FOR PUBLICATION

  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT


GREAT BASIN RESOURCE WATCH;               No. 14-16812
WESTERN SHOSHONE DEFENSE
PROJECT,                                    D.C. No.
             Plaintiffs-Appellants,      3:13-cv-00078-
                                            RCJ-VPC
                 v.

BUREAU OF LAND MANAGEMENT;                  OPINION
U.S. DEPARTMENT OF THE INTERIOR;
AMY LUEDERS, BLM State Director;
CHRISTOPHER J. COOK, BLM Mt.
Lewis Field Manager,
             Defendants-Appellees,

EUREKA MOLY, LLC,
    Intervenor-Defendant-Appellee.


      Appeal from the United States District Court
               for the District of Nevada
      Robert Clive Jones, District Judge, Presiding

        Argued and Submitted October 18, 2016
              San Francisco, California

               Filed December 28, 2016
2          GREAT BASIN RESOURCE WATCH V. BLM

    Before: Susan P. Graber and Mary H. Murguia, Circuit
        Judges, and Mark W. Bennett,* District Judge.

                     Opinion by Judge Graber


                            SUMMARY**


                        Environmental Law

    The panel affirmed in part, reversed in part, and vacated
in part the district court’s judgment, and remanded for further
proceedings in an action brought by plaintiffs challenging the
Bureau of Land Management’s approval of the Mt. Hope
Project, a proposed molybdenum mining operation near
Eureka, Nevada.

    Addressing plaintiffs’ challenge to several aspects of the
BLM’s analysis of the Project under the National
Environmental Policy Act, the panel held that the BLM’s
selection of baseline levels of certain air pollutants was
unreasonable, that the BLM’s analysis of cumulative air
impacts was deficient, that the BLM took the required “hard
look” at the potential impacts of poor pit-lake water quality
on ground water, and that the BLM’s discussion of long-term
mitigation and reclamation in the Final Environmental Impact
Statement was “reasonably complete.”


     *
     The Honorable Mark W. Bennett, United States District Judge for
the Northern District of Iowa, sitting by designation.
    **
       This summary constitutes no part of the opinion of the court. It has
been prepared by court staff for the convenience of the reader.
         GREAT BASIN RESOURCE WATCH V. BLM                     3

    The panel declined to address plaintiffs’ claim that the
BLM violated its duty to protect lands “withdrawn from
settlement, location, sale or entry” under Executive Order
Public Water Reserve No. 107 (Apr. 17, 1926). First, the
panel held that the BLM should be given an opportunity to fix
the errors in its analysis of the Project under NEPA before
challenges to the approval of the Project itself are entertained.
Second, the panel held that the proper analysis of the claim
turned in large part on whether four springs in the area of the
Project were “covered” by the Executive Order, but the
BLM’s position on that question was unclear. The panel
remanded for clarification.


                         COUNSEL

Roger Flynn (argued) and Jeffrey C. Parsons, Western
Mining Action Project, Lyons, Colorado; Julie Cavanaugh-
Bill, Cavanaugh-Bill Law Offices LLC, Elko, Nevada; for
Plaintiffs-Appellants.

Robert J. Lundman (argued) and Mark R. Haag; John C.
Cruden, Assistant Attorney General; Environment & Natural
Resources Division, United States Department of Justice,
Washington, D.C.; Luke Miller, Office of the Solicitor,
United States Department of the Interior, Washington, D.C.;
for Defendants-Appellees.

Francis M. Wilkstrom (argued), Salt Lake City, Utah, for
Intervenor-Defendant-Appellee.
4        GREAT BASIN RESOURCE WATCH V. BLM

                         OPINION

GRABER, Circuit Judge:

    Plaintiffs Great Basin Resource Watch and the Western
Shoshone Defense Project challenge Defendant Bureau of
Land Management’s (“BLM”) approval of the Mt. Hope
Project (“Project”), a proposed molybdenum mining
operation near Eureka, Nevada. Plaintiffs argue that the
BLM’s review of the Project under the National
Environmental Policy Act of 1969 (“NEPA”) was inadequate
and that the approval of the Project violated the Federal Land
Policy and Management Act of 1976 (“FLPMA”) and the
laws governing lands withdrawn under the executive order
known as Public Water Reserve No. 107 (“PWR 107”).
Because we conclude that the BLM’s environmental review
of the Project violated NEPA in several ways, we affirm in
part the district court’s judgment, reverse in part, vacate in
part, and remand for further proceedings.

                     BACKGROUND

A. The Mt. Hope Project

    The Mt. Hope Project “will be located in Eureka County,
Nevada approximately 23 miles northwest of the town of
Eureka . . . and will consist of a proposed molybdenum mine
including a power transmission line, a water well field, and
all associated facilities to be located on public land
administered by the BLM . . . and on private land controlled
by [Eureka Moly, LLC, the Project’s operator]. The Project
will utilize an open pit mining method and will process the
mined ore using a flotation and roasting process. A total of
8,355 acres of disturbance is proposed within the 22,886-acre
         GREAT BASIN RESOURCE WATCH V. BLM                   5

Project Area.” Bureau of Land Mgmt., U.S. Dep’t of Interior,
Mount Hope Project Record of Decision, Plan of Operations
Approval, and Approval of Issuance of Right-of-Way Grants,
p. i (Nov. 2012). Of those 22,886 acres, 22,608 are public
lands administered by the BLM. Id. at 6. “The 80-year
project will have an 18- to 24-month construction phase, 44
years of mining and ore processing, 30 years of reclamation,
and five years of post-closure monitoring. . . . Additionally,
long-term post-reclamation obligations will follow final
reclamation.” Id. at 1.

     The active mining phase of the Project will last 32 years,
during which time the mine will produce approximately 1.7
billion tons of waste rock. During that phase, pumps will be
used to extract water from the open mining pit; at the end of
the active mining phase, the pit will be allowed to fill slowly
with ground water, forming a mine-pit lake that is expected
to reach a depth of 900 feet. Pumping of ground water will
also take place in the Kobeh Valley, which is adjacent to Mt.
Hope, to provide fresh water for various mining and ore
extraction purposes.

B. Environmental Review of the Project

    Eureka Moly filed its first plan of operations for the
Project with the BLM in June 2006. The BLM determined
that approval of the Project was a “major Federal action”
under NEPA, 42 U.S.C. § 4332, and thus required the
preparation of an environmental impact statement (“EIS”).
The BLM released a draft EIS (“DEIS”) in December 2011.
After receiving nearly 2,000 comments on the DEIS, the
BLM prepared a final EIS (“FEIS”), which was released in
October 2012.
6        GREAT BASIN RESOURCE WATCH V. BLM

    Throughout the NEPA review process, Plaintiffs raised
concerns about several aspects of the Project. Many of those
concerns related to the adequacy of the BLM’s analysis of
environmental impacts in the DEIS and FEIS. In comments
on the DEIS, Plaintiffs criticized the BLM’s analysis of the
Project’s cumulative impacts, impacts to water quantity and
quality, and impacts to cultural, religious, and historical
resources. Plaintiffs renewed those criticisms in their
comments on the FEIS, and they offered fresh criticisms
concerning, among other things, the FEIS’ discussion of
funding for long-term mitigation and reclamation.

    In addition to criticizing the BLM’s analysis of
environmental impacts under NEPA, Plaintiffs expressed
their view to the BLM that approval of the Project would
violate the agency’s duties under the FLPMA and PWR 107.
In comments on both the DEIS and FEIS, Plaintiffs opined
that approval of the Project would violate FLPMA’s
requirement that the BLM “prevent unnecessary or undue
degradation of the lands” that it administers, 43 U.S.C.
§ 1732(b). Plaintiffs also pointed out that the Project would
affect some springs and water holes located on lands that they
claimed had been withdrawn by PWR 107.

    Plaintiffs were not alone in criticizing the BLM’s analysis
of the Project’s environmental effects. The Environmental
Protection Agency (“EPA”) reviewed the FEIS and found that
the BLM’s analyses of air impacts, water quantity impacts,
and the funding aspects of long-term mitigation were lacking.
Eureka County also criticized several aspects of the BLM’s
NEPA review, including the agency’s analysis of air impacts.
         GREAT BASIN RESOURCE WATCH V. BLM                   7

C. Approval of the Project

    In November 2012, a little more than a month after
releasing the FEIS, the BLM issued a record of decision
approving the Project. Plaintiffs petitioned for review of that
decision with the BLM’s State Director for Nevada, who
rejected the petition in January 2013. Plaintiffs then brought
this action in the district court under the Administrative
Procedure Act, alleging that the BLM’s review of the Project
under NEPA was deficient and that its approval of the Project
violated FLPMA and PWR 107. Soon after Plaintiffs filed
suit, the district court granted Eureka Moly leave to intervene
on the side of the BLM.

    The district court denied Plaintiffs’ motion for summary
judgment and granted the parties’ joint motion for entry of
judgment in favor of the BLM. Plaintiffs timely appeal from
that judgment.

                       DISCUSSION

A. NEPA Claim

    “A district court’s determination on summary judgment
that the BLM complied with NEPA is reviewed de novo.”
Klamath-Siskiyou Wildlands Ctr. v. BLM, 387 F.3d 989, 992
(9th Cir. 2004) (internal quotation marks omitted). “The
agency’s actions, findings, and conclusions will be set aside
if they are arbitrary, capricious, an abuse of discretion, or
otherwise not in accordance with law.” Id. (internal quotation
marks omitted).

   NEPA “is a procedural statute that requires . . . Federal
agencies to assess the environmental consequences of their
8        GREAT BASIN RESOURCE WATCH V. BLM

actions before those actions are undertaken.” Id. at 993. “For
major federal actions significantly affecting the quality of the
human environment, the agency is required to prepare an
[EIS]. An EIS is a thorough analysis of the potential
environmental impacts that provides full and fair discussion
of significant environmental impacts and informs
decisionmakers and the public of the reasonable alternatives
which would avoid or minimize adverse impacts or enhance
the quality of the human environment.” Id. (citations,
internal quotation marks, and alterations omitted).

    “[I]n reviewing the adequacy of an EIS, this circuit
employs a ‘rule of reason’ that asks whether an EIS contains
a reasonably thorough discussion of the significant aspects of
the probable environmental consequences. Under this
standard, once satisfied that a proposing agency has taken a
‘hard look’ at a decision’s environmental consequences, the
review is at an end.” Or. Nat. Res. Council v. Lowe, 109 F.3d
521, 526 (9th Cir. 1997) (per curiam) (citations, internal
quotation marks, and alterations omitted).

    Plaintiffs challenge several aspects of the NEPA analysis.
They assert that the BLM’s selection of baseline levels of
certain air pollutants was unreasonable and that the BLM’s
analysis of cumulative impacts was deficient. As we will
explain below, we agree. Plaintiffs also challenge the
adequacy of the BLM’s consideration of various mitigation
measures. With respect to those arguments, we either are not
persuaded or need not reach the issues.

    1. Air Pollution Baselines

   Plaintiffs first argue that the BLM did not assess
adequately the baseline levels of certain air pollutants when
         GREAT BASIN RESOURCE WATCH V. BLM                   9

conducting the air impacts analysis. Establishing appropriate
baseline conditions is critical to any NEPA analysis.
“Without establishing the baseline conditions which exist . . .
before [a project] begins, there is simply no way to determine
what effect the [project] will have on the environment and,
consequently, no way to comply with NEPA.” Half Moon
Bay Fishermans’ Mktg. Ass’n v. Carlucci, 857 F.2d 505, 510
(9th Cir. 1988). An agency need not conduct measurements
of actual baseline conditions in every situation—it may
estimate baseline conditions using data from a similar area,
computer modeling, or some other reasonable method. See
Or. Nat. Desert Ass’n v. Jewell, 840 F.3d 562, 570 (9th Cir.
2016) (holding that it would not necessarily be impermissible
for the BLM to estimate baseline conditions in one area by
extrapolating from another area). But whatever method the
agency uses, its assessment of baseline conditions “must be
based on accurate information and defensible reasoning.” Id.

    When determining baseline air pollution levels for the
Project, the BLM did not use actual measurements from the
Project site because none were available. In the DEIS, the
BLM used baseline values taken from measurements in Clark
County, Nevada—the county in which Las Vegas is
located—for some pollutants, and used the “default values”
for unmonitored rural areas suggested by the Nevada
Department of Environmental Protection’s (“NDEP”) Bureau
of Air Pollution Control for some other pollutants. The DEIS
noted that the baseline numbers drawn from the Clark County
measurements were “conservatively high” given the relatively
urban character of the monitoring locations.
10         GREAT BASIN RESOURCE WATCH V. BLM

    In preparing the FEIS, the BLM instructed Eureka Moly1
“to follow NDEP’s guidance in selecting the background
concentrations for the air quality analysis.” A permitting
supervisor from the NDEP’s Bureau of Air Pollution Control
had previously advised (by means of a short email) that the
agency “assumed” a baseline of zero for all pollutants other
than 10-micron particulate matter, and the FEIS adopts most
of those baseline values in place of the “conservatively high”
baseline values used in the DEIS. Specifically, the FEIS uses
baseline values of zero for carbon monoxide, nitrogen
dioxide, one- and three-hour time-averaged sulfur dioxide,
and lead, while the DEIS had used measured values from
Clark County for those pollutants. The FEIS continues to use
the same Clark County data for the two longest time-averaged
sulfur dioxide baselines, and it uses measurements taken at
Great Basin National Park2 for 2.5-micron particulate matter
baselines.

    Plaintiffs first argue that it was unreasonable for the BLM
to use data from Great Basin National Park, a pristine area
more than 100 miles away from the Project, to establish
baselines for 2.5-micron particulate matter. Although it is
true that this choice may have caused the agency to
underestimate the baselines for 2.5-micron particulate matter,
the BLM explained its choice adequately, and its explanation
is reasonable. The Project is located in a rural area, and the
BLM used data from a different rural area to estimate


     1
      Eureka Moly contracted with an air quality consulting firm, Air
Sciences, Inc., to conduct the air impacts analysis. That analysis, in turn,
was submitted to the BLM, which relied on it when preparing the FEIS.
    2
      The FEIS cites a different NDEP official as the source of the
baseline values for 2.5-micron particulate matter concentrations.
         GREAT BASIN RESOURCE WATCH V. BLM                   11

baseline conditions. Plaintiffs have not shown that this
choice rested on inaccurate information or indefensible
reasoning. Or. Nat. Desert Ass’n, 840 F.3d at 570.

    Plaintiffs’ arguments concerning the baseline choices for
10-micron particulate matter and the two longest time-
averaged sulfur dioxide concentrations are similarly
unconvincing. Like the baselines for 2.5-micron particulate
matter, the baselines for 10-micron particulate matter relied
on measurements taken at Great Basin National Park. The
baselines for the two sulfur dioxide concentrations were
“conservatively high,” as the BLM noted in the DEIS. By
acknowledging the shortcomings in its data while using those
data to make an estimate of baseline conditions, the BLM
complied with NEPA. See Lands Council v. Powell, 395 F.3d
1019, 1032 (9th Cir. 2005) (noting that “NEPA . . . requires
up-front disclosures of relevant shortcomings in the data or
models”).

    Finally, Plaintiffs argue that the BLM’s use of a zero
baseline value for the remaining pollutants was unreasonable.
The BLM and Eureka Moly respond that the choice of a zero
baseline for those pollutants was reasonable because it was
“based on recommendations from the [NDEP’s Bureau of Air
Pollution Control], the agency with Nevada-specific
expertise.” The FEIS similarly invokes the expertise of the
NDEP’s Bureau of Air Pollution Control (“BAPC”),
prefacing the table of baseline values with the note that “[t]he
BAPC was contacted to obtain representative background
concentrations for the modeling analysis.” And the air
impacts analysis prepared for Eureka Moly and submitted to
the BLM—the study that underlies the FEIS’ air impacts
analysis—also notes that the “NDEP-BAPC recommends
assuming zero background for” the remaining pollutants.
12         GREAT BASIN RESOURCE WATCH V. BLM

    It turns out, though, that the only “expert
recommendation” in the record is a short email from an
NDEP official—the email is, in fact, cited in the FEIS as the
sole source of the zero baseline value. That email reads, in
relevant part, as follows:

         In an un-monitored area, BAPC uses 10.2
         ìg/m^3 for a 24-hour average background and
         9.0 ìg/m^3 for an annual average background
         for PM10. All other pollutants are assumed
         to be 0. If there is on-going quality assured
         monitoring representative of an area, we can
         rely on that data to set a different background.
         I’m not aware of any monitoring being
         performed by BAPC in the area you propose.

(Emphasis added.) Crucially, this email does not explain how
or why the NDEP arrived at zero. Such a bare assertion of
opinion3 coming from an expert within the BLM, without any
supporting reasoning, would not pass muster in an EIS. See
Idaho Sporting Cong. v. Thomas, 137 F.3d 1146, 1150 (9th
Cir. 1998) (“NEPA requires that the public receive the
underlying environmental data from which a [reviewing
agency] expert derived her opinion.”), overruled on other
grounds by Lands Council v. McNair, 537 F.3d 981 (9th Cir.
2008) (en banc); see also Tri-Valley Cares v. U.S. Dep’t of

     3
      What value to use as a baseline concentration for a particular air
pollutant, in the absence of data, is a question of expert judgment, not one
of fact. There is no doubt that the baseline pollutant levels are not, as a
factual matter, zero; the question is what to use as an estimate of baseline
levels for purposes of modeling. In fact, the email to the NDEP official
asked for “some guidance on what background concentration values . . .
to use for a modeling analysis in [the] Mount Hope area.” (Emphasis
added.)
         GREAT BASIN RESOURCE WATCH V. BLM                   13

Energy, 671 F.3d 1113, 1124 (9th Cir. 2012) (“At a
minimum, an agency must support its conclusions with
studies that the agency deems reliable.”). The fact that it
comes from an expert at a state agency is of no significance
to the analysis. Cf. Nat. Res. Def. Council, Inc. v. Herrington,
768 F.2d 1355, 1412–14 (D.C. Cir. 1985) (“[I]n a rulemaking
which must be supported by substantial evidence, [an agency]
may not rely without further explanation on an unelaborated
order from another agency. Neither we as a reviewing court
nor participants in the rulemaking can possibly discover the
substantive basis of [the second agency’s] edict.”).

    We might reach a different conclusion had the NDEP
official explained why an estimate of zero was appropriate, or
had the BLM independently scrutinized that estimate and
decided that it was reasonable, and then explained why. But
none of that happened—the BLM simply used baseline
estimates of zero for some pollutants in reliance on one
conclusory sentence in an email from an NDEP official, an
email that itself contained no supporting reasoning. This
important information, which affects the air impacts analysis,
was essentially immune from meaningful scrutiny by the
public because the BLM never provided any data or
reasoning in support of it. A baseline estimate “must be
based on accurate information and defensible reasoning.” Or.
Nat. Desert Ass’n, 840 F.3d at 570. The BLM provided
neither when it came to its baseline estimates of zero.

    Eureka Moly argues that the FEIS’ air impacts analysis is
nonetheless adequate because it relies in part on the fact that
the NDEP’s Bureau of Air Pollution Control issued a Clean
Air Act permit for the Project. This argument evinces a
misunderstanding of the nature of NEPA and its relationship
to “substantive” environmental laws such as the Clean Air
14       GREAT BASIN RESOURCE WATCH V. BLM

Act. See S. Fork Band Council of W. Shoshone of Nev. v.
U.S. Dep’t of Interior, 588 F.3d 718, 726 (9th Cir. 2009) (per
curiam) (holding that a failure to discuss mercury emissions
from a nearby mining facility in an EIS was not excused by
the fact that the facility “operate[d] pursuant to a state permit
under the Clean Air Act,” because “[a] non-NEPA document
. . . cannot satisfy a federal agency’s obligations under
NEPA”). The failure to explain the zero baseline assumption
frustrated the BLM’s ability to take a “hard look” at air
impacts, and the reference to the Project’s Clean Air Act
permit did nothing to fix that error.

    The BLM argues that it corrected any error in its baseline
estimates by conducting a “double check” analysis following
the issuance of the FEIS. The BLM conducted this analysis
using measured baseline values from an undeveloped area in
New Mexico that EPA had suggested might have similar air
quality to the Project area. The BLM claims that those
measurements confirm that the pollution from the Project
would not violate air quality standards. Although that
statement may end up being true, a post-EIS
analysis—conducted without any input from the public—
cannot cure deficiencies in an EIS. Ctr. for Biological
Diversity v. U.S. Forest Serv., 349 F.3d 1157, 1169 (9th Cir.
2003). The public never had an opportunity to comment on
the “double check” analysis, frustrating NEPA’s goal of
allowing the public the opportunity to “play a role in . . . the
decisionmaking process.” Robertson v. Methow Valley
Citizens Council, 490 U.S. 332, 349 (1989).

    In conclusion, we hold that the BLM’s analysis of air
impacts in the FEIS was inadequate because the agency did
not provide any support for its use of baseline values of zero
for several air pollutants.
         GREAT BASIN RESOURCE WATCH V. BLM                   15

   2. Cumulative Impacts

    Plaintiffs next argue that the BLM’s analysis of
cumulative impacts was deficient. Plaintiffs point out that,
although the FEIS mentions that there will be cumulative
impacts stemming from the Project and nearby mining,
agricultural, and other activities, “there is no detailed
discussion about the . . . impacts,” nor is there a “quantified
assessment” of those impacts.

    The cumulative impact from an action means “the impact
on the environment which results from the incremental
impact of the action when added to other past, present, and
reasonably foreseeable future actions . . . . Cumulative
impacts can result from individually minor but collectively
significant actions taking place over a period of time.”
40 C.F.R. § 1508.7. Accordingly, “[i]n a cumulative impact
analysis, an agency must take a ‘hard look’ at all actions” that
may combine with the action under consideration to affect the
environment. Te-Moak Tribe of W. Shoshone of Nev. v. U.S.
Dep’t of Interior, 608 F.3d 592, 603 (9th Cir. 2010)
(emphasis added). Furthermore, simply listing all relevant
actions is not sufficient. Rather, “some quantified or detailed
information is required. Without such information, neither
the courts nor the public . . . can be assured that the [agency]
provided the hard look that it is required to provide.”
Neighbors of Cuddy Mountain v. U.S. Forest Serv., 137 F.3d
1372, 1379 (9th Cir. 1998).

    The BLM completed the first step of the cumulative
impacts analysis by identifying the relevant “past, present,
and reasonably foreseeable future actions,” 40 C.F.R.
§ 1508.7, that might affect the environment in the area of the
Project. And the BLM provided a “useful analysis of the
16       GREAT BASIN RESOURCE WATCH V. BLM

cumulative impacts” of those actions on some environmental
resources. Klamath-Siskiyou Wildlands Ctr., 387 F.3d at 994
(internal quotation marks citation omitted). For instance, the
FEIS includes a relatively thorough discussion of cumulative
impacts to water quantity, complete with a quantitative
analysis.

    However, the discussion of cumulative impacts to other
resources in the FEIS falls short. In particular, the discussion
of cumulative air impacts is insufficient. That discussion
reads, in relevant part, as follows:

            Each of the identified individual projects
        within the [study area], including existing and
        proposed mining operations, emit air
        pollutants. With the possible exception of
        motor vehicle emissions, the existing and
        proposed mining operations are the major
        sources of criteria pollutants within the [study
        area]. The modeling for the Proposed Action,
        as well as the Ruby Hill Mine . . . , shows that
        the levels of these pollutants are below the
        applicable standards. The Proposed Action
        would not result in a significant cumulative
        impact to air resources. The [reasonably
        foreseeable future actions] would result in
        additional emissions similar to those currently
        emitted by the existing operations within the
        [study area]. In addition, the major sources of
        pollutants (except for motor vehicle
        emissions) within the [study area] would
        operate under permit conditions established
        by the [NDEP BAPC] and therefore would not
        be significant.
           GREAT BASIN RESOURCE WATCH V. BLM                             17

    That analysis suffers from many of the same
shortcomings as the BLM’s analysis in Great Basin Mine
Watch v. Hankins, 456 F.3d 955 (9th Cir. 2006). There, we
faulted the BLM for failing to include “mine-specific or
cumulative data” in its analysis of cumulative impacts to air
resources. Id. at 973. The BLM had “merely stat[ed] that
ambient air quality data for the region currently reflects
impacts of existing mining operations in the airshed,” but did
not “identify and discuss the impacts that will be caused by
each successive project, including how the combination of
those various impacts is expected to affect the environment.”
Id. at 973–74 (internal quotation marks and alterations
omitted). For that reason, we held that the FEIS was
insufficient. Id. at 972–73. Similarly, the BLM in this case
did not provide sufficiently detailed information in its
cumulative air impacts analysis. The BLM made no attempt
to quantify the cumulative air impacts of the Project together
with the Ruby Hill Mine and vehicle emissions. Nor did the
BLM attempt to quantify or discuss in any detail the effects
of other activities, such as oil and gas development, that are
identified elsewhere in the FEIS as potentially affecting air
resources.

    The cumulative air impacts analysis also suffers from the
same problem that plagued the air impacts analysis—namely,
the choice of a baseline value of zero for certain pollutants.
It was impossible for the BLM to take a “hard look” at
cumulative air impacts given its unjustified use of a zero
baseline for those pollutants.4



    4
      Counsel for the BLM conceded during oral argument that if we were
to conclude that the assumption of a zero baseline for several air pollutants
rendered the air impacts analysis deficient, we would necessarily have to
18        GREAT BASIN RESOURCE WATCH V. BLM

     The BLM and Eureka Moly argue that the air impacts
analysis contained elsewhere in the FEIS suffices because
that other analysis takes into account existing emissions. But,
as already discussed, the modeling assumed baseline values
of zero for many pollutants and, therefore, the analysis
plainly does not take into account emissions from other
sources in the area. The BLM and Eureka Moly also argue
that the reference in the FEIS to the cumulative air impacts
analysis conducted in connection with the Ruby Hill
Mine—an unrelated mining project—renders the cumulative
air impacts analysis in this FEIS adequate. But the analysis
of the Ruby Hill Mine did not consider the Mt. Hope Project,
so its cumulative impacts analysis is of very limited
relevance.

    The cumulative air impacts portion of the FEIS fails to
“enumerate the environmental effects of [other] projects” or
“consider the interaction of multiple activities.” Or. Nat. Res.
Council Fund v. Brong, 492 F.3d 1120, 1133 (9th Cir. 2007).
Accordingly, we hold that the cumulative impacts portion of
the FEIS does not comply with NEPA.

     3. Mitigation: Mine-Pit Lake

    Plaintiffs’ next argument concerns the FEIS’ discussion
of the lake that will eventually form in the mining pit.
Plaintiffs argue that the BLM violated NEPA by failing to
consider mitigation measures aimed at reducing the possible
adverse environmental effects of poor pit-lake water quality.
Under NEPA, “an agency must . . . consider appropriate
mitigation measures that would reduce the environmental


conclude that the cumulative air impacts analysis suffered from the same
deficiency.
         GREAT BASIN RESOURCE WATCH V. BLM                   19

impact of the proposed action.” Protect Our Cmtys. Found.
v. Jewell, 825 F.3d 571, 581 (9th Cir. 2016). When reviewing
an agency’s discussion of mitigation measures, “[w]e need
only be satisfied that the agency took the requisite ‘hard look’
at the possible mitigating measures.” Okanogan Highlands
All. v. Williams, 236 F.3d 468, 473 (9th Cir. 2000).

    The FEIS states that “[i]nitial pit lake water quality is
predicted to be good” but that, “[a]s evaporation from the
lake surface concentrates the dissolved minerals, some water
quality constituent concentrations would be predicted to
increase over time relative to baseline concentrations and to
exceed the present Nevada water quality standards.” The
FEIS further predicts that “[t]here would be a low potential
for impacts to ground water quality due to the formation of a
ground water sink in the open pit,” but that the impact is “not
considered significant.” The FEIS states that “[a]ccess to the
open pit by humans and livestock would be restricted” and
that “[t]he lake is not intended to be a drinking water source
for humans or livestock or to be used for recreational
purposes.” Plaintiffs claim that the BLM failed to consider
any mitigation measures to address the potential effects of
poor pit-lake water quality. They argue that this omission is
problematic for two reasons: (1) the FEIS states that there is
a “low potential” for impacts to ground water quality, rather
than “no potential” for impacts, and (2) the pit-lake water
may at some point be needed by “future water users” in the
area.

    We hold that the BLM complied with NEPA in discussing
possible mitigation measures to address the effects that would
flow from poor pit-lake water quality. Although the BLM did
not include any discussion of possible mitigation measures in
the portion of the FEIS discussing pit-lake water quality,
20        GREAT BASIN RESOURCE WATCH V. BLM

other portions of the FEIS contain discussions of such
measures. The listing of “applicant committed practices”—
measures that Eureka Moly has promised to take and that are
“considered part of the operating procedures” of the
Project—states that the company will “periodically review
and update . . . pit lake studies to incorporate new information
accumulated during operations. . . . These updates would . . .
provide quantitative predictions of water quality during the
operational and post-closure period.” Additionally, the
agency responded to a comment on the DEIS5 by noting that
it would rely on future monitoring “to further understand the
ground water and surface water hydraulics and any potential
impacts to waters of the State. Based on further monitoring
and evaluation, additional mitigation measures . . . can be
implemented at any time . . . .”

    This sort of “wait and see” approach to mitigation does
not always suffice under NEPA. Putting off an analysis of
possible mitigation measures until after a project has been
approved, and after adverse environmental impacts have
started to occur, runs counter to NEPA’s goal of ensuring
informed agency decisionmaking. See Robertson, 490 U.S.
at 353 (“Without [a reasonably complete] discussion [of
mitigation], neither the agency nor other interested groups
and individuals can properly evaluate the severity of the
adverse effects.”). But that approach was reasonable in the
circumstances given the relatively low probability and
temporal remoteness of adverse impacts to ground water.
And though the BLM did not consider any mitigation
measures for the potential impact of poor pit-lake water
quality on “future water users,” it was not required to do so,

     5
       The comments on the DEIS and the BLM’s responses thereto are
included as appendices to the FEIS.
         GREAT BASIN RESOURCE WATCH V. BLM                    21

because the existence of any such users is speculative. See
San Luis Obispo Mothers for Peace v. Nuclear Regulatory
Comm’n, 449 F.3d 1016, 1030 (9th Cir. 2006) (“[A]n impact
statement need not discuss remote and highly speculative
consequences.”) (internal quotation marks omitted).

     To be sure, the BLM’s mitigation analysis in this case
was not as thorough as that of the agency in Okanogan
Highlands. In that case, the Forest Service prepared an EIS
for a mining project that would produce a mine-pit lake much
like the one here. Okanogan Highlands, 236 F.3d at 471.
The agency concluded in the EIS that “seepage from the open
pit is expected to have a low overall impact on ground water
quality in the vicinity of the pit,” but it nonetheless discussed
several mitigation measures, including monitoring. Id. at
474–75. We held that the agency had complied with NEPA
by considering “extensively the potential effects and
mitigation processes.” Id. at 477.

    In this case, by contrast, the BLM discussed only
monitoring. But the disparity in the scope and depth of the
agencies’ discussions in the two cases reflects important
differences between the projects being analyzed, rather than
a difference in the adequacy of the agencies’ analyses. The
mining project in Okanogan Highlands was set to last eight
to ten years, id. at 471, and the pit lake was expected to
overflow and discharge water that would exceed pollution
standards, id. at 474. Here, by contrast, the pit lake will fill
slowly, and will not begin to fill at all until after the end of
open pit mining, some 32 years after the start of the Project.
Furthermore, the water quality in the pit lake is expected to be
good at first. Faced with an adverse impact that is predicted
to be insignificant and that will not occur for decades, the
22        GREAT BASIN RESOURCE WATCH V. BLM

BLM in this case reasonably decided to rely on a monitoring
scheme to develop future mitigation measures.

   In short, we are satisfied that the BLM complied with
NEPA by taking a “hard look” at the potential impacts of
poor pit-lake water quality on ground water.

     4. Mitigation: Reclamation Bonding

    Plaintiffs argue that the BLM’s NEPA review was
deficient because the agency “never reviewed the
consideration or establishment of [financial guarantees] under
NEPA.” Plaintiffs argue that this failure rendered the
discussion of mitigation in the FEIS inadequate and prevented
the public from providing input into the reclamation bonding
process. The BLM and Eureka Moly respond that (1) NEPA
does not require that “third parties should be able to
participate in the process of determining financial
guarantees,” and (2) in any event, the FEIS contains an
adequate discussion of financial guarantees.

    The BLM’s regulations require that an operator who files
a plan of operations must, “[a]t a time specified by BLM, . . .
submit an estimate of the cost to fully reclaim [its]
operations.” 43 C.F.R. § 3809.401(d).6 Although the “time




     6
      Reclamation means taking measures . . . following disturbance of
public lands caused by operations to meet applicable performance
standards and achieve conditions required by BLM at the conclusion of
operations. . . . Components of reclamation include, where applicable:

         (1) Isolation, control, or removal of acid-forming, toxic,
         or deleterious substances;
           GREAT BASIN RESOURCE WATCH V. BLM                          23

specified by BLM” need not be the same as the time at which
the plan of operations is filed, the estimate must be submitted
and accepted before operations can begin, because “a
financial guarantee that meets the requirements of this
subpart [must be provided] before starting operations.” Id.
§ 3809.500. The regulations instruct operators to “estimate
the cost to reclaim your operations as if BLM were hiring a
third-party contractor to perform reclamation of your
operations after you have vacated the project area.” Id.
§ 3809.554(a).7 The financial guarantee provided by the
operator must cover this estimated cost. Id. § 3809.552(a).
In addition, the BLM may require “a trust fund or other



         (2) Regrading and reshaping to conform with adjacent
         landforms, facilitate revegetation, control drainage, and
         minimize erosion;

         (3) Rehabilitation of fisheries or wildlife habitat;

         (4) Placement of growth medium and establishment of
         self-sustaining revegetation;

         (5) Removal or stabilization of buildings, structures, or
         other support facilities;

         (6) Plugging of drill holes and closure of underground
         workings; and

         (7) Providing for post-mining monitoring, maintenance,
         or treatment.

43 C.F.R. § 3809.5.
    7
      The requirements of 43 C.F.R. § 3809.552 and 3809.554 apply to
operators, like Eureka Moly, that plan to use an individual financial
guarantee, rather than a “blanket” guarantee covering multiple operations,
§ 3809.560, or a pre-existing state-approved guarantee, § 3809.570.
24       GREAT BASIN RESOURCE WATCH V. BLM

funding mechanism . . . to ensure the continuation of long-
term treatment to achieve water quality standards and for
other long term, post-mining maintenance requirements. The
funding must be adequate to provide for construction, long-
term operation, maintenance, or replacement of any treatment
facilities and infrastructure, for as long as the treatment and
facilities are needed after mine closure. BLM may identify
the need for a trust fund or other funding mechanism during
plan review or later.” Id. § 3809.552(c).

    The BLM and Eureka Moly assert that the details of a
long-term funding mechanism and the amount of a financial
guarantee (also called a “reclamation bond”) need not be
discussed in an EIS because they are “regulatory
requirement[s] . . . driven by the NEPA-reviewed reclamation
plan.” For support, they cite the BLM Surface Management
Manual, which states that “[a]ny decision concerning the
need, amount, acceptability, and/or forfeiture of a financial
guarantee . . . do[es] not require an environmental review
under NEPA and [is] not to be included in NEPA documents
used to review a proposed operation.” BLM Surface
Management Manual at 2–6 (2012). They also cite our
decision in Center for Biological Diversity v. Salazar, 706
F.3d 1085, 1096 (9th Cir. 2013), for the proposition that
setting an amount for a financial guarantee does not trigger
NEPA requirements.

    Salazar does not support the position taken by the BLM
and Eureka Moly. In Salazar, we held that the BLM’s
approval of an update to an operator’s financial guarantee
was not a “major Federal action” for NEPA purposes where
the reclamation plan being funded by the guarantee had
already been approved and was not itself being changed. Id.
at 1095–96. We characterized the BLM’s action as consisting
         GREAT BASIN RESOURCE WATCH V. BLM                  25

of “the ministerial tasks of feeding reclamation data from the
[reclamation] plan into [a] software program, comparing [the]
estimate [from that program] with that of [the operator], and
then accepting [the operator’s] proposed bond amount, which
was greater than” the estimate. Id. at 1096. We held that
“[s]uch post-project-approval functions are the type of
monitoring and compliance activities that . . . do not trigger
NEPA’s requirements.” Id.

    For two reasons, this case differs from Salazar. First, the
reclamation plan here is in the process of being approved, and
determining the contours of the financial guarantee
(particularly the long-term funding mechanism) at this stage
is not a mere “ministerial task.” Second, Plaintiffs’ legal
theory for why NEPA requires a discussion of reclamation
funding differs from that advanced by the plaintiffs in
Salazar. In Salazar, the plaintiffs argued that the update to
the reclamation bond was a “major Federal action” requiring
the preparation of an EIS. Id. at 1095. By contrast,
Plaintiffs’ argument is that the approval of a plan of
operations requires an EIS; the EIS should discuss possible
reclamation and post-closure mitigation measures; and a
reasonably complete discussion of those measures requires
some discussion of the long-term funding mechanism and
reclamation bond.

    We need not address any further the broad argument that
reclamation bonding need never be discussed in NEPA
documents. We assume, without deciding, that long-term
mitigation and reclamation funding issues must be “discussed
in sufficient detail to ensure that environmental consequences
have been fairly evaluated.” Robertson, 490 U.S. at 352.
Making that assumption, we hold that the FEIS contains an
adequate discussion of those issues.
26       GREAT BASIN RESOURCE WATCH V. BLM

     The FEIS discusses several specific long-term mitigation
measures that the long-term funding mechanism may fund.
It also states that the funding mechanism “would be reviewed
annually during the operation phase of the Project and
potentially increased to meet the monitoring and mitigation
needs associated with the Project.” Elsewhere, the FEIS
discusses some of the long-term mitigation measures in more
detail. For instance, the FEIS considers, in several places, the
use of evapotranspiration cells to control long-term discharge
from mining waste.

    The FEIS also contains a relatively thorough discussion
of possible reclamation measures, complete with a proposed
timeline. As for the reclamation bond, the FEIS states that,
“[w]ithin three years following Plan approval and at least
every three subsequent years, [Eureka Moly] would update
the guarantee to reflect the actual disturbance and whatever
additional disturbance is planned for the Project phase
anticipated over the next three-year period. Changes to
equipment, consumables, and man power costs would also be
incorporated during the updates.”

    The BLM’s discussion of long-term mitigation and
reclamation in the FEIS is “reasonably complete” and does
not violate NEPA. Although the BLM could have discussed
its options vis-à-vis the long-term funding mechanism and
reclamation bond in more detail, its discussion of those
aspects of the long-term mitigation and reclamation plans is
not so deficient as to preclude the agency or the public from
“properly evaluat[ing] the severity of [the Project’s] adverse
effects” on the environment. Robertson, 490 U.S. at 352.
And the reclamation and long-term mitigation discussion,
taken as a whole, contains an adequate evaluation of the
effectiveness of possible reclamation and long-term
         GREAT BASIN RESOURCE WATCH V. BLM                 27

mitigation measures despite the relatively sparse treatment of
the funding aspects of those measures. See S. Fork Band
Council, 588 F.3d at 727 (“An essential component of a
reasonably complete mitigation discussion is an assessment
of whether the proposed mitigation measures can be
effective.”).

   5. Mitigation: Surface and Ground Water Quantity

    Plaintiffs next challenge the adequacy of the BLM’s
discussion of mitigation measures to address impacts to
surface and ground water quantity. The Project will require
a great deal of water to support mining and milling
operations. This water will come from two sources: ground
water pumped out of wells located in one of the valleys
surrounding Mt. Hope and water pumped from the open
mining pit. The predicted effects of the pumping on certain
stream and spring flows—unlike the predicted effect of the
pit lake on ground-water quality—are “potentially
significant.”

    The FEIS discusses several mitigation measures aimed at
addressing those impacts, including a monitoring scheme to
keep track of the status of spring and stream segments, water
hauling, and piping in water from other locations to replace
lost surface water. In non-technical—but accurate—terms,
many of the mitigation measures amount to measuring how
much each spring or stream segment’s flow has been reduced
and replacing that water. The replacement water—which the
BLM estimates at about 302 acre-feet of water, or nearly 100
million gallons, per year—“would at least initially come from
[Eureka Moly]’s existing water rights if additional water
rights have not yet been secured.”
28         GREAT BASIN RESOURCE WATCH V. BLM

    Plaintiffs contend that the discussion of mitigation
measures is inadequate because “there is no analysis of where
th[e] [replacement] water will come from, or the impacts
from its withdrawal.”8 Plaintiffs note that EPA criticized the
BLM for this omission during the NEPA process and asked
the BLM to prepare a supplemental EIS. Eureka Moly
responds that “the FEIS thoroughly analyzed the effect of
using water from [its] production wells, [so] the effect of
using some of it as substitute water was necessarily analyzed
because it is the same water.”

    Although Eureka Moly’s argument is factually
incorrect—the analysis of ground water pumping in the FEIS
does not take into account the roughly 200 gallons per minute
needed to replace depleted spring and stream water—that
error appears to be quite small, raising questions about
whether it might be harmless.9 See Idaho Wool Growers
Ass’n v. Vilsack, 816 F.3d 1095, 1104 (9th Cir. 2016) (“The
harmless-error analysis asks whether the [agency’s error]
materially impeded NEPA’s goals—that is, whether the error
caused the agency not to be fully aware of the environmental
consequences of the proposed action, thereby precluding
informed decisionmaking and public participation, or
otherwise materially affected the substance of the agency’s


    8
      Plaintiffs also appear to argue that the discussion of mitigation
measures is deficient because it puts off the development of a mitigation
plan until after monitoring reveals depletion. This argument is factually
incorrect—the FEIS includes a map showing the future location of
pipelines that could be used to bring water to depleted springs.
     9
      The analysis in the FEIS assumes a ground water pumping rate of
between 6,540 and 7,000 gallons per minute, so failing to include the
additional 200 gallons per minute needed to replace spring and stream
flows amounts to a roughly 3% error.
             GREAT BASIN RESOURCE WATCH V. BLM                       29

decision.”). But no party has briefed the issue of
harmlessness. And because the BLM’s NEPA analysis is
deficient in other respects, the ultimate disposition of this
appeal does not depend on the resolution of this portion of
Plaintiffs’ NEPA claim. Accordingly, we decline to reach
this portion of Plaintiffs’ NEPA claim.

B. PWR 107 Claim

    Plaintiffs’ other major claim is that the BLM violated its
duty to protect lands “withdrawn from settlement, location,
sale or entry” under the executive order known as PWR 107,
Public Water Reserve No. 107 (Apr. 17, 1926). Plaintiffs
also argue that PWR 107, which withdrew lands surrounding
certain springs and water holes, created an implied
reservation of water rights to the federal government in some
springs in the area of the Project, and that the Project will
unlawfully interfere with those water rights.

    We decline to address Plaintiffs’ PWR 107 claim, for two
reasons. First, the BLM should be given an opportunity to fix
the errors in its analysis of the Project under NEPA before
challenges to the approval of the Project itself are entertained.
“Having addressed the problems [with the EIS], the BLM
may decide to make different choices. NEPA is not a paper
exercise, and new analyses may point in new directions. . . .
The problems [with the approval of the Project itself] may
never arise once the BLM has had a chance to see the choices
before it with fresh eyes.” Or. Nat. Desert Ass’n v. BLM,
625 F.3d 1092, 1124 (9th Cir. 2010).10



    10
         For this reason, we also decline to address Great Basin’s FLPMA
claim.
30         GREAT BASIN RESOURCE WATCH V. BLM

    Second, the proper analysis of the PWR 107 claim turns
in large part on whether four springs11 in the area of the
Project are “covered” by PWR 107—that is, whether those
four springs are located on lands that were withdrawn by
PWR 107—but the BLM’s position on that question is
unclear.12 Prudence counsels in favor of remanding to the
agency to clarify its position, rather than addressing legal
questions that may end up being irrelevant to the disposition
of the claim. Cf. Su Hwa She v. Holder, 629 F.3d 958,
963–64 (9th Cir. 2010) (“[W]e lack the clairvoyance
necessary to confidently infer the reasoning behind the
[agency]’s conclusion. Rather than countenance a decision
that leaves us to speculate based on an incomplete analysis,
we remand the case to the [agency] for clarification.”
(footnote omitted)).



     11
      The springs at issue are McBride’s Spring, also referred to as SP-1
or Spring 612; Mt. Hope Spring, also referred to as SP-4 or Spring 619;
Garden Spring, also referred to as SP-2 or Spring 597; and Lone Mountain
Spring, also referred to as Spring 742.
     12
       The FEIS is internally contradictory, suggesting in some places that
the four springs are covered by PWR 107 and in other places that they are
not. We note that the BLM had previously submitted “Notification of
Public Water Reserve” forms for the four springs to the State of Nevada.
Each of those forms lists an amount of water that the United States wishes
to claim as a federal reserved water right and cites PWR 107 as authority
for the reservation. The notifications have never been rescinded. If, on
remand, the BLM decides that the springs are not important, it should at
the very least explain why it has apparently changed its position. Cf.
Encino Motorcars, LLC v. Navarro, 136 S. Ct. 2117, 2126 (2016) (“[A]n
‘unexplained inconsistency’ in agency policy is ‘a reason for holding an
interpretation to be an arbitrary and capricious change from agency
practice.’” (brackets omitted) (quoting Nat’l Cable & Telecomms. Ass’n
v. Brand X Internet Servs., 545 U.S. 967, 981 (2005))).
        GREAT BASIN RESOURCE WATCH V. BLM               31

    AFFIRMED in part, REVERSED in part, VACATED
in part, and REMANDED with instructions to vacate the
record of decision and remand to the BLM. The parties shall
bear their own costs on appeal.