Prepared for: Prepared by:

Arizona Public Service AECOM

Phoenix, AZ Fort Collins, CO

May 2014

Environment

Biological Assessment 

for the Four Corners Power Plant 

SCR Retrofit Project 
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

AA-1

List of Acronyms and Abbreviations

ANC acid neutralizing capacity

APS Arizona Public Service Company

BA Biological Assessment

BART Best Available Retrofit Technology

BISON-M Biota Information System of New Mexico

BLM Bureau of Land Management

cm centimeter

cm3 cubic centimeter

DPS distinct population segment

DSI dry sorbent injection

EIS Environmental Impact Statement

EPA U.S. Environmental Protection Agency

EPRI Electric Power Research Institute

ESA Endangered Species Act

FCPP Four Corners Power Plant

FIP Federal Implementation Plan

FLAG Federal Land Manager’s Air Quality Related Values Work Group

FR Federal Register

ft feet

g gram

H+ hydronium ion

H2SO4 sulfuric acid

ha hectare

HCl hydrogen chloride

HF hudrogen fluoride

in inch

IPaC Information, Planning, and Conservation (USFWS)

km kilometer

L liter

m meter

m2 square meter

mm millimeter

ml milliliter

MW megawatt

N nitrogen

NAAQS National Ambient Air Quality Standard

NEPA National Environmental Policy Act

NHNM Natural Heritage New Mexico

NNNHP Navajo Nation Natural Heritage Program

NOX nitrogen oxide

NRCS Natural Resources Conservation Service

PM particulate matter

PM10 particulate matter with an aerodynamic diameter of 10 microns or less

PM2.5 particulate matter with an aerodynamic diameter of 2.5 microns or less

PSD Prevention of Significant Deterioration

S sulfur

SCR Selective Catalytic Reduction

SO2 sulfur dioxide

SO3 sulfite

SWReGAP South West Regional Gap Analysis Project
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

AA-2

t/Kt tons/kiloton

tpy tons per year

U.S. United States

USC United States Code

USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey

WHO World Health Organization

YOY young-of-the-year

yr year

0.1N 10 percent Normal

95UCL 95 percent upper confidence limit
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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Contents

1.0 Project Background............................................................................................................1

2.0 Proposed Action .................................................................................................................2

2.1 Action Area.............................................................................................................................. 4

2.2 Species Considered in the Analysis....................................................................................... 6

2.3 Acid Deposition from SCR Operations...................................................................................8

2.4 Particulate Matter....................................................................................................................8

3.0 Species Accounts and Environmental Baseline Conditions.......................................10

3.1 Birds.......................................................................................................................................10

3.1.1 Natural History and Habitat Association................................................................10

3.1.2 Potential Presence in the Deposition Area ...........................................................13

3.2 Fish........................................................................................................................................13

3.2.1 Natural History and Habitat Association................................................................13

3.2.2 Potential Presence in the Deposition Area ...........................................................15

3.3 Plants.....................................................................................................................................15

3.3.1 Natural History and Habitat Association................................................................15

3.3.2 Potential Presence in the Deposition Area ...........................................................17

4.0 Effects of the Proposed Action .......................................................................................20

4.1 SCR Installation ....................................................................................................................20

4.2 Acid Deposition on Soils .......................................................................................................20

4.3 Acid Deposition in Surface Water.........................................................................................21

4.4 Particulate Matter..................................................................................................................21

4.5 Plants.....................................................................................................................................22

4.5.1 Impact Evaluation...................................................................................................22

4.5.2 Determination.........................................................................................................23

4.6 Birds and Fish .......................................................................................................................23

4.6.1 Impact Evaluation...................................................................................................23

4.6.2 Determination.........................................................................................................23

5.0 Cumulative Effects............................................................................................................25

6.0 References .........................................................................................................................27
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List of Tables

Table 2-1 Threatened, Endangered, Proposed and Candidate Species Considered 

in this Analysis ....................................................................................................................... 6

Table 2-2 Modeled Annual Acid Deposition from FCPP in Top 2 cm of Soil from 

Operation of Units 4 and 5 with SCR installed .....................................................................9

List of Figures

Figure 2-1 Location of Proposed Construction at FCPP........................................................................3

Figure 2-2 Deposition Area Boundaries .................................................................................................5

Figure 3-1 Potential Habitat for Mancos Milk-vetch in Deposition Area..............................................18

Figure 3-2 Potential Habitat for Mesa Verde Cactus in Deposition Area ............................................19
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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1.0 Project Background

Arizona Public Service Company (APS) operates the Four Corners Power Plant (FCPP), a privately 

owned and operated coal-fired power plant located on the Navajo Nation, about 25 miles west of 

Farmington, New Mexico. The facility currently consists of two power generating units, Units 4 and 5, 

with a total capacity of approximately 1,500 megawatts (MW). 

On August 24, 2012, the United States Environmental Protection Agency (EPA) promulgated a sourcespecific Federal Implementation Plan (FIP) requiring the FCPP to achieve emissions reductions required 

by the Clean Air Act's Best Available Retrofit Technology (BART) provision (77 Federal Register [FR]

51620). At the time the FIP was issued, APS operated five units with a total capacity of 2,100 MW. The 

FIP established two, alternative compliance options. APS could retrofit all five units at FCPP to meet 

certain emission limits (Option 1) or, under an alternative plan proposed by APS, it could install Selective 

Catalytic Reduction (SCR) controls on Units 4 and 5 in 2018 and retire Units 1, 2 and 3 by January 1, 

2014 (Option 2). APS selected Option 2 and retired Units 1, 2, and 3 at the end of 2013. Units 4 and 5 

will continue to operate, but a Selective Catalytic Reduction (SCR) system on each unit is needed to 

reduce nitrogen oxides (NOX) emissions to the required limit in the FIP. Construction of the SCR systems

is expected to start in mid-2015 in order to meet a FIP-imposed operations deadline of July, 2018. The 

FCPP SCR Retrofit Project will decrease NOX emissions from Units 4 and 5 by approximately 18,600 

tons per year (tpy), in addition to the emission reductions from shutdown of Units 1 through 3. Besides a 

reduction in NOx emissions, EPA is requiring Units 4 and 5 to meet a specific particulate matter (PM) 

emission limit that will be achieved through operation of existing baghouses.

A Prevention of Significant Deterioration (PSD) permit application was submitted to the EPA Region 9 in 

April 2014 (AECOM 2014), to address potential emissions increases related to the installation of the 

SCR systems at FCPP. Because the FCPP is located in an attainment area, the project must be 

evaluated to determine whether the proposed major modification will result in a significant net emissions 

increase and be subject to PSD permitting requirements. A major modification is defined as a physical 

change or change in the method of operation at a major source that results in both a significant 

emissions increase and a significant net emissions increase of a regulated pollutant. A netting analysis

that accounts for contemporaneous emission increases and decreases (such as the shutdown of Units 1 

through 3) is required for emissions of these pollutants. In accordance with PSD rules, the 

contemporaneous period begins 5 years prior to the start of construction and ends when the project 

begins operating. Because the installation of SCR systems on coal-fired power plants leads to potential 

increases in emissions of sulfuric acid (H2SO4) mist, respirable particulate (particulate matter with an 

aerodynamic diameter of 10 microns or less [PM10]), and fine particulate matter (particulate matter with 

an aerodynamic diameter of 2.5 microns or less [PM2.5]), a PSD applicability and a netting analysis were

performed. Because the shutdown of Units 1 through 3 will lead to significant decreases in the 

emissions of PM10 and PM2.5 from the FCPP, it was determined (as demonstrated in the PSD 

application) based upon an emissions netting analysis, that only emissions of H2SO4 mist from Units 4 

and 5 will be subject to PSD requirements.

While the PSD permitting process is not subject to the National Environmental Policy Act (NEPA), EPA

requires an analysis of potential impacts to federally listed species from the federal action (i.e., PSD 

permit issuance) under the Endangered Species Act (ESA). In order to evaluate the potential impacts, 

the future emissions and deposition of acid-generating compounds of sulfur and nitrogen were predicted 

using AERMOD, a steady-state plume model that incorporates air dispersion. This Biological 

Assessment (BA) evaluates the potential impacts to listed or proposed species or designated or 

proposed critical habitat under the ESA (16 United States Code [USC] § 1531 et seq. 1973) that may be 

caused by the installation and operation of SCR systems on Units 4 and 5.
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2.0 Proposed Action

The FCPP SCR Retrofit Project involves the installation of emissions control technology at an existing 

coal-fired power plant. In order to limit NOX emissions from Units 4 and 5, APS is planning to install SCR

equipment on both units. The use of SCR tends to oxidize some sulfur dioxide (SO2) to sulfites (SO3),

which results in increased H2SO4 mist, PM10, and PM2.5 emissions. In order to minimize H2SO4, PM10, 

and PM2.5 emission increases, APS proposes to install a dry sorbent injection (DSI) system on each unit 

using hydrated lime as the sorbent. 

A pneumatic dry sorbent truck unloading system and silo will be installed. Hydrated lime will be received 

by truck and pneumatically conveyed to a storage silo. The air emission sources associated with the use 

of lime will be truck travel on paved roads and a vent on the silo, which will have a baghouse for 

emissions control. The lime silo will be approximately 14 feet in diameter and 80 feet tall, including lime 

transport equipment beneath the silo.

The SCR systems require the injection of ammonia as a reagent. The ammonia reagent for the SCR 

systems can be supplied by anhydrous ammonia, aqueous ammonia, or by conversion of urea to 

ammonia. APS has not yet selected the type of reagent, a decision that will be based on engineering 

designs when they are developed. A pneumatic urea pellet truck unloading system and silo may be 

installed if the urea reagent option is selected for the SCR systems, or an ammonia truck unloading 

station and storage tank will be installed if either the aqueous or anhydrous ammonia option is selected 

for the SCR systems.

Truck traffic will increase due to the delivery of reagent and hydrated lime for the DSI system. The 

amount of increased truck traffic will vary depending upon the reagent option selected.

Project construction 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. New sources of air 

emissions consist of silos for storage of the sorbents and reagents and increased road traffic for delivery 

of these sorbents and reagents, as well as a temporary increase in particulate matter and fugitive 

emissions from the use of construction equipment. Figure 2-1 displays the locations of Units 4 and 5 and 

their stacks, the proposed silos, and the roads to be used by trucks to supply reagent and sorbent on the 

plant site.

Construction of the SCR systems is expected to start in mid-2015 or early 2016 with operation planned 

by July 2018. All project-related construction will be limited to industrial areas within the FCPP fenceline 

in the middle of paved, disturbed areas or within existing buildings that lack habitat for any federally listed 

species. Construction will be performed with heavy equipment such as earth-movers, cranes, and trucks. 

The areas that will be directly affected by construction are within an industrial part of the FCPP lease that 

is built-up and lacks habitat for listed plants and wildlife. Therefore, this BA focuses on those portions of 

the action area that contain habitat that could be affected by changes to emissions resulting from the 

Proposed Action, delineated by determining where deposition of FCPP emissions is the highest.
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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Figure 2-1 Location of Proposed New Sources at FCPP
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2.1 Action Area

The action area is defined as all areas that may be affected by the federal action directly or indirectly. It is 

used to determine which species or critical habitat may be affected by delineating the geographic extent 

to evaluate. In the SCR process, sulfuric acid combines with ammonia to form particulates. For 

evaluating the potential effects of sulfuric acid and PM emissions from FCPP, the area of highest 

particulate deposition was used to represent the action area. The area of highest deposition for the 

FCPP SCR Retrofit Project is the same as the Deposition Area delineated for the Four Corners Power 

Plant and Navajo Mine Energy Project Environmental Impact Statement (EIS) based on air deposition 

modeling that considered the types of FCPP emissions, the prevailing winds, and the terrain. The action 

area will be called the Deposition Area for the remainder of this BA.

To delineate the Deposition Area, an initial screening process using preliminary air deposition modeling 

was conducted using the CALPUFF model. A study by the Electric Power Research Institute 

(EPRI 2011) indicated that the metals from coal-fired power plants that typically contribute most to 

ecological risk include arsenic, cadmium, chromium, and mercury. In addition, the ecological toxicity of 

antimony, lead, copper, and selenium have been widely studied for their potential risk to humans and 

wildlife. Therefore, these eight metals were selected for modeling the deposition of particulates to 

determine the extent of the Deposition Area because it is anticipated that the primary ecological risk 

drivers are among these metals.

A screening procedure was applied to estimate potential changes to soil concentrations of the selected 

metals associated with 25 years of cumulative deposition from future continuous full load operations of 

all five units operating as they did until the closure of Units 1, 2, and 3. The purpose of this screening 

procedure was only to delineate boundaries of the area of highest deposition of emissions from the 

FCPP stacks (Deposition Area). It was not used to establish baseline conditions of metals in the 

environment.

The estimated amount of emitted metals in the air and the concentrations projected to be deposited as 

particulates on the soil surface were calculated based on modeling. These projections were compared to 

available measured soil concentrations of these metals within San Juan County, New Mexico, derived 

from the U.S. Geological Survey (USGS) PLUTO database for San Juan County, New Mexico 

(USGS 2012). This database, used to represent the current concentrations of soil metals, was developed 

through analyses of soil samples collected from San Juan County between 1965 and 1994 (during the 

period of operation of all five units at the FCPP) in support of USGS programs and was used to calculate 

the 95 percent upper confidence limit (95UCL) on the mean for each of the eight metals. The future 

deposition-related surface soil concentration of each metal calculated to accumulate over 25 years was 

computed (based on CALPUFF modeling) and compared to the corresponding 95UCL of the soil 

concentrations derived from the PLUTO data.

The Deposition Area, shown with the black and white dashed outline in Figure 2-2, was determined by 

delineating the area where the predicted incremental increase in soil concentration of any of the metals 

after 25 years of future full load plant operations with SCR installed on Units 4 and 5 is projected to be 

more than one percent of current concentrations (based on the PLUTO data). Although it was delineated 

based on metals deposition, the Deposition Area has been used to identify the area of the highest 

potential deposition of all particulates from the FCPP, including the sulfuric acid and PM resulting from 

operation of the SCRs that are analyzed in this BA. H2SO4 forms either very small aerosol droplets or 

solid products resulting from chemical reactions in the air. “Particulate” is the term for particles found in 

the air including solid products and liquid droplets. Both forms of particulates may be deposited on the 

ground through either wet deposition (precipitation) or dry deposition.
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Figure 2-2 Deposition Area Boundaries
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This approach is reasonable to calculate the effects of emissions resulting from the Proposed Action 

because H2SO4 and PM are deposited as particulates in the same way that the modeled particulates are 

deposited. The Deposition Area is the best representation of where the highest concentration of 

particulate matter and acidic compounds from future operations of FCPP Units 4 and 5 would be 

deposited based upon available information. Beyond this area, the very small increase in deposition 

associated with FCPP future emissions would be sufficiently low to be considered discountable1

. The 

Deposition Area, including a portion of the San Juan River, represents the action area that was used to 

identify federally listed or proposed species and their habitats and any potential impacts from acid and 

PM deposition that may result from future FCPP operations with SCR.

2.2 Species Considered in the Analysis

In order to address potential impacts to federally listed, proposed and candidate species, per direction 

from the U.S. Fish and Wildlife Service (USFWS), the USFWS Information, Planning, and Conservation 

(IPaC) system and New Mexico Field Office county list for San Juan County, New Mexico, were 

reviewed. Based on this review, the potential for occurrence of listed, proposed, and candidate species

in the Deposition Area is summarized in Table 2-1. The Deposition Area does not extend beyond San 

Juan County, New Mexico. Of these 12 species identified as potentially occurring in San Juan County, 8

were identified as potentially occurring within the Deposition Area based on: 

1. Information from the USFWS, Navajo Nation Natural Heritage Program (NNNHP), and Natural 

Heritage New Mexico (NHNM);

2. Habitat requirements and the known distribution of these species from review of literature (Biota 

Information System of New Mexico [BISON-M] 2012; Mikesic and Roth 2008; USFWS 2012, 

2011a,b, 2002a,b, 1985,1984); and 

3. Mapping and analysis developed for the Habitat Model and Biological Survey Results for the 

Four Corners Power Plant and Associated Transmission Lines (referred to as the “Habitat 

Model” [AECOM 2013a]). 

Table 2-1 Threatened, Endangered, Proposed and Candidate Species Considered in this 

Analysis

Group Name ESA Status

Potential Occurrence within 

Deposition Area

Birds Southwestern willow 

flycatcher 

(Empidonax traillii extimus)

Endangered Known to occur. Habitat found in 

cottonwood/willow and tamarisk 

vegetation communities along rivers and 

streams.

Birds Mexican spotted owl 

(Strix occidentalis lucida)

Threatened May occur in the limited acreage of 

canyons and dense forests. Habitat 

includes mixed-conifer forest, pine-oak 

forest, and riparian areas

 

1 Using a percentage of background as a threshold for deposited metals is consistent with the acidic deposition 

screening approach established by the Federal Land Manager’s Air Quality Related Values Work Group 

(FLAG 2011). Given that the FLAG Deposition Analysis Threshold is based on 2 percent of natural background 

rather than measured background, a 1 percent threshold of measured soil concentration was determined to be a 

conservative screening threshold. Any soil concentration with an accumulation of less than 1 percent of 

background under future conditions (25 years of accumulation) was determined to be discountable.
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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Table 2-1 Threatened, Endangered, Proposed and Candidate Species Considered in this 

Analysis

Group Name ESA Status

Potential Occurrence within 

Deposition Area

Birds Whooping Crane (Grus 

Americana) 

Experimental 

Population

Does not occur. Whooping cranes within 

New Mexico were included in the 

reintroduced Rocky Mountain population. 

In 1997, the remnant Rocky Mountain 

whooping crane population was 

designated experimental nonessential 

and the last remaining wild bird died in 

the spring 2002.

Birds Yellow-billed cuckoo 

(Coccyzus americanus)

Proposed May occur. Habitat may exist along the 

San Juan River in relatively dense, 

wooded, streamside riparian habitat. 

Mammals Black-footed ferret

(Mustela nigripes)

Endangered Does not occur although habitat (prairie 

dog colonies) exists. Considered 

extirpated in New Mexico with the last 

confirmed occurrence documented in 

1934 (BISON-M 2012).

Mammals Canada lynx (Lynx 

canadensis)

Candidate Does not occur. Habitat does not occur in 

Deposition Area.

Fishes Colorado pikeminnow 

(Ptychocheilus lucius)

Endangered; 

Designated 

critical habitat

May occur. The San Juan River within the 

Deposition Area is part of the designated 

critical habitat.

Fishes Razorback sucker 

(Xyrauchen texanus)

Endangered; 

Designated 

critical habitat

May occur. The San Juan River within the 

Deposition Area is part of the designated 

critical habitat.

Fishes Roundtail chub (Gila 

robusta)

Candidate May occur. While there may be habitat, 

this species has not been reported in the 

Deposition Area. There is a record of 

occurrence to the west in the San Juan 

River.

Plants Mancos milk-vetch 

(Astragalus humillimus)

Endangered May occur. Relatively small amount of 

habitat (approximately 750 acres) in 

Deposition Area. 

Plants Knowlton's cactus 

(Pediocactus knowltonii)

Endangered Does not occur. Deposition Area is 

outside the known range of this species. 

The only viable population exists south of 

La Boca, Colorado, in San Juan County, 

New Mexico (USFWS 1985).

Plants Mesa Verde cactus 

(Sclerocactus mesaeverdae)

Threatened May occur. Not reported south of the San 

Juan River. However, suitable habitat is 

found within the Deposition Area.
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2.3 Acid Deposition from SCR Operations

The installation of SCRs at FCPP will greatly decrease NOX emissions from Units 4 and 5 (approximately 

18,600 tpy reduction) and slightly increase particulate matter and sulfuric acid mist emissions compared 

to current operating conditions associated with the two units. Because the Deposition Area extends less 

than 50 kilometers (km) from the FCPP at its furthest distance, more detailed air dispersion and 

deposition modeling needed to predict the effects of stack emissions from future FCPP operations was 

performed using AERMOD (version 12345). This modeling calculated the annual quantities of acidforming compounds emitted and deposited from operation of FCPP Units 4 and 5 with SCR systems. In 

order to use a single value to represent the acid-forming compounds deposited from FCPP emissions, 

the results were converted to combined total hydronium ions. A single value to represent the 

concentration of acidic compounds is necessary to enable comparison between the quantity from FCPP 

future operations deposited on the ground and the capacity of the environment to respond to this acid 

deposition, discussed in Section 4.0. 

Hydrochloric acid and hydrogen fluorine emission factors were based on emission factors for coal-fired 

electric generating units prepared by EPRI (2009). Sulfuric acid emission factors were provided by APS 

based on engineering estimates. Table 2-2 presents the findings of the deposition modeling for all acidforming compounds emitted from FCPP stacks under the future operations of Units 4 and 5 with SCR as 

described under the Proposed Action. This modeling did not account for the substantial reductions in 

emissions due to the shutdown of Units 1 through 3.

2.4 Particulate Matter

The National Ambient Air Quality Standards (NAAQS) were developed to establish a limit on pollutants 

considered harmful to public health and the environment. The primary standards provide public health 

protection and the secondary standards provide for protection against decreased visibility and damage to 

animals, crops, vegetation, and buildings. According to air modeling performed in support of this PSD 

permit application (AECOM 2013b), although an increase in PM10 and PM2.5 emissions is projected due 

to increased sulfuric acid mist, the future operations of Units 4 and 5 with SCR will be well below both the 

primary and secondary NAAQS for PM10 and PM2.5.
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Table 2-2 Modeled Annual Acid Deposition from FCPP in Top 2 cm of Soil from Operation of Units 4 and 5 with SCR installed

Acid 

Deposition

H2SO4

(g/m2

/yr)

SO2

(g/m2

/yr)

NOX

(g/m2

/yr)

S 

(g/m2/yr)

N 

(g/m2/yr)

HCl 

(g/m2/yr)

HF 

(g/m2/yr)

Total H+

equivalents 

/m2

/yr*

S Deposition 

(H+ equivalents

/ha/yr)**

N 

Deposition 

(kg/ha/yr)**

Maximum 0.071 0.049 0.012 0.048 0.0037 0.0075 0.026 0.0047 29.9 0.037

Average 

within 10 km 

Radius

0.0037 0.0069 0.0014 0.0047 0.00043 0.00058 0.0020 0.0018 2.9 0.004

Average 

within 

Deposition 

Area

0.0015 0.0025 0.00051 0.0017 0.00016 0.00027 0.00094 0.0016 1.1 0.002

* Assumes each mole of S results in 2 H+ equivalents and each mole of N, HCl, and HF result in 1 H+ equivalent.

** Total sulfur or nitrogen deposition from combined sources listed in the table.

g/m2

/yr = grams per meter squared per year

kg/ha/yr = kilograms per hectare per year

H+ – Hydronium ion

H2SO4 – Sulfuric acid

HCl – Hydrogen chloride

HF – Hydrogen fluoride

N – Nitrogen

NOX – Nitrogen oxides

S – Sulfur

SO2 – Sulfur dioxide
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3.0 Species Accounts and Environmental Baseline Conditions

Eight federally endangered, threatened, proposed or candidate species (two plant, three fish, and three 

bird species) have the potential to occur within the Deposition Area. In order to identify species 

potentially present within the Deposition Area, vegetation cover types identified by the SWReGAP data 

within the Deposition Area were reviewed. Additionally, the existing Habitat Model (AECOM 2013a), 

which used modeling and field surveys to characterize baseline habitat conditions in an area that 

encompasses the Deposition Area, was used in this analysis. The baseline conditions described resulted 

from the effects of all past and present activities in the Deposition Area. Past and present activities in the 

Deposition Area include urbanization, dryland and irrigated agriculture, operation of the San Juan 

Generating Station, and water diversions, all of which affect species and their habitat.

The Habitat Model and the subsequent field surveys (AECOM 2013a) identified areas of expected 

suitable habitat within the Deposition Area for the eight species. It should be noted that the availability of 

suitable habitat does not necessarily indicate that the species is present. For example, although the 

Habitat Model identified potential habitat for the black-footed ferret, it is not addressed in this BA 

because it is considered extirpated in New Mexico by the USFWS, with the last confirmed occurrence

documented in 1934 (BISON-M 2012).

3.1 Birds

Two federally listed bird species and one bird species proposed for listing may occur along the San Juan 

River within the Deposition Area: Mexican spotted owl, southwest willow flycatcher, and yellow-billed 

cuckoo.

3.1.1 Natural History and Habitat Association 

Mexican Spotted Owl

The Mexican spotted owl was listed as threatened on March 16, 1993 (58 FR 14248-14271), and a

Recovery Plan was released on June 6, 1995 (60 FR 29913-29951). The USFWS released the final 

Mexican Spotted Owl Recovery Plan, First Revision (Recovery Plan) in December 2012 (USFWS 2012). 

Critical habitat was designated for the Mexican spotted owl in 2004 and includes approximately 

8.6 million acres on Federal lands in Arizona, Colorado, New Mexico, and Utah (69 FR 53182).

According to the Final Recovery Plan (USFWS 2012), the primary threats to the Mexican spotted owl 

population in the U.S. (but likely not in Mexico) have transitioned from timber harvest to an increased risk 

of stand-replacing wildland fire.

The Mexican spotted owl is one of three recognized subspecies of spotted owl in North America. The 

Mexican spotted owl is a permanent resident in the interior mountain ranges of western North America, 

ranging from southern Utah and central Colorado south through the mountains of Arizona, New Mexico, 

and extreme west Texas. The species typically occupies old growth forest in mixed conifer, pine-oak 

woodland, deciduous riparian, or a combination of these habitats that will support a home range of 

1,400 to 4,500 acres (Ehrlich et al. 1988; Gutierrez et al. 1995). An undisturbed core area of 

approximately 600 acres centered on the nest site is the currently recommended disturbance buffer 

(Gutierrez et al. 1995).

Mexican spotted owls typically inhabit steep canyons with mature or old growth forest, but they also may 

occur in canyons with steep cliffs and relatively little forest habitat. In the northern portion of the Mexican 

spotted owl’s range, including Utah, Colorado, and parts of far northern Arizona and New Mexico owls 

occur primarily in steep-walled, rocky canyons (USFWS 2012). These canyon systems vary in the 

amount of forest cover present, but in general they are less heavily forested than are canyons occupied 

farther south. Pinyon-juniper woodlands and mixed-conifer forest are prominent cover types used in 

these canyon systems (Ganey and Dick 1995), but in some cases these canyons are entirely or largely 
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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lacking forest or woodland cover. Mexican spotted owl habitat typically has a structured canopy, a 

perennial water source, and a rodent-dominated prey base of adequate size (Gutierrez et al. 1995). 

Mated pairs of owls defend a breeding territory at least during the nesting season (March through 

August). Clutch size is small (generally 1 to 3 eggs), and eggs hatch in early May. A second clutch may 

be laid if the first fails. The females brood the young owlets almost constantly the first couple of weeks, 

then may be away hunting for several hours a day. Owlets fledge at 4 to 5 weeks old (early to mid-June), 

and leave the nest before they can fly, moving to the tree branches or the ground while still under 

parental care. Dispersal from the nest area usually occurs from mid-September to early October. 

Mexican spotted owls breed sporadically, and not all birds nest every year. Local conditions, particularly 

for the prey base, may govern nesting success (USFWS 2013a).

Southwestern Willow Flycatcher

The southwestern willow flycatcher was listed as endangered, without designated critical habitat, on 

February 27, 1995 (60 FR 10693-10715). Critical habitat was later designated on July 22, 1997 

(62 FR 39129-39147). A court decision in 2001 resulted in a subsequent Final Rule on Critical Habitat on 

October 19, 2005 (70 FR 60885-61009). Critical habitat for the southwestern willow flycatcher was 

recently revised in 2013 (78 FR 343-534). In total, approximately 1,227 stream miles have been 

designated as critical habitat, with a lateral extent including riparian areas and streams that occur within 

the 100-year flood plain or flood-prone areas totaling 208,973 acres. A 5-year review of the subspecies 

was completed by the USFWS in 2005 (73 FR 14995-14997).

According to the Final Recovery Plan for the southwestern willow flycatcher (USFWS 2002a), the 

primary threat to this species is the extensive loss and modification of breeding habitat with consequent 

reductions in population levels. Destruction and modification of riparian habitats have been caused 

mainly by the reduction or elimination of surface and subsurface water due to diversion and groundwater 

pumping; changes in flood and fire regimes due to dams and stream channelization; clearing and 

controlling vegetation; livestock grazing; changes in water and soil chemistry due to disruption of natural 

hydrologic cycles; and establishment of invasive non-native plants (USFWS 2002a). Concurrent with 

habitat loss have been increases in brood parasitism by the brown-headed cowbird (Molothrus ater), 

which inhibit reproductive success and further reduce population levels (USFWS 2002a, 2013c).

The southwestern willow flycatcher is restricted to riparian habitats along rivers, streams, or wetlands 

(Hiatt and Boone 2003). Four specific types of breeding habitats have been described for the 

southwestern willow flycatcher. The first is comprised of dense stands of willows 10 to 23 feet in height, 

with no distinct overstory. This community is often associated with sedges, rushes, or other herbaceous 

wetland plants. A second habitat type includes nearly monotypic, dense stands of saltcedar or Russian 

olive up to 33 feet in height. These species form a dense, closed canopy, with no distinct understory 

layer. Native broadleaf-dominated communities composed of a single species (often a willow species) or 

mixtures of native broadleaf trees and shrubs (cottonwood, willows, boxelder, ask, alder) form a third 

habitat type. The final habitat type is a mixture of native and exotic riparian species (Sogge et al. 1997). 

Regardless of the vegetation species composition, all of these habitats share common structural 

characteristics. Occupied southwestern willow flycatcher habitats always have dense vegetation in the 

interior, and dense areas are often interspersed with small clearings, open water, or areas of sparse 

shrubs. Habitat patches can vary in size and shape, with some occupied areas being relatively dense, 

linear, contiguous stands, and others being large, irregularly shaped mosaics of dense vegetation 

intermingled with open areas. Habitat patch sizes can range from as little as 2 acres to several hundred 

or a thousand acres. Southwestern willow flycatchers may occur at elevations as high as 7,875 feet 

above mean sea level. They also inhabit willow or cottonwood riparian areas that extend out into desert 

regions (Terres 1980). Migration and winter habitat could differ from breeding habitat for this subspecies. 

During migration, riparian habitat along major southwestern drainages is commonly utilized, but a close 

association with water may not always exist. These drainages might be considered stopover areas, and 

could be very important migration habitat for the southwestern willow flycatcher (USFWS 2002a). 
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Egg-laying can begin as early as late May, but typically occurs in early to mid-June. Clutch size is usually 

3 or 4 eggs for initial nests. Incubation last between 12 and 13 days from the date the last egg is laid, 

and eggs typically hatch within 24 to 48 hours of each other. Chicks can be present in the nest mid-June 

through early August and fledging typically ensues from late June through mid-August. Adults then 

depart from breeding areas between mid-August to mid-September (Sogge et al. 1997).

Yellow-billed Cuckoo

In 1998, the USFWS received a petition to list the yellow-billed cuckoo under the ESA stating that the 

species is endangered in a significant portion of its range and that this range is coterminous with a valid 

subspecies, the western yellow-billed cuckoo (Coccyzus americanus occidentalis). In 2001, the USFWS 

published a 12-month petition finding (66 FR 38611-38626) concluding that the western yellow-billed 

cuckoo constituted a valid distinct population segment (DPS) and that the DPS was warranted for listing; 

however, this action was precluded by higher priority listing actions, and the DPS was placed on the 

candidate species list. The Western U.S. DPS of the yellow-billed cuckoo was proposed for listing as 

threatened on October 3, 2013 (78 FR 61621-61666).

According to the species assessment for the yellow-billed cuckoo (USFWS 2013c), the primary threat to 

this species is similar to that listed for the southwestern willow flycatcher above, including extensive loss 

and modification of breeding habitat with consequent reductions in population levels. Destruction and 

modification of riparian habitats have been caused mainly by reduction or elimination of surface and 

subsurface water due to diversion and groundwater pumping; changes in flood and fire regimes due to 

dams and stream channelization; clearing and controlling vegetation; livestock grazing; changes in water 

and soil chemistry due to disruption of natural hydrologic cycles; and establishment of invasive nonnative plants (USFWS 2002a). Concurrent with habitat loss have been increases in brood parasitism by 

the brown-headed cowbird (Molothrus ater), which inhibit reproductive success and further reduce 

population levels (USFWS 2002a, 2013c). Additionally, the use of pesticides is suspected to have some 

adverse impact on the yellow-billed cuckoo but has not been proven (USFWS 2013c).

The species formally ranged throughout much of North America from southern Canada, south to 

northern Mexico (66 FR 38611-38626). However, in recent years, the species’ distribution in the west 

has declined precipitously throughout its range and the species is nearly extinct west of the Continental 

Divide, primarily due to habitat loss (BISON-M 2002). Based on historic accounts, the western yellowbilled cuckoo was once widespread and locally common in California and Arizona, locally common in a 

few river reaches in New Mexico, locally common in portions of Oregon and Washington, and generally 

local and uncommon in scattered drainages of arid and semiarid portions of western Colorado, western 

Wyoming, Idaho, Nevada, and Utah (USFWS 2013b).

In the arid west, yellow-billed cuckoos are riparian specialists (Floyd et al. 2007). Cuckoos typically 

inhabit large stands of mature, dense willows, but they also use smaller patches of mesquite, tamarisk, 

hackberry, and other wood vegetation (Floyd et al. 2007). Cuckoos typically do not utilize conifer and 

mixed broadleaf/conifer forests and/or urban areas (Bennet and Keinath 2003). Western yellow-billed 

cuckoos typically breed in large blocks of riparian habitat that is characterized by an overstory of 

cottonwood trees and a dense subcanopy or shrub layer (regenerating canopy trees, willows, or other 

riparian shrubs) almost exclusively near water (66 FR 38611-38626). Yellow-billed cuckoos breed in 

North America from March through August (BISON-M 2002).

The western yellow-billed cuckoo is a long-distance, complete neotropical migrant and generally one of 

the last migrants to arrive on breeding grounds in the U.S. (Hughes 1999). In San Juan County, they 

breed in the summer. The typical clutch size is 1 to 5 eggs. The nestlings are fledged from the nest 

approximately seven days after hatching and migrate south at three to four weeks of age 

(BISON-M 2002). Cuckoos depart for wintering grounds beginning in late August to mid-September. The 

migratory route of the western yellow-billed cuckoo is not well known because few specimens collected 

on wintering grounds have been ascribed to the western or eastern subspecies (Bennett and 
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Keinath 2003). The western yellow-billed cuckoo likely moves down the Pacific Slope of Mexico and 

Central America to northwestern South America.

3.1.2 Potential Presence in the Deposition Area

Mexican Spotted Owl

Approximately 800 acres of potential nesting habitat for the Mexican spotted owl occurs within the 

Deposition Area (AECOM 2013c).

Southwestern Willow Flycatcher and Yellow-billed Cuckoo

The riparian areas along the San Juan River contain suitable habitat for numerous sensitive species 

according to the Habitat Model. The southwestern willow flycatcher and yellow-billed cuckoo are

associated with riparian habitats. Approximately 6,700 acres of suitable habitat exist within the 

Deposition Area (AECOM 2013c). 

The southwestern willow flycatcher is a breeding resident in San Juan County, New Mexico, with small 

breeding populations occurring along the San Juan River drainage (USFWS 2002a). Occurrence 

records exist for this species within the Deposition Area (NNNHP 2011).

The BLM Farmington Field Office documented occurrences of yellow-billed cuckoos at five of their San 

Juan River tract management parcels during 2002 and 2003 surveys between the Hogback and 

Bloomfield, New Mexico. However, given this species documented use of saltcedar, this species could 

occur in the Deposition Area where saltcedar and other riparian vegetation occur.

3.2 Fish

Two federally listed fish species and one candidate fish species may occur within the San Juan River 

within the Deposition Area: Colorado pikeminnow, razorback sucker, and roundtail chub. 

3.2.1 Natural History and Habitat Association

Colorado Pikeminnow

The Colorado pikeminnow was designated endangered prior to the implementation of the ESA in 1973 

(32 FR 4001, March 11, 1967). Critical habitat was designated on March 21, 1993 (59 FR 13374-13400).

Habitat requirements for this species vary depending on the life stage and time of year. Young-of-the 

year (YOY) and juveniles prefer shallow backwaters, while adults prefer pools, eddies, and deep runs 

(Miller et al. 1982). Adults seem to prefer depths of about 2 to 7 feet, velocities of 0 to 0.2 feet per 

second, and boulder/silt substrates (Valdez et al. 1982). Juveniles and YOY usually are found over silt or 

sand bottoms with minimal current (Tyus et al. 1982). During peak runoff in the spring and early summer, 

fish usually move into backwater areas of flooded riparian zones to avoid swift velocities, feed, and 

prepare for the upcoming spawning period (Valdez and Wick 1983). As adults mature, they become 

highly mobile during the spawning period, which occurs after peak runoff from mid-June to mid-August. 

Larvae drift downstream from spawning sites beginning in late June and continue until late August.

According to the recovery goals for the Colorado pikeminnow (USFWS 2002b), threats to this species 

include streamflow regulation, habitat modification, competition with and predation by non-native fish 

species, and pesticides and pollutants. Of these threats, streamflow regulation and associated habitat 

modification as a result of the construction of water management structures (i.e., dams, reservoirs, weirs) 

are identified as primary threats to fish populations, while the competition and predation due to nonnative fish is also a major threat (USFWS 2002b). The potential role of pesticides and pollutants in 

suppressing populations of the Colorado pikeminnow is not well understood (USFWS 2002b). Pollutants 

identified in the recovery goals include petroleum products, heavy metals (e.g., mercury, lead, zinc, 

copper), non-metals (i.e., selenium), and radionuclides. Impacts to this fish species as a result of acid 

deposition have not been identified.
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The Colorado pikeminnow has been documented within the San Juan River from Shiprock, New Mexico, 

to the Lake Powell inflow (USFWS 2002b). Lake Powell defines the downstream distribution with 

irrigation diversions blocking any upstream movement (USFWS 2002b). 

Critical habitat for this species is found within the Deposition Area (59 FR 13399-13400). In San Juan 

County, New Mexico, critical habitat is located within the San Juan River and its 100-year floodplain, 

extending from the State Route 371 bridge near Farmington, New Mexico to Neskahai Canyon in the 

San Juan arm of Lake Powell up to the full pool elevation. 

Razorback Sucker

The razorback sucker was listed as endangered on October 23, 1991 (56 FR 54957-54967) with critical 

habitat designated on March 21, 1994 (59 FR 13374-13400). Habitat requirements for this species 

reflect both riverine and reservoir environments. General habitats used by adults include eddies, pools, 

and backwaters during the non-breeding period (July through March) (Maddux et al. 1993). Osmundson 

and Kaeding (1991) summarized seasonal habitat use as follows: pools and eddies from November 

through April, runs and pools from July through October, runs and backwaters in May, and backwaters 

and flooded gravel pits during June. Juveniles seem to prefer shallow water and minimal flow in 

backwaters, tributary mouths, off-channel impoundments, and lateral canals (Maddux et al. 1993). The 

spawning period for razorback suckers in the Upper Colorado River Basin usually occurs in April through 

mid-June. Spawning in the Green River has been documented at the confluence with the Yampa River 

(Modde et al. 1996).

According to the recovery goals for the razorback sucker (USFWS 2002c), threats to this species include 

streamflow regulation, habitat modification, competition with and predation by non-native fish, and 

pesticides and pollutants. Of these threats, streamflow regulation and associated habitat modification as 

a result of the construction of water management structures (i.e., dams, reservoirs, weirs) are identified 

as primary threats to these fish populations, while the competition and predation due to non-native fish is 

also a major threat (USFWS 2002c). The potential role of pesticides and pollutants in suppressing 

populations of razorback suckers is not well understood (USFWS 2002c). Pollutants identified in the 

recovery goals include petroleum products, heavy metals (e.g., mercury, lead, zine, copper), nonmetals 

(i.e., selenium), and radionuclides. Impacts to this fish species as a result of acid deposition have not 

been identified.

The razorback sucker is stocked in the San Juan River a location near Shiprock. Designated critical 

habitat extends from the Hogback Diversion, approximately in the middle of the Deposition Area, to the 

San Juan arm of Lake Powell (59 FR 13399-13400).

Roundtail Chub

The Lower Colorado River DPS of the roundtail chub is a federal candidate species (78 FR 70104, 

70126, 2013). Adult roundtail chubs inhabit the most permanent water in cool to warm water midelevation streams, typically using pools and eddies, adjacent to rapids and boulders. They are often 

found near cover (e.g., rocks, plant roots) and in pools behind irrigation diversions. Juveniles prefer the 

margins of flowing water and backwater areas. Spawning occurs in late spring over gravel bottoms in 

runs and pools with ≥25-centimeter (cm) water depth. This species is found within the San Juan and 

Mancos Rivers. Rarely encountered in recent surveys; they have been found from Shiprock to near Lake 

Powell with most between Shiprock and Aneth (River Miles 107-140). 

According to the listing status for the roundtail chub (USFWS 2013d), threats to this species include 

streamflow regulation, habitat modification, competition with and predation by nonnative fish species, 

and pesticides and pollutants. Pesticide and pollutants were not specifically identified as a threat to the 

roundtail chub, but the decrease in water quality due to pollutants was identified in the listing status 

document (USFWS 2013d). Impacts to this fish species as a result of acid deposition have not been 

identified.
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3.2.2 Potential Presence in the Deposition Area

USFWS (2012) reported that there were no wild roundtail chub, Colorado pikeminnow, or razorback 

sucker collected during their 2010 collection/monitoring effort; however, stocked Colorado pikeminnow 

and razorback sucker were collected. One roundtail chub was collected in 2009 and 2008. Prior to 

these two collections, the next previous collection of roundtail chub occurred during the fall 2002 

collection. Colorado pikeminnow and razorback sucker are stocked in the San Juan River and these 

stocked populations represent the majority of the fish of these species within the San Juan River 

(USFWS 2012). Additionally, data from the NHNM indicates that the Colorado pikeminnow was 

identified within 10 km of the FCPP in 2002 (NHNM 2011). 

3.3 Plants

Suitable habitat exists within the Deposition Area for two listed species of plants, the Mesa Verde cactus 

and the Mancos milk-vetch (AECOM 2013c).

3.3.1 Natural History and Habitat Association

Mancos Milk-vetch

The Mancos milk-vetch was listed as federally endangered on June 27, 1985 (50 FR 26568-26572). 

Mancos milk-vetch is a diminutive, tufted perennial growing in clumps up to 30 cm (12 inches [in]) across 

with a dense crown of persistent spiny leaf stalks; no other mat-forming Astragalus species has 

persistent, subspinescent petioles (USFWS 2011a). Stems are up to 1 cm (0.4 in) long and are crowded 

with leaves up to 4 cm (1.6 in) long (USFWS 2011a). Flower branches support 1 to 3 lavender/purplish 

flowers with a conspicuous lighter-colored spot in the throat of the corolla tube (USFWS 2011a). Mancos 

milk-vetch flowers in late April and early May (USFWS 2011a). Larger plants may produce over 

100 flowers in a growing season and fruits mature by mid-June (USFWS 2011a). The fruit is egg-shaped 

and laterally compressed measuring about 4.5 millimeters (mm) (0.2 in) long and 2 mm (0.1 in) in 

diameter (USFWS 2011a), and each produces 4 to 9 seeds (USFWS 2011a). In New Mexico, monitoring 

results revealed that it takes two growing seasons for seedlings to mature with flowering into the third or 

fourth year as compared to other species of Astragalus, which typically take one growing season to 

bloom (USFWS 2011a).

According to the final recovery plan for the Mancos milk-vetch (USFWS 1989), the primary threats to this

species include the destruction and modification of habitat due to surface disturbance as a result of oil, 

gas, and transmission line development and the direct collection of individuals by commercial and private 

collectors. Acid deposition from power plant operations has been identified as a potential threat;

however, there are no data to suggest that acid deposition has actually posed a threat to this species 

(USFWS 1989).

This species occurs on sandstone substrate ledges and mesa tops in cracks or shallow bowl-like 

depressions (tinajas) that accumulate sandy soils and rainfall (USFWS 2011a). Populations are found 

along the Colorado Plateau subdivision of the Great Basin Desert of northwestern New Mexico and 

southwestern Colorado within pinyon-juniper woodland and desert scrub communities (USFWS 2011a). 

Potential habitat corresponds to rimrock outcrops of the Point Lookout and Cliffhouse members of the 

Mesa Verde sandstone series with flat or gently sloping surfaces at an average elevation of 

1,854 meters (m) (5,650 feet [ft]) (USFWS 2011a). This species is confined to large sheets of exfoliating 

whitish-tan colored sandstone (USFWS 2011a) alongside Fraxinus anomala (single leaf ash), Brickellia

microphyla var. scabra (scabrous bricklebush), Cercocarpus intricatus (small leaf mohagany), and 

Ipomopsis roseata (rosy ipomopsis) (USFWS 2011a). Overall cover is very low (less than five percent), 

and resource competition for all of these species is minimal (USFWS 2011a). At a broader landscape 

scale, dominant plant associates are Achnatherum hymenoides (Indian ricegrass), Gutierrezia sarothrae

(broom snakeweed), Yucca angustissima (narrow leaf yucca), and Artemisia tridentata (big sagebrush) 

(USFWS 2011a).
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Mancos milk-vetch is a narrow endemic known only from the Four Corners region of New Mexico, San 

Juan County, and adjacent Montezuma County, Colorado. Species distribution closely follows a narrow 

band of Mesozoic (Point Lookout and Cliff House) sandstone along a 10-mile section of the Hogback 

geologic formation (USFWS 2011a). Prior to 1989, there were a total of 13 known populations with 3 of 

these located on Ute Mountain Ute tribal lands in Colorado (USFWS 2011a). Since the completion of the 

recovery plan in 1989, the Colorado populations have not been monitored (USFWS 2011a). New plots 

were installed for Bureau of Land Management (BLM) and State of New Mexico lands starting in 1990 

(USFWS 2011a). Only the Navajo Nation found their 13 previously known populations, along with one 

new population, allowing for some long-term comparisons to past population numbers (USFWS 2011a).

Major individual site differences with regard to Mancos milk-vetch seedling density and mature plant 

cover have been observed (USFWS 2011a). Despite these differences, it appears that maximum 

population development and density occur on larger, relatively flat surfaces with numerous cracks and 

tinajas that accumulate soil and rainfall (USFWS 2011a). This observation is supported by distinct site 

differences found between the BLM and State of New Mexico plots.

Mesa Verde Cactus

The Mesa Verde cactus was listed as federally threatened on October 30, 1979 (44 FR 62471-62474). 

Habitat is primarily salt-desert scrub communities in the Fruitland and Mancos shale formations, and in 

the Menefee Formation overlying Mancos shale. This species is most frequently found on the tops of 

hills or benches and along slopes. Mesa Verde cactus is a perennial desert plant that grows slowly and 

has a lifespan of approximately 20 years (USFWS 2011b). It is distinguished within the Sclerocactus 

genus by an almost total lack of central spines (0 to 1), but also a sporadic occurrence of a single 

hooked central spine per areole (USFWS 2011b). Stems are mostly pale gray-green, 3.2 to 11 cm long 

(1.3 to 4.3 in), and 3.8 to 8 cm in diameter (1.5 to 3.1 in), with 13 to 17 ribs with spines from 6 to 13 mm 

(0.2 to 0.5 in) long, in clusters of 8 to 11 (USFWS 2011b). Flowers are 1 to 3 cm (0.4 to 1.2 in) wide and 

1 to 3.5 cm (0.4 to 1.4 in) long with purple mid-stripes and golden to cream-colored margins on the outer 

tepals (USFWS 2011b). Flowers in the southern end of its range tend to have smaller, pinkish flowers 

(USFWS 2011b). Fruits are green becoming tan at maturity, and seeds are dull black 2.5 to 3 mm

(~0.1 in) long (USFWS 2011b). Average stem length for a mature plant is 9 cm (3.5 in) (USFWS 2011b).

According to the final recovery plan for the Mesa Verde cactus (USFWS 2012), the primary threats to 

this species include the destruction and modification of habitat due to surface disturbance as a result of 

oil, gas, and transmission line development and the direct collection of individuals by commercial and 

private collectors.

At the time of the USFWS Mesa Verde Cactus Recovery Plan (USFWS 1984), the known distribution of 

Mesa Verde cactus in San Juan County extended from the Colorado/New Mexico border east to 

Waterflow, New Mexico, approximately 15 miles west and 10 miles south of Shiprock, New Mexico 

(USFWS 1984). There was one isolated population located one mile south of Sheep Springs, New 

Mexico (USFWS 1984). Three of the five known populations existed on the Navajo Nation and a fourth 

existed east of the Hogback and north of Waterflow, New Mexico on Bureau of Land Management (BLM) 

administered lands, Public Service Company of New Mexico lands, and other private lands (USFWS 

1984). The 1984 recovery plan estimated the rangewide population to be approximately 5,000 to 10,000 

plants within an estimated 120 x 48 km (75 x 30 miles ) rectangular area (USFWS 2011b). 

Additional cactus populations and locations have been discovered on Navajo Nation lands after the plan 

was finalized in 1984 (USFWS 2011b). Distribution within this range is not continuous and is sporadic 

and widely scattered (USFWS 2011b). Density greatly varies within populations with the highest known 

concentration being a 40 km (25 mi) swath around Shiprock, New Mexico, which may be an artifact of 

numerous botanical surveys conducted due to increased development pressures (USFWS 2011b). Of 

the known populations of Mesa Verde cactus, at least 80 percent of these occur on Navajo Nation lands, 

15 percent on Ute Mountain Ute lands, and 5 percent on small blocks of BLM and New Mexico State 
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lands (USFWS 2011b). Currently, there are no discoveries known on lands outside of these four 

landowners (Navajo Nation, Ute Mountain Ute, BLM, and State of New Mexico), but not all habitat 

potentially suitable for Mesa Verde cactus has been surveyed (USFWS 2011b).

3.3.2 Potential Presence in the Deposition Area

Modeled potential habitat for the Mancos milk-vetch and Mesa Verde cactus is depicted in Figures 3-1

and 3-2. Based on the model, habitat for the Mancos milk-vetch is confined to a narrow band located to 

the west of the FCPP. Known distributions for the Mancos milk-vetch are located within a 10 km radius of 

the FCPP (NMNH 2011; NNNHP 2011). Potential occurrence of the Mesa Verde cactus would be limited 

to suitable habitat within the northwest portion the Deposition Area, as this species has not been 

reported south of the San Juan River (Heil 2013).

Field surveys for rare plants were conducted to verify habitat models and quantify habitat quality in 2012 

and 2013 (AECOM 2013a,d). Surveys, where conducted within the Deposition Area, did not locate any 

populations of Mancos milk-vetch or Mesa Verde cactus, but did identify suitable habitat for both species 

within the Deposition Area (AECOM 2013a,d). A population of Mancos milk-vetch was located to the 

west of the Deposition Area along portions of the FCPP transmission lines (AECOM 2013a,d).
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Figure 3-1 Potential Habitat for Mancos Milk-vetch in Deposition Area
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Figure 3-2 Potential Habitat for Mesa Verde Cactus in Deposition Area
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4.0 Effects of the Proposed Action

4.1 SCR Installation

As shown in Figure 2-1, the construction activities would be performed in an industrial area without any 

habitat or listed species present. Truck traffic may add to the noise level at the plant but that increase 

would be a small addition in this industrial area. The increased truck traffic to deliver sorbent and reagent 

to the FCPP would occur on paved roads that have varying levels of existing traffic. While there may be 

an increased potential for collisions with listed species within the Deposition Area due to this additional 

traffic, the current disruption of species and habitats due to existing traffic levels has already established 

avoidance of major roads by birds in the Deposition Area. There are no listed mammals that would be 

affected by traffic.

Materials handling was analyzed in the NAAQS modeling prepared in support of the EIS (AECOM 

2013b) and determined that projected future changes under the Proposed Action would not exceed the

standards. It is unlikely that emissions from construction and operation of Units 4 and 5 would adversely 

affect the environment outside the FCPP fenceline. Therefore, the only potential impacts to listed species 

and their habitat are those within the Deposition Area outside the FCPP fenceline.

4.2 Acid Deposition on Soils

Soil acidity affects the chemical properties and leaching potential of other contaminants emitted from the 

FCPP because metals are less soluble in water as pH increases. If the metals are less soluble, they are 

less mobile in the soil profile and therefore less biologically available to plants and animals. Due to the 

relatively high alkalinity of all soils within the Deposition Area (median pH of 8.2 based on the soil 

surveys [Natural Resources Conservation Service {NRCS} 2009, 2008a,b] and 7.8 for the soil samples 

collected within the Deposition Area in 2013), it was believed at the start of the analysis of impacts that 

the high buffering capacity of the soils would minimize the effects of acid deposition, and this hypothesis 

was tested. 

An evaluation of the acid neutralization potential of the soils was used to determine whether acid 

deposition would affect species habitats within the Deposition Area. The testing procedure was based on 

the Sobek method described in “Field and Laboratory Methods Applicable to Overburdens and 

Minesoils” (EPA 1978). The process involves treating the soil sample with a known quantity of 

standardized HCl and determining the amount of unconsumed acid by titration with standardized sodium 

hydroxide.

To establish the neutralization potential of the soils within the Deposition Area, laboratory tests were 

performed on 17 soil samples collected during the 2013 field sampling effort. Composites of the 30 cm 

soil depths were thoroughly mixed in proportion to the amount of soil depth represented (typically 0 to 

2 cm, 2 to15 cm, and 15 to 30 cm). The laboratory test results were checked and validated by AECOM. 

To determine whether the quantity of acid deposition coming from the FCPP would affect the pH of the 

soils within the Deposition Area, a comparison of the soil acid neutralizing capacity (ANC) to the 

maximum deposition of acid-forming hydronium ions was conducted (see Table 2-2). The lowest value 

for the ANC (6 t/Kt2 of 0.1 Normal (0.1N) HCl) from the laboratory testing was selected for comparison 

based on the assumption that, if 25 years of acidic deposition would be neutralized without significantly 

changing the alkalinity in the soil with the lowest measured ANC, then there would be no effect on the 

other soils in the deposition area with more buffering capacity. 

 

2 t/Kt = tons/kiloton = parts per thousand
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This evaluation was completed by comparing the total volume of acid deposited in the top 2 cm of soil to 

the ANC for the same amount of soil. The impact of 25 years of acid deposition from the FCPP on the 

soil ANC was determined using the following basic steps:

• In the top 2 cm of a 1 m2 area, there are 20,000 cm3 or 32,000 g (using a typical soil density of 

1.6 g/cm3

). 

• To neutralize the soil with the lowest ANC (6 t/Kt of 0.1N HCl), it took 2.4 ml of 0.1N HCl per 2 g 

or 1.2 ml 0.1N HCl per g. 

• To neutralize 32,000 g of soil with the lowest ANC requires 38,400 ml or 38.4 L of 0.1N HCl

(32,000 g * 1.2 ml/g 0.1N HCl = 38,400 ml 0.1N HCl) 

• 38.4 L of 0.1N HCl contains 3.84 moles (equivalents) of hydronium ions (H+

)

• As shown in Table 2-1, the maximum acid deposition predicted is 0.0047 H+ equivalents per 

square meter per year or approximately 0.119 H+ equivalents/m2 in 25 years. 

• Neutralization of the maximum deposition predicted over 25 years would utilize 3 percent of the 

acid neutralizing capacity of the soil with the lowest ANC (0.119 H+ eq/m2

/25 years [from 

deposition] divided by 3.84 H+ equivalents/m2 [existing neutralization capacity]).

The use of the buffering capacity for the soil with the lowest ANC, which is the soil that would be the 

most affected by acid deposition, provides the most conservative estimate of the effect that acid 

deposition would have on the soil. The calculations of the buffering capacity assumed that all acid 

deposition would accumulate in the top 2 cm of soil over 25 years, which also results in a conservative 

estimate because it is likely that some of the acidic deposition would move from the soil surface by 

erosion or leaching. Most of the soil samples collected from the Deposition Area had much higher ANC 

values (maximum = 174 t/Kt; median = 85 t/Kt), requiring greater amounts of acid deposition to reduce 

the soil pH. Based on this analysis, it can be concluded that the soil within the Deposition Area has the 

ability to accept much more acidic deposition than would be generated by FCPP emissions before any 

significant change to soil pH would occur.

Soil acidity affects the chemical properties and leaching potential of metals because they are typically 

less soluble in water as pH increases. If the metals are less soluble, they are less mobile in the soil 

profile, less likely to leach through the soil into the groundwater, and less biologically available to plants 

and animals. For example, the Natural Resources Conservation Service (NRCS 2000) recommends 

increasing the pH of contaminated soils to 6.5 or higher to make heavy metals (such as those emitted 

from the FCPP stack) less available to plants and animals. Because the addition of acid deposition from 

FCPP stack emissions would not reduce the soil pH to less than 6.5, metals in the soils in the area of 

highest potential deposition (Deposition Area) would not be more mobile than under current conditions.

4.3 Acid Deposition in Surface Water

Between Farmington and Shiprock, the average pH of the San Juan River, where designated critical 

habitat for the Colorado pikeminnow occurs, is over 8.0 (Bliesner and Lamarra 2004) with average 

annual flow rates of more than 1,700 cubic feet per second at Farmington (USGS 2013), which is just 

upstream from the Deposition Area. With the high flows in the San Juan River, the small amount of acid 

deposition directly onto the river would have little or no effect on the pH of the fish habitat due to the high 

pH in the stream and the fact that acidic compounds would be diluted by the large amount of water and 

high flows.

4.4 Particulate Matter

As demonstrated in the air modeling performed in support of the EIS (AECOM 2013b), the NAAQS for 

PM10 and PM2.5 would not be exceeded during future operations of Units 4 and 5 as a result of the 

addition of SCR sytems. Because the NAAQS are developed to be protective of the environment, it can 
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22

be concluded that the PM emissions will not adversely affect the environment or the populations and 

habitat of listed species.

4.5 Plants

4.5.1 Impact Evaluation

This discussion focuses on the potential impact of the change in sulfuric acid mist emissions. There have 

been limited studies on the effects of sulfuric acid mist on vegetation, especially in the western U.S. 

where acid deposition has never been demonstrated to be of concern to the environment. Compounds 

containing sulfur and nitrogen, such as SO2, NOX, and sulfuric acid, all contribute to acid deposition 

when concentrations and climatic conditions are “right” for acid to form in the atmosphere. One source of 

information useful for documentation of the effects of acid deposition on plants is a review of multiple 

studies on the effects of SO2, NOX, and sulfuric acid mist deposition on vegetation summarized by the 

World Health Organization (WHO 2000). One purpose of this document was to develop guidelines in the 

form of maximum critical loads for the deposition of acid-forming air pollutants on vegetation

(WHO 2000). The WHO (2000) report was developed to evaluate risks to the environment and public 

health in Europe, which has different climatic conditions from the Deposition Area under analysis in this 

BA. Because acid deposition in the environment is not identified as a concern, there are no similar 

studies in the southwestern U.S. or comparable climates, and details on the effects of acid deposition are 

not generally measured or reported in this region. Therefore, the threshold values from the WHO report 

are the best data available for comparative purposes. 

The effect of SO2 deposition on vegetation is largely determined by the surrounding environmental 

conditions (e.g., humidity, temperature, and light intensity) (WHO 2000). Environmental conditions such 

as drought, temperature, genetic factors, and the presence of other air pollutants appeared to affect the 

potential for injuries or growth weights experienced by plant species. In general, the studies indicated 

that short-term peak exposures of plants to acid deposition had limited impact on plant health, and that 

most effects on vegetation were the result of long-term exposure to levels of SO2, NOX, and sulfuric acid 

mist above what is identified as the critical load.

After acidic mist is deposited on leaf surfaces, evaporation of the associated water will adjust the 

concentrations of the remaining solutes (WHO 2000). Deposition of sulfuric acid mist tends to be greater 

on forested areas and vegetation at higher altitudes and the effects on vegetation are dependent on the 

concentration of sulfate in the mist and the length of time of the exposure (WHO 2000). The WHO report 

bases its sulfuric acid mist guidelines on equivalent particulate sulfate concentrations because the 

sulfate concentration in the cloud water is difficult to measure. 

Annually, the minimum WHO critical load guideline value for SO2 based on effects on terrestrial 

vegetation is 250 sulfur equivalents per hectare per year. As shown in Table 2-2, the estimated 

maximum annual average SO2 concentration in the Deposition Area attributed to FCPP emissions was 

calculated to be 29.9 sulfur equivalents/ha/yr, well below the threshold in the WHO (2000) report.

The WHO report presents evidence that NOX in rain, clouds, and fog can have adverse effects on 

vegetation and establishes a threshold for critical levels of nitrogen on vegetation. The minimum 

guideline value for nitrogen on an annual basis is 5 kg/ha/yr. As shown in Table 2-2, the estimated 

maximum annual nitrogen deposition from FCPP emissions in the Deposition Area is predicted to be 

0.037 kg/ha/yr.

While it is difficult to translate the potential effects of acid deposition on plants in Europe described in the 

WHO (2000) report to impacts on southwestern U.S. vegetation, the WHO thresholds provide a 

quantitative measure for comparison where other data are unavailable. Major differences in the plant 

communities and climatic conditions, such as the short stature of vegetation and lack of continuous cloud 

cover and fog in the Deposition Area, would result in different (and probably less severe) responses to 

acidic deposition on sensitive plant species. By comparing the acid deposition from FCPP to the WHO 
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23

thresholds for sulfur and nitrogen deposition, it can be shown that the predicted annual deposition of 

acidic compounds on vegetation in the Deposition Area is a small fraction of the lowest critical load value 

that has been shown to affect plant health.

BLM vegetation transect data for grazing allotments within the Deposition Area can be used to describe 

current conditions of plant health at a specific point in time, and offer additional information. Rangeland 

health assessments were conducted during the growing season in the following years: 2000 

(Cottonwood Arroyo), 2005 (South Hogback), 2010 (North Hogback), 2012 (Twin Mounds), and 2013

(Shumway). The BLM vegetation transect documentation demonstrated that the rangeland areas in the 

Deposition Area are, for the most part, considered relatively healthy, based on BLM standards for 

healthy rangelands, and do not appear to be affected by emissions from the FCPP. Primary impacts to 

rangeland health were identified from invasive species and drought. There is no mention of effects from 

acid deposition on vegetation in any of the BLM rangeland assessment worksheets. 

Additional documentation of vegetative community health is available from the field surveys conducted 

as described above in Section 3.3.2. Field surveys were conducted to identify suitable habitat and plant 

presence, and also quantify habitat quality. The results of the surveys demonstrated that habitat for the 

sensitive plants varied from low to high. The areas identified as low quality habitat were due to the areas 

missing key habitat characteristics such as altitude, range, substrate, or topography. No areas were 

identified as low quality habitat due to effects of acid deposition from the FCPP.

4.5.2 Determination

No adverse effects on soils or the ecosystem would result from FCPP SCR Retrofit Project-related 

construction, operation, and emissions. The only potential impacts to vegetation would be indirect, 

coming from the FCPP emissions deposited in the Deposition Area. All construction activities would 

occur in an industrial area that is already disturbed and lacks vegetation or potential habitat for listed 

plants. Acid deposition on plant leaves is expected to be minimal and will be further reduced by wind and 

rain throughout the year. Due to the arid environment, lack of continuous cloud cover, and predominance 

of lower elevation areas near the FCPP, effects from the acid mist emissions from the FCPP are not

anticipated to impact the vegetation communities and sensitive plant species present in the deposition 

area. However, studies regarding the impacts of acid mist emissions on sensitive plant species are 

limited. The Proposed Action will not contribute to the problems described in Section 3.3.1 that 

contributed to the listing of these species. Due to these factors, the acid deposition “may affect, but is not 

likely to adversely affect” the Mancos milk-vetch and Mesa Verde cactus or their habitats, resulting from 

the installation and operation of the FCPP SCR Retrofit Project.

4.6 Birds and Fish

4.6.1 Impact Evaluation

Similar to the impact analysis of plant species, there have been limited studies on the effects of sulfuric 

acid mist on wildlife and fish species. The presence of feathers is likely to limit any direct exposure of 

birds to acid deposition. Acid deposition on plant leaves is expected to be minimal, and will be reduced 

by wind and rain throughout the year, making impacts from ingestion of plants within the Deposition Area 

negligible. The small amount of acidic deposition would not likely accumulate in local water bodies and 

would be diluted due to stream flows and turnover of lake water, resulting in no impacts to fish species. 

The pH levels in the San Juan River within the Deposition Area have frequently above 8, and would 

likely need a substantial amount of acidic deposition to reach a level of concern. Federal ambient water 

quality criteria recommends a pH range of 6.5 to 9 for aquatic organisms (EPA 2009). 

4.6.2 Determination

No adverse effects on soils, water bodies, or the ecosystem would result from FCPP SCR Retrofit 

Project-construction, operation, and related emissions. All construction activities would occur in an 
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24

industrial area that is already disturbed and lacks vegetation or potential habitat for listed birds and fish. 

The only potential impacts to birds would be indirect, coming from the FCPP emissions deposited in the 

Deposition Area. Therefore, the ecosystem within the Deposition Area would not be altered by the small 

increase in acidic deposition. However, there is a lack of research on the effects of sulfuric acid mist on 

wildlife and fish species. The Proposed Action will not contribute to the problems described in Sections

3.1.1 and 3.2.1 that contributed to the listing of these species. Due to these factors, the acid deposition 

“may affect, but is not likely to adversely affect” federally listed endangered, threatened, or candidate

wildlife and fish species or their habitats, resulting from the installation and operation of the FCPP SCR 

Retrofit Project.
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5.0 Cumulative Effects

Cumulative effects are defined in the ESA Section 7 Consultation Handbook (USFWS 1998) as the 

incremental impacts of future state, private, or Tribal activities that are reasonably certain to occur within 

the project area or proximity to the project area. Future EPA actions that are unrelated to the Proposed 

Action are not considered in this section because they would be subject to separate consultation 

pursuant to Section 7 of the ESA.

The impacts discussed in this BA are those attributable to the increases in H2SO4 mist, PM10, and PM2.5

emissions from the installation of SCR systems at the FCPP. These analyses did not account for the 

reduction in emissions related to the shutdown of Units 1 through 3. Including the shutdown of Units 1, 2, 

and 3, the project will result in the following actual emission changes (AECOM 2014):

• NOx—34,000 tpy decrease 

• SO2—3,100 tpy decrease 

• PM—650 tpy decrease

• PM10—217 tpy decrease

• PM2.5—128 tpy decrease

A wide variety of activities that may contribute to the loss of a federally listed species are known to occur 

in the project region. These activities include but are not limited to energy development, mining, 

recreation, human population expansion, irrigation and water diversion activities, agriculture, livestock 

grazing, and introductions of non-native wildlife, plant, or aquatic species. Many of these activities are 

expected to continue on tribal, state and private lands within the habitat and known range of various 

federally listed wildlife, fish, and plant species, and could contribute to cumulative effects to the species 

within the project area. Species with small population sizes, endemic locations, or slow reproductive 

rates, generally would be more susceptible to cumulative effects. In general, the severity of the 

cumulative effects would depend on factors such as the sensitivity of the species impacted, seasonal 

intensity of use, type of project activity, and physical parameters (e.g., topography). Details regarding 

specific cumulative effects to the federally listed species identified as potentially occurring within the 

Project area are discussed below.

Mesa Verde Cactus and Mancos Milk-vetch

There are no known occurrences of threatened, endangered, or candidate plant species within the 

Deposition Area. Future activities that may impact suitable habitat for these species include oil and gas 

exploration and development, mining, fire management, livestock grazing, noxious weed management, 

and agricultural activities. These activities may result in the disturbance of habitat which may lead to the 

indirect loss of individual plants. 

Mexican Spotted Owl, Southwestern Willow Flycatcher, and Yellow-billed Cuckoo 

Reasonably foreseeable future activities that may impact threatened, endangered, or candidate bird 

species include oil and gas exploration and development, mining, fire management, livestock grazing, 

noxious weed management, utility and agricultural activities. These activities may result in the 

disturbance of habitat which may lead to the indirect loss or the direct loss of individual birds as a result 

of vehicle collisions, loss of nests, etc.
Biological Assessment for the Four Corners Power Plant SCR Retrofit Project

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Colorado Pikeminnow, Razorback Sucker, and Roundtail Chub

Reasonably foreseeable future activities that may impact sensitive fish species and suitable habitat

include water depletions, surface disturbance, and potential water quality effects associated with portions 

of the San Juan River. These activities may result in the indirect loss or the direct loss of individual 

species as a result of water toxicity.
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