United States Department of the Interior 

NATIONAL PARK SERVICE 

1849 C Street, N.W. 

Washington. D.C. 20240 

IN REPLY REFER TO: 

NOV 2 0 2009 

N3615 (2350) 

Ms. Anita Lee (Air-3) 

U.S. Environmental Protection Agency Region 9 

75 Hawthorne Street 

San Francisco, California 94105-3901 

Dear Ms. Lee: 

The National Park Service (NPS) appreciates the opportunity to comment on the Environmental 

Protection Agency's (EPA) Advanced Notice of Proposed Rulemaking (ANPR) regarding 

Assessment of Anticipated Visibility Improvements at Surrounding Class I Areas and Cost 

Effectiveness of Best Available Retrofit Technology (BART) for Four Comers Power Plant 

(FCPP) and Navajo Generating Station (NGS) (74 FR 44313). These comments supplement the 

information we provided in our July 24, 2009, letter to Deborah Jordan regarding visibility 

impacts and control options for nitrogen oxides emissions in determining BART for the NGS. 

Emissions from the FCPP and NGS have significant impacts on numerous, spectacularly scenic 

Class I areas managed by the NPS, including, Grand Canyon, Canyonlands, Mesa Verde, Bryce 

Canyon and Zion National Parks. Emissions also affect other park units with incomparable 

scenic values, like Glen Canyon National Recreation Area, Chaco Canyon, and Canyon de 

Chelly. When we consider the costs of additional pollution controls for nitrogen oxides (NOx) in 

the context ofthe cumulative impacts, we conclude that applying selective catalytic reduction 

(SCR) to control these emissions is technically feasible, cost-effective, and will substantially 

improve visibility in many protected areas. 

The comments we are providing today focus on 1) issues regarding background ammonia levels 

used in air quality models, 2) the techniques used to assess the degree of visibility improvement 

expected from application of control technology, and 3) detailed comments on the BART costs 

and technologies related to FCPP. 

Comments on Background Ammonia (NH32 

The background NH3 concentrations used in the CALPUFF model need to represent NH3 

available to form ammonium nitrate across the transport pathway from the source to the 

receptors of interest, not just the NH3 concentration at the specific receptor. NPS CALPUFF 

analyses for NGS and FCPP followed guidance from the Western Regional Air Partnership 

(WRAP) BART modeling protocol' to use a default value of 1 part per billion (ppb) NH3 as a 

reasonable representation ofNH3. 

1 Western Regional Air Partnership BART Modeling Protocol. 2006. hrtp://pah.cert.ucr.eduJaqrn/308/bart.shtrnl 
2 

Monitoring data to refine the background NH3values are limited. Sather et al. (2008)2 measured 

NH3 at several locations in the Four Comers area and reported that measured NH3values vary 

spatially with higher values near oil and gas, mobile, and industrial sources. Values at Mesa 

Verde National Park were the lowest measured, likely because NH3 had already reacted to form 

ammonium sulfate and ammonium nitrate. NH3values were lower in winter than summer. We 

agree with EPA's approach to calculate monthly NH3values for Mesa Verde National Park, 

based on the range of monitored NH3values in the Four Comers area from the Sather report 

(monthly values ranged from 1.0 ppb in winter to 1.5 ppb in summer). 

NH3measurements are not available at other Class I areas in the FCPP and NGS domain. We 

agree with EPA that available Interagency Monitoring of Protected Visual Environments 

(IMPROVE) monitoring data can be used to estimate a minimum value for the NH3necessary to 

account for sulfate and nitrate at the monitors. The EPA used NH3 calculations from 14 

IMPROVE monitors to derive a reasonable monthly estimate ofNH3 available in the modeling 

domain (ranging from 0.7 ppb in winter to 1.3 in summer). 

The NH3values used in CALPUFF modeling for Arizona Public Service and Salt River Project 

for the winter months (0.2-0.5 ppb) are too low. It is necessary to represent not only the 

ammonia at the receptor, but also ammonia available along the transport pathway from the 

source. 

Rather than continue disagreement over the absolute values to represent NH3in the modeling 

domain, it is important to view the CALPUFF modeling results in a relative sense to consider 

cumulative visibility impacts across multiple Class I areas and across alternative control options. 

Comments on Techniques to Assess Visibility Improvement 

We support the EPA's consideration ofthe visibility improvement that is expected to occur at 

multiple Class I areas. We believe that all BART assessments should consider the cumulative 

amount of visibility improvement that control technologies would achieve at all Class I areas 

affected by emissions from the BART source. While it is appropriate to assess a single Class I 

area to determine if a BART-eligible source is subject to BART requirements, the assessment of 

BART factors, which includes the cost of emission controls, must weigh the full degree of 

improvement expected for incurring costs. 

To date, most BART assessments we have reviewed provide information on the change in the 

98th percentile impacts at one or more Class I areas. It is often possible to use the air quality 

modeling information developed by states or the sources during the subject-to-BART assessment 

to compile a measure of visibility improvement for Class I areas in the model domain. While 

this only reflects the change ofthe 98th percentile at the most affected receptor in the Class I 

area, it is a useful measure for understanding not only the magnitude of visibility improvement, 

but the geographic scope of the benefit from applying a given set of emissions controls. The 

enclosed maps illustrate the visibility improvement at 16 Class I areas affected by the FCPP and 

at 11 Class I areas affected by NGS in response to installation of Selective Catalytic Reduction 

(SCR) controls with combustion controls for the 98th percentile impact averaged over 2001-2003 

CALPUFF modeling results. The cumulative benefit calculated by the NPS for FCPP is 27.25 

2 Sather, M.E. et ai., 2008, J of Environmental Monitoring 10, 1319-1325. 
3 

deciviews (dv) and for NGS is 23.2 dv. The EPA applied this same methodology in Tables 26 

and 35 of the ANPR. We support this level of assessment and support using the cumulative 

visibility impact across all affected Class I areas when assessing a cost-effectiveness measure, 

such as dollars per dv. 

Tables 27 and 36 provide an Alternative Visibility Metric, which takes the 98th percentile change 

at the most affected receptor and multiplies this value times the land area ofthe Class I area. 

We have concerns regarding this metric. Our first concern is that the 98th percentile change for 

the most affected receptor is not representative of chan~es across the entire Class I land area. 

To address this concern would require assessing the 98t percentile impacts for all receptors in 

the Class I area and determining the land area associated with each receptor. This reveals our 

second concern that information required to better assess visibility improvement across the entire 

Class I area goes way beyond that developed by the states or sources when conducting BART 

analyses. We also question whether such level of assessment would improve on the simple 

summation of peak impacts technique as a means to consider multiple Class I area benefits when 

making a BART determination. Furthermore, the Alternative Visibility Metric would value 

larger Class I areas more so than smaller Class I areas, whereas the Regional Haze Rule treats all 

mandatory Class I areas equally. In summation, we believe the technique used to sum impacts 

shown in Tables 26 and 35 should be used to develop a cost per dv improvement measure to be 

compared with BART decisions made in developing the EPA presumptive BART emissions 

rates, as well as with BART decisions completed by other States and other EPA Regions. 

Summary of Comments on the Technical Information for the FCPP BART Determination 

We have enclosed detailed comments regarding APS's proposed NOxBART analyses. These 

comments are summarized below. 

According to the EPA's Clean Air Markets (CAM) database, the FCPP was the second largest 

stationary source of NOx in the U.S. in 2008, at 40,311 tons. Because Arizona Arizona Public 

Service (APS) overestimated the costs of Selective Catalytic Reduction (SCR) and 

underestimated its benefits, we relied primarily upon our own analyses ofthe BART cost and 

benefit factors. Our analyses indicate that FCPP causes visibility impairment in all 16 Class I 

areas within 300 km, and that FCPP causes the greatest cumulative impact upon Class I area 

visibility of any single source we have evaluated to date. When we consider the costs of BART 

in the context of the cumulative impacts from FCPP, we conclude that applying SCR to control 

these emissions is technically feasible, cost-effective, and will substantially improve visibility in 

these protected areas. Please note that we reached a similar conclusion in our July 24,2009, 

comments regarding NOx controls at NGS, i.e., SCR at NGS is technically feasible, costeffective, and will substantially improve visibility in multiple Class I areas. 

One of the options suggested by the BART Guidelines to evaluate cost-effectiveness is cost per 

dv. Compared to the typical control cost analysis in which estimates fall into the range of $2,000 

- $10,000 per ton of pollutant removed, spending millions of dollars per dv to improve visibility 

may appear extraordinarily expensive. However, our compilation3 ofBART analyses across the 

U.S. reveals that the average cost per dv proposed by either a state or a BART source is $10 

3 http://www.wrapair.org/forums/ssj flbart. html 
4 

- $17 million,4 with a maximum of almost $50 million per dv proposed by Colorado at the 

Martin Drake power plant in Colorado Springs. 

We applied this cumulative approach to the FCPP analysis and found that the cumulative impact 

from the baseline condition on visibility is 46.6 dv across the 16 Class I areas modeled. We 

compared the visibility improvement resulting from combustion controls and SCR to the range 

of costs we generated for each unit and found that SCR @ 0.07 lb/mmBtu (24-hour average) 

would improve visibility by 27 dv at a Total Annual Cost of $42.3 million (@ 0.05 Ib/mmBtu, 

annual average). This yields a cost-effectiveness estimate of$1.9 - $2.7 million/dv (depending 

upon the unit), which is more cost-effective than the $10 - $17 million per deciview that, on 

average, states and sources have determined was cost-effective for their chosen BART strategies. 

S02BART 

In the late 1990's, APS initiated a dialog with four environmental interest groups involved in 

environmental issues in the western United States: Environmental Defense, the Grand Canyon 

Trust, Western Resource Advocates and the New Mexico Citizens for Clean Air and Water. The 

dialog focused on the issue of visibility in the western United States, and on improved S02 

control primarily because that pollutant had much higher visibility impact than NOx emissions. 

In 2003, APS and the environmental groups agreed on a proposal geared to further reduce S02 

emissions at the FCPP utilizing an l8-month test program. The test program involved certain 

phased operational changes and scrubber chemical process changes to increase annual S02 

control levels from 72% to 85% without triggering operational problems. APS and the 

environmental groups jointly presented that proposal to the EPA, the Navajo EPA and the NPS. 

With the support of these groups, APS initiated the test program in early 2004. The test program 

was completed during the summer of2005. APS prepared a report concluding that the plant was 

not only able to meet the goal set in the proposal, but could also improve the annual average S02 

controls to an 88% removal efficiency. At that elevated control level, the plant was able to cut 

its annual S02 emissions by more than 55%, compared to the pre-test level. 

After the testing program, the Navajo Nation and the stakeholders group requested that EPA 

include these negotiated, additional S02 emissions reductions into a source-specific Federal 

Implementation Plan (FIP) for the FCPP. APS agreed to increase the amount of S02 emissions it 

was eliminating from its exhaust stream from 72% to 88%, thereby reducing its annual emissions 

of S02 to the atmosphere by about 25,000 tons per year. APS and the environmental groups then 

worked with the reviewing agencies to incorporate the higher sulfur dioxide controlleve1 as an 

enforceable emission limit for the plant through the FIP. 

The FIP, published in the May 7,2007, Federal Register, provides EPA's policy on whether the 

agreed-upon S02 controls are BART equivalent, with excerpts provided here: 

"APS, in partnership with the Navajo Nation, several environmental groups and Federal 

agencies, conducted a test program to determine if the efficiency of the existing scrubbers 

at FCPP could be improved from the recent historical level of 72% S02 removal to 85%. 

The test program, which was completed in spring of 2005, was successful and the plant 

4 For example, PacifiCorp has stated in its BART analysis for its Bridger Unit #2 that "The incremental cost 

effectiveness for Scenario I compared with the baseline for the Bridger WA, for example, is reasonable at $580,000 

per day and $18.5 million per deciview." 
5 

was able to achieve a plant-wide annual S02 removal of 88%. The parties involved in the 

test program have agreed that this rule should propose to require 88% efficiency for the 

FCPP. 

The EPA believes that the S02 controls proposed today for FCPP are close to or the 

equivalent of a regional haze BART determination for 802. For example, the BART 

Guidelines published by EPA in 2005 establish a presumption for the control of S02 from 

uncontrolled large utility boilers of either 95% control or 0.15 IbslMMBtu, but suggest 

that for electric generating units with pre-existing post-combustion S02 controls of at 

least 50% removal efficiency, states consider cost effective scrubber upgrades designed 

to improve the system's overall S02 removal efficiency, 70 FR 39104,39171 (July 6, 

2005). The conclusion that the S02 controls proposed today are close to or the 

equivalent of BART takes into consideration not only the BART Guidelines but also the 

early reductions for Regional Haze that this action will achieve through the modifications 

to the existing S02 scrubbers. As explained in today's companion notice for NGS 

published elsewhere in this Federal Register, EPA previously determined that the S02 

emission limits in the 1991 FIP for NGS provide for a greater degree of reasonable 

progress toward the Regional Haze national goal than would BART. See 56 FR 50172. 

As a result, EPA does not consider it necessary or appropriate to develop a regional haze 

plan to address the BART requirements under 40 CFR 51.308 for the Navajo Reservation 

for S02." (emphasis added) 

While we agree with the overall premise that 88% emission control is likely to represent BART 

on a plant-wide basis, we believe that EPA must follow its own BART Guidelines and its fivestep BART process, and make formal BART determinations for each unit at FCPP to show how 

the 88%-control target, with appropriate emission limits, represents a solution that is more than 

"close to" BART. As we commented in a letter to EPA on November 6, 2006, on the previous 

Federal Implementation Plan (FIP) actions, we do not believe that the previous FIP actions 

satisfy the BART requirements. 

Over the past several months, we have worked with your staff to evaluate FCPP and NGS under 

EPA's BART Guidelines, and we are very appreciative of their expertise and assistance. We 

look forward to continuing this cooperative working relationship as this process advances. We 

believe that good communication and sharing of information will help expedite this process, and 

suggest that you contact Don Shepherd (don shepherd(i{inps.gov, or 303-969-2075) if you have 

any questions regarding these or our July 24, 2009, comments. 

Sincerely, 

Michael D. Snyder 

Regional Director 

Enclosures 
7 

Colleen McKaughan 

US EPA Region 9 

75 Hawthorne Street 

San Francisco, CA 94105 

Ken Cronin 

Tribal Caucus Coordinator / 

Regional Planning Organization Specialist (WRAP) 

National Tribal Environmental Council 

4520 Montgomery Blvd. Suite 3 

Albuquerque, NM 87109 

IMR: John Reber 

GRCA: Martha Hahn 

MEVE: George San Miguel 

ARD: Julie Thomas-McNamee 

FWS: Tim Allen 

ARD-DEN: Permit Review Group, Reading and Project File, Chris Shaver 

ARD-DEN: bpolkowsky:bp:x6944: 10/26/2009: