“Overall Project Purposes” May Include Multiple Interrelated Applicant Goals Under Clean Water Act § 404(b)(1)

Case: Save The Colorado v. City and County of Denver (Intervenor Respondent–Appellant: Denver Water)
Court: United States Court of Appeals for the Tenth Circuit
Date: September 15, 2026

I. Introduction

This published Tenth Circuit decision arises from Denver Water’s long-planned Gross Reservoir expansion—part of the “Moffat System Collection Project”—designed to address predicted shortages and operational vulnerability created by the utility’s heavy reliance on its separate South System. Because raising Gross Dam required placing fill material in South Boulder Creek wetlands at the dam’s base, Denver Water needed a Clean Water Act (“CWA”) § 404 permit from the U.S. Army Corps of Engineers (“Corps”). The Corps issued the permit in 2017 after a fourteen-year NEPA/CWA review, and Denver Water completed major construction in 2026—but could not fill the reservoir due to a district court injunction.

Environmental groups (Save the Colorado and others) challenged the permit and NEPA documentation, contending the Corps (i) defined project purpose too narrowly, (ii) used an inadequate cost methodology, and (iii) failed to sufficiently analyze climate change’s effect on feasibility and streamflow. The district court agreed, vacated the NEPA documents and permit, and permanently enjoined enlargement activities (including diversion and tree removal). The Tenth Circuit reversed, dissolved the injunction, and ordered judgment against the plaintiffs.

II. Summary of the Opinion

III. Analysis

A. Precedents Cited

1. NEPA’s role and judicial deference

• Seven Cnty. Infrastructure Coal. v. Eagle County, 605 U.S. 168 (2025): The opinion uses Seven Cnty. to frame NEPA as procedural—meant “to inform agency decisionmaking, not to paralyze it”—and to justify “substantial deference” to agency technical judgments when reviewing NEPA compliance. This backdrop supports the panel’s unwillingness to require a particular modeling approach for climate impacts or a more granular cost analysis at an early screening stage.
• Dep't of Transp. v. Pub. Citizen, 541 U.S. 752 (2004): Cited for the proposition that an EIS is not required where an agency issues a finding of no significant impact, though here the Corps prepared an EIS. The citation serves primarily as canonical NEPA scaffolding for the opinion’s procedural posture.

2. Jurisdiction and appealability (administrative-remand rule; practical finality)

• Rocky Mountain Wild v. Dallas, 98 F.4th 1263 (10th Cir. 2024): Provides the two-part framework for the administrative-remand rule and recognizes permitting/ROD decisions as “adjudicative.” The panel relies on Rocky Mountain Wild to analyze a potential finality defect and then invokes its practical-finality exception.
• W. Energy All. v. Salazar, 709 F.3d 1040 (10th Cir. 2013) and New Mexico ex rel. Richardson v. Bureau of Land Mgmt., 565 F.3d 683 (10th Cir. 2009): Both support characterizing permitting as adjudicative for finality purposes.
• Ausmus v. Perdue, 908 F.3d 1248 (10th Cir. 2018): Cited via Rocky Mountain Wild for when practical finality applies—particularly where a remand effectively directs an outcome, risking unreviewability. Here, the permanent injunction would effectively bar the project regardless of remand, justifying appellate review.

3. Mootness (constitutional vs. prudential; partial relief)

• Rio Grande Silvery Minnow v. Bureau of Reclamation, 601 F.3d 1096 (10th Cir. 2010) and Wyoming v. U.S. Dep't of Agric., 414 F.3d 1207 (10th Cir. 2005): Provide the operative test—whether the requested decision will have “some effect in the real world.”
• Audubon of Kan., Inc. v. U.S. Dep't of Interior, 67 F.4th 1093 (10th Cir. 2023): Supplies the redressability-throughout-litigation requirement and ties mootness to standing doctrine.
• WildEarth Guardians v. Pub. Serv. Co. of Colo., 690 F.3d 1174 (10th Cir. 2012): Used for burden allocation: the party asserting mootness bears the burden.
• Caddo Nation of Okla. v. Wichita & Affiliated Tribes, 877 F.3d 1171 (10th Cir. 2017) and Airport Neighbors All., Inc. v. United States, 90 F.3d 426 (10th Cir. 1996): Establish that NEPA/CWA challenges may become moot after completion, but not if partial relief remains available (e.g., enjoining use/operation pending compliance).
• Sierra Club v. U.S. Army Corps of Eng'rs, 803 F.3d 31: Quoted as an example of partial relief—wholly or partly enjoining operation pending further analysis—keeping controversy alive.
• Hillsdale Env't Loss Prevention, Inc. v. U.S. Army Corps of Eng'rs, 702 F.3d 1156 (10th Cir. 2012): Central to the mootness holding: even if alternatives analysis is no longer meaningful post-construction, remand might yield additional mitigation or permit conditions, providing partial redress.
• Winzler v. Toyota Motor Sales U.S.A., Inc., 681 F.3d 1208 (10th Cir. 2012) and Sierra Club, Inc. v. Bostick, 787 F.3d 1043 (10th Cir. 2015): Frame prudential mootness as remedial discretion; the court declines to reach it because it resolves the case on the merits.

4. APA arbitrariness and the Corps’ “clear demonstration” burden

• Am. Wild Horse Campaign v. Raby, 144 F.4th 1178 (10th Cir. 2025) (quoting New Mexico ex rel. Richardson v. Bureau of Land Mgmt., 565 F.3d 683): Supplies the familiar arbitrary-and-capricious formulations the court uses to evaluate the three claimed deficiencies.
• Hillsdale Env't Loss Prevention, Inc. v. U.S. Army Corps of Eng'rs, 702 F.3d 1156 (10th Cir. 2012): Provides the key gloss on “clearly demonstrate” under 40 C.F.R. § 230.10(a)(3): the Corps need only take a “hard look” and reach a “meaningful conclusion based on the evidence,” not prove correctness de novo in court.

5. Purpose definition and alternatives screening

• Greater Yellowstone Coal. v. Flowers, 359 F.3d 1257 (10th Cir. 2004) (quoting Sylvester v. U.S. Army Corps of Eng'rs, 882 F.2d 407 (9th Cir. 1989)): Used to confirm the Corps must take into account the applicant’s objectives in the alternatives analysis; it supports the panel’s acceptance of Denver Water’s specific goals as legitimate components of “overall project purposes.”
• Sylvester v. U.S. Army Corps of Eng'rs, 882 F.2d 407 (9th Cir. 1989): Invoked by plaintiffs to argue the Corps may not define a purpose to “preclude the existence of” practicable alternatives; the panel distinguishes this concern by pointing to the numerous remaining alternatives after screening.
• Del. Riverkeeper Network v. U.S. Army Corps of Eng'rs, 869 F.3d 148 (3d Cir. 2017) and Friends of Santa Clara River v. U.S. Army Corps of Eng'rs, 887 F.3d 906 (9th Cir. 2018): Cited for the textual inference that “overall project purposes” (plural) can encompass multiple purposes.

6. Interpretation canons and regulatory deference limits

• Ysleta Del Sur Pueblo v. Texas, 596 U.S. 685 (2022) (quoting Henson v. Santander Consumer USA, Inc., 582 U.S. 86 (2017)): Supports the presumption that different language conveys different meaning, deployed to distinguish “basic purpose” from “overall project purposes.”
• Kisor v. Wilkie, 588 U.S. 558 (2019): Limits Auer deference to genuinely ambiguous regulations; the panel finds § 230.10(a)(2) unambiguous and thus denies any need to defer to agency interpretation.

7. Methodology discretion (costing and climate modeling)

• Utahns for Better Transp. v. U.S. Dep't of Transp., 305 F.3d 1152 (10th Cir. 2002) and Habitat Educ. Ctr., Inc. v. U.S. Forest Serv., 673 F.3d 518 (7th Cir. 2012): Reinforce that agencies need “more than nothing” but are not required to produce extraordinarily detailed estimates; agencies may “draw the line” on data collection.
• Nat'l Audubon Soc'y v. U.S. Army Corps of Eng'rs, 991 F.3d 577 (4th Cir. 2021) and W. Watershed Project v. U.S. Bureau of Land Mgmt., 76 F.4th 1286 (10th Cir. 2023): Cited to support deference to agency scientific judgments and reasoned refusal to rely on contested modeling approaches.

B. Legal Reasoning

1. The opinion’s key doctrinal move: “basic purpose” ≠ “overall project purposes”

The centerpiece of the decision is a textual reading of 40 C.F.R. § 230.10(a). The Corps identified the Moffat Project’s basic purpose as “to provide supplemental water supply,” which triggered the non-water-dependent presumption under § 230.10(a)(3). But it defined the overall project purposes more specifically to include Denver Water’s interrelated objectives—delivering firm yield to the Moffat Treatment Plant and addressing the operational imbalance between systems.

The panel rejects plaintiffs’ attempt to collapse these phrases into a single “most general” purpose. It relies on:

• Textual difference (different words imply different meaning);
• Plurality (“overall project purposes”); and
• Functional context (basic purpose is used for water-dependence classification, while overall purposes guide alternatives screening and therefore may be more applicant-specific).

This interpretive holding matters because it validates a common Corps practice: using a general “basic purpose” to determine presumptions, while using a more tailored “overall purpose” to decide what alternatives are practicable “in light of” the project’s aims.

2. Deference under the APA and the “clearly demonstrate” standard

Even though the project was non-water-dependent and thus subject to a heightened showing under § 230.10(a)(3), the court emphasizes that judicial review remains deferential. Drawing from Hillsdale Env't Loss Prevention, Inc. v. U.S. Army Corps of Eng'rs, it frames the question as whether it was arbitrary and capricious for the Corps to find it had “clearly demonstrated” LEDPA status—i.e., whether the Corps took a “hard look” and reached a “meaningful conclusion based on the evidence,” not whether the court is independently persuaded.

3. Cost screening: planning-level comparisons are acceptable if explained

The Corps used a “relative development cost” approach: estimated capital cost (“rough order of magnitude”) plus a 50% multiplier for contingent costs. The panel accepts this because the record contained:

• supporting documentation explaining why granular contingent-cost estimates were “implausible” at early screening stages;
• an explanation of how the 50% figure was derived (aggregating typical percentages for discrete components); and
• third-party consultant review concluding the estimate was suitable for comparison of alternatives even if not for final budgeting.

The court thus treats the cost methodology dispute as a classic APA “methodology choice” question: the agency may select a method so long as it reasonably explains reliability and fit for purpose.

4. Climate change: qualitative discussion plus reasoned limits on quantification

The court’s climate analysis is not a rejection of climate impacts as relevant; it assumes (for the appeal) that climate change goes to “logistics” and feasibility under § 230.10(a)(2). But it holds that the Corps reasonably declined to quantify streamflow impacts because the administrative record supported significant uncertainty and lack of a generally accepted method to convert temperature changes into incremental streamflow/reservoir changes for the region.

The panel also addresses a specific feasibility concern (Moffat Tunnel capacity) by crediting the Corps’s explanation that only part of the additional firm yield depended on the Tunnel; the remainder would come from reoperation of the broader collection system with storage in the enlarged reservoir.

C. Impact

1. CWA § 404(b)(1) alternatives analysis: broader validation of multi-purpose “overall purposes”

The decision establishes (at least within the Tenth Circuit) a clear interpretive rule: “overall project purposes” in 40 C.F.R. § 230.10(a)(2) may encompass multiple related applicant objectives and need not be reduced to a single general purpose merely because the Corps identified a general “basic purpose” for water-dependence classification. Practically, this strengthens applicants’ ability—especially municipal utilities and infrastructure sponsors—to defend alternatives screening that incorporates operational reliability, system integration constraints, and service-area delivery requirements, not just generic supply augmentation.

2. NEPA alternatives: reinforcing deference and “reasonable range” flexibility

By aligning its NEPA analysis with Seven Cnty. Infrastructure Coal. v. Eagle County, the panel reinforces that NEPA does not compel maximal modeling sophistication; rather, it requires a reasonably explained evaluation adequate to inform decisionmaking. Litigants challenging EIS alternatives analyses may face a higher bar when the record contains reasoned explanations for methodological limits and when numerous alternatives were screened and considered.

3. Climate change litigation posture: “explain why not,” not “model no matter what”

The opinion is likely to be cited for the proposition that agencies may address climate impacts qualitatively—without quantitative modeling—if they document model uncertainty, data limitations, and the lack of generally accepted methods for the particular environmental variable and geography. Future challengers will likely need to focus less on “you didn’t model” and more on “your reasons for not modeling are unsupported or pretextual,” or show that the agency ignored a mature, widely accepted method already used in comparable decisions.

4. Remedies and mootness: post-construction cases can survive if mitigation remains possible

Although the court does not reach remedy disputes after reversing on the merits, its mootness analysis—grounded in Hillsdale Env't Loss Prevention, Inc. v. U.S. Army Corps of Eng'rs—signals that completed construction will not necessarily moot NEPA/CWA challenges where agencies retain discretion to impose additional mitigation or permit conditions. This may encourage continued litigation even when the “build” is done, but also provides agencies and permittees a pathway to argue that remaining relief is limited and should be cabined to mitigation rather than project redesign.

IV. Complex Concepts Simplified

• Clean Water Act § 404 permit: Authorization from the Corps to discharge dredged or fill material into “waters of the United States,” often implicated by construction in wetlands/streams.
• LEDPA (Least Environmentally Damaging Practicable Alternative): The Corps may permit a discharge only if no other practicable alternative would cause less harm to aquatic ecosystems (and not create other significant adverse consequences). (40 C.F.R. § 230.10(a))
• Non-water-dependent project presumption: If the project’s basic purpose can be met without being in/near the aquatic site, less damaging practicable alternatives are presumed available “unless clearly demonstrated otherwise.” (40 C.F.R. § 230.10(a)(3))
• “Basic purpose” vs. “overall project purposes”: In this opinion, “basic purpose” is a high-level description used to decide whether the project is water-dependent; “overall project purposes” may be more detailed and can include multiple related goals used to evaluate practicable alternatives. (40 C.F.R. § 230.10(a)(2)–(3))
• NEPA EIS and ROD: An Environmental Impact Statement evaluates significant effects and alternatives; a Record of Decision documents the agency’s final choice and rationale.
• APA “arbitrary and capricious” review: Courts do not decide what they would do; they ask whether the agency considered relevant factors and provided a rational explanation supported by the record.
• Constitutional mootness vs. prudential mootness: Constitutional mootness asks whether a court can still grant any effective relief; prudential mootness asks whether relief, though possible, is no longer worth the judicial effort as a matter of remedial discretion.
• Auer/Kisor deference: Courts may defer to an agency’s interpretation of its own ambiguous regulation, but under Kisor v. Wilkie only if the regulation is genuinely ambiguous; if unambiguous, no such deference applies.

V. Conclusion

The Tenth Circuit’s decision in Save The Colorado v. City and County of Denver is most significant for its textual holding that 40 C.F.R. § 230.10(a)(2)’s “overall project purposes” may reflect multiple interrelated applicant objectives and are not interchangeable with the “basic purpose” used for water-dependence analysis. Coupled with strong deference to agency methodology on cost estimation and climate-change treatment, the opinion fortifies agency and applicant flexibility in § 404(b)(1) and NEPA alternatives analyses—so long as the administrative record explains the choices made and the limits adopted.