&EPA
United States
Environmental Protection
Agency
January 2023
Executive Summary
Final Determination of the
U.S. Environmental Protection Agency
Pursuant to Section 404(c) of the Clean Water Act
Pebble Deposit Area, Southwest Alaska
mmm.
Office of Water, Washington, DC
www.epa.gov/bristolbay
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January 2023
Executive Summary
Final Determination of the
U.S Environmental Protection Agency
Pursuant to Section 404(c) of the Clean Water Act
Pebble Deposit Area, Southwest Alaska
U.S. Environmental Protection Agency
Office of Water
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Cover Photo Credits
Main photo: Upper Talarik Creek (Joe Ebersole, USEPA)
Thumbnail 1: Fishing boats at Naknek, Alaska (USEPA)
Thumbnail 2: Sockeye salmon in the Wood River (Thomas Quinn, University of Washington)
Thumbnail 3: Salmon drying at Koliganek (Alan Boraas, Kenai Peninsula College)
Thumbnail 4: Age-0 coho salmon in the Chignik watershed (Jonny Armstrong)
Preferred citation: USEPA (U.S. Environmental Protection Agency). 2023. Final Determination of the
U.S Environmental Protection Agency Pursuant to Section 404(C) of the Clean Water Act, Pebble Deposit
Area, Southwest Alaska. Office of Water, Washington DC.
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EXECUTIVE SUMMARY
The U.S. Environmental Protection Agency (EPA) is prohibiting the specification of and restricting the
use for specification of certain waters in the Bristol Bay watershed as disposal sites for certain
discharges of dredged or fill material associated with development of a mine at the Pebble deposit, a
large ore body in southwest Alaska. EPA is exercising its authority under Section 404(c) of the Clean
Water Act (CWA) (Box ES-1) and its implementing regulations at 40 Code of Federal Regulations (CFR)
Part 231 because the discharges of dredged or fill material associated with developing a mine evaluated
in this final determination will have unacceptable adverse effects on anadromous1 fishery areas in the
Bristol Bay watershed. Development of a mine at the Pebble deposit has been the subject of study for
more than two decades. This final determination is based on this extensive record of scientific and
technical information and applies only to certain discharges of dredged or fill material associated with
developing the Pebble deposit, not to any other resource development projects in the State of Alaska.
Alaska's Bristol Bay watershed (Figure ES-1) is an area of unparalleled ecological value, boasting salmon
diversity and productivity unrivaled anywhere in North America. The Bristol Bay watershed provides intact,
connected habitats—from headwaters to ocean—that support abundant, genetically diverse wild Pacific
salmon populations. These salmon populations, in turn, help to maintain the productivity of the entire
ecosystem, including numerous other fish and wildlife species. The region's salmon resources have
supported Alaska Native cultures for thousands of years and continue to support one of the last intact
salmon-based cultures in the world. Together, the Bristol Bay watershed's largely undisturbed aquatic
habitats and productive salmon populations create this globally significant ecological and cultural resource.
The streams, wetlands, and other aquatic resources of the Bristol Bay watershed also provide the
foundation for world-class, economically important, commercial and sport fisheries for salmon and
other fishes. The Bristol Bay watershed supports the world's largest runs of Sockeye Salmon, producing
approximately half of the world's Sockeye Salmon. These Sockeye Salmon represent the most abundant
and diverse populations of this species remaining in the United States. Bristol Bay's Chinook Salmon
runs are also frequently at or near the world's largest, and the region also supports significant Coho,
Chum, and Pink salmon populations. Because no hatchery fishes are raised or released in the watershed,
Bristol Bay's salmon populations are entirely wild and self-sustaining. Bristol Bay is remarkable as one
of the last places on Earth with such bountiful and sustainable harvests of wild salmon. One of the main
factors leading to the success of these fisheries is the fact that its diverse aquatic habitats are largely
untouched and pristine, unlike the waters that support many other salmon fisheries worldwide.
1 Anadromous fishes hatch in freshwater habitats, migrate to sea for a period of relatively rapid growth, and then
return to freshwater habitats to spawn. For the purposes of this final determination, "anadromous fishes" refers
only to Coho or Silver salmon (Oncorhynchus kisutch), Chinook or King salmon [0. tshawytscha), Sockeye or Red
salmon [0. nerka), Chum or Dog salmon [0. keta), and Pink or Humpback salmon [0. gorbuscha).
Final Determination
ES-1
January 2023
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Executive Summary
Figure ES I. The Bristol Bay watershed, composed of the Togiak, Nushagak, Kvichak, Naknek, Egegik, and Ugashik River watersheds and
the North Alaska Peninsula. Only selected towns and villages are shown on this map.
~
~
Approximate Pebble Deposit Location
Towns and Villages
Watershed Boundary
Parks, Refuges, or Preserves
Lake Clark
National Park
and Preserves
Wood-Tikchik,;
State Park
Pedro Bi
NUSHAGAK
lliamna Lake
'$0 Togiak National'
Wildlife fWfuge
Togiak
ingham^?
Cook Inlet
lanokot
Katmar
''©/"National Park
and Preserve
lg Salmon
Becharof
National
Wildlife
tRefuge/
Bristol Bay
Alaska
Peninsuli
t NWR
'Aniakchak
" National
Preserve
nortkala:
PENINSULA
Alaska
Maritime
NWR A
Izenbek
NWR
Kilometers
Final Determination
ES-2
January 2023
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Executive Summary
Roughly 50 to 70 percent of Bristol Bay's Sockeye and large numbers of its Coho, Chinook, Pink, and
Chum salmon are sustainahly harvested in subsistence, commercial, and recreational fisheries before
they can return to their natal lakes and streams to spawn. Thus, these salmon resources have significant
nutritional, cultural, economic, and recreational value within and beyond the Bristol Bay region. The
total economic value of the Bristol Bay watershed's salmon resources, including subsistence uses, was
estimated at more than $2.2 billion in 2019 (McKinley Research Group 2021). The Bristol Bay
commercial salmon fishery generates the most significant component of this economic activity, resulting
in 15,000 jobs and an economic benefit of $2.0 billion in 2019, $990 million of which was in Alaska
(McKinley Research Group 2021). Beyond their economic and environmental value, the diverse fishery
and other aquatic and terrestrial resources of the Bristol Bay watershed, which depend upon the
complex of healthy streams, wetlands, and other waters, are irreplaceable because they are inseparable
from the cultures of the native people they support. Section 3 of this final determination provides an
overview of the streams, wetlands, and other aquatic resources of the Bristol Bay watershed and
discusses their role in supporting important subsistence, commercial, and recreational fisheries.
BOX ES-1. SECTION 404 OF THE CLEAN WATER ACT
The objective of the Clean Water Act (CWA) is to restore and maintain the chemical, physical, and
biological integrity of the nation's waters. Section 404(c) of the CWA authorizes the U.S. Environmental
Protection Agency (EPA) to (1) prohibit or withdraw the specification of any defined area as a disposal
site, and (2) deny, restrict, or withdraw the use of any defined area for specification as a disposal site,
whenever it determines, after notice and opportunity for public hearings, that the discharge of dredged
or fill material into the area will have an unacceptable adverse effect on municipal water supplies,
shellfish beds and fishery areas (including spawning and breeding areas), wildlife, or recreational
areas. EPA has used its CWA Section 404(c) authority judiciously, having completed only 13 CWA
Section 404(c) actions in the 50-year history of the CWA prior to this final determination.
Proposed Mine at the Pebble Deposit
The Pebble deposit, a large, low-grade deposit containing copper-, gold-, and molybdenum-bearing
minerals, is located at the headwaters of the pristine Bristol Bay watershed. The Pebble deposit
underlies portions of the South Fork Koktuli River (SFK), North Fork Koktuli River (NFK), and Upper
Talarik Creek (UTC) watersheds, which drain to two of the largest rivers in the Bristol Bay watershed,
the Nushagak and Kvichak Rivers (Figure ES-2).
Final Determination
ES-3
January 2023
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Executive Summary
Figure ES-2. Major waterbodies within the Nushagak and Kvichak River watersheds.
Lake Clark
National Park
and Preserve
Wood-Tikchik
State Park
Port Alsworth
Rive/-
NUSHAGAK
'Nondalton
Creek
Pedro Bai
J
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Executive Summary
Since 2001, Northern Dynasty Minerals Ltd. (NDM) and subsequently the Pebble Limited Partnership
(PLP)2 have been conducting data collection and analysis as part of efforts to pursue the development of
a large-scale mine at the Pebble deposit. Given current mining technology and the high density of water
resources in the area, the discharge of dredged or fill material into waters of the United States is
expected to be necessary to develop the Pebble deposit. Such discharges would require a CWA Section
404 permit from the U.S. Army Corps of Engineers (USACE). In December 2017, PLP submitted a CWA
Section 404 permit application to USACE to develop a mine at the Pebble deposit, which triggered the
development of an Environmental Impact Statement (EIS) pursuant to the National Environmental
Policy Act (NEPA). In response to the CWA Section 404 permit review/NEPA review process, PLP
submitted a revised permit application in June 2020 (the 2020 Mine Plan) (PLP 2020).
In the 2020 Mine Plan, PLP proposes to develop the Pebble deposit as a surface mine at which 1.3 billion
tons of ore would be mined over 20 years. The project consists of four primary elements: (1) the mine
site situated in the SFK, NFK, and UTC watersheds (Figure ES-3); (2) the Diamond Point port; (3) the
transportation corridor, including concentrate and water return pipelines; and (4) the natural gas
pipeline and fiber optic cable. The first element, a fully developed mine site, would include an open pit,
bulk tailings storage facility (TSF), pyritic TSF, a 270-megawatt power plant, water management ponds
(WMPs), water treatment plants (WTPs), milling and processing facilities, and supporting infrastructure
(Figure ES-4). Under the 2020 Mine Plan, PLP would progress through four distinct mine phases:
construction, operations (also referred to as production), closure, and post-closure. The construction
period would last approximately four years, followed by 20 years of operation. Closure, including
physical reclamation of the mine site, is projected to take approximately 20 years. Post-closure
activities, including long-term water management and monitoring, would last for centuries (USACE
2020a). The potential direct and indirect impacts from construction and operation of the 2020 Mine
Plan on streams, wetlands, and other waters across the mine site area (Figure ES-5) have been evaluated
in detail.
On July 24, 2020, USACE published a Notice of Availability for the Final EIS (FEIS) in the Federal Register
(USACE 2020a), and on November 20, 2020, USACE issued its Record of Decision (ROD) denying PLP's
CWA Section 404 permit application on the basis that the 2020 Mine Plan would not comply with the
CWA Section 404(b)(1) Guidelines and would be contrary to the public interest (USACE 2020b). By
letter dated November 25, 2020, USACE notified PLP that the proposed project failed to comply with the
CWA Section 404(b)(1) Guidelines because, even after consideration of proposed mitigation measures,
"the proposed project would cause unavoidable adverse impacts to aquatic resources which would
result in Significant Degradation to aquatic resources" (USACE 2020b: Transmittal Letter, Page 1).
On January 19, 2021, PLP filed a request for an appeal of the USACE permit denial with USACE. USACE
accepted the appeal on February 25, 2021, and review of the appeal is ongoing.
2 PLP was created in 2007 by co-owners NDM and Anglo American PLC to design, permit, construct, and operate a
long-life mine at the Pebble deposit (Ghaffari et al. 2011). In 2013, NDM acquired Anglo American's interest in PLP,
and NDM now holds a 100 percent interest in PLP (Kalanchey et al. 2021).
Final Determination
ES-5
January 2023
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Executive Summary
Figure ES-3. Mine site hydrography. Figure 2-1 from PLP's June 8, 2020 Clean Water Act Section 404 permit application (PLP 2020).
Main Water
Management Pond
North Fork Koktuli
Watershed
TSF
Laydown
Upper Talarik Creek
Watershed
vjT Jfm
Bulk Tailings\
Storage Cell
Pyritic Tailings and
PAG Waste Rock
Storage Facility
MINE SITEL n
ACCESS ROAD(
North Fork K°
South Fork Koktuli
Watershed
°ktu!i Rr
lliamna
Airfield
lliamna
Newhalen
FIGURE 2-1
Mine Site Hydrography
Bulk Tailings Storage Cell
Water Managment Pond
TSF Laydown
Pyritic Tailings and PAG Waste Rock Storage
Facility
Open Pit
Overburden Stockpiles
Mill Site Process Plant
Quarry
03 Watershed Boundary
Access Road
Natural Gas & Concentrate Pipelines
Township Boundary
lliamna Lake
Final Determination
ES-6
January 2023
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Executive Summary
Figure ES-4. Mine site map. Figure 1-4 from PLP's June 8, 2020 Clean Water Act Section 404 permit application (PLP 2020).
Sediment
Pond
Growth
Medium
Potable Water
Well Field
Stockpile
Sediment
Pond
Sediment
Pond
Main Water
Management Pond
Mill Camp and
Administration Buildings
-Container Yard
Concentrate Process
PumpHo^e-"— Plant
. Power Plant
Seepage Collection Pond —
Seepage
| Collection
\ System
Landfl
Incin
II and
irator
Concentrate and
Natural Gas Pipelines
Crusher and »
Conveyor ,
Truck Shop Pad
Quarry A-
Mill Site
Laydown Area
TSF Overburden
Stockpile
TSF Laydown
PAG Tailings
and Waste Rock
Storage Facility
Quarry B
Bulk Tailings
Storage Facility
Quarry C
¦mbankment'
Explosive
Storage
Pad
Growth
Medium
Stockpile
QuarryB
Open Pit Water
Management Pond
Sediment
Pond
Open Pit
Overburden-
Stockpile
Sediment
Pond
Sediment
Pond
WTP 1
TSF South
Embankment
Seepage
Collection'
System
Seepage
Recycle
Pond
Sedimenl
Pond
FIGURE 1-4
Mine Site Map
Mine Site Footprint
££ Haul/Service/Access Road
Mine Site Access Road
---¦ Concentrate & Natural Gas Pipelines
50' Contour (Existing)
~ Township Boundary
Section Boundary
0—^^=^^5M"eS
Scale 1:46,000
Alaska State Plane Zone 5 (units feet)
1983 North American Datum
Final Determination
ES-7
January 2023
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Executive Summary
Figure ES-5. Mine site analysis area for wetlands and other waters. Figure 4.22-1 from the FEIS (USAGE 2020a: Section 4.22).
US Army Corps
of Engineers
PEBBLE PROJECT EIS
ANALYSIS AREA FOR INDIRECT IMPACTS
OF FRAGMENTATION ON WETLANDS
AND OTHER WATERS
FIGURE 4.22-1
Miles
Fragmented Wetland Area
[J Mine Site Direct Impacts
^ Collection Ditch
^ Diversion Channel
NWI Classes
Aquatic Bed
( ) Herbaceous
Broad Leaved Deciduous Shrubs
Deciduous Forest
Evergreen Shrubs
Ponds
Lakes
Rivers/Streams (Intermittent)
Rivers/Streams (Perennial)
v Wetland/Upland Mosaic
Uplands/Mapped Wetlands Extent
Watershed
* Collection ditch and diversion channel
locations are approximate and based on
the Pebble Mine Site Operations Water
Management Plan (Knight Piesold 2018a)
Sources: PLP 2019-RFI116; PLP 2019 RFI-153
Final Determination
ES-8
January 2023
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Executive Summary
The USACE permit denial addresses only PLP's specific permit application for the 2020 Mine Plan; it
does not address any other potential plans to develop the Pebble deposit. Information regarding the
Pebble deposit and the 2020 Mine Plan can be found in Section 2 of this final determination.
2014 Proposed Determination
For more than a decade, many Alaska Native communities in the Bristol Bay watershed; subsistence,
commercial, and recreational fishing interests; conservation groups; and others have raised concerns
about the potential impacts that a large-scale mine at the Pebble deposit could have on the region's
socially, ecologically, and economically important fishery areas. Starting in May 2010, these groups and
others began requesting that EPA use its CWA Section 404(c) authority to protect the region's fishery
areas. In February 2011, EPA decided to conduct an ecological risk assessment before considering
additional steps. In January 2014, after three years of study, two rounds of public comment, and
independent, external peer review, EPA released its Assessment of Potential Mining Impacts on Salmon
Ecosystems of Bristol Bay, Alaska3 (Bristol Bay Assessment or BBA) (EPA 2014). In July 2014, after
careful consideration of available information, including the findings of the BBA and consultation with
PLP and the State of Alaska, EPA Region 10 published a proposed determination under Section 404(c) of
the CWA to restrict the use of certain waters in the SFK, NFK, and UTC watersheds as disposal sites for
dredged or fill material associated with mining the Pebble deposit (2014 Proposed Determination) for
public comment.
As a result of litigation brought by PLP, EPA Region 10's CWA Section 404(c) review process was halted
in November 2014 until EPA and PLP resolved the case in a May 2017 settlement agreement. As a
condition of that settlement agreement, EPA Region 10 initiated a process to propose to withdraw the
2014 Proposed Determination, and EPA ultimately withdrew the 2014 Proposed Determination in
August 2019. In October 2019, 20 tribal, fishing, environmental, and conservation groups challenged
EPA's withdrawal of the 2014 Proposed Determination. The ultimate result of the litigation that began in
October 2019 was an October 29, 2021 decision by the U.S. District Court for the District of Alaska to
vacate EPA's 2019 decision to withdraw the 2014 Proposed Determination and remand the action to the
Agency for reconsideration.
The District Court's vacatur of EPA's 2019 decision to withdraw the 2014 Proposed Determination had
the effect of reinstating the 2014 Proposed Determination and reinitiating EPA's CWA Section 404(c)
review process. The next step in the CWA Section 404(c) review process required the Region 10
Regional Administrator to decide whether to withdraw the 2014 Proposed Determination or prepare a
recommended determination within 30 days. On November 23, 2021, EPA Region 10 published in the
Federal Register a notice extending the applicable time requirement through May 31, 2022, to provide
sufficient time to consider available information and determine the appropriate next step in the CWA
3 EPA conducted the BBA consistent with its authority under CWA Section 104(a) and (b). For more information
about EPA's efforts in Bristol Bay or copies of the Bristol Bay Assessment, see http://www.epa.gov/bristolbay.
Final Determination
ES-9
January 2023
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Executive Summary
Section 404(c) review process. In its notice, EPA concluded that it should consider information that had
become available since EPA issued the 2014 Proposed Determination before making a decision.
Information regarding the 2014 Proposed Determination and the history of EPA's work in the Bristol
Bay watershed can be found in Section 2 of this final determination.
2022 Proposed Determination
To determine the appropriate next step in this CWA Section 404(c) process, EPA Region 10 considered a
wide array of information that had become available since it issued the 2014 Proposed Determination,
including the following:
• More than 670,000 public comments submitted to EPA Region 10 in response to the 2014 Proposed
Determination.
• PLP's CWA Section 404 permit application, including the 2020 Mine Plan (PLP 2020).
• USACE's FEIS evaluating the 2020 Mine Plan, including the FEIS appendices, technical support
documents, and references (USACE 2020a).
• The 12-week coordination process between EPA, the U.S. Fish and Wildlife Service, and USACE in
spring 2020 to evaluate PLP's proposed project for compliance with the CWA Section 404(b)(1)
Guidelines.
• USACE's ROD denying PLP's CWA Section 404 permit application for the 2020 Mine Plan, including
the ROD supporting documents (USACE 2020b).
• NDM's Pebble Project Preliminary Economic Assessment dated September 9, 2021 (Kalanchey et al.
2021).
• Updated data regarding fishery resources in the Bristol Bay watershed.
• New scientific and technical publications.
In January 2022, consistent with its regulatory procedures for proposed determinations at 40 CFR
231.3(a), EPA Region 10 notified USACE, the Alaska Department of Natural Resources (ADNR), PLP,
Pebble East Claims Corporation, Pebble West Claims Corporation, and Chuchuna Minerals4 (the Parties)
of EPA Region 10's intention to issue a revised proposed determination because, based on a review of
information available to that date, it continued to believe that the discharge of dredged or fill material
associated with mining the Pebble deposit could result in unacceptable adverse effects on important
fishery areas. EPA Region 10 provided the Parties with an opportunity to consult with the Region and to
submit information for the record to demonstrate that no unacceptable adverse effects would result
4 EPA Region 10 notified Chuchuna Minerals because USACE's FEIS for the 2020 Mine Plan indicates that it is
reasonably foreseeable for discharges associated with mining the Pebble deposit to expand in the future into
portions of areas where Chuchuna Minerals holds mining claims.
Final Determination
ES-10
January 2023
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Executive Summary
from discharges associated with mining the Pebble deposit or that actions could be taken to prevent
unacceptable adverse effects on important fishery areas.
ADNR, PLP, and Chuchuna Minerals submitted response letters asserting legal, policy, scientific, and
technical arguments, and EPA met individually with PLP and Chuchuna Minerals. Based on the
information provided to the Agency, ADNR, PLP, and Chuchuna Minerals did not demonstrate to the
satisfaction of EPA Region 10 that no unacceptable adverse effects would occur as a result of the
discharge of dredged or fill material associated with mining the Pebble deposit (Section 2.2.2). Thus,
EPA Region 10 decided that the appropriate next step in this CWA Section 404(c) process was the
publication of a revised proposed determination (the 2022 Proposed Determination).
In May 2022, EPA Region 10 published in the Federal Register a notice of availability for the 2022
Proposed Determination under Section 404(c) of the CWA to prohibit the specification of and restrict
the use for specification of certain waters in the SFK, NFK, and UTC watersheds as disposal sites for the
discharge of dredged or fill material associated with mining the Pebble deposit (87 FR 32021, May 26,
2022). The notice started a public comment period ending on July 5, 2022. On June 16 and 17, 2022, EPA
Region 10 held three public hearings on the 2022 Proposed Determination: two in-person hearings in
the Bristol Bay region (in Dillingham and Iliamna) and one virtual hearing. More than 186 people
participated in the three hearings, 111 of whom provided oral statements.
EPA Region 10 received requests to extend the public comment period, as well as requests not to extend
the public comment period. EPA Region 10 considered each of these requests and found good cause
existed pursuant to 40 CFR 231.8 to extend the public comment period through September 6, 2022 (87
FR 39091, June 30, 2022).
On September 6, 2022, EPA Region 10 published in the Federal Register a notice to extend the period for
the EPA Region 10 Regional Administrator to evaluate public comments. According to the notice, EPA
found good cause existed pursuant to 40 CFR 231.8 to extend the time period provided in 40 CFR
231.5(a) to either withdraw the proposed determination or to prepare a recommended determination
through no later than December 2, 2022, to help ensure full consideration of the extensive
administrative record including all public comments (87 FR 54498, September 6, 2022). In addition to
the testimony taken at the hearings, EPA Region 10 received more than 582,000 written comments
during the public comment period.
EPA Region 10 completed its review of the extensive administrative record, including all public
comments. The Regional Administrator determined that the discharge of dredged or fill material
associated with developing the Pebble deposit would be likely to result in unacceptable adverse effects
on anadromous fishery areas and, thus, prepared a recommended determination. The recommended
determination, along with the administrative record, was transmitted to EPA's Assistant Administrator
for Water on December 1, 2022, for review and final action.
Final Determination
ES-11
January 2023
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Executive Summary
The Final Determination
On December 2, 2022, the Assistant Administrator for Water notified the Parties5 that she had received
EPA Region 10's recommended determination and, consistent with EPA's CWA Section 404(c)
regulations at 40 CFR 231.6, provided them the opportunity to notify EPA of their intent to take
corrective action to prevent unacceptable adverse effects on anadromous fishery areas from certain
discharges of dredged or fill material associated with developing the Pebble deposit.
ADNR and PLP submitted response letters asserting legal, policy, scientific, and technical arguments that
each had previously raised during consultation with EPA prior to issuance of the proposed
determination and in public comments on the proposed determination. EPA also met with ADNR and
other representatives from the State of Alaska. USACE and Chuchuna Minerals also submitted response
letters. None of the Parties identified corrective action to prevent unacceptable adverse effects
satisfactory to the Assistant Administrator for Water. Section 2 of this final determination includes a
summary of the Assistant Administrator for Water's consultation with the Parties.
Following review of EPA Region 10's recommended determination and the extensive administrative
record supporting the Regional Administrator's decision, including all public comments, the Assistant
Administrator for Water has determined that certain discharges of dredged or fill material associated
with developing the Pebble deposit into certain waters of the United States will have unacceptable
adverse effects on anadromous fishery areas and affirms the recommended determination.6 Section 4 of
this final determination provides the basis for EPA's findings regarding unacceptable adverse effects on
anadromous fishery areas.
As demonstrated in the FEIS and ROD, construction and routine operation of the mine proposed in the
2020 Mine Plan would result in the discharge of dredged or fill material into waters of the United States,
including streams, wetlands, lakes, and ponds overlying the Pebble deposit and within adjacent
watersheds. The direct effects (i.e., resulting from placement of fill in aquatic habitats) and certain
secondary effects of such discharges (i.e., associated with discharges of dredged or fill material, but not
resulting from the actual placement of such material) would result in the total loss of aquatic habitats
important to anadromous fishes. These losses would result from the construction and routine operation
of the various components of the mine site, including the open pit, bulk TSF, pyritic TSF, power plant,
WMPs, WTPs, milling/processing facilities, and supporting infrastructure. According to the FEIS and
ROD, discharges of dredged or fill material to construct and operate the mine site proposed in the 2020
Mine Plan would result in the total loss of approximately 99.7 miles (160.5 km) of stream habitat,
representing approximately 8.5 miles (13.7 km) of anadromous fish streams and 91 miles (147 km) of
additional streams that support anadromous fish streams. Such discharges of dredged or fill material
5 Consistent with EPA's regulations, the USACE representative who received this notification was the Chief of
Engineers.
6 EPA has made additional clarifications throughout this final determination based on EPA Office of Water's review
of the recommended determination and administrative record, as well as final consultation with the Parties,
conducted consistent with 40 CFR 231.6.
Final Determination
ES-12
January 2023
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Executive Summary
also would result in the total loss of approximately 2,108 acres (8.5 km2) of wetlands and other waters
in the SFK and NFK watersheds that support anadromous fish streams.
Additional secondary effects of the proposed discharges of dredged or fill material at the mine site
would degrade anadromous fishery areas downstream of the mine site. Specifically, the stream, wetland,
and other aquatic resource losses from the footprint of the 2020 Mine Plan would reverberate
downstream, depriving downstream anadromous fish habitats of nutrients, groundwater inputs, and
other ecological subsidies from lost upstream aquatic resources. Further, streamflow alterations from
water capture, withdrawal, storage, treatment, or release at the mine site are another secondary effect of
the discharge of dredged or fill material associated with the construction and routine operation of the
2020 Mine Plan. Such streamflow alterations would adversely affect approximately 29 miles (46.7 km)
of anadromous fish streams downstream of the mine site due to greater than 20 percent changes in
average monthly streamflow.7 These streamflow alterations would result in major changes in ecosystem
structure and function and would reduce both the extent and quality of anadromous fish habitat
downstream of the mine. As recognized in the FEIS, all instances of complete loss of aquatic habitat and
most impairment to fish habitat function would be permanent and "no other wild salmon fishery in the
world exists in conjunction with an active mine of this size" (USACE 2020a: Page 4.6-9).
Although Alaska has many streams and wetlands that support salmon, individual streams, stream
reaches, wetlands, lakes, and ponds play a critical role in supporting individual salmon populations and
protecting the genetic diversity of Bristol Bay's wild salmon populations. The diverse array of watershed
features across the region creates and sustains a diversity of aquatic habitats that support multiple
populations of salmon with asynchronous run timings and habitat use patterns (i.e., biocomplexity, after
Hilborn et al. 2003). These population differences are reflected in salmon genetic diversity and
adaptation to local conditions within Bristol Bay's component watersheds (e.g., Quinn et al. 2012) and
provide stability to the overall system (Schindler et al. 2010). Impacts of the 2020 Mine Plan are
concentrated in the SFK and NFK watersheds, which are a part of the Nushagak River watershed. Recent
analysis specific to the Nushagak River watershed underscores the important role that the streams,
wetlands, lakes, and ponds across the entire Nushagak River watershed, including those that would be
adversely affected by the 2020 Mine Plan, play in stabilizing the Nushagak River's productive Sockeye
and Chinook salmon fisheries (Brennan et al. 2019). Similarly, both the Koktuli River (the SFK and NFK
are tributaries to the Koktuli River) and UTC have been documented to support genetically distinct
populations of Sockeye Salmon (Dann et al. 2012, Shedd et al. 2016, Dann et al. 2018). Loss of salmon
habitats and associated salmon diversity in the SFK, NFK, and UTC watersheds would erode both the
habitat complexity and biocomplexity that help buffer these populations from sudden and extreme
changes in abundance, and ultimately maintain their productivity.
7 Streamflow alterations would vary seasonally. Streamflow reductions exceeding 20 percent of average monthly
streamflow would occur in at least one month per year in at least 13.1 miles (21.4 km) of anadromous fish streams
downstream of the mine site, and operation of the 2020 Mine Plan would increase streamflow by more than 20
percent of baseline average monthly streamflow in at least 25.7 miles (41.3 km) of downstream anadromous fish
streams due to WTP discharges.
Final Determination
ES-13
January 2023
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Executive Summary
In addition to supporting genetically distinct salmon populations, the streams and wetlands draining the
Pebble deposit area provide key habitat for numerous other fish species and supply water,
invertebrates, organic matter, and other resources to downstream waters (Meyer et al. 2007, Colvin et
al. 2019, Koenig et al. 2019). This is particularly true in dendritic stream networks like the SFK, NFK, and
UTC systems, which have a high density of headwater streams. As a result, headwater streams and
wetlands play a vital role in maintaining diverse, abundant anadromous fish populations—both by
providing important fish habitat and supplying the energy and other resources needed to support
anadromous fishes in connected downstream habitats.
EPA has determined the discharge of dredged or fill material for the construction and routine operation
of the 2020 Mine Plan will have unacceptable adverse effects on anadromous fishery areas in the SFK
and NFK watersheds. In this regard, EPA makes independent unacceptability findings, each of which is
based on one or more factors, including the large amount of permanent loss of anadromous fish habitat
(including spawning and breeding areas); the particular importance of the permanently lost habitat for
juvenile Coho and Chinook salmon; the degradation of and thus damage to additional downstream
spawning and rearing habitat for Coho, Chinook, and Sockeye salmon due to the loss of ecological
subsidies provided by eliminated streams, wetlands, and other waters; and the resulting erosion of and
thus damage to habitat complexity and biocomplexity within the SFK and NFK watersheds, both of
which are key to the abundance and stability of salmon populations within these watersheds. EPA has
also determined that discharges of dredged or fill material associated with developing the Pebble
deposit anywhere in the mine site area (Figure ES-5) within the SFK and NFK watersheds that would
result in the same or greater levels of loss or streamflow changes as the 2020 Mine Plan also will have
unacceptable adverse effects on anadromous fishery areas in these watersheds, because such discharges
would involve the same aquatic resources characterized as part of the evaluation of the 2020 Mine Plan.
These conclusions support the prohibition described in Section 5.1 of this final determination.
Further, EPA has determined the discharge of dredged or fill material for the construction and routine
operation of a mine at the Pebble deposit anywhere in the SFK, NFK, and UTC watersheds will have
unacceptable adverse effects on anadromous fishery areas if the effects of such discharges are similar or
greater in nature and magnitude to the adverse effects of the 2020 Mine Plan. In this regard, EPA makes
independent unacceptability findings, each of which is based on one or more factors, including the
pristine condition and ecological importance of anadromous habitat throughout the SFK, NFK, and UTC
watersheds; how aquatic habitats across these three watersheds function similarly to support
productive anadromous fishery areas; the large amount of permanent loss of anadromous fish habitat;
the degradation of and thus damage to additional downstream spawning and rearing habitat for Coho,
Chinook, and Sockeye salmon due to the loss of ecological subsidies provided by the eliminated streams,
wetlands, and other waters; and the resulting erosion of and thus damage to habitat complexity and
biocomplexity within the SFK, NFK, and UTC watersheds, both of which are key to the abundance and
stability of salmon populations within these watersheds. This conclusion supports the restriction
described in Section 5.2 of this final determination.
Final Determination
ES-14
January 2023
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Executive Summary
Overview of Prohibition and Restriction in the Final
Determination
This final determination includes two parts: a prohibition and a restriction, which are described in more
detail in Sections 5.1 and 5.2, respectively.
Prohibition
The EPA Assistant Administrator for Water has determined that the discharges of dredged or fill
material for the construction and routine operation of the mine identified in the 2020 Mine Plan (PLP
2020) at the Pebble deposit will have unacceptable adverse effects on anadromous fishery areas in the
SFK and NFK watersheds. Based on information in PLP's CWA Section 404 permit application, the FEIS,
and the ROD, such discharges would result in the following aquatic resource losses and streamflow
changes:
• The loss of approximately 8.5 miles (13.7 km) of documented anadromous fish streams (Section
4.2.1).
• The loss of approximately 91 miles (147 km) of additional streams that support anadromous fish
streams (Section 4.2.2).
• The loss of approximately 2,108 acres (8.5 km2) of wetlands and other waters that support
anadromous fish streams (Section 4.2.3).
• Adverse impacts on approximately 29 additional miles (46.7 km) of anadromous fish streams
resulting from greater than 20 percent changes in average monthly streamflow (Section 4.2.4).
EPA has also determined that discharges of dredged or fill material for the construction and routine
operation of a mine to develop the Pebble deposit anywhere in the mine site area within the SFK and
NFK watersheds that would result in the same or greater levels of loss or streamflow changes as the
2020 Mine Plan also will have unacceptable adverse effects on anadromous fishery areas in these
watersheds, because such discharges would involve the same aquatic resources characterized as part of
the evaluation of the 2020 Mine Plan.
Sections 4.2.1 through 4.2.4 describe the basis for EPA's determination that each of the above losses and
changes to streamflow independently will have unacceptable adverse effects on anadromous fishery
areas (including spawning and breeding areas).
Accordingly, the Assistant Administrator for Water prohibits the specification of waters of the United
States within the Defined Area for Prohibition (Figures ES-6, ES-7, and ES-8) as disposal sites for the
discharge of dredged or fill material for the construction and routine operation of the 2020 Mine Plan.
For purposes of the prohibition, the "2020 Mine Plan" is (1) the mine plan described in PLP's June 8,
2020 CWA Section 404 permit application (PLP 2020) and the FEIS (USACE 2020a); and (2) future
proposals to construct and operate a mine to develop the Pebble deposit with discharges of dredged or
fill material in the Defined Area for Prohibition that would result in the same or greater levels of loss or
Final Determination
ES-15
January 2023
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Executive Summary
streamflow changes as the mine plan described in PLP's June 8, 2020 CWA Section 404 permit
application.8 Because each of the losses or streamflow changes described in Sections 4.2.1 through 4.2.4
independently will have unacceptable adverse effects on anadromous fishery areas, future proposals to
construct and operate a mine to develop the Pebble deposit that result in any one of these losses or
streamflow changes will be subject to the prohibition.
Restriction
The Assistant Administrator for Water has determined that discharges of dredged or fill material
associated with future proposals to construct and operate a mine to develop the Pebble deposit will
have unacceptable adverse effects on anadromous fishery areas (including spawning and breeding
areas) anywhere in the SFK, NFK, and UTC watersheds if the adverse effects of such discharges are
similar or greater in nature9 and magnitude10 to the adverse effects of the 2020 Mine Plan described in
Sections 4.2.1 through 4.2.4 of this final determination.
Accordingly, the Assistant Administrator for Water restricts the use of waters of the United States within
the Defined Area for Restriction (Figures ES-7 and ES-8) for specification as disposal sites for the
discharge of dredged or fill material associated with future proposals to construct and operate a mine to
develop the Pebble deposit that would either individually or cumulatively result in adverse effects
similar or greater in nature and magnitude to those described in Sections 4.2.1 through 4.2.4 of this final
determination. Because each of the losses or streamflow changes described in Sections 4.2.1 through
4.2.4 independently will have unacceptable adverse effects on anadromous fishery areas, proposals to
discharge dredged or fill material that result in any one of these losses or streamflow changes will be
subject to the restriction. To the extent that future discharges are subject to the prohibition, the
restriction will not apply.
8 By clarifying that the "2020 Mine Plan" includes, for the purposes of the prohibition, future proposals to construct
and operate a mine to develop the Pebble deposit with discharges of dredged or fill material in the Defined Area for
Prohibition that would result in the same or greater levels of loss or streamflow changes as the mine plan described
in PLP's June 8,2020 CWA Section 404 permit application, EPA ensures that future applicants cannot circumvent
the prohibition by proposing small changes in the location of discharges within the mine site that would not result
in any change to the levels of aquatic resource loss or streamflow change, or that would result in greater levels of
aquatic resource loss or streamflow change. In doing so, EPA gives full effect to the purpose of the prohibition to
prevent adverse effects at the mine site that EPA has already determined are unacceptable.
9 Nature means type or main characteristic (see Cambridge Dictionary available at:
https://dictionary.cambridge.org/us/dictionary/english/nature).
10 Magnitude refers to size or importance (see Cambridge Dictionary available at:
https://dictionary.cambridge.org/us/dictionary/english/magnitude).
Final Determination
ES-16
January 2023
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Executive Summary
Figure ES-6. The Defined Area for Prohibition at the 2020 Mine Plan mine site. Figure based on information from PLP (2020), USGS
(2021a), and USGS (2021).
Final Determination
ES-17
January 2023
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Executive Summary
Figure ES-7. The Defined Area for Restriction and the Defined Area for Prohibition overlain on
wetlands from the National Wetlands Inventory (USFWS 2021).
NUSHAGAK
KVICHAK
Pebble Deposit
Defined Area for
Restriction
Defined Area for
Prohibition
2020 Mine Footprint
NWI Wetlands
Nushagak and Kvichak
Watersheds
South Fork Koktuli, North
~ Fork Koktuli, and Upper
Talarik Creek Watersheds
N
A
A
0 3
6
j_|
Miles
— O
— cn
10
i_l
Kilometers
Final Determination
ES-18
January 2023
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Executive Summary
Figure ES-8. The Defined Area for Restriction and the Defined Area for Prohibition overlain on
streams and waterbodies from the National Hydrography Dataset (USGS 2021b).
NUSHAGAK
KVICHAK
Anadromous Fish Streams
Pebble Deposit
Defined Area for
Restriction
Defined Area for
Prohibition
2020 Mine Footprint
NHD Streams and
Waterbodies
Nushagak and Kvichak
Watersheds
South Fork Koktuli, North
~ Fork Koktuii, and Upper
Talarik Creek Watersheds
0 3 6
1 I I l__l I 1 I I
Miles
0 5 10
l—I—1—1—I—I—I—l_l
Kilometers
lliamna Lake
Final Determination
ES-19
January 2023
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Executive Summary
Evaluation of Portions of the CWA Section 404(b)(1) Guidelines
EPA's CWA Section 404(c) regulations provide that consideration should be given to the "relevant
portions of the Section 404(b)(1) Guidelines" in evaluating the "unacceptability" of effects (40 CFR
231.2(e)). EPA's consideration of the relevant portions of the CWA Section 404(b)(1) Guidelines further
confirm EPA's unacceptable adverse effects determinations.
Specifically, EPA has determined that direct and secondary effects of the discharge of dredged or fill
material for the construction and routine operation of the 2020 Mine Plan would result in significant
degradation under the CWA Section 404(b)(1) Guidelines. Additionally, EPA has determined that direct
and secondary effects of the discharge of dredged or fill material associated with future proposals to
construct and operate a mine at the Pebble deposit that would result in adverse effects that are the
same, similar or greater than the adverse effects of the 2020 Mine Plan would also result in significant
degradation under the CWA Section 404(b)(1) Guidelines. These findings are based on the significantly
adverse effects of the discharge of dredged or fill material on special aquatic sites, life stages of
anadromous fishes, anadromous fish habitat, and aquatic ecosystem diversity, productivity, and stability
under the CWA Section 404(b)(1) Guidelines.
EPA evaluated PLP's two compensatory mitigation plans and neither plan adequately mitigates adverse
effects described in this final determination to an acceptable level. For informational purposes, EPA also
evaluated additional potential compensation measures proposed by PLP and others over the past
decade (see Appendix C of this final determination). Available information demonstrates that known
compensation measures are unlikely to adequately mitigate effects described in this final determination
to an acceptable level. Information regarding evaluation of the CWA Section 404(b)(1) Guidelines can be
found in Section 4.3 of this final determination.
Information about Other Adverse Effects of Concern on
Aquatic Resources
While not a basis for EPA's final determination, EPA has identified additional potential adverse effects of
concern on aquatic resources within the SFK, NFK, and UTC watersheds from discharges of dredged or
fill material associated with developing the Pebble deposit.11 First, adverse effects could result from
accidents and failures, such as a tailings dam failure. Uncertainty exists as to whether severe accidents
or failures could be prevented over a management horizon of centuries (or in perpetuity), particularly in
such a geographically remote area. If such events were to occur, they would have profound ecological
ramifications. Second, there are potential adverse impacts associated with the ancillary project
components beyond the mine site, such as along the transportation corridor and at the Diamond Point
port. Third, there are potential adverse impacts associated with the reasonably foreseeable expansion of
11 EPA provides an alternative basis for its determination that relies on a broader set of considerations in Section
4.4 of this final determination. To the extent statements in this final determination outside of Section 4.4 conflict
with statements within Section 4.4, for purposes of the alternative basis for EPA's determination the text of Section
4.4 governs.
Final Determination
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January 2023
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Executive Summary
the 2020 Mine Plan evaluated in the FEIS. The FEIS finds that it is reasonably foreseeable that the mine
proposed in the 2020 Mine Plan would expand in the future to mine approximately 8.6 billion tons of
ore over 78 years. The FEIS estimates that the discharge of dredged or fill material for the construction
and operation of this expanded mine would result in the total loss of approximately 430 miles (6921
km) of streams at the expanded mine site, representing approximately 43.5 miles (70 km) of
anadromous fish streams and approximately 386 miles (621 km) of additional streams that support
anadromous fish streams. Further, the FEIS estimates that discharges of dredged or fill material to
construct and operate the expanded mine site would also result in the total loss of more than 10,800
acres (43.7 km2) of wetlands and other waters that support anadromous fish streams. EPA has already
determined that the adverse effects of the discharges evaluated in this final determination are
unacceptable and the additional losses that would result from the Expanded Mine Scenario would
represent extraordinary and unprecedented levels of anadromous fish habitat loss and degradation,
dramatically expanding the scope and scale of unacceptable adverse effects in the SFK, NFK, and UTC
watersheds. For example, significant additional anadromous fish habitat losses and degradation in the
SFK, NFK, and UTC watersheds caused by future expansion of the mine would threaten genetically
distinct Sockeye Salmon populations in both the Koktuli River and UTC.
See Section 6 of this final determination for a discussion of other concerns and considerations.
Authority and Justification for Undertaking a CWA Section
404(c) Review at this Time
Congress enacted CWA Section 404(c) to provide EPA the ultimate authority, if it chooses on a case-by-
case basis, to prohibit, withdraw, deny, or restrict the use of any defined area for specification as a
disposal site for the discharge of dredged or fill material into waters of the United States "whenever" the
Agency makes the required determination under the statute (33 USC 1344(c); 40 CFR 231.1(a), (c); 44
FR 58076; Mingo Logan Coal Co. v. EPA, 714 F.3d 618, 612-13 (D.C. Cir. 2013)). EPA may exercise its
CWA Section 404(c) authority "at any time," including before a permit application has been submitted, at
any point during the permitting process, and after a permit has been issued (Mingo Logan Coal Co., 714
F.3d at 613; 33 U.S.C. 1344(c); 40 CFR 231.1(a), (c); 44 FR 58076).
EPA has reviewed the available information, including the relevant portions of the USACE permitting
record, and this information supports EPA's determinations that the discharges of dredged or fill
material evaluated in this final determination will have unacceptable adverse effects on anadromous
fishery areas within the SFK, NFK, and UTC watersheds.
By acting now, EPA makes clear its assessment of the effects of certain discharges of dredged or fill
material associated with developing the Pebble deposit into certain waters of the United States within
the SFK, NFK, and UTC watersheds in light of the significant loss of and damage to important
anadromous fishery areas. The federal government, the State of Alaska, federally recognized tribal
governments, PLP, and many other interested parties have devoted significant resources over many
years of study, engagement, and review. Considering the extensive record, it is not efficient or effective
Final Determination
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January 2023
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Executive Summary
to engage in one or more additional multi-year NEPA and CWA Section 404 processes for future
proposals to discharge dredged or fill material associated with developing the Pebble deposit into
waters of the United States within the SFK, NFK, or UTC watersheds that will result in adverse effects
that EPA has already determined are unacceptable. By acting now, based on an extensive and carefully
considered record, EPA promotes regulatory certainty for all interested parties, including USACE and
the regulated community; facilitates planning by proponents; and avoids unnecessary expenditure of
additional resources by all interested parties (see 44 FR 58077). Ultimately, by acting now, EPA also
facilitates "comprehensive rather than piecemeal protection" of important aquatic resources (see id.) by
ensuring the protection of valuable anadromous fishery areas in the SFK, NFK, and UTC watersheds
against unacceptable adverse effects from the discharges evaluated in this final determination.
Conclusion
Discharges of dredged or fill material to construct and operate the 2020 Mine Plan's proposed mine site
alone would result in the permanent loss of approximately 8.5 miles (13.7 km) of anadromous fish
streams, 91 miles (147 km) of additional streams that support anadromous fish streams, and
approximately 2,108 acres (8.5 km2) of wetlands and other waters in the SFK and NFK watersheds that
support anadromous fish streams. These discharges would also result in streamflow alterations that
would adversely affect approximately 29 miles (46.7 km) of additional anadromous fish streams
downstream of the mine site due to greater than 20 percent changes in average monthly streamflow.
The aquatic resources that would be lost or damaged play an important role in supporting salmon
populations in the SFK, NFK, and UTC watersheds.
EPA has determined that the large-scale loss of and damage to headwater streams, wetlands, and other
aquatic resources that support salmon populations in the SFK, NFK, and UTC watersheds from the
discharge of dredged or fill material for the construction and routine operation of the 2020 Mine Plan
will have unacceptable adverse effects on anadromous fishery areas in the SFK, NFK, and UTC
watersheds.
To prevent these unacceptable adverse effects, this final determination prohibits the specification of
certain waters of the United States in the SFK and NFK watersheds as disposal sites for the discharge of
dredged or fill material for the construction and routine operation of the 2020 Mine Plan, including
future proposals to construct and operate a mine to develop the Pebble deposit with discharges of
dredged or fill material into waters of the United States that would result in the same or greater levels of
aquatic resource loss or streamflow changes as the 2020 Mine Plan.
This final determination also restricts the use for specification of certain waters of the United States in
the SFK, NFK, and UTC watersheds as disposal sites for the discharge of dredged or fill material
associated with future proposals to construct and operate a mine to develop the Pebble deposit with
discharges of dredged or fill material into waters of the United States that would result in adverse effects
Final Determination
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January 2023
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Executive Summary
similar or greater in nature and magnitude to the adverse effects of the 2020 Mine Plan (see Section 5 of
this final determination).
Proposals to discharge dredged or fill material into waters of the United States associated with
developing the Pebble deposit that are not subject to this determination remain subject to all statutory
and regulatory authorities and requirements under CWA Section 404.
In light of the immense and unique economic, social, cultural, and ecological value of the aquatic
resources in the region, including the fishery areas in the SFK, NFK, and UTC watersheds, and their
susceptibility to damage, EPA will carefully evaluate all future proposals to discharge dredged or fill
material in the region.
References
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habitat mosaics and fish production across river basins. Science 364:783-786.
Colvin, S. A. R., S. M. P. Sullivan, P. D. Shirey, R. W. Colvin, K. 0. Winemiller, R. M. Hughes, K. D. Fausch, D.
M. Infante, J. D. Olden, K. R. Bestgen, R. J. Danehy, and L. Eby. 2019. Headwater streams and wetlands
are critical for sustaining fish, fisheries, and ecosystem services. Fisheries 44:73-91.
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Final Determination
ES-23
January 2023
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Executive Summary
Koenig, L. E., A. M. Helton, P. Savoy, E. Bertuzzo, J. B. Heffernan, R. 0. Hall, and E. S. Bernhardt. 2019.
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Meyer, J. L., D. L. Strayer, J. B. Wallace, S. L. Eggert, G. S. Helfman, and N. E. Leonard. 2007. The
contribution of headwater streams to biodiversity in river networks. Journal of the American Water
Resources Association 43:86-103.
PLP (Pebble Limited Partnership). 2020. Pebble Project Department of the Army Application for Permit
POA-2017-00271 (dated June 8, 2020). Anchorage, AK.
Quinn, T. P., H. B. Rich, D. Gosse, and N. Schtickzelle. 2012. Population dynamics and asynchrony at fine
spatial scales: a case history of sockeye salmon (Oncorhynchus nerka) population structure in Alaska,
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Schindler, D. E., R. Hilborn, B. Chasco, C. P. Boatright, T. P. Quinn, L. A. Rogers, and M. S. Webster. 2010.
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Shedd, K. R., T. H. Dann, H. A. Hoyt, M. B. Foster, and C. Habicht. 2016. Genetic Baseline of North American
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Final Determination
ES-24
January 2023
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