                United States Court of Appeals
                           For the Eighth Circuit
                       ___________________________

                               No. 13-1936
                       ___________________________

                         El Dorado Chemical Company

                      lllllllllllllllllllll Plaintiff - Appellant

                                          v.

United States Environmental Protection Agency; Gina McCarthy,1 Administrator,
     United States Environmental Protection Agency; Ron Curry,2 Regional
    Administrator, United States Environmental Protection Agency Region 6

                     lllllllllllllllllllll Defendants - Appellees
                                      ____________

                    Appeal from United States District Court
                for the Western District of Arkansas - El Dorado
                                ____________

                          Submitted: January 13, 2014
                            Filed: August 15, 2014
                                ____________

Before GRUENDER, BRIGHT, and KELLY, Circuit Judges.


     1
       Gina McCarthy is substituted for her predecessor, Lisa P. Jackson, as
Administrator of the U.S. Environmental Protection Agency. Fed. R. App. P.
43(c)(2).
     2
       Ron Curry, Region 6 Administrator of the U.S. Environmental Protection
Agency, is substituted for his predecessor, Sam Coleman, Acting Region 6
Administrator of the U.S. Environmental Protection Agency. Fed. R. App. P.
43(c)(2).
                                  ____________

KELLY, Circuit Judge.

       El Dorado Chemical Company (EDCC) operates a chemical manufacturing
plant in El Dorado, Arkansas. As a byproduct of its operation, the plant discharges
dissolved minerals, including sulfate and chloride, into two unnamed tributaries (UTA
and UTB); these tributaries reach downstream to Flat Creek and Haynes Creek. In
2004, Arkansas imposed more stringent limits on the dissolved minerals EDCC could
discharge into these bodies of water, and granted EDCC three years to comply. In
response, EDCC initiated a Third Party Rulemaking to increase the levels of dissolved
minerals permitted in both UTA and UTB. Arkansas adopted these revisions and
submitted them to the U.S. Environmental Protection Agency (EPA) for approval.
The EPA rejected the changes, citing concerns that the revisions did not adequately
protect the aquatic life in Flat Creek and Haynes Creek. EDCC moved for judicial
review, and the district court3 upheld the EPA’s decision, granting summary judgment
in favor of the EPA. EDCC now appeals, arguing the EPA overstepped its authority
in considering the effects on aquatic life in the two creeks. Because we find the EPA
had the authority to look at downstream effects, and because EDCC failed to
adequately demonstrate the affected waters would be protected, we affirm.

                                  I. Background

                    A. Statutory and Regulatory Framework

       Since 1972, the states and the federal government have worked together “to
restore and maintain the chemical, physical, and biological integrity of the Nation’s



      3
      The Honorable Susan O. Hickey, United States District Court Judge for the
Western District of Arkansas.

                                         -2-
waters,” in a partnership governed by the Clean Water Act (CWA).4 33 U.S.C.
§ 1251(a). With this goal in mind, the CWA authorizes states to establish water
quality standards for bodies of water within its borders. 33 U.S.C. § 1313(a)–(c).
Water quality standards “define[] the water quality goals of a water body, or portion
thereof, by designating the use or uses to be made of the water and by setting criteria
necessary to protect the uses.” 40 C.F.R. § 131.2. They comprise (1) the designated
use(s) of the waters (e.g., water supply, propagation of fish, or recreation), 40
C.F.R. § 131.10; (2) the water quality criteria necessary to safely permit those
designated uses, 40 C.F.R. § 131.11; and (3) antidegradation requirements to protect
waters whose quality is better than required, 40 C.F.R. § 131.12. 40 C.F.R. § 131.6.
States must review their water quality standards at least every three years. 33
U.S.C. § 1313(c)(1). And under the CWA, each state must create a “continuing
planning process” (CPP) to, among other things, govern the process for revising its
water quality standards. 40 C.F.R. § 130.5(a). “In designating uses of a water body
and the appropriate criteria for those uses, the State shall take into consideration the
water quality standards of downstream waters and shall ensure that its water quality
standards provide for the attainment and maintenance of the water quality standards
of downstream waters.” 40 C.F.R. § 131.10(b).

       Although states assume the primary role in determining water quality
standards, 40 C.F.R. § 131.4, states must submit proposed standards and revisions to
the EPA for approval. 33 U.S.C. § 1313(c)(2); 40 C.F.R. §§ 131.5, 131.21. The EPA
must ensure proposed water quality standards meet the requirements of the CWA. 33
U.S.C. § 1313(c)(3). Designated uses must be “consistent with the requirements of
the [CWA],” and water quality criteria must “protect the designated water uses.” 40
C.F.R. § 131.5(a)(1)–(2). The EPA is empowered to issue its own water quality
standards if a state does not make appropriate adjustments to its proposed standards,



      4
       The statute is also known as the Federal Water Pollution Control Act.

                                          -3-
and the EPA may also promulgate revised or new standards “when necessary to meet
the requirements of the [CWA].” 33 U.S.C. § 1313(c)(3)–(4).

        Water quality standards in Arkansas are developed by the Arkansas Pollution
Control and Ecology Commission (the Commission). Ark. Code Ann. § 8-4-201(b).
The Arkansas Department of Environmental Quality administers and enforces the
state’s water quality standards.5 Ark. Code Ann. § 8-4-203(a). It does so through a
permitting program, the National Pollutant Discharge Elimination System (NPDES).6
See 33 U.S.C. § 1342. Under the NPDES program, a point source7 cannot discharge
a pollutant unless the discharge is authorized by an NPDES permit. See id.; see also
33 U.S.C. § 1311. These permits contain, inter alia, numerical discharge limits. Like
water quality standards, NPDES permits must first be submitted to the EPA for
approval, unless the EPA waives this requirement. 33 U.S.C. § 1342(d)–(e); Arkansas
v. Oklahoma, 503 U.S. 91, 102 (1992) (“[The EPA] retains authority to block the
issuance of any state-issued permit that is outside the guidelines and requirements of
the [CWA].”).




      5
       We refer to these two entities collectively as “Arkansas.”
      6
      NPDES permits are issued by the EPA or, in those jurisdictions in which the
EPA has authorized the state to issue permits, by a state agency subject to EPA
approval. 33 U.S.C. § 1342(a)–(d); see also Approval of Arkansas’ NPDES Program,
51 Fed. Reg. 44518-01 (Dec. 10, 1986).
      7
        The CWA defines “point source” as “any discernible, confined and discrete
conveyance, including but not limited to any pipe, ditch, channel, tunnel, conduit,
well, discrete fissure, container, rolling stock, concentrated animal feeding operation,
or vessel or other floating craft, from which pollutants are or may be discharged.” 33
U.S.C. § 1362(14).

                                          -4-
                       B. EDCC’s Third Party Rulemaking

       EDCC’s chemical manufacturing facility discharges its wastewater into UTB,
which flows into UTA. UTA, in turn, reaches downstream to Flat Creek. Flat Creek
then flows into Haynes Creek. Arkansas has designated UTA, Flat Creek, and Haynes
Creek for use as, among other things, perennial gulf coastal fisheries, and UTB as a
seasonal gulf coastal fishery. This case involves Arkansas’ attempt to revise the water
quality criteria for UTA and UTB in response to EDCC’s Third Party Rulemaking.

       In June 2004, EDCC renewed its NPDES permit. This new permit contained
more stringent limits on the dissolved minerals EDCC could discharge than the
previous permit. EDCC had until June 1, 2007, to comply with the new limits. On
August 31, 2006, before the new limits became effective, EDCC filed a petition for
a Third Party Rulemaking with Arkansas, seeking to modify Arkansas’ water quality
standards.8 Specifically, EDCC sought to make two changes. First, EDCC wanted
to remove the “domestic water supply” designated uses of UTA, UTB, and parts of
Flat Creek and Haynes Creek. Second, EDCC wanted to increase the maximum
permissible concentrations of chloride, sulfate, and total dissolved solids (“TDS”) for
those same bodies of water.

      Arkansas approved both of EDCC’s proposed changes on June 22, 2007, and
submitted them to the EPA for approval. Because these four bodies of water were not
currently used as sources for the domestic water supply, in November 2007 the EPA



      8
       Arkansas permits site-specific modifications to its water quality standards “to
accommodate important economic or social development in a local area,” Ark. Admin.
Code 014.04.2-3 Reg. 2.306, and permits third parties to petition for such an
amendment, Ark. Code Ann. § 8-4-202(c)(1). See also 33 U.S.C. § 1313(e)(3)(F)
(authorizing states to establish a “continuing planning process” that includes
procedures for revising water quality standards).

                                         -5-
approved the removal of the domestic water supply designated uses for all four bodies
of water.

       The EPA did not, however, approve the revised water quality criteria—i.e., the
proposed sulfate, chloride, and TDS limits. In January 2008, the EPA informed
Arkansas that it lacked adequate supporting evidence, so Arkansas supplemented its
documentation. Again in April 2009, the EPA rejected the proposed rule regarding
the higher mineral concentrations and identified additional information necessary to
make a determination. In response, EDCC conducted another study and submitted
further documentation, which it argued was substantially more comprehensive than
what the EPA had accepted and approved in a prior Third Party Rulemaking.
Nevertheless, the EPA emphasized its concern that the proposed revisions would have
negative effects on aquatic life in Flat Creek and Haynes Creek. Toxicity testing
submitted by EDCC had indicated reproductive problems to the water flea in the
creeks when exposed to the maximum proposed mineral concentrations.

        After receiving the EPA’s latest concerns, EDCC did not run any additional
tests or commission further studies on the impact to aquatic life in Flat and Haynes
Creek. Instead, EDCC petitioned Arkansas to re-open the Third Party Rulemaking.
This time, EDCC rescinded its proposed changes to the water quality criteria for Flat
Creek and Haynes Creek; the sulfate, chloride, and TDS limits would thus revert back
to the more strict levels. However, EDCC sought to re-adopt its proposed—and less
strict—sulfate, chloride, and TDS limits for UTA and UTB. Arkansas agreed. As a
result, on December 3, 2010, Arkansas rescinded the previously approved changes to
the sulfate, chloride, and TDS limits in Flat and Haynes Creeks, and re-adopted the
proposed criteria for UTA and UTB.

       Arkansas submitted this new rule to the EPA for approval. The EPA again
requested more information before making a determination, particularly with regard
to the potential effects of the revised criteria for UTA and UTB on Flat and Haynes

                                         -6-
Creeks. EDCC, communicating through and to Arkansas, responded by explaining
that because it removed Flat and Haynes Creeks from the Rulemaking, it would not
address questions concerning those two bodies of water. EDCC no longer wanted to
change the sulfate, chloride, and TDS concentrations for the creeks. On August 31,
2011, the EPA issued a final decision letter disapproving the revised water quality
criteria. As the EPA explained, it “determined that supporting documentation remains
insufficient to demonstrate that the site-specific minerals criteria for the waterbodies
associated with EDCC are appropriately protective of aquatic life.” The EPA
highlighted its concerns that EDCC failed to consider how the revised criteria for
UTA and UTB would affect the downstream water quality in Haynes and Flat Creeks
and that its supporting evidence was scientifically flawed.

       In October 2011, EDCC filed a complaint in the Western District of Arkansas
seeking judicial review of the EPA’s decision to disapprove the proposed water
quality criteria. EDCC claimed it provided the EPA with the necessary documentary
support and the EPA based its disapproval on inappropriate factors. Both EDCC and
the EPA filed cross motions for summary judgment, and the district court granted
summary judgment to the EPA. EDCC now appeals, arguing the EPA usurped the
role that Congress delegated to Arkansas to develop water quality standards and the
EPA’s decision is contrary to EDCC’s scientific evidence.

                                    II. Discussion

                               A. Standard of Review

       “We review de novo a district court’s decision whether an agency’s action
violates the A[dministrative Procedure Act (APA)].” Thomas v. Jackson, 581 F.3d
658, 664 (8th Cir. 2009) (quotation omitted).




                                          -7-
       As an initial matter, EDCC argues that the district court applied the incorrect
standard of review in upholding the EPA’s decision. According to EDCC, the EPA
had to present “compelling evidence, based on strong science,” in order to reject
Arkansas’ proposed water quality standards. The burden is, in EDCC’s view, on the
EPA. EDCC acknowledges, nonetheless, that judicial review of administrative
decisions is governed by the APA. 5 U.S.C. § 706. Section 706 provides, inter alia,
that the reviewing court shall uphold agency actions, findings, and conclusions unless
they are “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance
with law.” 5 U.S.C. § 706(2)(A). An agency decision is arbitrary or capricious if:

      the agency has relied on factors which Congress has not intended it to
      consider, entirely failed to consider an important aspect of the problem,
      offered an explanation for its decision that runs counter to the evidence
      before the agency, or is so implausible that it could not be ascribed to a
      difference in view or the product of agency expertise.

Cent. S.D. Co-op Grazing Dist. v. Sec’y of U.S. Dep’t of Agric., 266 F.3d 889, 895
(8th Cir. 2001) (quoting Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut.
Auto. Ins. Co., 463 U.S. 29, 43 (1983)). Thus, “[t]he scope of our review is narrow
and we are not to substitute our judgment for that of the agency.” Id. (citing Motor
Vehicle Mfrs., 463 U.S. at 43). “If an agency’s determination is supportable on any
rational basis, we must uphold it.” Voyageurs Nat’l Park Ass’n v. Norton, 381 F.3d
759, 763 (8th Cir. 2004).

       EDCC fails to harmonize the APA’s general “arbitrary and capricious” standard
with its proposed “compelling evidence” standard. Rather, EDCC suggests the
arbitrary and capricious standard—and the district court’s order by extension—
undermines the primacy of states under the CWA. See 33 U.S.C. § 1251(b) (“It is the
policy of the Congress to recognize, preserve, and protect the primary responsibilities
and rights of States to prevent, reduce, and eliminate pollution, to plan the
development and use (including restoration, preservation, and enhancement) of land

                                         -8-
and water resources, and to consult with the Administrator in the exercise of his
authority under this chapter.”). This suggestion ignores the statutory reality that states
do not have unfettered discretion under the CWA. States may establish and revise
water quality standards, yet all new and revised water quality standards must be
submitted to the EPA. 33 U.S.C. § 1313(c)(2)(A). The EPA has the power to reject
a state’s proposed water quality standard, and even promulgate its own standards in
some circumstances. Id. § 1313(c)(3) (“If the Administrator determines that any such
revised or new standard is not consistent with the applicable requirements of this
chapter, he shall . . . notify the State and specify the changes to meet such
requirements. If such changes are not adopted by the State . . . the Administrator shall
promulgate such standard . . . .”).

       Despite EDCC’s insistence, the EPA is permitted—and in fact statutorily
required—to scrutinize a state’s water quality standards. Under the CWA, the EPA
must determine whether a state’s water quality standard is “consistent with the
[CWA’s] requirements.” 33 U.S.C. § 1313(a)(3)(C), (c)(2)(A). As the Fifth Circuit
has noted, “[n]othing indicates a congressional intent to restrict EPA’s review of state
standards” or require deference to the states’ determinations. Miss. Comm’n on
Natural Res. v. Costle, 625 F.2d 1269, 1275–76 (5th Cir. 1980) (rejecting the state’s
argument that the EPA could only disapprove of a state standard if it is “arbitrary,
capricious, or totally unreasonable”). And the APA, in turn, indicates that we should
uphold the EPA’s decision unless it is arbitrary or capricious. 5 U.S.C. § 706(2)(A);
accord Costle, 625 F.3d at 1276. Similarly, we have held that when reviewing agency
action we grant deference to the agency’s “high level of technical expertise.” Cent.
S.D. Co-op, 266 F.3d at 894 (quotation omitted).

       EDCC points to an EPA administrative decision that suggests when the EPA
interprets state water quality standards for purposes of issuing NPDES permits, it
ought to uphold the state’s interpretation of that standard absent a state’s “clear error.”
In re Ina Road Water Pollution Control Facility, 2 E.A.D. 99, 100 (EAB 1985). In a

                                           -9-
footnote, the administrator noted the EPA could substitute its own interpretation if it
had compelling reasons, such as “strong scientific or technological support.” Id. at
101 & n.7.

       EDCC’s reliance on this case and its progeny is misplaced. Even if this case
somehow altered our application of the APA’s arbitrary and capricious standard, Ina
Road Water Pollution involves a different step in the regulatory structure. In Ina Road
Water Pollution, the EPA had already approved the state’s water quality standards and
was interpreting those standards in issuing NPDES permits.9 By contrast, the EPA in
this case is deciding in the first instance whether to approve Arkansas’ water quality
standards. And water quality standards serve as guidelines for setting applicable
limitations in individual NPDES permits. Contrary to EDCC’s urging, even if Ina
Road Water Pollution set out a general standard for NPDES permits, it is not
inconsistent for the EPA to give greater deference to states when interpreting and
applying standards that the EPA has already found comply with the CWA.

                         B. Scope of the EPA’s Authority

       That said, we may still find the EPA’s decision was arbitrary and capricious if
it acted outside the scope of its authority by “rel[ying] on factors which Congress has
not intended it to consider.” Cent. S.D. Co-op, 266 F.3d at 894 (quotation omitted).



      EDCC’s main argument is that the EPA usurped Arkansas’ role in setting water


      9
         Before the EPA can issue an NPDES permit, the state must certify, or waive
its right to certify, that the discharge authorized by the permit will comply with the
state’s water quality standards. 33 U.S.C. § 1341(a); 40 C.F.R. §§ 122.4(b), 124.53.
In Ina Road Water Pollution, Arizona certified that a permit’s effluent limitations
complied with its water quality standards, but the EPA disagreed and imposed more
strict limits. Ina Road Water Pollution, 2 E.A.D. at 100.

                                         -10-
quality standards. More specifically, EDCC contends the EPA exceeded its authority
by looking at the downstream effects on Flat Creek and Haynes Creek. The EPA cited
concern that changing the mineral concentrations in UTA and UTB would negatively
impact the aquatic life in Flat and Haynes Creeks, and rejected Arkansas’ revised
water quality criteria. One test in particular indicated “sub-lethal reproductive effects
to the water flea . . . for Flat and Haynes Creeks.” Even if this test result was
valid—which EDCC disputes—EDCC argues the EPA should have cabined its
inquiry to the impact of the revised water quality criteria on UTA and UTB.
According to EDCC, only states—not the EPA—may consider downstream effects in
establishing water quality criteria.

      EDCC cites two regulations in support of its position. The first regulation
describes a state’s duty when establishing water quality standards:

      In designating uses of a water body and the appropriate criteria for those
      uses, the State shall take into consideration the water quality standards
      of downstream waters and shall ensure that its water quality standards
      provide for the attainment and maintenance of the water quality
      standards of downstream waters.

40 C.F.R. § 131.10(b). This regulation prescribes the factors states must consider
when setting water quality standards, but says nothing about the EPA’s role in this
process. A second regulation describes the EPA’s review process for states’ proposed
water quality standards:

      [The] EPA is to review and to approve or disapprove of State-adopted
      water quality standards. The review involves a determination of:

      (1) Whether the State has adopted water uses which are consistent with
      the requirements of the Clean Water Act;
      (2) Whether the State has adopted criteria that protect the designated
      water uses;


                                          -11-
      (3) Whether the State has followed its legal procedures for revising or
      adopting standards;
      (4) Whether the State standards which do not include the uses specified
      in section 101(a)(2) of the Act are based upon appropriate technical and
      scientific data and analyses, and;
      (5) Whether the State submission meets the requirements included in
      § 131.6 of this part.

40 C.F.R. § 131.5; see also 40 C.F.R. § 131.6 (outlining the “[m]inimum requirements
for water quality standards submission”). EDCC argues that because § 131.5, the
regulation outlining the EPA’s review process, does not explicitly mention effects on
downstream waters, the EPA may not disapprove water quality criteria on that basis.
Instead, according to EDCC, § 131.5 only reserves authority for the EPA to look at
in-stream effects.

        According to the EPA, however, it has the statutory and regulatory authority to
ensure water quality standards are maintained downstream when a state revises
upstream water quality standards. In its brief on appeal, the EPA pointed to both the
state’s requirements under § 131.10(b) and the EPA’s review under § 131.5, reading
them in harmony: “In determining whether state-adopted criteria are sufficiently
protective of designated water uses per 40 C.F.R. § 131.5(a)(2), EPA reviews the
criteria to ensure all requirements are met, including those imposed in § 131.10(b).”
Despite EDCC’s alternative reading, “[i]t is well established that an agency’s
interpretation need not be the only possible reading of a regulation—or even the best
one—to prevail.” Decker v. Nw. Envtl. Def. Ctr., 133 S. Ct. 1326, 1337 (2013).
When evaluating competing interpretations, “we defer to [the] agency’s interpretations
. . . unless we find that a regulation is contrary to unambiguous statutory language,
that the agency’s interpretation of its own regulation is plainly erroneous or
inconsistent with the regulation, or that application of the regulation [is] arbitrary or
capricious.” Nack v. Walburg, 715 F.3d 680, 684 (8th Cir. 2013) (quotation omitted).
This is true, “even if the agency’s interpretation of its own regulation is expressed


                                          -12-
merely in a brief to the court rather than through other means.” Id. at 685 (citing Talk
Am., Inc. v. Mich. Bell Tel. Co., 131 S. Ct. 2254, 2261 (2011)). We cannot say the
EPA’s reading of its own regulations—that it may look at downstream waters when
evaluating a state’s water quality standards—is plainly erroneous.

        First, § 131.5 does not state the EPA is limited to looking at in-stream effects
when approving or disapproving water quality standards. Rather, it directs the EPA
to review the state’s water quality standards—that its designated uses comply with the
CWA and that the criteria protect those uses. Section 131.5 does not, by its terms,
prohibit the EPA from considering “[w]hether the State has adopted criteria that
protect the designated uses” of downstream, as well as in-stream, waters.
Section 131.6 further indicates the EPA has authority to review downstream waters;
it outlines what information a state must submit to the EPA when seeking review of
water quality standards. In addition to including the designated water uses and water
quality criteria, the state must also supply the “[m]ethods used and analyses conducted
to support water quality standards revisions.” 40 C.F.R. § 131.6(b). As § 131.10(b)
directs, part of a state’s analysis for its water quality standards must be the
maintenance of downstream waters. It follows that the EPA may not only receive, but
may also review this methodology.

       Second, the CWA itself supports the EPA’s interpretation. The EPA has both
the authority and obligation to ensure that revisions to a state’s water quality standards
“meet[] the requirements of [the CWA].” 33 U.S.C. § 1313(c)(3). The CWA
endorses a holistic approach to the nation’s waterways. See, e.g., 33 U.S.C.
§ 1315(b)(1)(B) (“Each State shall prepare and submit to the [EPA] . . . an analysis
of the extent to which all navigable waters of such State provide for the protection and
propagation of a balanced population of shellfish, fish, and wildlife, and allow
recreational activities in and on the water.”) (emphasis added); 33 U.S.C. § 1341(a)(2)
(when issuing NPDES permits, “[w]henever such a discharge may affect, as
determined by the [EPA], the quality of the waters of any other State, the [EPA] . . .

                                          -13-
shall so notify such other State, the licensing or permitting agency, and the [permit]
applicant”). Congress passed the CWA to “restore and maintain the chemical,
physical, and biological integrity of the Nation’s waters.” 33 U.S.C. § 1251(a);
Arkansas, 503 U.S. at 105–07 (citing the CWA’s “broad purpose” as one justification
for the EPA’s authority, in the NPDES context, to regulate upstream pollution sources
in order to achieve downstream water quality standards). EDCC’s myopic reading of
the CWA would run roughshod over its purpose.

       Finally, EDCC argues that the NPDES permitting program provides sufficient
protection for downstream waters, which would then preserve the purpose of the
CWA. Under NPDES, “no permit shall issue . . . if the [EPA] objects in writing to the
issuance of such permit as being outside the guidelines and requirements of [the
CWA].” 33 U.S.C. § 1342(d)(2). And “[n]o permit may be issued . . . [w]hen the
conditions of the permit do not provide for compliance with the applicable
requirements of CWA, or regulations promulgated under CWA,” or “[w]hen the
imposition of conditions cannot ensure compliance with the applicable water quality
requirements of all affected States.” 40 C.F.R. § 122.4(a), (d). Nevertheless, the
EPA’s interpretation of its own regulations is not rendered plainly erroneous simply
because the EPA may preserve downstream water quality standards at a later step in
the regulatory process. The NPDES program provides EPA with the opportunity to
ensure downstream waters are protected from point source pollution. Yet EDCC does
not explain why NPDES must be the exclusive means for protecting downstream
waters. Neither the CWA nor the related regulations compel this reading. EDCC’s
contention is further weakened by the fact that under NPDES, the EPA may waive
objections to a particular permit application, and may even waive notice of a permit
application entirely for specific categories of point source pollution. 33 U.S.C.
§ 1342(d)(3), (e). Consequently, we find the EPA did not act arbitrarily or
capriciously by denying Arkansas’ revised water quality standards based, in part, on
possible downstream effects.



                                        -14-
                               C. Evidentiary Support

      Arkansas, not the EPA, bears the burden of adducing evidence the proposed
water quality criteria meet the requirements of the CWA. See, e.g., 40 C.F.R.
§§ 131.6, 131.21. Here, the EPA determined that Arkansas’ supporting
documentation was insufficient to demonstrate that the proposed water quality criteria
are “appropriately protective of aquatic life” in UTA, UTB, and Flat and Haynes
Creeks. The EPA must have a rational basis for its determination. Voyageurs, 381
F.3d at 763 (“If an agency’s determination is supportable on any rational basis, we
must uphold it.”). On appeal, EDCC argues the EPA lacked a rational basis. In doing
so, EDCC emphasizes the limited nature of its proposed changes and questions the
EPA’s reliance on purportedly unreliable and otherwise deficient evidence. We
address each argument in turn.

       EDCC first points out its proposed changes are relatively moderate. EDCC
sought, with Arkansas’ approval, to raise the chloride criteria for UTA and UTB from
14 mg/L to 16 mg/L and 23 mg/L respectively. The revised criteria, EDCC
emphasizes, are still more restrictive than the EPA’s own recommendations or those
approved in other rulemakings for other sites. Under the CWA, the EPA publishes
water quality criteria guidelines “reflecting the latest scientific knowledge.” 33 U.S.C.
§ 1314(a)(1). And in 1988, the EPA published national guidance criteria for chloride,
setting limitations at 230 mg/L for chronic toxicity. Water Quality Criteria, 53 Fed.
Reg. 19028-01 (May 26, 1988). The proposed criteria in this case are substantially
lower than the guideline criteria; yet adherence to the guidelines is not sufficient, on
its own, to warrant EPA approval. The EPA must still determine whether the
proposed criteria otherwise comply with the CWA. And state water quality criteria
must “protect the designated water uses.” 40 C.F.R. § 131.5(a)(2). We cannot agree
that the moderate nature of the proposed changes, standing alone, is sufficient to find
the EPA’s decision lacked a “rational basis.”



                                          -15-
      EDCC also questions the EPA’s interpretation of and reliance on the scientific
evidence in the record. To assess this argument, we must consider two comprehensive
studies that EDCC commissioned through GBMC & Associates (GBMC): one in
2006 and—in response to the EPA’s request for more support—another in 2009. The
goal of these studies was to demonstrate EDCC’s proposed water quality criteria
would protect the designated uses of UTA, UTB, and the two creeks. Despite these
studies, the EPA found insufficient evidence that these bodies of water would remain
protected given the proposed increased mineral concentrations. EDCC contends that
the EPA ignored the extensive scientific evidence and that EPA’s conclusions—drawn
from specific tests in the record—about the in-stream and downstream effects of the
revised criteria are simply incorrect.

       The first study was conducted in 2006 when EDCC, through GBMC, prepared
a “Site Specific Water Quality Study for Chloride, Sulfate, and TDS.” EDCC,
through Arkansas, then submitted this study to the EPA as the requisite documentation
that the revised water quality criteria still adequately protected designated uses. See
40 C.F.R. § 131.6(b). As part of this 2006 study, GMBC conducted an “Aquatic Life
Field Study” to “document whether the designated aquatic life use was being
maintained” in UTA and UTB and to determine whether “the permitted discharges
from EDCC are beneficial or detrimental to the maintenance of those uses.”
According to the Aquatic Life Field Study, the revised water quality criteria maintain
UTA and UTB’s designated use as seasonal fisheries, including preserving the
supporting biotic communities necessary for fishery use. EDCC asserts the EPA
failed to acknowledge these findings when disapproving the proposed mineral
concentrations.

       The EPA did not ignore the study’s conclusion, but it did question whether the
study was helpful in determining whether the designated uses were being maintained.
In this Aquatic Life Field Study, GMBC sampled the aquatic life in UTA and UTB,
in part, by comparing downstream waters (impacted by EDCC’s current discharge)

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to other bodies of water, called “reference reaches” (not impacted by EDCC’s current
discharge). In its disapproval, the EPA questioned EDCC’s reliance on reference
reaches that were already impacted by significant dissolved mineral pollution.
Regardless, even if EDCC and the EPA could agree on the choice of proper reference
reaches, and assuming the study’s conclusions were sound, the study did not analyze
any effects on Flat and Haynes Creeks. At best then, the 2006 study was incomplete.
As a result, the EPA informed Arkansas (which in turn informed EDCC) that the
evidence was inadequate; more information was needed, particularly about Flat and
Haynes Creeks. The EPA identified information still needed and additional tests that
could be run.

       In response to this request for additional documentation, EDCC asked GMBC
in 2009 to prepare the “Aquatic Life Supplemental Report.” As part of this study,
whole effluent toxicity testing (WET testing) was conducted on spiked water samples
created to simulate the mineral concentrations proposed in the initial Rulemaking for
all four bodies of water. These spiked water samples were then compared to current
water samples, “control samples,” from UTA, UTB, and Flat and Haynes Creeks.
GMBC analyzed the effects on the fathead minnow and water flea. EPA had
requested such a test “to demonstrate the ability of the approved criteria to support the
aquatic life . . . .” GMBC concluded that the proposed criteria were adequately
protective of aquatic life in all four bodies of water. Yet despite this conclusion, the
study also acknowledged negative reproductive effects on the water flea in Flat and
Haynes Creeks: the water fleas did not die more rapidly, but had fewer offspring when
exposed to the proposed chloride, sulfate, and TDS concentrations than the water fleas
in the control samples. GMBC explained this result “may or may not be directly
related to the dissolved minerals.” It suggested historic oil and gas activities in the
area could be responsible.

       After receiving the 2009 study, the EPA remained critical of the proposed
criteria. The EPA acknowledged “that non-point sources and other factors out of

                                          -17-
EDCC’s control are possible contributors to the increased mineral loads in Flat and
Haynes Creeks.” However, the EPA would not rely on the study’s mere speculation
as to the cause of the negative test results. The existence of other contributing factors
“does not . . . relieve the 3rd party of the burden to propose criteria that will be
protective of the aquatic life uses for these waters.” The EPA suggested changing the
criteria to protective levels and analyzing the test results more thoroughly. EDCC
declined to do so. Instead, EDCC petitioned Arkansas to re-open the Third Party
Rulemaking with the specific goal of rescinding the revisions to the criteria for the
two creeks. EDCC does not abandon its argument that the EPA erred, therefore, in
looking downstream at the effects of the proposed criteria on these two creeks (which
were no longer subject to the revised criteria); but its primary argument is that the
WET test results are not sufficiently valid to support the EPA’s action.

       EDCC first argues the WET test’s methodology was unsound. Though it
followed the EPA’s instructions to use synthetic water, EDCC asserts that use of
synthetic water for this test was both inappropriate and unreliable. EDCC points to
an EPA manual regarding how to conduct WET tests for the NPDES program. See
40 C.F.R. § 136.3, Table IA (referencing the EPA manual). The manual indicates that
when determining the effects of the discharge on already contaminated water, WET
testing should be conducted using water collected from the point of discharge (i.e., not
synthetic water). The objective of the test in the NPDES context, however, is to
determine whether a point source, and its existing discharge, is complying with its
permit. Here, the EPA sought to evaluate the effects on aquatic life if the state revised
water quality criteria by increasing specific dissolved mineral limits.

      EDCC also contends the EPA could consider only those WET tests that were
conducted pursuant to the NPDES requirements due to Arkansas’ EPA-approved
procedures for modifying water quality criteria as detailed in Arkansas’ CPP.
Arkansas’ CPP requires third parties seeking to revise water quality standards to
“demonstrat[e] that existing aquatic life uses will be maintained.” The CPP permits

                                          -18-
parties to submit recent WET tests, conducted pursuant to NPDES requirements, as
evidence. Notably, however, the Arkansas’ CPP does not preclude the EPA from
requesting or considering other evidence.

        Finally, EDCC argues the “anomalous” test results for the water flea from the
2009 study are not relevant: they were based on synthetic waters created to reflect
proposed revised criteria for Haynes and Flat Creeks—i.e., these studies were
conducted before EDCC moved to reopen the Rulemaking to rescind any proposed
changes for the creeks. However, the EPA did not rely on the 2009 study to
definitively state the revised criteria for UTA and UTB did not protect aquatic life.
Instead, the EPA explained the study was a red flag requiring further explanation. The
test results suggest that altering the mineral levels in the creeks could lead to problems
for their aquatic life. And changing the mineral levels upstream could alter mineral
levels downstream. The EPA had the authority to consider the downstream effects of
revisions to UTA’s and UTB’s water quality standards, and could deny revisions if
not adequately assured of downstream waters’ protection. The EPA’s continued
reference to this test was thus not irrational.

       Rather than addressing the EPA’s concerns about the 2009 study and the
potential effects on the creeks, EDCC rescinded the Arkansas-approved water quality
criteria revisions to Flat and Haynes Creeks. EDCC then insisted that, as a result, the
EPA could no longer look at potential effects in those two bodies of water. In turn,
according to EDCC, the WET test results were irrelevant: EDCC asserted “[s]ince
these waterbodies are no longer part of the 2011 Rulemaking approved by the
Commission, specific questions regarding the status of those water bodies will not be
addressed . . . .” In short, EDCC refused to supply more information about possible
effects on Flat and Haynes Creeks. While EDCC now criticizes the EPA’s decision
to disapprove the revisions for UTA and UTB based on the 2009 study’s “isolated”
and “anomalous” test, the EPA looked to this test because Arkansas and EDCC
presented little other information regarding effects on Haynes and Flat Creeks. We

                                          -19-
cannot say the EPA’s refusal to approve the proposed water quality criteria on the
basis of incomplete information was arbitrary or capricious. Particularly in light of
the deference we grant to the EPA on review, we find there was a rational basis for the
EPA’s disapproval. See Lockhart v. Kenops, 927 F.2d 1028, 1034 (8th Cir. 1991)
(“[O]ur deference to the agency is greatest when reviewing technical matters within
its area of expertise, particularly its choice of scientific data and statistical
methodology . . . .”) (quotation omitted).

                            D. Mass Balance Approach

        The EPA also found the method Arkansas used to derive the water quality
criteria—the “mass balance approach”—was “scientifically indefensible.” The mass
balance approach does not, standing alone, derive criteria adequately protective of the
existing designated uses. The EPA explained in its letter that Arkansas should have
considered, inter alia, stream flow conditions; results from properly conducted toxicity
tests; the downstream water quality standards; facility design flow capacity; and inputs
from other point sources in the watershed. The mass balance approach determined the
dissolved mineral limits necessary to account for EDCC’s discharge. That does not,
however, indicate that the criteria, and EDCC’s discharge, are protective of aquatic
life. The EPA’s disapproval of the mass balance approach in this context was not
arbitrary or capricious.




                                   III. Conclusion

      We cannot find the EPA was arbitrary or capricious in rejecting Arkansas’




                                         -20-
proposed water quality standards. Accordingly, we affirm the district court.10
                      ______________________________




      10
        We note that nothing precludes Arkansas from resubmitting proposed water
quality standards with more adequate documentation. The EPA explained in its
decision that in the event the evidence does not support EDCC’s proposed revision,
Arkansas could “conduct a full use attainability analysis (UAA) to determine an
appropriate level of aquatic life use for an area that has been historically impacted by
industry.” In other words, Arkansas could attempt to further revise the designated
uses, as well as the water quality criteria. During oral argument the parties also
acknowledged the construction of a wastewater pipeline, which could diminish
EDCC’s discharge and thus its need for these specific water quality criteria revisions.

                                         -21-
