Water Quality “As a Whole,” Not Parameter-by-Parameter: The Texas Supreme Court Clarifies Tier 2 Antidegradation Review and APA Fact‑Finding in Save Our Springs Alliance v. TCEQ

I. Introduction

The Texas Supreme Court’s decision in Save Our Springs Alliance, Inc. v. Texas Commission on Environmental Quality and The City of Dripping Springs, No. 23‑0282 (Tex. Apr. 11, 2025), is a major administrative and environmental law precedent. It settles two recurring and contentious questions:

1. How must TCEQ apply its Tier 2 “antidegradation” standard? Is the agency required to conduct a parameter‑by‑parameter analysis (where any non‑de minimis change in a single numeric water‑quality parameter such as dissolved oxygen is automatically “degradation”), or may it evaluate overall water quality of the water body as a whole?
2. What does the Texas Administrative Procedure Act (APA) require by way of “underlying facts” in a final order? Specifically, must TCEQ provide detailed, parameter‑specific findings (e.g., pre‑ and post‑discharge concentrations) whenever it makes an “ultimate” finding such as “no degradation” under its own rules?

At stake was a permit issued by TCEQ to the City of Dripping Springs authorizing discharge of up to 822,500 gallons per day of highly treated wastewater into Onion Creek, a high‑quality segment in the Edwards Aquifer region. Save Our Springs Alliance (SOS), an environmental nonprofit, opposed the permit, arguing that:

• Modeling showed a drop in dissolved oxygen (DO) at the discharge point from at least 6.44 mg/L to about 5.0 mg/L, and
• Such a change is more than de minimis in that parameter and thus constitutes prohibited “degradation” under Tier 2 as a matter of law, irrespective of other evidence.

SOS also argued that TCEQ’s final order was invalid under APA § 2001.141 because it did not set out specific, parameter‑level “underlying facts” explaining why this DO drop did not amount to more than de minimis degradation.

The Court rejected both lines of attack, affirming the court of appeals and upholding the permit. In doing so, it:

• Expressly endorses TCEQ’s “whole water body” approach to Tier 2 antidegradation review and rejects a rigid parameter‑by‑parameter reading of “degradation.”
• Narrows the reach of APA § 2001.141(d) by holding that “underlying facts” are required only when an agency’s ultimate finding is cast in statutory language mandated by its enabling act—not when it applies its own rules, and not here.
• Emphasizes deference and burden allocation in contested‑case permitting—especially the “prima facie” presumption of permit validity under Government Code § 2003.047.

Together, these holdings significantly shape water‑quality permitting challenges in Texas and clarify what environmental protestants must prove to overturn TCEQ permitting decisions.

II. Summary of the Opinion

A. Procedural and Factual Background

The City of Dripping Springs, facing rapid population growth and a desire to maximize “beneficial reuse” of treated effluent, applied in 2015 for a TCEQ permit authorizing discharge of up to 995,000 gallons per day of treated wastewater into Walnut Springs and then Onion Creek. Onion Creek is a “classified segment” (Segment 1427) designated for high aquatic‑life use with a site‑specific DO criterion of 5.0 mg/L (24‑hour mean).

Under Texas’s EPA‑approved water‑quality standards (30 Tex. Admin. Code ch. 307), any new or increased discharge into high‑quality water must pass:

• Tier 1 antidegradation review: existing uses and water quality sufficient to protect those uses must be maintained.
• Tier 2 antidegradation review: no “degradation” (defined as “a lowering of water quality by more than a de minimis extent, but not to the extent that an existing use is impaired”) of waters better than “fishable/swimmable” unless justified for important economic or social development.

TCEQ’s Executive Director (ED) performed technical review, required significantly more stringent effluent limits (notably, much lower phosphorus and nitrogen limits and higher DO in effluent), and modeled DO in Onion Creek. With these constraints, TCEQ’s modeling predicted DO would not fall below 5.0 mg/L. EPA and the U.S. Fish and Wildlife Service thereafter withdrew objections, concluding there would be no significant degradation and existing uses would be maintained.

After public comment, TCEQ issued a draft permit. Numerous protestants requested a contested‑case hearing at the State Office of Administrative Hearings (SOAH). Through settlement, all protestants except SOS withdrew in exchange for further restrictions (including lowering the maximum discharge to 822,500 gpd, additional storage infrastructure, and UV disinfection).

At SOAH, once TCEQ’s administrative record was introduced, the ED and the City enjoyed a statutory prima facie presumption that the draft permit complied with all state and federal legal requirements and protected health and the environment. SOS sought to rebut this presumption, primarily arguing:

• Increased nutrients (TP and TN) would fuel algal growth and reduce DO, harming aquatic life and endangered species.
• A DO drop from at least 6.44 mg/L to predicted levels around 5.0 mg/L (and as low as 4.87 mg/L in one QUAL‑TX run) exceeded a 10% threshold and thus, in SOS’s view, constituted “degradation” per se.
• TCEQ’s rules and implementation procedures required a parameter‑by‑parameter determination of degradation, rather than a holistic evaluation of water quality.

The Administrative Law Judge (ALJ) held a multi‑day hearing, received extensive expert testimony, and issued a detailed Proposal for Decision (PFD) concluding:

• The permit (as modified) satisfied Tier 1 and Tier 2 antidegradation requirements.
• TCEQ followed the proper antidegradation implementation procedures.
• TP, TN, and DO effluent limits were adequately protective of Onion Creek’s aquatic life.
• The ED’s and City’s experts were more credible and better versed in the applicable standards and models than SOS’s experts.
• SOS’s parameter‑by‑parameter antidegradation theory misread TCEQ’s rules, which focus on changes in water quality as a whole.

TCEQ adopted the PFD (with minor edits), issued 142 findings of fact and 22 conclusions of law, and granted the permit, expressly adopting the ED’s responses to public comments.

SOS sought judicial review. The trial court reversed, accepting SOS’s parameter‑by‑parameter approach and holding the permit invalid as a matter of law based on (allegedly) undisputed non‑de minimis changes in DO and nutrients.

The court of appeals (El Paso) split. The majority reversed the trial court and affirmed TCEQ’s order, holding that:

• The rules, “as they are written,” authorize a qualitative “whole water” antidegradation review.
• Substantial evidence supported TCEQ’s Tier 1 and Tier 2 findings.

The dissent, using a parameter‑focused frame, concluded the nutrient increases were sufficiently large to constitute degradation as a matter of law.

B. The Supreme Court’s Holding

The Supreme Court, in an opinion by Justice Devine, affirmed the court of appeals and upheld TCEQ’s final order. It held:

1. Tier 1: Substantial evidence supported TCEQ’s determination that DO in Onion Creek would meet the 5.0 mg/L site‑specific criterion and that existing uses would be maintained.
2. Tier 2: TCEQ’s practice of assessing “degradation” in terms of overall “water quality” (evaluating multiple parameters qualitatively and quantitatively) is consistent with the text of 30 Tex. Admin. Code § 307.5 and TCEQ’s implementation procedures. The rules do not require a pure parameter‑by‑parameter approach in which any non‑de minimis change in a single parameter is automatically disqualifying.
3. APA § 2001.141: TCEQ’s order complied with the APA. SOS failed to preserve any specific complaint about omitted underlying facts in its administrative motion for rehearing. In any event, no additional “underlying facts” were required, because TCEQ’s antidegradation findings are made under its rules, not under statutory language mandating particular criteria or findings in the enabling act (Water Code § 26.027).

The Court emphasized that its task was limited: to determine whether TCEQ complied with state law and its own rules, not to revisit EPA’s federal approvals or reengineer Texas’s antidegradation regime in light of SOS’s reading of federal policy.

III. Detailed Analysis

A. Precedents and Authorities Cited

1. Administrative law standards: substantial evidence and arbitrariness

The Court canvassed core Texas administrative law precedents to frame the standard of review:

• Substantial evidence:
  • Ammonite Oil & Gas Corp. v. Railroad Commission, 698 S.W.3d 198 (Tex. 2024) – substantial evidence is a “reasonableness” or “rational basis” test, giving “significant deference” to the agency’s expertise.
  • Mireles v. Texas Department of Public Safety, 9 S.W.3d 128 (Tex. 1999) – the question is not whether the agency’s decision is “correct,” but whether some reasonable basis in the record supports it.
  • Public Utility Commission v. Texas Industrial Energy Consumers, 620 S.W.3d 418 (Tex. 2021) – agency decisions carry a presumption of validity; challengers bear the burden to show otherwise.
• Deference and separation of roles:
  • N.E. Independent School District v. Riou, 598 S.W.3d 243 (Tex. 2020) – warns against courts “usurping the agency’s adjudicative authority” through reweighing evidence.
• Arbitrariness:
  • City of El Paso v. Public Utility Commission, 883 S.W.2d 179 (Tex. 1994); Gulf States Utilities Co. v. Public Utility Commission, 809 S.W.2d 201 (Tex. 1991) – an agency acts arbitrarily if it fails to consider a mandatory factor, considers an irrelevant factor, ignores applicable rules, or reaches a result so unreasonable as to be impermissible.

These authorities buttress the Court’s refusal to accept SOS’s invitation to reweigh the expert testimony and modeling or to treat the lowest modeled DO result (4.87 mg/L) as binding.

2. Construction of agency rules

On how to construe TCEQ’s antidegradation rules and implementation procedures, the Court relied on:

• TCEQ v. Maverick County, 642 S.W.3d 537 (Tex. 2022):
  • Agency rules are interpreted like statutes, according to their plain meaning, technical usage, or defined terms.
  • Court must not “add to or subtract from” the promulgated language or rewrite defined terms with alternative verbiage.
  • Critical to rejecting SOS’s attempt to recast “lowering of water quality” as “lowering of any water‑quality parameter.”
• Dyer v. TCEQ, 646 S.W.3d 498 (Tex. 2022):
  • Confirms that under Government Code § 2003.047, TCEQ (not the ALJ) is the ultimate fact finder.
  • TCEQ may revisit the record, reweigh evidence, and modify the ALJ’s findings and conclusions, if grounded in the record and explained.
  • Reinforces that the ALJ’s PFD is not binding on the Commission, a theme relevant to SOS’s attempt to recast the evidence.

3. APA “underlying facts” requirement

The Court’s APA analysis draws heavily on earlier Texas cases interpreting § 2001.141(d):

• Texas Health Facilities Commission v. Charter Medical‑Dallas, Inc., 665 S.W.2d 446 (Tex. 1984)
  • Distinguishes between:
    • Basic findings (or “underlying facts”), which should be specific, non‑conclusory, and expressed as the agency’s own findings, not mere recitations of evidence; and
    • Ultimate findings, which often mirror statutory standards (e.g., “public necessity” or “no degradation”).
  • Holds that § 2001.141(d) requires underlying facts only where the ultimate finding is “set forth in statutory language,” i.e., where the enabling statute itself mandates criteria the agency must apply.
  • Examples: mandatory criteria in former article 4418h § 3.10(b) (e.g., need, financial feasibility) required supporting basic findings; other non‑mandated factors did not.
• Texas Health Facilities Commission v. Presbyterian Hospital North, 690 S.W.2d 564 (Tex. 1985)
  • Applied Charter Medical to invalidate an order where “findings” were mere summaries of testimony or lacked sufficient specificity to support statutory criteria.
• Western Texas Utilities Co. v. Office of Public Utility Counsel, 896 S.W.2d 261 (Tex. App.—Austin 1995, no writ)
  • Clarifies that ultimate findings need underlying facts only when tied to mandatory statutory criteria.
• Hooks v. Texas Department of Water Resources, 645 S.W.2d 874 (Tex. App.—Austin 1983, writ ref’d n.r.e.)
  • Explains that objections to omitted findings must be raised on motion for rehearing with sufficient specificity to preserve them for judicial review.
• BFI Waste Systems of North America, Inc. v. Martinez Environmental Group, 93 S.W.3d 570 (Tex. App.—Austin 2002, pet. denied)
  • Similarly stresses that complaints about insufficient findings are waived unless properly preserved in a rehearing motion.

The Court uses these authorities to reach two key conclusions:

1. SOS did not preserve its specific claim about missing underlying facts in its rehearing motion, which contained only generalized assertions, not the particularized demands it later articulated on appeal.
2. Even on the merits, no underlying facts were required, because the “antidegradation” standard comes from TCEQ’s own rules, not from a statutory command in Water Code § 26.027, which merely allows denial of permits that conflict with law.

4. Federal Clean Water Act context

While the Court emphasizes that federal law compliance is not directly at issue, it situates Texas’s antidegradation program within the Clean Water Act framework:

• 33 U.S.C. §§ 1251–1389 (the Clean Water Act), particularly:
  • § 1251(a) – stating the Act’s objective to restore and maintain the “chemical, physical, and biological integrity” of U.S. waters.
  • § 1313(c) – requiring EPA approval and triennial review of state water‑quality standards.
  • § 1342(d) – EPA’s authority to review and veto state discharge permits.
• 40 C.F.R. § 131.12 – the federal antidegradation rule, which sets minimum requirements but leaves some implementation discretion to states.
• 63 Fed. Reg. 51164, 51193 (Sept. 24, 1998) – EPA’s approval of Texas’s assumption of the NPDES program, recognizing that EPA has not mandated a parameter‑by‑parameter approach and that Texas uses a “waterbody‑by‑waterbody approach.”
• EPA policy documents (handbooks, memoranda), which the Court notes are guidance, not binding law, and which even EPA acknowledges do not impose legal obligations.

The Court underscores that neither federal statutes nor EPA guidance override the plain text of Texas’s rules, and that EPA has explicitly accepted Texas’s whole‑waterbody approach for Tier 2 review.

B. The Court’s Core Legal Reasoning

1. Tier 1: Existing uses and DO criterion

Tier 1 of Texas’s antidegradation policy requires that “existing uses and water quality sufficient to protect those existing uses must be maintained.” For Onion Creek, the key numeric criterion is a minimum 24‑hour mean DO of 5.0 mg/L, tailored to its designation as a “high aquatic life use” water (30 Tex. Admin. Code §§ 307.7(b)(3)(A)(i), .10(1), App’x A).

SOS argued that Tier 1 was violated because one of the City’s QUAL‑TX models predicted DO could drop to 4.87 mg/L at the critical condition, below the 5.0 mg/L criterion.

The Court responds in several steps:

1. Conflicting modeling: TCEQ’s own modeling, using stricter effluent limits imposed during technical review, predicted DO would not fall below 5.0 mg/L. Under substantial evidence review, TCEQ was not required to adopt the City’s lowest modeled result.
2. More conservative assumptions: All model runs (by City and TCEQ) used the higher, original requested discharge volume of 995,000 gpd. The final permit authorizes only 822,500 gpd. Thus, even TCEQ’s modeling was conservative relative to the actual authorized discharge.
3. Existing uses preserved: With a DO of at least 5.0 mg/L and other protective limits (including stringent nutrient and disinfection requirements), substantial evidence supports TCEQ’s findings that the discharge will not impair existing uses such as high aquatic life and recreation.

The Court therefore rejects SOS’s Tier 1 challenge under the substantial evidence standard.

2. Tier 2: “Degradation” and the whole‑waterbody approach

a. The text of the antidegradation rule

Tier 2 (30 Tex. Admin. Code § 307.5(b)(2)) provides, in relevant part:

No activities subject to regulatory action that would cause degradation of waters that exceed fishable/swimmable quality are allowed unless it can be shown to the satisfaction of the commission that the lowering of water quality is necessary for important economic or social development. Degradation is defined as a lowering of water quality by more than a de minimis extent, but not to the extent that an existing use is impaired.

The Court emphasizes:

• The definition of degradation uses the phrase “lowering of water quality,” not “lowering of any water‑quality parameter.”
• “Water quality” is a concept that inherently encompasses multiple physical, chemical, and biological attributes—not a single numeric value.
• Reading “water quality” as “any individual parameter” would improperly rewrite the rule, contrary to Maverick County’s interpretive principles.

Thus, as a matter of text, Tier 2’s focus is the condition of the water body as a whole.

b. Implementation procedures and parameters of concern

SOS argued that TCEQ’s 2010 “Procedures to Implement the Texas Surface Water Quality Standards” (IPs) mandated a parameter‑by‑parameter approach. The Court carefully reads those procedures and reaches the opposite conclusion:

• The IPs recognize that multiple “parameters of concern”—including DO, nutrients, bacteria, solids, metals, etc.—collectively shape water quality.
• The IPs provide methods for evaluating individual parameters (e.g., modeling DO, assessing nutrient loading), but this is consistent with a whole‑water approach: evaluating overall health begins with analyzing components.
• The IPs expressly describe antidegradation review as a qualitative assessment based on narrative and numeric criteria, informed by data but not reducible to a single numeric trigger.

The Court highlights, as especially revealing, the IPs’ treatment of “assimilative capacity” and their examples of when degradation is “likely” to occur.

c. Assimilative capacity and screening thresholds

The IPs describe a screening concept of “assimilative capacity” (loosely, the existing “room” between baseline ambient water quality and the applicable criterion). They state:

New discharges that use less than 10% of the existing assimilative capacity of the water body at the edge of the mixing zone are usually not considered to constitute potential degradation as long as the aquatic ecosystem in the area is not unusually sensitive to the pollutant of concern. New discharges that use 10% or greater of the existing assimilative capacity are not automatically presumed to constitute potential degradation but will receive further evaluation.

From this, the Court draws key points:

• Even when a particular parameter uses >10% of the assimilative capacity, this does not automatically constitute degradation.
• Instead, such a result triggers “further evaluation”—a qualitative, case‑specific analysis of water quality.
• Critically, the IPs explicitly state: “this screening procedure is not applicable to dissolved oxygen,” undermining SOS’s attempt to derive a DO‑specific bright line from the assimilative capacity discussion.

d. The 0.5 mg/L DO example

SOS relied heavily on an IPs example under “Examples where degradation is likely to occur”:

Increased loading of oxygen‑demanding substances that is projected to decrease dissolved oxygen by more than 0.5 mg/L for a substantial distance in a water body that has exceptional quality aquatic life and a relatively unique and potentially sensitive community of aquatic organisms.

SOS argued: if a 0.5 mg/L decrease in DO is “likely” degradation in this example, then a 1.44 mg/L drop (6.44 → 5.0 mg/L) in Onion Creek must be degradation a fortiori.

The Court dismantles this argument:

1. The example is expressly limited to:
   • Waters with “exceptional aquatic life use,” not “high aquatic life use” like Onion Creek; and
   • A projected decrease “for a substantial distance” in the water body, whereas the modeling for Onion Creek showed DO returning to baseline very quickly downstream of the discharge.
2. More fundamentally, the IPs themselves caution that the listed examples:
   • “do not define degradation”;
   • are “general guidelines”; and
   • require case‑specific determinations depending on the water body and aquatic communities, such that “lower increases in loading may constitute degradation in some circumstances, and higher loadings may not” in others.

Accordingly, the 0.5 mg/L DO example is not a binding threshold; it merely identifies a scenario “where degradation is likely,” triggering closer scrutiny, not per se failure. The ultimate question remains whether water quality is lowered more than de minimis, taking all relevant factors into account.

e. Section 307.5(c)(2)(B) and parameter‑specific references

SOS and certain amici pointed to 30 Tex. Admin. Code § 307.5(c)(2)(B), which states:

For dissolved oxygen, analyses of degradation under Tier 2 must utilize the same critical conditions as are used to protect instream criteria. For other parameters, appropriate conditions may vary.

The Court reads this provision as:

• Recognizing that DO analysis must use the same critical conditions as are used to protect DO criteria (e.g., worst‑case low‑flow, high‑temperature conditions), and
• Implying that other parameters may require different critical conditions.

But this cross‑reference to parameter‑specific **methods** does not change the Tier 2 **standard**, which remains “lowering of water quality by more than a de minimis extent.” It confirms that parameters are analyzed individually as part of the inquiry—but the ultimate decision is holistic and qualitative, not mechanistically parameter‑by‑parameter.

f. Clean Water Act goals do not override rule text

SOS invoked the Clean Water Act’s stated objective to maintain the “chemical, physical, and biological integrity” of U.S. waters, and EPA guidance advocating robust antidegradation programs. The Court acknowledges this policy background but stresses:

• EPA has approved Texas’s water‑quality standards and implementation procedures, including its waterbody‑by‑waterbody approach to Tier 2.
• EPA policy documents and guidance do not have the force of law and cannot override or rewrite Texas rules.
• The Court’s role is to interpret and enforce Texas rules “as they are written,” not to import extra‑textual federal policy preferences.

Thus, even if one could read EPA documents as favoring a parameter‑by‑parameter approach, that does not change the meaning of § 307.5(b)(2).

g. No improper “collapse” of Tier 1 and Tier 2

SOS alleged TCEQ improperly “collapsed” Tier 2 into Tier 1 by focusing solely on preservation of existing uses and ignoring degradation of better‑than‑necessary water quality. The Court agrees the tiers differ in function but notes there is “substantial overlap”:

• Both tiers require protection of existing uses.
• Tier 2 goes further by protecting high‑quality waters from more‑than‑de‑minimis lowering of water quality, even if uses are preserved.

The Court finds that:

• TCEQ’s findings separately recognize degradation and existing uses (e.g., FOF 78, 88, 90), and
• TCEQ conducted a genuine Tier 2 review, considering changes to DO and nutrients in light of Onion Creek’s uses and overall water quality.

If SOS’s argument is that TCEQ did not use the precise definitional phrase “no more than a de minimis extent” in its findings, the Court dismisses this as hyper‑technical: the findings sufficiently track the Tier 2 standard, and nothing in the APA requires exact duplication of definitional phrasing.

3. APA § 2001.141 and “underlying facts”

a. The statutory framework

APA § 2001.141(b), (d) provides:

• § 2001.141(b) – A final agency decision in a contested case must include “separately stated findings of fact and conclusions of law.”
• § 2001.141(d) – If a finding of fact is “set forth in statutory language,” it must be accompanied by “a concise and explicit statement of the underlying facts supporting the finding.”

Working through Charter Medical and its progeny, the Court distinguishes:

• Ultimate findings in statutory language (e.g., “no degradation,” “public necessity”), which may require underlying facts if the statute mandates those criteria; and
• Ultimate findings grounded only in agency rules or non‑mandatory statutory factors, which do not automatically trigger § 2001.141(d).

b. Preservation: SOS’s rehearing motion was too general

Before reaching the substance, the Court holds SOS failed to preserve its complaint. Its motion for rehearing did not:

• Identify specific ultimate findings (e.g., FOFs 85–90) allegedly lacking supporting underlying facts; or
• Specify what underlying facts were missing (e.g., baseline and post‑discharge numeric values for DO and nutrients, calculated percentage changes, etc.).

Citing Hooks and BFI Waste, the Court reiterates:

• To preserve an APA fact‑finding complaint, the party must raise it in a rehearing motion “with the requisite degree of specificity.”
• Vague references to “lack of underlying facts” are insufficient; the motion must designate the allegedly omitted findings with particularity, so the agency has an opportunity to correct or justify them.

SOS’s failure to do so bars judicial review of that complaint.

c. No “statutory language” finding was at issue

Even if preserved, the Court holds § 2001.141(d) does not require more detailed findings here, because:

• The only relevant statute, Water Code § 26.027(a), (b),:
  • Authorizes TCEQ to issue discharge permits,
  • Specifies certain application content requirements, and
  • Allows TCEQ to “refuse to issue a permit” when it finds issuance would violate any state or federal law or rule.
• Section 26.027 does not mandate any particular criteria TCEQ must apply to grant a permit (nor does it require TCEQ to make affirmative findings that the permit complies with each and every law or rule).
• The antidegradation criteria instead derive from TCEQ’s own rule, § 307.5, not from statutory text.

Under Charter Medical, only statutorily mandated criteria—those the Legislature has specifically required the agency to apply—trigger the underlying‑facts requirement. By contrast:

• TCEQ’s conclusion that “[t]he proposed discharge will comply with the applicable antidegradation requirements” is an application of its rule, not a statutory criterion embedded in the enabling act.
• Thus, the finding is not “set forth in statutory language” for purposes of § 2001.141(d), and no additional underlying facts were required by the APA.

The Court also warns of the “absurd” consequences of SOS’s reading: if § 26.027’s general reference to “any state or federal law or rule” triggered § 2001.141(d), TCEQ would have to:

• Make and support with underlying facts a negative finding that each permit complies with every potentially applicable statute, regulation, and rule; and
• Do so in every contested case, despite the statutory “prima facie” presumption in § 2003.047 that draft permits comply with all legal requirements unless protestants carry a rebuttal burden.

This, the Court concludes, would be “impossibly onerous” and inconsistent with the design of § 2003.047.

Accordingly, TCEQ’s extensive findings—including those describing the modeling results, DO criteria, effluent limits, and ultimate conclusion that there is no more‑than‑de‑minimis lowering of water quality—suffice under the APA.

C. Impact and Implications

1. Environmental regulation and antidegradation

The decision cements several principles that will shape future water‑quality permitting and challenges in Texas:

• Whole‑waterbody focus for Tier 2
  • Antidegradation review must consider overall water quality, taking into account multiple parameters, narrative criteria, and site‑specific factors.
  • A single parameter change—even a significant one numerically—does not automatically equate to “degradation” as a matter of law.
  • TCEQ retains discretion to decide, case‑by‑case, whether the cumulative effect is more than de minimis.
• Parameters as inputs, not dispositive triggers
  • Numeric modeling of DO, nutrients, and other pollutants is essential, but serves as evidence—not as binding legal thresholds unless the rule expressly says so.
  • EPA’s recommended screening thresholds (e.g., a 10% assimilative capacity “cap”) and IPs examples (e.g., 0.5 mg/L DO drop in exceptional waters) are guidance, not strict legal rules.
• Flexibility for TCEQ
  • TCEQ’s Tier 2 review remains a qualitative expert judgment, informed by science but not mechanically determined by any single metric.
  • This preserves flexibility to weigh competing evidence, apply professional judgment, and adopt stringent permit conditions tailored to local conditions.

From an environmental‑protection perspective, this approach has both strengths and risks:

• Strength: It allows TCEQ to consider complex ecological interactions rather than being locked into simplistic numerical triggers that may be over‑ or under‑protective in particular settings.
• Risk: It may make it harder for challengers to win on purely legal grounds; instead, they must convince TCEQ (and then courts under a deferential standard) that, on balance, water quality will be materially lowered, not just that a parameter moves by X percent.

2. Litigation strategy for challengers and permittees

The opinion significantly affects litigation strategy in contested‑case hearings and subsequent judicial review:

• Parameter‑by‑parameter theories weakened
  • Opponents can no longer argue that any more‑than‑de‑minimis change in a single parameter automatically violates Tier 2.
  • Instead, they must present persuasive expert testimony connecting parameter changes to concrete ecological harm and overall lowering of water quality.
• Importance of the “prima facie” presumption
  • Once TCEQ’s administrative record is admitted, the draft permit is presumed legally and technically sound (§ 2003.047(i-1)).
  • Protestants must present evidence that the permit violates a specifically applicable legal requirement—not just raise general concerns.
  • The Court’s APA analysis underscores this burden allocation; TCEQ is not required to disprove every hypothetical violation.
• Preservation of error is critical
  • Any alleged deficiency in findings, including missing underlying facts, must be raised with specificity in the motion for rehearing before the agency.
  • Generalized objections will not preserve sophisticated APA arguments for judicial review.
• Role of expert credibility
  • The ALJ’s finding that TCEQ’s and the City’s experts were more experienced with Texas standards and modeling tools was important.
  • Courts will be reluctant to disturb the Commission’s reliance on such credibility determinations under substantial evidence review.

3. Administrative law: narrowing § 2001.141(d)

The decision further clarifies and arguably narrows when § 2001.141(d) demands underlying facts:

• Agency rules are not “statutory language”
  • Ultimate findings framed in the language of an agency rule (e.g., “no degradation,” “complies with antidegradation requirements”) do not automatically require supporting basic findings under § 2001.141(d).
  • That requirement is triggered only when the Legislature itself has prescribed mandatory criteria or findings in the enabling statute.
• Enabling statutes phrased at a very high level do not create specific fact‑finding duties
  • Section 26.027’s broad authorization to deny permits that conflict with “any state or federal law or rule” is not itself a set of criteria requiring itemized factual support.
  • It would be unworkable to demand that every TCEQ order recite underlying facts for each possible law or rule that might be implicated.

This reasoning will be cited in future cases where challengers argue that an agency’s order is invalid because it did not fully dissect each element of compliance in separate findings. Agencies can rely on the decision to defend orders that:

• Contain sufficiently clear and specific factual findings on the key disputed issues, and
• Apply their rules and standards, even where those rules echo broad statutory goals.

D. Complex Concepts Simplified

1. Antidegradation policy and tiers

An “antidegradation policy” is a regulatory scheme designed to prevent backsliding in water quality. The idea is:

• Tier 1: Protect current uses of the water (e.g., fishing, swimming, aquatic life). You cannot impair existing uses.
• Tier 2: For waters that are cleaner than strictly necessary for uses (i.e., “high quality” or better than fishable/swimmable), you generally may not allow significant degradation, even if uses would remain unimpaired.
• Tier 3: “Outstanding national resource waters” receive the highest protection—no lowering of water quality is allowed, with limited exceptions.

This case deals with Tiers 1 and 2 for a high‑quality segment (Onion Creek).

2. “De minimis” and “degradation”

“De minimis” is Latin for “about minimal things.” In law, it means changes too small or trivial to matter legally. Under Texas’s Tier 2:

• Degradation occurs when water quality is lowered by more than a de minimis extent—but not so much that it impairs existing uses (that level of harm would also violate Tier 1).
• Thus, the key Tier 2 question is: does the permit cause a non‑trivial deterioration of overall water quality?

3. Dissolved oxygen (DO) and aquatic life

Dissolved oxygen is the amount of oxygen gas present in water, usually measured in milligrams per liter (mg/L). Aquatic organisms need adequate DO to survive; too little DO leads to stress or death, especially for sensitive species.

Water‑quality standards specify minimum DO levels tailored to the designated aquatic life use (e.g., high, intermediate, or exceptional). For Onion Creek, TCEQ set a site‑specific minimum mean DO of 5.0 mg/L for “high aquatic life use.”

4. Assimilative capacity

“Assimilative capacity” refers, in essence, to how much pollution a water body can receive without violating a particular water‑quality criterion. If baseline water quality is much better than the criterion, there may be significant assimilative capacity; if it is already close to the criterion, capacity is small.

States and EPA sometimes use percentage of assimilative capacity consumed (e.g., 10%) as a screening tool to decide whether a proposed discharge is likely to cause “degradation” and thus warrants more intensive analysis.

5. Narrative vs numeric criteria

Water‑quality standards typically include:

• Numeric criteria: Specific numbers (e.g., “DO shall not be less than 5.0 mg/L (24‑hour mean)”).
• Narrative criteria: More qualitative statements (e.g., “nutrients must not cause excessive algal growth that impairs uses”).

Antidegradation review integrates both: numeric modeling and measurements, plus narrative judgments about ecological condition and use protection.

6. Contested‑case hearings and substantial evidence review

A “contested case” is like a trial within the administrative agency system:

• An ALJ conducts an evidentiary hearing, hears witnesses, and issues a Proposal for Decision (PFD) with recommended findings and conclusions.
• The agency’s governing body (here, TCEQ) may adopt, modify, or reject the PFD, as long as it stays within the evidentiary record and explains any material changes.

On judicial review, the court applies the “substantial evidence” standard:

• The court asks only whether some reasonable basis in the record supports the agency’s decision.
• The court may not reweigh evidence or decide which experts it finds more persuasive.

IV. Conclusion: Key Takeaways

The Texas Supreme Court’s decision in Save Our Springs Alliance v. TCEQ establishes and clarifies several important principles:

1. Antidegradation is about water quality as a whole. “Degradation” under Tier 2 means a more‑than‑de‑minimis lowering of overall water quality, not merely any non‑trivial change in a single parameter. TCEQ lawfully applies a qualitative, whole‑waterbody review that considers multiple parameters, narrative criteria, and site‑specific conditions.
2. Numeric changes in DO or nutrients are evidence, not automatic violations. Projected reductions in DO from 6.44 mg/L to about 5.0 mg/L at the discharge point, with rapid recovery downstream, do not, by themselves, compel a finding of degradation. The agency must—and did—evaluate how such changes affect aquatic life and overall water quality.
3. Implementation procedures guide, but do not rigidly dictate, outcomes. Screening tools like assimilative‑capacity percentages and examples of “likely” degradation (e.g., 0.5 mg/L DO drops in exceptional waters) prompt closer review but do not set inflexible legal thresholds.
4. The APA’s “underlying facts” requirement is limited. Section 2001.141(d) requires underlying factual support only for findings cast in statutory language that the Legislature has made mandatory criteria in an enabling act. It does not apply to ultimate findings under agency rules alone, nor to general statutory authorizations like Water Code § 26.027.
5. Preservation and burdens matter. Protestants must:
   • Overcome the statutory presumption that draft permits comply with all legal and technical requirements, and
   • Preserve specific complaints (including about missing findings) in motions for rehearing to the agency before seeking judicial review.

The decision strengthens TCEQ’s hand in defending permits against antidegradation challenges and reinforces a deferential, text‑driven approach to reviewing Texas administrative orders. For environmental advocates, it signals that future challenges must focus less on bright‑line numeric triggers and more on developing compelling, science‑grounded evidence that a given discharge will materially lower water quality in fact—not merely move individual parameters by a given amount.