               (tpy)               effectiveness ($/ton)
----------------------------------------------------------------------------------------------------------------
                4.508                        1.090                        1,420                         768
----------------------------------------------------------------------------------------------------------------

SOFA+SNCR
    We relied on control costs developed for the IPM for direct capital
costs for SNCR.\156\ We then used methods provided by the CCM for the
remainder of the SOFA+SNCR analysis. Specifically, we used the methods
in the CCM to calculate total capital investment, annual costs
associated with operation and maintenance, to annualize the total
capital investment using the CRF, and to sum the total annual costs.
---------------------------------------------------------------------------

    \156\ IPM, Chapter 5, Appendix 5-2B.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' reflecting an SNCR retrofit of
typical difficulty in the IPM control costs. Colstrip Unit 2 burns sub-
bituminous PRB coal having a low sulfur content of 0.91 lb/MMBtu
(equating to a SO2 rate of 1.8 lb/MMBtu).\157\ As explained
in our analysis for Colstrip Unit 1, it was not necessary to make
allowances in the cost calculations to account for equipment
modifications or additional maintenance associated with fouling due to
the formation of ammonium bisulfate. EPA's detailed cost calculations
for SOFA+SNCR can be found in the docket.
---------------------------------------------------------------------------

    \157\ Cost and Quality of Fuels for Electric Utility Plants 1999
Tables, Energy Information Administration, DOE/EIA-0191(99), June
2000, Table 24.
---------------------------------------------------------------------------

    We used a urea reagent cost estimate of $450 per ton taken from
PPL's September 2011 submittal.\158\ To estimate the average cost
effectiveness (dollars per ton of emissions reductions) we divided the
total annual cost by the estimated NOX emissions reductions.
We summarize the costs from our SOFA+SNCR cost analysis in Tables 93,
94, and 95.
---------------------------------------------------------------------------

    \158\ NOX Control Update to PPL Montana's Colstrip
Generating Station BART Report Prepared for PPL Montana, LLC, by
TRC, September 2011, p. 4-1.

  Table 93--Summary of NOX BART Capital Cost Analysis for SOFA+SNCR on
                             Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       4,507,528
Capital Investment SNCR.................................       8,873,145
                                                         ---------------
    Total Capital Investment SOFA+SNCR..................      13,380,673
------------------------------------------------------------------------

 Table 94--Summary of NOX BART Total Annual Cost Analysis for SOFA+SNCR
                           on Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................       1,090,395
Total Annual Cost SNCR..................................       2,165,732
                                                         ---------------
    Total Annual Cost SOFA+SNCR.........................       3,256,127
------------------------------------------------------------------------

                      Table 95--Summary of NOX BART Costs for SOFA+SNCR on Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions  reductions           Average cost
           (MM$)               Total annual cost (MM$)               (tpy)               effectiveness ($/ton)
----------------------------------------------------------------------------------------------------------------
               13.381                        3.256                        2,072                       1,571
----------------------------------------------------------------------------------------------------------------

SOFA+SCR
    We relied on control costs developed for the IPM for direct capital
costs for SCR.\159\ We then used methods in the CCM for the remainder
of the SOFA+SCR analysis. Specifically, we used the methods in the CCM
to calculate total capital investment, annual costs associated with
operation and maintenance, to annualize the total capital investment
using the CRF, and to sum the total annual costs.
---------------------------------------------------------------------------

    \159\ IPM, Chapter 5, Appendix 5-2A.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' in the IPM control costs, which
reflects an SCR retrofit of typical difficulty. We used an aqueous
ammonia (29%) cost of $240 per ton,\160\ and a catalyst cost of $6,000
per cubic meter.\161\ To estimate the average cost effectiveness
(dollars per ton of emissions reductions) we divided the total annual
cost by the estimated NOX emissions reductions. We summarize
the costs from our SOFA+SCR cost analysis in Tables 96, 97, and 98.
---------------------------------------------------------------------------

    \160\ Email communication with Fuel Tech, Inc., March 2, 2012.
    \161\ Cichanowicz 2010, p. 6-7.

   Table 96--Summary of NOX BART Capital Cost Analysis for SOFA+SCR on
                             Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       4,507,528
Capital Investment SCR..................................      78,263,720
                                                         ---------------
    Total capital Investment SOFA + SCR.................      82,771,248
------------------------------------------------------------------------

Table 97--Summary of NOX BART Total Annual Cost Analysis for SOFA+SCR on
                             Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................       1,090,395

Total Annual Cost SCR...................................       9,830,104
                                                         ---------------
    Total Annual Cost SOFA+SCR..........................      10,920,499
------------------------------------------------------------------------

                       Table 98--Summary of NOX BART Costs for SOFA+SCR on Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
  Total capital investment                                   Emissions  reductions           Average cost
           (MM$)               Total annual cost (MM$)             (tons/yr)             effectiveness ($/ton)
----------------------------------------------------------------------------------------------------------------
               82.771                       10.920                        3,376                       3,235
----------------------------------------------------------------------------------------------------------------

Factor 2: Energy Impacts
    An SNCR process reduces the thermal efficiency of a boiler as the
reduction reaction uses thermal energy from the boiler.\162\ Therefore,
additional coal must be burned to make up for the decreases in power
generation. Using CCM calculations we determined the additional coal
needed for Unit 2 equates to 75,800 MMBtu/yr. For an SCR, the new
ductwork and the reactor's catalyst layers decrease the flue gas
pressure. As a result, additional fan power is necessary to maintain
the flue gas flow rate through the ductwork. SCR systems require
additional electric power to meet fan requirements equivalent to
approximately 0.3% of the plant's electric output.\163\ Both SCR and
SNCR require some minimal additional electricity to service
pretreatment and injection equipment, pumps, compressors, and control
systems. The additional energy requirements that would be involved in
installation and operation of the evaluated controls are not
significant enough to warrant eliminating any of the options evaluated.
Note that cost of the additional energy requirements has been included
in our calculations.
---------------------------------------------------------------------------

    \162\ CCM, Section 4.2, Chapter 1, p. 1-21.
    \163\ CCM, Section 4.2, Chapter 2, p. 2-28.
---------------------------------------------------------------------------

Factor 3: Non-Air Quality Environmental Impacts
    The non-air quality environmental impacts for Colstrip Unit 2 are
the same as for Colstrip Unit 1, see previous discussion for Colstrip
Unit 1.
Factor 4: Remaining Useful Life
    EPA has determined that the default 20-year amortization period is
most appropriate to use as the remaining useful life of the facility.
Without commitments for an early shut down, EPA cannot consider a
shorter amortization period in our analysis. Thus, this factor does not
impact our BART determination because the annualized cost was
calculated over a 20 year period in accordance with the BART
Guidelines.
Factor 5: Evaluate Visibility Impacts
    We conducted modeling for Colstrip Unit 2 as described in section
V.C.3.a. Table 99 presents the visibility impacts of the 98th
percentile of daily maxima for each Class I area from 2006 through
2008. Table 100 presents the number of days with impacts greater than
0.5 deciviews for each Class area from 2006 through 2008.

                    Table 99--Delta Deciview Improvement for NOX Controls on Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
                                                            Improvement from  Improvement from  Improvement from
              Class I area                 Baseline impact   SOFA+SCR (delta  SOFA+SNCR (delta     SOFA (delta
                                          (delta deciview)      deciview)         deciview)         deciview)
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.......................             0.402             0.185             0.083             0.055
Theodore Roosevelt NP...................             0.895             0.423             0.269             0.190
UL Bend WA..............................             0.889             0.406             0.269             0.185
Washakie WA.............................             0.392             0.143             0.089             0.063
Yellowstone NP..........................             0.289             0.091             0.071             0.063
----------------------------------------------------------------------------------------------------------------

                  Table 100--Days Greater Than 0.5 Deciview for NOX Controls on Colstrip Unit 2
                                               [Three year total]
----------------------------------------------------------------------------------------------------------------
              Class I Area                 Baseline (days)   Using SOFA+SCR    Using SOFA+SNCR     Using SOFA
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.......................                 8                 5                 5                 7
Theodore Roosevelt NP...................                54                14                25                35
UL Bend WA..............................                66                17                41                46
Washakie WA.............................                12                 5                 8                11
Yellowstone NP..........................                 4                 2                 2                 2
----------------------------------------------------------------------------------------------------------------

Step 5: Select BART
    We propose to find that BART for NOX is SOFA+SNCR at
Colstrip Unit 2 with an emission limit of 0.15 lb/MMBtu (30-day rolling
average). Of the five BART factors, cost and visibility improvement
were the critical ones in our analysis of controls for this source.
    In our BART analysis for NOX at Colstrip Unit 2, we
considered SOFA, SOFA+SNCR, and SOFA+SCR. The comparison between our
SOFA, SOFA+SNCR, and SOFA+SCR analysis is provided in Table 101.

                                Table 101--Summary of NOX BART Analysis Comparison of Control Options for Colstrip Unit 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Visibility Impacts \1\
                                   Total capital     Total annual      Average cost    Incremental cost ------------------------------------------------
         Control option          investment (MM$)     cost (MM$)       effectiveness     effectiveness   Visibility  Improvement     Fewer days > 0.5
                                                                          ($/ton)           ($/ton)          (delta deciviews)           deciview
--------------------------------------------------------------------------------------------------------------------------------------------------------
SOFA+SCR.......................            82.771            10.920             3,235             5,877  0.423 TRNP.............  40 TRNP
                                                                                0.406 UL Bend..........  49 UL Bend
SOFA+SNCR......................            13.380             3.256             1,571             3,322  0.269 TRNP.............  29 TRNP
                                                                                0.269 UL Bend..........  25 UL Bend
SOFA...........................             4.508             1.090               768               \2\  0.190 TRNP.............  19 TRNP
                                                                                0.185 UL Bend..........  20 UL Bend
--------------------------------------------------------------------------------------------------------------------------------------------------------
TRNP--Theodore Roosevelt National Park.
UL Bend--UL Bend Wilderness Area.
\1\ The visibility improvement described in this table represents the change in the maximum 98th percentile impact over the modeled 3-year
  meteorological period (2006 through 2008) at the Class I areas in the table.
\2\ Incremental cost is not applicable to the option that has the lowest effectiveness.

    We have concluded that SOFA, SOFA+SNCR, and SOFA+SCR are all cost
effective control technologies. SOFA has a cost effectiveness value of
$768 per ton of NOX emissions reduced. SOFA+SNCR is more
expensive than SOFA, with a cost effectiveness value of $1,571 per ton
of NOX emissions reduced. SOFA+SCR is more expensive than
SOFA or SOFA+SNCR, having a cost effectiveness value of $3,235 per ton
of NOX emissions reduced. This is well within the range of
values we have considered reasonable for BART and that states have
considered reasonable for BART.
    We have weighed costs against the anticipated visibility impacts
for Colstrip Unit 2. Any of the control options would have a positive
impact on visibility; however, the cost of SOFA+SCR ($3,322) is not
justified by the visibility improvement of 0.423 deciviews at TRNP and
0.404 deciviews at UL Bend. The lower cost of SOFA+SNCR ($1,571/ton) is
justified when the visibility improvement is considered. SOFA+SNCR
would have a visibility improvement of 0.269 deciviews at Theodore
Roosevelt NP and 0.269 deciviews at UL Bend WA and it would result in
29 fewer days above 0.5 deciviews at Theodore Roosevelt NP and 25 fewer
days above 0.5 deciviews at UL Bend WA. In addition, application of
SOFA+SNCR at both Colstrip Units 1 and 2 would have a combined modeled
visibility improvement of 0.501 deciviews at Theodore Roosevelt NP and
0.451 deciviews at UL Bend WA. We consider these improvements to be
substantial, especially in light of the fact that Theodore Roosevelt NP
and UL Bend WA are not projected to meet the URP. We propose that the
NOX BART emission limit for Colstrip Unit 2 should be based
on what can be achieved with SOFA + SNCR.
    The proposed BART emission limit of 0.15 lb/MMBtu allows for a
sufficient margin of compliance for a 30-day rolling average limit that
would apply at all times, including startup, shutdown, and
malfunction.\164\ We are also proposing monitoring, recordkeeping, and
reporting requirements as described in our proposed regulatory text for
40 CFR 52.1395.
---------------------------------------------------------------------------

    \164\ As discussed in the BART Guidelines, section V (70 FR
39172, July 6, 2005), and Section 302(k) of the CAA, emissions
limits such as BART are required to be met on a continuous basis.
---------------------------------------------------------------------------

    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' We propose a compliance
deadline of five (5) years from the date our final FIP becomes
effective because of the equipment installation and potential
combustion modifications that will be required.
SO2
    Colstrip Unit 2 is already controlled by wet venturi scrubbers,
which are identical to Colstrip Unit 1 scrubbers, for simultaneous
particulate and SO2 control. The venturi scrubbers utilize
the alkalinity of the fly ash to achieve an estimated SO2
removal efficiency of 75%.\165\ Based on emissions data from CAMD, for
the baseline period 2008 through 2010, the average SO2
emission rate was 0.418 lb/MMBtu and the average SO2
emissions were 5,548 tpy.\166\
---------------------------------------------------------------------------

    \165\ Colstrip Initial Response, p. ES-3.
    \166\ Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm.
---------------------------------------------------------------------------

Step 1: Identify All Available Technologies
    The Colstrip Unit 2 venturi scrubber currently achieves greater
than 50% removal of SO2. The available technologies for
Colstrip Unit 2 are the same as those for Colstrip Unit 1; see Step 1
analysis for Colstrip Unit 1.
Step 2: Eliminate Technically Infeasible Options
    Elimination of bypass reheat is not a feasible option because
Colstrip Unit 2 is designed so that there is no bypass of flue gas.
Installation of perforated trays is not a feasible option because the
existing scrubber design already includes this technology in the form
of wash trays. Finally, the use of organic acid additives is not a
feasible option because the reactivity of the lime would neutralize the
acids, making the additives ineffective.
    Lime injection or lime injection with an additional scrubber vessel
are technically feasible control options because lime injection is
currently used to control SO2 emissions at Colstrip Units 3
and 4.

Step 3: Evaluate Control Effectiveness of Remaining Control Technology
    An annual emission rate of 0.015 lb/MMBtu can be achieved with lime
injection without an additional scrubber vessel. PPL stated that this
is the lowest emission rate that could be achieved without adding an
additional scrubber vessel.\167\ An annual emission rate of 0.08-0.09
lb/MMBtu can be achieved with lime injection with an additional
scrubber vessel. This is the emission rate that is being achieved at
Colstrip Units 3 and 4 according to emissions data from CAMD.\168\ The
control effectiveness of each of the control options was calculated
using the controlled emission rates that were provided by PPL.
---------------------------------------------------------------------------

    \167\ Colstrip Addendum, p. 4-1.
    \168\ Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm/.
---------------------------------------------------------------------------

    A summary of control efficiencies, emission rates, and resulting
emissions and emission reductions, is provided in Table 102. EPA's
detailed emissions calculations for Colstrip 2 can be found in the
docket.

              Table 102--Summary of BART Analysis Control Technologies for SO2 for Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
                                               Control       Annual emission
             Control option                 effectiveness    rate (lb/MMBtu)      Emissions         Remaining
                                               (%) \1\             \2\         reduction (tpy)   emissions (tpy)
----------------------------------------------------------------------------------------------------------------
Lime Injection with Additional Scrubber               79.7             0.080             4,129             1,049
 Vessel.................................
Lime Injection..........................              62.0             0.150             3,212             1,966
Existing Controls (Baseline) \3\........  ................             0.395  ................             5,178
----------------------------------------------------------------------------------------------------------------
\1\ Control efficiency is provided relative to the emission rate with current controls.
\2\ Emission rates are provided on an annual basis.
\3\ Baseline emissions for 2008 through 2010 from Clean Air Markets--Data and Maps: http://camddataandmaps.epa.gov/gdm/.

Step 4: Evaluate Impacts and Document Results
Factor 1: Costs of Compliance
    We relied on capital costs and direct annual costs provided by PPL
when determining the cost of compliance for both lime injection and
lime injection with an additional scrubber vessel.169 170
All costs presented here for the Colstrip Unit 2 SO2 control
options are in year 2007 dollars. EPA's cost calculations for Colstrip
2 can be found in the docket.
---------------------------------------------------------------------------

    \169\ Colstrip Initial Response, Table A4-6(c).
    \170\ Colstrip Addendum, Table 4.1-4.
---------------------------------------------------------------------------

Lime Injection
    We summarize our cost analysis for lime injection in Tables 103,
104, and 105.

  Table 103--Summary of SO2 Capital Cost Analysis for Lime Injection on
                             Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment................................       3,000,000
------------------------------------------------------------------------

 Table 104--Summary of SO2 BART Annual Cost Analysis for Lime Injection
                           on Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Direct Annual Cost................................       1,600,000
Indirect Annual Cost....................................         283,200
                                                         ---------------
  Total Annual Cost.....................................       1,883,200
------------------------------------------------------------------------

                   Table 105--Summary of SO2 BART Costs for Lime Injection on Colstrip Unit 2
----------------------------------------------------------------------------------------------------------------
  Total Capital Investment                                   Emissions  reductions           Average cost
           (MM$)               Total Annual Cost (MM$)               (tpy)              effectiveness  ($/ton)
----------------------------------------------------------------------------------------------------------------
                3.000                        1.883                        3,212                         586
----------------------------------------------------------------------------------------------------------------

Lime Injection With an Additional Scrubber Vessel
    We summarize our cost analysis for lime injection with an
additional scrubber vessel cost analysis in Tables 106, 107, and 108.

 Table 106--Summary of SO2 Capital Cost Analysis for Lime Injection With
            an Additional Scrubber Vessel on Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment, Lime Injection................       3,000,000

Capital Investment, Scrubber Vessel.....................      25,000,000
                                                         ---------------
  Total Capital Investment..............................      28,000,000
------------------------------------------------------------------------

 Table 107--Summary of SO2 BART Annual Cost Analysis for Lime Injection
          With an Additional Scrubber Vessel on Colstrip Unit 2
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Direct Annual Cost................................       1,450,000
Indirect Annual Cost....................................       2,643,200
                                                         ---------------
  Total Annual Cost.....................................       4,093,200
------------------------------------------------------------------------

 Table 108--Summary of SO2 BART Costs Analysis for Lime Injection With an Additional Scrubber Vessel on Colstrip
                                                     Unit 2
----------------------------------------------------------------------------------------------------------------
  Total installed capital                                    Emissions  reductions           Average cost
         cost (MM$)            Total annual cost (MM$)               (tpy)               effectiveness ($/ton)
----------------------------------------------------------------------------------------------------------------
              $28.000                       $4.093                        4,129                         991
----------------------------------------------------------------------------------------------------------------

Factor 2: Energy Impacts
    According to PPL, the pressure drop of the venturi scrubbers is
maintained in the range of 17 to 20 inches of water column. The
injection of lime will be accompanied by little to no increase in
pressure drop, but it will require a small increase in pump power
consumption. This is included in the cost analysis in the additional
operations and maintenance expenses of $125,000 per year.\171\ The
additional energy requirements are not significant enough to warrant
eliminating either lime injection or lime injection with an additional
scrubber vessel.
---------------------------------------------------------------------------

    \171\ Colstrip Initial Response, p. 4-16.
---------------------------------------------------------------------------

Factor 3: Non-Air Quality Environmental Impacts
    Adding lime to the scrubbers will require more frequent descaling
operations that would increase the quantity of solid waste from
descaling operations. Transporting this waste stream for disposal would
use natural resources for fuel and would have associated air quality
impacts. The disposal of the solid waste itself would be to a landfill
and could possibly result in groundwater or surface water contamination
if a landfill's engineering controls were to fail. EPA's analysis
indicates that the environmental impacts associated with the proper
transport and land disposal of the solid waste should not be
significant. Therefore, the non-air quality environmental impacts do
not warrant eliminating either lime injection addition or lime
injection addition with an additional scrubber vessel.
Factor 4: Remaining Useful Life
    EPA has determined that the default 20-year amortization period is
most appropriate to use as the remaining useful life of the facility.
Without commitments for an early shut down, EPA cannot consider a
shorter amortization period in our analysis. Because the remaining
useful life of the source is equal to that assumed for amortization of
control option capital investments, this factor does not impact our
BART determination.
Factor 5: Evaluate Visibility Impacts
    We conducted modeling for Colstrip Unit 2 as described in section
V.C.3.a. Table 109 presents the visibility impacts of the 98th
percentile of daily maxima for each Class I area from 2006 through
2008. Table 110 presents the number of days with impacts greater than
0.5 deciviews for each Class I area from 2006 through 2008.

                      Table 109--Delta Deciview Improvement for SO2 Controls on Colstrip 2
----------------------------------------------------------------------------------------------------------------
                                                                              Improvement from
                                                                              lime injection +  Improvement from
                       Class I area                          Baseline impact     additional      lime  injection
                                                            (delta deciview)   scrubber vessel  (delta deciview)
                                                                              (delta deciview)
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.........................................             0.402             0.140             0.111
Theodore Roosevelt NP.....................................             0.895             0.280             0.225
UL Bend WA................................................             0.889             0.179             0.143
Washakie WA...............................................             0.392             0.141             0.119
Yellowstone NP............................................             0.289             0.090             0.067
----------------------------------------------------------------------------------------------------------------

                    Table 110--Days Greater Than 0.5 Deciview for SO2 Controls on Colstrip 2
                                               [Three year total]
----------------------------------------------------------------------------------------------------------------
                                                                                Using lime
                                                                                injection +       Using lime
                       Class I area                          Baseline (days)     additional         injection
                                                                               scrubber vessel
----------------------------------------------------------------------------------------------------------------
North Absaroka WA.........................................                 7                 7                 7
Theodore Roosevelt NP.....................................                52                33                37
UL Bend WA................................................                68                39                44
Washakie WA...............................................                12                 7                 8
Yellowstone NP............................................                 4                 2                 3
----------------------------------------------------------------------------------------------------------------

Step 5: Select BART
    We propose to find that BART for SO2 is lime injection
with an additional scrubber vessel at Colstrip Unit 2 with an emission
limit of 0.08 lb/MMBtu (30-day rolling average). Of the five BART
factors, cost and visibility improvement were the critical ones in our
analysis of controls for this source.
    In our BART analysis for SO2 at Colstrip Unit 2, we
considered lime injection and lime injection with an additional
scrubber vessel. The comparison between our lime injection and lime
injection with an additional scrubber vessel analysis is provided in
Table 111.

   Table 111--Summary of EPA SO2 BART Analysis Comparison of Lime Injection and Lime Injection With an Additional Scrubber Vessel for Colstrip Unit 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Incremental                  Visibility impacts \1\
                                     Total capital   Total annual    Average cost        cost      -----------------------------------------------------
          Control option              investment      cost (MM$)     effectiveness   effectiveness    Visibility improvement
                                         (MM$)                          ($/ton)         ($/ton)         (delta deciviews)      Fewer days > 0.5 deciview
--------------------------------------------------------------------------------------------------------------------------------------------------------
Lime Injection with Additional              28.000           4.093             991           2,410  0.280 TRNP...............  7 TRNP
 Scrubber Vessel.                                                                                0.179 UL Bend............  8 UL Bend
Lime Injection....................           3.000           1.883             586             \2\  0.225 TRNP...............  6 TRNP
                                                                                0.143 UL Bend............  7 UL Bend
--------------------------------------------------------------------------------------------------------------------------------------------------------
TRNP--Theodore Roosevelt National Park.
UL Bend--UL Bend Wilderness Area.
\1\ The visibility improvement described in this table represents the change in the maximum 98th percentile impact over the modeled 3-year
  meteorological period (2006 through 2008) at the Class I areas in the table.
\2\ Incremental cost is not applicable to the option that has the lowest effectiveness.

    We have concluded that lime injection and lime injection with an
additional scrubber vessel are both cost effective control
technologies. Lime injection has a cost effectiveness value of $586 per
ton of SO2 emissions reduced. Lime injection with an
additional scrubber vessel is more expensive than lime injection, with
a cost effectiveness value of $919 per ton of SO2 emissions
reduced. Both of these costs are well within the range of values we
have considered reasonable for BART and that states have considered
reasonable for BART.
    We have weighed costs against the anticipated visibility impacts at
Colstrip Unit 2. Either of the control options would have a positive
impact on visibility. We have concluded that the cost of lime injection
with an additional scrubber vessel ($991/ton) is justified by the
visibility improvement of 0.280 deciviews at Theodore Roosevelt NP and
0.179 deciviews at UL Bend WA and it would result in seven fewer days
above 0.5 deciviews at Theodore Roosevelt NP and eight fewer days above
0.5 deciviews at UL Bend WA. In addition, the application of lime
injection with an additional scrubber vessel on both Colstrip Units 1
and 2 would result in a combined modeled visibility improvement of
0.592 deciviews at Theodore Roosevelt NP and 0.384 deciviews at UL Bend
WA. We consider these improvements to be substantial, especially in
light of the fact that Theodore Roosevelt NP and UL Bend WA are not
projected to meet the URP. We propose that the SO2 BART
emission limit for Colstrip Unit 2 should be based on what can be
achieved with lime injection with an additional scrubber vessel.
    The proposed BART emission limit of 0.08 lb/MMBtu allows for a
sufficient margin of compliance for a 30-day rolling average limit that
would apply at all times, including startup, shutdown, and
malfunction.\172\ We are also proposing monitoring, recordkeeping, and
reporting requirements as described in our proposed regulatory text for
40 CFR 52.1395.
---------------------------------------------------------------------------

    \172\ As discussed in the BART Guidelines, section V (70 FR
39172, July 6, 2005), and Section 302(k) of the CAA, emissions
limits such as BART are required to be met on a continuous basis.
---------------------------------------------------------------------------

    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' We propose a compliance
deadline of five (5) years from the date our final FIP becomes
effective because of the equipment installation that will be required.
PM
    Colstrip Unit 2 currently has venturi scrubbers designed to control
PM emissions. A description of a venturi scrubber can be found under
the PM section of the BART analysis for Colstrip Unit 1. The venturi
scrubbers at Colstrip unit 2 are designed to have at least 98% control
efficiency and have shown control efficiencies approximating 99.5%. The
present emission rate is 0.0525 lb/MMBtu.\173\
---------------------------------------------------------------------------

    \173\ Colstrip Addendum, p. 6-1.

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

    Based on our modeling described in section V.C.3.a. PM contribution
to the baseline visibility impairment is low. Table 112 shows the
maximum baseline visibility impact and percentage contribution to that
impact from coarse PM and fine PM.

    Table 112--Colstrip Unit 2 Visibility Impact Contribution From PM
------------------------------------------------------------------------
    Maximum baseline
   visibility impact      % Contribution coarse   % Contribution fine PM
       (deciview)                   PM
------------------------------------------------------------------------
                0.895                     0.95                     3.88
------------------------------------------------------------------------

    The PM contribution to the baseline visibility impact for Colstrip
Unit 2 is very small; therefore, any visibility improvement that could
be achieved with improvements to the existing PM controls would be
negligible. We are proposing that the existing PM control device
represents BART.
    Colstrip Unit 2 must meet the filterable PM emission standard of
0.1lb/MMBtu in accordance with its Final Title V Operating Permit
OP0513-06. This requirement appears in Permit Condition B.2.;
and was included in the permit pursuant to ARM 17.8.340 and 40 CFR part
60, subpart D.
    Taking into consideration the above factors we propose basing the
BART emission limit on what Colstrip Unit 2 is currently meeting. The
units are exceeding a PM control efficiency of 99%, and therefore we
are proposing that the current control technology and the emission
limit of 0.1lb/MMBtu for PM/PM10 as BART. We find that the
BART emission limit can be achieved through the operation of the
existing venturi scrubbers. Thus, as described in our BART Guidelines,
a full five-factor analysis for PM/PM10 is not needed for
Colstrip Unit 2.
    As we have noted previously, under section 51.308(e)(1)(iv), ``each
source subject to BART [is] required to install and operate BART as
expeditiously as practicable, but in no event later than 5 years after
approval of the implementation plan revision.'' Since we propose a BART
emission limit that represents current operations and no installation
is necessary, we propose a compliance deadline of 30 days from the date
our final FIP becomes effective.
v. Corette
Background
    PPL Montana's Corette Power Plant (Corette), located in Billings,
Montana, consists of one electric utility steam generating unit. We
previously provided in Section V.C. our reasoning for proposing that
this unit is BART-eligible and why it is subject to BART. As explained
in section V.C., the document titled ``Identification of BART Eligible
Sources in the WRAP Region'' dated April 4, 2005 provides more details
on the specific emission units at each facility. Corette's boiler has a
nominal gross capacity of 162 MW. The boiler began commercial operation
in 1968 and is a tangentially fired pulverized coal boiler that burns
PRB sub-bituminous coal as their exclusive fuel.
    Although the gross capacity of Corette is below the 750 MW cutoff
for which use of the BART Guidelines is mandatory, we have nonetheless
followed the guidelines as they ``provide useful advice in implementing
the BART provisions of the regional haze rule.'' \174\
---------------------------------------------------------------------------

    \174\ 70 FR 39108 (July 6, 2005).
---------------------------------------------------------------------------

    We requested a five factor BART analysis for Corette from PPL and
the Company submitted that analysis in August 2007 along with updated
information in June 2008 and September 2011. PPL's five factor BART
analysis information is contained in the docket for this action and we
have taken it into consideration in our proposed action.
NOX
    The Corette boiler is a tangential-fired unit with existing low-
NOX burners and CCOFA. The unit is subject to an annual
NOX emission limit of 0.4 lb/MMBtu.
Step 1: Identify All Available Technologies
    We identified the following NOX control technologies are
available: SOFA, SNCR, and SCR. Descriptions for each of these
NOX control technologies can be found in the Colstrip 1
evaluation above.
Step 2: Eliminate Technically Infeasible Options
    Based on our review all the technologies identified in Step 1
appear to be technically feasible for Corette. In particular, both SCR
and SNCR have been widely employed to control NOX emissions
from coal-fired power plants.175 176 177
---------------------------------------------------------------------------

    \175\ Institute of Clean Air Companies (ICAC) White Paper, SCR
Controls of NOX Emissions from Fossil Fuel-Fired Electric
Power Plants, May 2009, pp. 7-8.
    \176\ Control Technologies to Reduce Conventional and Hazardous
Air Pollutants from Coal-Fired Power Plants, Northeast States for
Coordinated Air Use Management (NESCAUM), March 31, 2011, p. 16.
    \177\ ICAC White Paper, SNCR for Controlling NOX
Emissions, February 2008, pp. 6-7.
---------------------------------------------------------------------------

Step 3: Evaluate Control Effectiveness of Remaining Control Technology
    At tangentially fired boilers firing sub-bituminous coal, SOFA in
combination with CCOFA and LNB, can typically achieve emission rates
below 0.15 lb/MMBtu on an annual basis.\178\ However, due to certain
issues unique to Corette, a rate of 0.20 lb/MMBtu is more realistic.
Specifically, these issues include: (1) That the furnace is undersized,
has a high heat rate, and therefore runs hotter than newer units
designed for low NOX emissions; and (2) the nature of the
particular PRB coal burned. The 0.20 lb/MMBtu rate represents a 26.8%
reduction from the current baseline (2008 through 2010) rate of 0.274
lb/MMbtu.
---------------------------------------------------------------------------

    \178\ Low NOX Firing Systems and PRB Fuel; Achieving
as Low as 0.12 LB NOX/MMBtu, Jennings, P., ICAC Forum,
Feb. 2002.
---------------------------------------------------------------------------

    The post-combustion control technologies, SNCR and SCR, have been
evaluated in combination with combustion controls. That is, the inlet
concentration to the post-combustion controls is assumed to be 0.20 lb/
MMBtu. This allows the equipment and operating and maintenance costs of
the post-combustion controls to be minimized based on the lower inlet
NOX concentration. Typically, SNCR reduces NOX an
additional 20 to 30% above LNB/combustion controls without excessive
NH3 slip.\179\ Assuming that a minimum 25% additional
emission reduction is achievable with SNCR, SOFA combined with SNCR can
achieve an overall control efficiency of 44.9%. SCR can achieve
performance emission rates as low as 0.04-0.07 lb/MMBtu on an annual
basis.\180\ Assuming that an annual emission rate of 0.05 lb/MMBtu is
achievable with SOFA+SCR, this equates to an overall control efficiency
of 81.2%. A summary of control

efficiencies, emission rates, and resulting emission reductions for the
control options under consideration are provided in Table 113. EPA's
detailed emissions calculations for Corette can be found in the docket.
---------------------------------------------------------------------------

    \179\ White Paper, SNCR for Controlling NOX
Emissions, Institute of Clean Air Companies, pp. 4 and 9, February
2008.
    \180\ Srivastava, R., Hall, R., Khan, S., Lani, B., and
Culligan, K., ``Nitrogen oxides emission control options for coal-
fired utility boilers,'' Journal of Air and Waste Management
Association 55(9):1367-88 (2005). Available at: http://www.netl.doe.gov/technologies/coalpower/ewr/pubs/NOx%20control%20Lani%20AWMA%200905.pdf.

                    Table 113--Summary of NOX BART Analysis Control Technologies for Corette
----------------------------------------------------------------------------------------------------------------
                                               Control
             Control option                 effectiveness    Annual emission      Emissions         Remaining
                                                 (%)        rate  (lb/MMBtu)  reduction  (tpy)  emissions  (tpy)
----------------------------------------------------------------------------------------------------------------
SOFA+SCR................................              81.2             0.050             1,320               305
SOFA+SNCR...............................              44.9             0.150               730               895
SOFA....................................              26.9             0.200               435             1,190
No Controls (Baseline) \1\..............  ................             0.274  ................             1,625
----------------------------------------------------------------------------------------------------------------
\1\ Baseline emissions were determined by averaging the annual emissions from 2008 to 2010 as reported to the
  CAMD database available at http://camddataandmaps.epa.gov/gdm/.

Step 4: Evaluate Impacts and Document Results
Factor 1: Costs of Compliance
    Refer to the Colstrip Unit 1 section above for general information
on how we evaluated the cost of compliance for NOX controls.
EPA's cost calculations for NOX controls at Corette can be
found in the docket.
SOFA
    We relied on estimates submitted by PPL in 2008 for capital costs
and direct annual costs for SOFA.\181\ We then used the CEPCI to adjust
capital costs to 2010 dollars (see Table 114). Annual costs were
determined by summing the indirect annual cost and the direct annual
cost (see Table 115).
---------------------------------------------------------------------------

    \181\ Addendum to PPL Montana's J.E. Corette Generating Station
BART Report Prepared for PPL Montana, LLC; Prepared by TRC
(``Corette Addendum''), June 2008, Table 5.1-3.

Table 114--Summary of NOX BART Capital Cost Analysis for SOFA on Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Capital Investment SOFA...........................       3,350,365
------------------------------------------------------------------------

 Table 115--Summary of NOX BART Annual Cost Analysis for SOFA on Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Indirect Annual Cost..............................         330,375
Total Direct Annual Cost................................         315,754
                                                         ---------------
  Total Annual Cost.....................................         646,129
------------------------------------------------------------------------

                            Table 116--Summary of NOX BART Costs for SOFA on Corette
----------------------------------------------------------------------------------------------------------------
  Total installed capital                                    Emissions  reductions           Average cost
        cost  (MM$)            Total annual cost  (MM$)              (tpy)              effectiveness  ($/ton)
----------------------------------------------------------------------------------------------------------------
                3.351                        0.646                          435                       1,487
----------------------------------------------------------------------------------------------------------------

SOFA+SNCR
    We relied on control costs developed for the IPM for direct capital
costs for SNCR.\182\ We then used methods provided by the CCM for the
remainder of the SOFA+SNCR analysis. Specifically, we used the methods
in the CCM to calculate total capital investment, annual costs
associated with operation and maintenance, to annualize the total
capital investment using the CRF, and to sum the total annual costs.
---------------------------------------------------------------------------

    \182\ IPM, Chapter 5, Appendix 5-2B.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' reflecting an SNCR retrofit of
typical difficulty in the IPM control costs. Corette burns sub-
bituminous PRB coal having a low sulfur content of 0.24 lb/MMBtu.\183\
As explained in our analysis for Colstrip Unit 1, it was not necessary
to make allowances in the cost calculations to account for equipment
modifications or additional maintenance associated with fouling due to
the formation of ammonium bisulfate. EPA's detailed cost calculations
for SOFA+SNCR can be found in the docket.
---------------------------------------------------------------------------

    \183\ Cost and Quality of Fuels for Electric Utility Plants 1999
Tables, Energy Information Administration, DOE/EIA-0191(99), June
2000, Table 24.
---------------------------------------------------------------------------

    We used a urea reagent cost estimate of $450 per ton taken from
PPL's September 2011 submittal.\184\ To estimate the average cost
effectiveness (dollars per ton of emissions reductions) we divided the
total annual cost by the estimated NOX emissions reductions.
We summarize the costs from our SPFA+SNCR cost analysis in Tables 117,
118, and 119.
---------------------------------------------------------------------------

    \184\ NOX Control Update to PPL Montana's J.E.
Corette Generating Station BART Report, September 2011, Prepared for
PPL Montana, LLC by TRC, p. 8.

  Table 117--Summary of NOX BART Capital Cost Analysis for SOFA+SNCR on
                                 Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       3,350,365
Capital Investment SNCR.................................       6,464,691
                                                         ---------------
  Total Capital Investment SOFA + SNCR..................       9,815,056
------------------------------------------------------------------------

 Table 118--Summary of NOX BART Total Annual Cost Analysis for SOFA+SNCR
                               on Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................         646,129
Total Annual Cost SNCR..................................       1,248,062
                                                         ---------------
  Total Annual Cost SOFA+SNCR...........................       1,894,191
------------------------------------------------------------------------

                          Table 119--Summary of NOX BART Costs for SOFA+SNCR on Corette
----------------------------------------------------------------------------------------------------------------
  Total installed capital                                    Emissions  reductions           Average cost
         cost (MM$)            Total annual cost (MM$)               (tpy)               effectiveness ($/ton)
----------------------------------------------------------------------------------------------------------------
                9.815                        1.894                          730                       2,596
----------------------------------------------------------------------------------------------------------------

SOFA+SCR
    We relied on control costs developed for the IPM for direct capital
costs for SCR.\185\ We then used methods in the CCM for the remainder
of the SOFA+SCR analysis. Specifically, we used the methods in the CCM
to calculate total capital investment, annual costs associated with
operation and maintenance, to annualize the total capital investment
using the CRF, and to sum the total annual costs.
---------------------------------------------------------------------------

    \185\ IPM, Chapter 5, Appendix 5-2A.
---------------------------------------------------------------------------

    We used a retrofit factor of ``1'' in the IPM control costs, which
reflects an SCR retrofit of typical difficulty. We used an aqueous
ammonia (29%) cost of $240 per ton,\186\ and a catalyst cost of $6,000
per cubic meter.\187\ To estimate the average cost effectiveness
(dollars per ton of emissions reductions) we divided the total annual
cost by the estimated NOX emissions reductions. We summarize
the costs from our SOFA+SCR cost analysis in Tables 120, 121, and 122.
---------------------------------------------------------------------------

    \186\ Email communication with Fuel Tech, Inc., March 2, 2012.
    \187\ Cichanowicz 2010, p. 6-7.

  Table 120--Summary of NOX BART Capital Cost Analysis for SOFA+SCR on
                                 Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Capital Investment SOFA.................................       3.350,365
Capital Investment SCR..................................      42,958,390
                                                         ---------------
  Total Capital Investment SOFA+SCR.....................      46,308,755
------------------------------------------------------------------------

 Table 121--Summary of NOX BART Total Annual Cost Analysis for SOFA+SCR
                               on Corette
------------------------------------------------------------------------
                       Description                           Cost ($)
------------------------------------------------------------------------
Total Annual Cost SOFA..................................         646,129
Total Annual Cost SCR...................................       5,281,486
                                                         ---------------
  Total Annual Cost SOFA+SCR............................       5,927,615