U.S. Environmental Protection Agency 

Region 9 

Clean Air Act Permit 

October 2014 

Cultural Resources Report under the National Historic Preservation Act

Four Corners Power Plant SCR Project

1. Introduction

Pursuant to Section 106 of the National Historic Preservation Act (NHPA) the U.S. Environmental Protection 

Agency (EPA) must consider the effects of its permit actions on properties listed in or eligible for inclusion in the 

National Register of Historic Places. EPA Region 9 is currently reviewing a PSD permit application for the Four 

Corners Power Plant (FCPP) on Navajo Nation in Fruitland, New Mexico. As such, EPA must meet its obligations 

under Section 106 for this project prior to issuing a final permit decision. 

2. Description of the Undertaking

Arizona Public Service Company (APS) co-owns and operates the FCPP. The FCPP is a coal-fired power plant, 

utilizing pulverized coal-boilers, located on the Navajo Nation about 25 miles west of Farmington, New Mexico 

(see Figure 1). The FCPP currently consists of two 750 megawatt (MW) coal-fired electric steam-generating units 

(EGUs), with a total capacity of approximately 1,500 MW, and other ancillary equipment such as coal storage, 

lime handling operations and dry ash handling operations. 

On August 24, 2012, EPA promulgated a source-specific Federal Implementation Plan (FIP) requiring the FCPP to 

achieve emission reductions required by the CAA’s best available retrofit technology (BART) requirements.1In a 

letter dated December 30, 2013, APS notified EPA that as part of the compliance strategy for the BART FIP it 

would permanently shut down three existing EGUs – Units 1, 2, and 3 by January 1, 2014. As of January 2014, 

the FCPP now consists of the two remaining 750 MW EGUs – Units 4 and 5 – and the existing ancillary 

equipment. APS will further comply with the requirements of EPA’s BART FIP by installing SCR systems on Units 4 

and 5 to reduce emissions of nitrogen oxides (NOX) by approximately 80% from current levels. The installation of 

SCR to comply with EPA’s BART FIP is causing a significant net emission increase of sulfuric acid mist (SAM), 

which is the reason this project must obtain a permit from EPA Region 9. The installation of SCR systems on 

Units 4 and 5 are expected to improve visibility at 16 nearby national parks and wilderness areas, such as Mesa 

Verde National Park. The new and affected emission units associated with the FCPP SCR Project are: 

i Units 4 and 5 will be modified by adding new SCR emissions controls. SCR will be added to substantially 

reduce NOX emissions. The SCR systems will be located after each EGU’s economizer and before the air 

preheater. 

i Because the SCR emissions controls will cause a significant net emissions increase in SAM emissions, APS 

is proposing to install and operate dry sorbent injection (DSI) system as BACT to minimize SAM 

emissions. The DSI system will be located after the air preheater and just before the baghouse and wet 

FGD. 

i Truck traffic will increase due to the delivery of reagent for the DSI system resulting in increased fugitive 

emissions from paved plant roads. 

i Truck traffic will also increase due to the delivery of urea pellets, 29% aqueous ammonia, or anhydrous 

ammonia for the SCR system resulting in increased fugitive emissions from paved plant roads. 

 

1

For more information on EPA’s BART FIP, please see 77 Fed. Reg. 51620 (Aug. 24, 2012). 
Page 2 of 6 

NHPA - FCPP SCR Project 

EPA Region 9 

i A new pneumatic dry sorbent truck unloading system and silo will be installed; and 

i A new pneumatic urea pellet truck unloading system and silo may be installed if this reagent option is 

selected for the SCR system or a new ammonia truck unloading station and storage tank will be installed 

if either the aqueous or anhydrous ammonia option is selected for the SCR system. 

Construction of the FCPP SCR Project will involve the use of heavy equipment for site preparation and 

installation of SCR on Units 4 and 5 and for construction of associated structures such as silos for storage of the 

sorbents and reagents and baghouses on the silos for control of PM10 and PM2.5 emissions. Construction of the 

SCR systems is expected to start in mid-2015 or early 2016 with operation planned by July 2018. All projectrelated construction will be limited to industrial areas within the FCPP fenceline in the middle of paved, 

disturbed areas or within existing buildings. Construction will be performed with heavy equipment such as 

earth-movers, cranes, and trucks. 

3. Area of Potential Effects

The construction and operation of the FCPP SCR Project will occur only within the existing footprint of the FCPP. 

As such, the area of potential effects (APE) includes the existing footprint of the FCPP power plant as seen in 

Figure 2. In addition, the FCPP SCR Project will increase emissions of SAM to the atmosphere from the FCPP 

while reducing emissions of NOX. SAM and NOX emissions both have the potential to reduce visibility and 

increase acid deposition. As such, we are considering the APE to also include a 50 km radius around the FCPP as 

shown in Figure 3. This area encompasses the expected acid deposition area for the FCPP. 

4. Historic Properties within the APE

EPA was advised by the Navajo Nation Tribal Historic Preservation Officer (THPO) that the FCPP itself is eligible 

for inclusion in the National Register of Historic Places. The FCPP has been in existence since the late 1960’s and 

has been an integral part of the economy and community of Navajo Nation since that time. 

In addition, the area in which the construction of the FCPP SCR Project and associated infrastructure, such as the 

urea storage and processing facilities and dry storage injection silos, is within the built-up environment of the 

power plant. The area shown in Figure 2 has been mechanically excavated and leveled and contains an 

established complex of structures, roads, parking areas, and electrical lines to the degree that the area no longer 

resembles natural conditions. 

APS contracted with Statistical Research, Inc. (SRI), to perform a Class I cultural resources investigation and a 

Class III pedestrian survey of the FCPP lease area. The survey of the built-up area was performed from 

November 9 to November 25, 2013, during a Class III intensive pedestrian survey of the full FCPP plant lease. 

This survey covered everything that is not occupied by existing ash disposal structures or inundated by Morgan 

Lake. In the built-up areas, a systematic survey was conducted where the ground surface was visible and less 

disturbed. 

Several archaeological sites in the area were recorded in 1961 and reported by Sciscenti and Greminger in 1962. 

As part of the Class I cultural resources records search, SRI reviewed previous archaeological reports and records 

and tried to locate previously documented sites. No archaeological sites were recorded in the vicinity of the 

proposed construction area for the SCRs and associated infrastructure prior to FCPP construction during the 

1961 survey, and no sites were documented in this area during the 2013 survey. 
Page 3 of 6 

NHPA - FCPP SCR Project 

EPA Region 9 

There are numerous other properties with 50 km (or potentially within 50 km) of the FCPP that are already listed 

on the National Register of Historic Places. See Table 1. Further there is the potential for other properties that 

are eligible for inclusion in the National Register to be located within 50 km of the FCPP. However, as discussed 

below the potential effects on these properties, other than to the FCPP, relates only to impacts of SAM and NOX

emissions on visibility and acid deposition. EPA’s evaluation applies to any area or property within 50 km of the 

FCPP and all properties of cultural significance that may exist are expected to incur that same effects. As such, a 

detailed review of other potentially affected historic properties was not conducted. 

5. Effects on Historic Properties

Four Corners Power Plant 

The onsite construction and operation of the FCPP SCR Project will not diminish the integrity of the location, 

design, setting, materials, workmanship, feeling, or association of the FCPP. This undertaking is necessary to 

ensure the FCPP is able to continue operating into the future in compliance with the Clean Air Act. While the 

undertaking will result in additional equipment at the plant, these changes are expected to be minimal and will 

not change the overall significance of the FCPP to the Navajo Nation. 

Visibility Impacts on Historic Properties 

Emissions of SAM and NOX – which are associated with the FCPP SCR Project – have the potential to impact 

visibility in the nearby area. Reduced visibility could adversely affect visual elements of nearby historic 

properties. As such, EPA evaluated visibility impacts associated with the FCPP. 

As stated above, on August 24, 2012, EPA promulgated a source-specific FIP requiring the FCPP to achieve 

emission reductions required by the Clean Air Act’s BART requirements. The installation of SCR to comply with 

EPA’s BART FIP, is causing a significant net emission increase of SAM, which is the reason this Project must 

obtain a permit from EPA Region 9. However, the FCPP SCR Project involves the installation of SCR to reduce 

approximately 80% of the NOX emissions from Units 4 and 5 to improve visibility at 16 nearby national parks and 

wilderness areas, such as Mesa Verde National Park. 

So while the FCPP SCR Project may result in an increase of up to 237 tons per year in SAM emissions it will also 

cause over 19,000 tpy reductions in nitrogen oxides emissions. SAM and NOX emission both have the potential 

to affect visibility. Given the overall large reductions in visibility impacting pollutants from the FCPP SCR Project, 

EPA expects a net improvement in visibility. 

Acid Deposition on Historic Properties 

Acid deposition (also known as acid rain) has the potential to adversely affect historic properties. Acid rain and 

the dry deposition of acidic particles contribute to the corrosion of metals (such as bronze) and the deterioration 

of paint and stone (such as marble and limestone). These effects can significantly reduce the societal value of 

buildings, bridges, other items of cultural significance. As required by the Clean Air Act, EPA implements the Acid 

Rain Program, of which FCPP is a part, to reduce the cumulative effects of acid rain. 

As part of this permit action, EPA also consulted with the U.S. Fish and Wildlife Service regarding endangered 

species and a biological assessment (BA) was prepared. The BA evaluates acid deposition from the FCPP SCR 

Project.2 Acid deposition associated with the FCPP can occur as a result of emissions of SAM, sulfur dioxide, 

nitrogen dioxide, sulfur, nitrogen, hydrochloric acid, and hydrofluoric acid. The BA considers total acid 

 

2

 The BA for this action and other information relating to EPA’s consultation with the USFWS is a part of EPA’s 

administrative record for its permit decision. 
Page 4 of 6 

NHPA - FCPP SCR Project 

EPA Region 9 

deposition from all of these emissions at FCPP. However, similar to the impacts on visibility, the FCPP SCR 

Project is expected to result in overall decreases in acid deposition forming pollutants (decrease of 19,000 tpy of 

NOX and an increase in 237 tpy of SAM). As such, no adverse effects of acid deposition are expected to occur as a 

result of the FCPP SCR Project. 

6. Public Comment Period and Response to Comments

On July 24, 2014, EPA Region 9 provided notice of, and requested public comment on, EPA’s proposed action 

relating to the PSD permit application for the addition of SCR systems at FCPP. The public comment period on 

this proposed action ended on September 24, 2014. Region 9 made this report available for public comment 

during the public comment period. In addition, EPA also solicited participation in the section 106 consultation 

process to surrounding tribes and state historic preservation officers. No other parties requested to join the 

consultation process. EPA held three formal public hearings on the proposed permit decision on August 27 and 

28. Two hearings were held on the Navajo Nation and the other was held in Farmington, New Mexico. A court 

reporter was present at the hearings, as was a Diné language interpreter for oral translation. EPA received oral 

and written comments from numerous individuals during the public comment period. All timely comments 

received equal weight, regardless of the method used to submit them. Here, we address those comments 

received related to this report. 

6.1 Comments and Responses

Comment 1: 

(Commenters: Mike Eisenfeld and San Juan Citizens Alliance) 

Commenters are concerned about the impact of sulfuric acid on the cultural resources in the area. Sulfuric acid 

is a component of acid rain. According to EPA's own website, "acid rain accelerates the decay of building 

materials and paints, including irreplaceable buildings, statues, and sculptures that are part of our nation's 

cultural heritage." See, http://www.epa.gov/acidrain/effects/. The commenter stated tht the Navajo Nation and 

surrounding area is well known for its numerous cultural buildings, carvings, petroglyphs, traditional cultural 

properties (TCPs), and other cultural sites and features. According to the commenter, EPA must more precisely 

assess whether the increase in SAM emissions from the proposed project will cause harm to cultural sites and 

TCP's on and off the Navajo Nation for EPA to fulfill National Historic Preservation Act Section 106 consultations 

for the PSD permit project. 

Response to Comment 1: 

The EPA agrees with the commenter that the Section 106 consultation requirements of the National Historic 

Preservation Act apply to this permitting action, including the implementing regulations at 36 CFR part 800. In 

meeting these requirements, the EPA has already initiated consultation with the Navajo Nation Tribal Historic 

Preservation Officer, invited surrounding tribes and states to join the consultation process, determined the area 

of potential effects, identified historic properties in the area, developed a cultural resources report, and made 

the cultural resources report available for public comment. The EPA will not issue a final permit until the section 

106 process is complete. 

EPA disagrees that a more precise assessment of whether the increase in SAM emissions from the proposed 

project will cause harm to cultural resources in warranted. Section 5 of this report addresses the potential 

affects from acid rain through acid deposition on cultural resources: 
Page 5 of 6 

NHPA - FCPP SCR Project 

EPA Region 9 

“Acid deposition (also known as acid rain) has the potential to adversely affect historic properties...Acid 

deposition associated with the FCPP can occur as a result of emissions of SAM, sulfur dioxide, nitrogen 

dioxide, sulfur, nitrogen, hydrochloric acid, and hydrofluoric acid...However, similar to the impacts on 

visibility, the FCPP SCR Project is expected to result in overall decreases in acid deposition forming 

pollutants (decrease of 19,000 tpy of NOx and an increase in 237 tpy of SAM). As such, no adverse effects 

of acid deposition are expected to occur as a result of the FCPP SCR Project.” (pp 3-4, Cultural Resources 

Report) 

To the extent the commenter believes a more precise identification of historic properties is warranted, the EPA 

also disagrees. The identification of historic properties is discussed in Section 4: 

“No archaeological sites were recorded in the vicinity of the proposed construction area for the SCRs and 

associated infrastructure prior to FCPP construction during the 1961 survey, and no sites were 

documented in this area during the 2013 survey. There are numerous other properties with 50 km (or 

potentially within 50 km) of the FCPP that are already listed on the National Register of Historic Places. See 

Table 1. Further there is the potential for other properties that are eligible for inclusion in the National 

Register to be located within 50 km of the FCPP. However, as discussed below the potential effects on 

these properties, other than to the FCPP, relates only to impacts of SAM and NOx emissions on visibility 

and acid deposition. EPA’s evaluation applies to any area or property within 50 km of the FCPP and all 

properties of cultural significance that may exist are expected to incur [the] same effects. As such, a 

detailed review of other potentially affected historic properties was not conducted.” (pp. 2-3, Cultural 

Resources Report) 

In addition, 36 CFR 800.4(b)(1) of the NHPA regulations describes the level of effort required for identifying 

historic properties: 

The agency official shall take into account past planning, research and studies, the magnitude and nature 

of the undertaking, the nature and extent of the potential effects on historic properties, and the likely 

nature and location of historic properties within the area of potential effects. 

The EPA has met this requirement by identifying the historic properties, or potentially historic properties, within 

the construction area of the SCR project; and, by identifying the historic properties listed on the National Register 

of Historic Places within 50 km of the FCPP. Identification of other properties potentially eligible for inclusion in 

the National Register, beyond those within the FCPP SCR Project footprint, is not warranted given the nature and 

extent of the potential effects to these properties. The only potential effects to these properties would be related 

to visibility and acid deposition, and the extent of these effects (as discussed above) can be evaluated without 

identification of individual properties. Therefore, EPA’s assessment is sufficient and complies with the 

requirements of section 106 of the NHPA.

Comment 2: 

(Commenter: BHP Billiton) 

One commenter indicated that the EPA appropriately considered the proposed FCPP operations, project 

construction activities and projected air emissions (including a 50 km radius around FCPP) in its cultural 
Page 6 of 6 

NHPA - FCPP SCR Project 

EPA Region 9 

resources impact analysis. The commenter stated that EPA correctly determined that the proposed action would 

not adversely affect cultural resources as: 

• No archeological sites are present in the vicinity of the proposed construction area; 

• Construction activities will be limited to existing industrial areas; and 

• Installation of the SCR system will result in a significant reduction of acid deposition forming 

pollutants, NOx emissions and net improvement in visibility at 16 nearby national parks and 

wilderness areas. 

Response to Comment 2: 

The EPA acknowledges this comment. 

6.0 Conclusion

Based on the information reviewed, EPA is proposing a finding of no adverse effect to historic properties for the 

FCPP SCR Project. The EPA will provide our finding to the Navajo Nation THPO for the consulting party 30-day 

review. The THPO shall have 30 days from receipt to review the finding. The EPA may proceed with issuance of a 

final permit decision after the close of the 30 day review period if the THPO has agreed with the finding or has 

not provided a response. 



Figure 1 Location of Four Corners Power Plant
Unit 4 Unit 5

Stack 4 & 5

DSI Silo

Urea

Facilities

SCR SCR

0 125 250 500

Feet

!( Point Source

Road Source

Fence

!(

!(

!(

! FCPP Lease

!

Urea Facilities

DSI Silo

Stacks 4 & 5

Inset Not to Scale

[

Location of Proposed SCRs

and Associated Facilities at the FCPP