EPA Deregulation Timeline: From 2017 to the 2025 Agenda

Abstract

The trajectory of environmental governance in the United States has historically been defined by a tension between economic expansion and ecological preservation. However, the administration of President Donald J. Trump, encompassing his first term (2017–2021) and the aggressive initiation of his second term (2025–present), represents a distinct and transformative era in this continuum. This report provides an exhaustive, multi-dimensional analysis of the Environmental Protection Agency (EPA) during these periods. It dissects the ideological shift from "cooperative federalism" to "energy dominance," the structural deconstruction of the administrative state, and the specific scientific and legal mechanisms employed to deregulate the nation’s air, water, and chemical safety frameworks. By synthesizing legal theory, atmospheric chemistry, hydrology, and toxicology, this analysis elucidates the profound shift in the burden of proof required for environmental protection and the long-term implications for the American landscape.

Part I: The Ideological and Structural Foundations for EPA Deregulation

The transformation of the EPA under the Trump administration cannot be understood merely as a series of isolated regulatory rollbacks. Rather, it is the manifestation of a coherent ideological framework that redefines the relationship between the federal government, the market, and the environment. This framework, developed during the first term and radically accelerated in the second, rests on two pillars: the doctrine of "Energy Dominance" and the deconstruction of the "Administrative State."

1.1 From Protection to Production: The Doctrine of Energy Dominance

Since its founding in 1970, the EPA’s mandate has been to protect human health and the environment, often acting as a check on industrial excesses. The Trump administration, however, explicitly reframed the agency's mission, subordinating environmental regulation to the imperatives of domestic energy production. This was not simply a call for "balance" but a declaration of "Energy Dominance"—a geopolitical and economic strategy positing that maximizing the extraction of fossil fuels (coal, oil, and natural gas) is a prerequisite for national security and economic prosperity.¹

1.1.1 The First Term (2017–2021): The Proof of Concept

In the first term, this doctrine was operationalized through Executive Order 13778 and the "Promoting Energy Independence and Economic Growth" order. These directives compelled agencies to review and rescind any regulation that "burdened" the development or use of domestically produced energy resources. Under Administrators Scott Pruitt and Andrew Wheeler, the agency began the arduous process of reversing Obama-era rules, specifically targeting the Clean Power Plan and the Waters of the United States (WOTUS) rule.³ The administration’s approach was characterized by a "retreat" from federal oversight, often justified by a narrow reading of statutory authority.

1.1.2 The Second Term (2025–Present): The "Day of Deregulation"

The second term, commencing in January 2025, dispensed with the tentative nature of the first. On January 20, 2025, President Trump signed the "Unleashing American Energy" Executive Order, which declared it the official policy of the United States to maximize production on federal lands and waters.² This order went further than its predecessors by mandating that all regulatory requirements be grounded in "clearly" demonstrated statutory authority, a direct nod to the Supreme Court's evolving jurisprudence on the "Major Questions Doctrine".²

This ideological fervor culminated on March 12, 2025, when EPA Administrator Lee Zeldin announced the "biggest deregulatory action in U.S. history".⁵ In a coordinated "Day of Deregulation," Zeldin unveiled a list of 31 specific actions targeting the agency's most significant rules. The rhetoric employed was striking; Zeldin described the actions as "driving a dagger straight into the heart of the climate change religion".⁵ This statement signaled a departure from technocratic debates over cost-benefit analysis to a cultural and ideological confrontation with the premise of environmental regulation itself. The 31 actions were not merely pauses but targeted removals of the Biden administration's entire environmental legacy, including the Clean Power Plan 2.0, the methane rules for oil and gas (OOOOb/c), and the Mercury and Air Toxics Standards.⁷

1.2 The Deconstruction of the Administrative State

The implementation of this doctrine required a reshaping of the EPA’s institutional structure. The administration viewed the career civil service—the scientists, lawyers, and policy analysts who serve across administrations—as a "deep state" obstacle to reform.⁸

1.2.1 Personnel and "Hollowing Out"

During the first term, the EPA experienced a significant exodus of personnel. The administration utilized hiring freezes and budget cuts to reduce the workforce, leading to the lowest staffing levels since the Reagan administration.¹ Scientific advisory boards were purged of academic researchers, who were replaced by industry-affiliated consultants. The administration argued that academics receiving EPA grants had conflicts of interest, a rationale that effectively disqualified the nation's leading environmental researchers from advising the agency.⁹

In the second term, this strategy was institutionalized through the revival of concepts similar to "Schedule F," which reclassifies career civil servants as political appointees, stripping them of tenure protections. Project 2025, the blueprint that heavily influenced the second term's transition, called for the elimination of "duplicative" departments and the rotation of senior executives to regional offices to break up entrenched bureaucratic power.¹⁰ Administrator Zeldin’s March 2025 announcement included a directive to "Reconstitute the Science Advisory Board (SAB) and the Clean Air Scientific Advisory Committee (CASAC)," signaling a renewed effort to align the agency’s scientific intake with its political objectives.⁵

Part II: Atmospheric Science and the Regulation of Greenhouse Gases

The regulation of greenhouse gases (GHGs) under the Clean Air Act (CAA) represents the most contentious arena of EPA policy. The Trump administration’s actions in this domain rely on a complex interplay of legal theory and technical disputes regarding the thermodynamics of power generation.

2.1 The Battle Over Power Plants: Efficiency vs. Transformation

The central legal and technical debate concerns Section 111(d) of the Clean Air Act, which requires the EPA to determine the "Best System of Emission Reduction" (BSER) for existing pollution sources.

2.1.1 The Clean Power Plan (CPP) and Generation Shifting

The Obama-era Clean Power Plan determined that the "best system" for reducing carbon emissions was the interconnected electric grid itself. Because electricity is fungible, the system could reduce emissions by shifting generation from high-emitting coal plants to lower-emitting natural gas and renewable sources. This "generation shifting" approach regulated "outside the fence line" of individual power plants.¹²

2.1.2 The Affordable Clean Energy (ACE) Rule (First Term)

The first Trump EPA repealed the CPP, arguing that Section 111(d) only authorized the agency to regulate physical equipment "inside the fence line" of a specific facility. In its place, they promulgated the Affordable Clean Energy (ACE) rule in 2019.¹²

Technical Analysis: Heat Rate Improvements. The ACE rule defined BSER as "heat rate improvements" (HRI) at coal-fired power plants. The heat rate is the amount of fuel energy (in British Thermal Units or BTUs) required to generate one kilowatt-hour (kWh) of electricity. Lowering the heat rate improves efficiency.

• The Mechanism: The rule encouraged upgrades to boiler feed pumps, air preheaters, and turbine blades.

• The Rebound Effect: Critics and atmospheric scientists identified a perverse incentive known as the "rebound effect." By improving the efficiency of a coal plant, the marginal cost of generating electricity at that plant decreases. In a competitive wholesale electricity market, a cheaper plant is dispatched more often. Therefore, while the plant emits less CO2 per unit of electricity, it might run for more hours, potentially increasing its total absolute emissions.¹²

Legal challenges led to the ACE rule being vacated by the D.C. Circuit in 2021, but the Supreme Court ultimately vindicated the Trump administration's legal theory in West Virginia v. EPA (2022). The Court ruled that "generation shifting" was a "major question" requiring explicit congressional authorization, which the CAA did not provide.¹⁴

2.1.3 The Repeal of Clean Power Plan 2.0 (Second Term)

In response to West Virginia, the Biden administration issued "Clean Power Plan 2.0" in 2024, which based BSER on technology standards like Carbon Capture and Sequestration (CCS) and hydrogen co-firing—technologies that can be applied "inside the fence".¹⁶

On March 12, 2025, Administrator Zeldin listed Clean Power Plan 2.0 as a priority for reconsideration and repeal.⁵ The administration’s argument is twofold:

1. Technological Feasibility: They argue that CCS and green hydrogen are not "adequately demonstrated" or commercially viable at scale, rendering the standards a de facto mandate to shut down coal plants, which would violate the West Virginia precedent.¹⁸

2. Grid Reliability: The administration contends that forcing the retirement of baseload coal generation threatens the stability of the electric grid, particularly as electricity demand rises from data centers and electrification.⁵

2.2 The Endangerment Finding: Striking at the Root

While the battles over the CPP and ACE focused on how to regulate, the second Trump term moved to question whether to regulate at all. The legal foundation for all EPA climate rules is the 2009 "Endangerment Finding," which concluded that six greenhouse gases—carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—threaten public health and welfare.²⁰

In July 2025, Administrator Zeldin announced an intention to rescind the Endangerment Finding.²⁰ This is a radical legal and scientific maneuver. To succeed, the EPA must construct a new administrative record demonstrating that the scientific consensus on climate change has fundamentally shifted or was flawed in 2009.

• The Scientific Argument: The administration is likely to rely on "Gold Standard Science" principles (discussed in Part V) to exclude models reliant on high-sensitivity climate projections (like RCP8.5) and to emphasize uncertainties regarding the direct toxicity of ambient CO2.²¹

• The Implication: If the Endangerment Finding is rescinded, the EPA would lose its legal authority (and obligation) to regulate GHG emissions from motor vehicles, power plants, and oil and gas wells. This would effectively dismantle the federal climate regulatory apparatus without a single vote in Congress.⁷

Part III: Methane and the Oil & Gas Sector

Methane is a short-lived but potent climate forcer. While it persists in the atmosphere for only about 12 years (compared to centuries for CO2), it traps heat far more effectively. The Intergovernmental Panel on Climate Change (IPCC) estimates its Global Warming Potential (GWP) at roughly 83 times that of CO2 over a 20-year period.²³

3.1 Atmospheric Chemistry and the "Methane Gap"

Methane removal from the atmosphere occurs primarily through oxidation by the hydroxyl radical (OH). This reaction produces carbon dioxide and water vapor. Because methane is a precursor to tropospheric ozone (smog), reducing methane emissions has the dual benefit of mitigating near-term warming and improving air quality.²⁴

A critical scientific challenge in regulating methane is the discrepancy between "bottom-up" and "top-down" estimates.

• Bottom-Up: Regulatory inventories typically estimate emissions by counting equipment (valves, flanges, compressors) and multiplying by an assumed "leak factor."

• Top-Down: Studies using satellites and aircraft to measure actual atmospheric concentrations of methane consistently find emissions are 4 to 6 times higher than bottom-up inventories suggest.²⁶ This "methane gap" is largely attributed to "super-emitters"—intermittent, massive leaks from malfunctions or unlit flares that standard inventories miss.

3.2 The OOOOb/c Rules and the 2025 Reconsideration

In 2024, the EPA finalized the "OOOOb" (for new sources) and "OOOOc" (for existing sources) rules. These regulations were designed to close the methane gap by requiring:

1. Zero-Emissions Equipment: Phasing out gas-driven pneumatic controllers, which vent methane by design.

2. Super-Emitter Program: Empowering third parties to use remote sensing to detect large leaks and forcing operators to investigate.

3. Flare Monitoring: Requiring continuous monitoring of flares to ensure they are actually lit and burning gas efficiently.²⁸

In 2025, the Trump EPA targeted these rules for reconsideration. The oil and gas industry argued that the requirements for continuous flare monitoring were technically infeasible due to supply chain constraints and the lack of reliable monitoring equipment.²⁹ Accepting this argument, the EPA issued an Interim Final Rule in July 2025, delaying compliance deadlines by 18 months.³⁰

Scientific Consequence: By delaying the implementation of continuous monitoring and the super-emitter program, the EPA allows the "methane gap" to persist. The administration’s reliance on industry self-reporting, combined with a proposal to eliminate the Greenhouse Gas Reporting Program (Subpart W), creates a data vacuum. Without rigorous monitoring, "fugitive emissions" from unlit flares and leaking tanks will continue to enter the troposphere undetected, undermining any theoretical claims of "clean" natural gas production.³²

Part IV: Hydrology and the Definition of "Waters of the United States"

The definition of "Waters of the United States" (WOTUS) under the Clean Water Act (CWA) determines the geographic reach of federal pollution protections. This definition is not merely a legal line on a map; it dictates the fate of vast hydrological networks that underpin water quality and flood resilience.

4.1 The Science of Connectivity: Ephemeral Streams

The core scientific dispute revolves around "ephemeral streams"—channels that flow only after precipitation events. In the arid American West, ephemeral streams constitute the majority of the river network.

• Hydrological Connectivity: Scientific consensus establishes that ephemeral streams are functionally connected to downstream navigable waters. They transport sediment, nutrients, and organic carbon essential for aquatic food webs. They also recharge groundwater aquifers.³⁴

• Wetland Functions: Wetlands that are geographically isolated (lacking a surface connection) still perform critical functions, such as filtering agricultural runoff (denitrification) and storing floodwaters.

4.2 The Navigable Waters Protection Rule (Term 1)

In its first term, the Trump EPA promulgated the Navigable Waters Protection Rule (NWPR) in 2020. This rule adopted a restrictive definition based on the opinion of Justice Antonin Scalia in the 2006 Rapanos case. It excluded ephemeral streams and wetlands without a "continuous surface connection" to navigable waters.³⁶

Impact Analysis: A machine learning analysis of the NWPR found that it deregulated approximately 690,000 stream miles and removed protections for one-fourth of all wetlands in the U.S..³⁷ This massive deregulation meant that developers and industrial operations could fill in wetlands or discharge pollutants into ephemeral streams without a federal permit. The economic valuation of the lost flood prevention benefits from these deregulated wetlands was estimated at over $250 billion.³⁸

4.3 The "Sackett Plus" Rule (Term 2)

The legal landscape shifted decisively with the Supreme Court's 2023 ruling in Sackett v. EPA. The Court rejected the "significant nexus" test (which protected waters based on their chemical/biological connection) and mandated a test requiring a "continuous surface connection".³⁹

While Sackett compelled a narrowing of WOTUS, the second Trump term sought to go even further. In late 2025, the EPA proposed a new rule (the "Sackett Plus" approach) that would remove "interstate waters" as a standalone category of jurisdiction.41 Historically, interstate waters were federally regulated regardless of their navigability to prevent cross-border pollution disputes. By removing this category, the administration effectively cedes the management of complex interstate watersheds entirely to state discretion.

Technical Implication: This creates a fragmentation of watershed management. A polluter in an upstream state could discharge into a non-navigable interstate stream, degrading water quality in a downstream state, with the EPA claiming it lacks jurisdiction to intervene.42

Part V: Toxic Pollutants and Industrial Effluents

The regulation of toxic discharges from industry involves complex chemistry and the selection of "Best Available Technology" (BAT). The Trump EPA’s actions in this area demonstrate a consistent preference for older, cheaper technologies over advanced, zero-discharge systems.

5.1 Steam Electric Power Generating Effluent Guidelines (ELGs)

Coal-fired power plants are significant sources of toxic metals, particularly selenium (Se), arsenic (As), and mercury (Hg), which are concentrated in the wastewater from flue gas desulfurization (scrubbers) and ash transport.⁴³

5.1.1 The Bioaccumulation Problem

Selenium is a metalloid that is particularly dangerous in aquatic environments due to bioaccumulation. It enters the food web through algae and insects, concentrating at each trophic level. In fish and waterfowl, elevated selenium levels cause reproductive failure (teratogenicity) and spinal deformities, even when water concentrations appear low.⁴⁴

5.1.2 Technology: Precipitation vs. Membranes

• Chemical Precipitation (CP): The traditional treatment method involves adding chemicals (like iron or organosulfides) to precipitate metals as solids. While effective for mercury and arsenic, CP is often ineffective at removing soluble forms of selenium (selenate).

• Membrane Filtration / Biological Treatment: Advanced technologies, such as biological reactors or reverse osmosis membranes, can remove selenium to very low levels. The 2015 and 2024 rules mandated these technologies.⁴⁵

5.1.3 The 2025 Reconsideration

In the second term, the EPA announced a reconsideration of the 2024 ELG rule.7 The administration argues that membrane technologies are prohibitively expensive and technically complex, potentially forcing "peaker" plants to close. The proposal suggests reverting to standards based on chemical precipitation or offering broad exemptions for "low-utilization" plants.46

Scientific Consequence: Allowing low-utilization plants to discharge wastewater treated only with chemical precipitation means that pulses of selenium-rich water will continue to enter aquatic ecosystems. Because selenium bioaccumulates, even intermittent discharges can have lasting ecological impacts.47

5.2 The Mercury and Air Toxics Standards (MATS)

The MATS rule regulates emissions of mercury from power plant smokestacks. Mercury released into the air eventually deposits into waterbodies, where it is methylated by bacteria into methylmercury—a potent neurotoxin that accumulates in fish and poses risks to human fetal brain development.³²

In the first term, the EPA attacked the legal justification for MATS by altering the cost-benefit analysis. The agency argued that the "co-benefits" of the rule—the massive health benefits gained from reducing particulate matter (PM2.5) as a side effect of installing mercury controls—should not be counted. By considering only the direct benefits of mercury reduction (quantified narrowly as lost IQ points), the EPA claimed the costs to industry outweighed the benefits.³²

In the second term, the administration placed the 2024 strengthening of MATS on its deregulation list, labeling it as a rule that "improperly targeted" coal plants.⁷ This signals a return to a regulatory philosophy that dismisses co-benefits and prioritizes the economic solvency of the coal sector over the neurotoxicological protection of the population.

Part VI: Chemical Safety and Pesticide Regulation

The EPA’s Office of Chemical Safety and Pollution Prevention (OCSPP) oversees the registration of pesticides and industrial chemicals. The Trump administration’s approach here has been characterized by a skepticism of epidemiological evidence when it conflicts with agricultural utility.

6.1 Chlorpyrifos and the Neurodevelopmental Debate

Chlorpyrifos is a widely used organophosphate insecticide. Its primary mechanism of action in pests is the inhibition of acetylcholinesterase (AChE), an enzyme essential for nerve function. Without AChE, acetylcholine builds up in the synapse, leading to overstimulation and death.⁴⁸

The Scientific Conflict:

• Toxicology (Animal Studies): Traditional toxicology focuses on the dose required to inhibit AChE. Industry proponents argue that if exposure is kept below the level of AChE inhibition, the chemical is safe.

• Epidemiology (Human Studies): Long-term cohort studies (like those from Columbia University) have linked prenatal exposure to chlorpyrifos with neurodevelopmental deficits in children—including lower IQ, autism spectrum traits, and attention disorders—at levels below those that cause AChE inhibition. This suggests alternative mechanisms of toxicity, potentially involving oxidative stress or interference with other signaling pathways.⁴⁹

6.1.1 The Policy Reversal

In the first term, the EPA rejected a petition to ban chlorpyrifos, dismissing the epidemiological evidence as "uncertain" because the raw data could not be independently re-analyzed (due to patient privacy). The Biden administration subsequently banned chlorpyrifos tolerances on food.

In the second term, Administrator Zeldin moved immediately to reverse this ban. On January 20, 2025, the EPA issued a regulatory freeze delaying the ban's reinstatement and opened a comment period to restore the pesticide's use.⁵¹ The administration argues that the pesticide is essential for crop protection and that the EPA should rely on "Gold Standard" toxicology (animal studies) rather than "unverified" epidemiology.⁵²

6.2 TSCA and Risk Evaluation

Under the Toxic Substances Control Act (TSCA), the EPA evaluates the risks of existing chemicals. In the first term, the EPA adopted a narrow interpretation of "conditions of use," often excluding "legacy uses" (like chemicals leaching from old landfills) or spills from its risk calculations. In the second term, the administration has proposed further revisions to the risk evaluation process to ensure consistency with the "Gold Standard Science" executive order, which likely portends a higher evidentiary bar for restricting chemical manufacturing.⁵³

Part VII: The Reformation of Scientific Integrity

Perhaps the most enduring legacy of the Trump EPA will be its structural changes to how science is used in policymaking. The administration viewed the existing scientific apparatus not as a neutral arbiter, but as a biased interest group.

7.1 "Secret Science" and the Gold Standard

In the first term, the EPA proposed the "Strengthening Transparency in Regulatory Science" rule, colloquially known as the "Secret Science" rule. It aimed to prohibit the EPA from using studies where the underlying raw data was not publicly available.⁵⁴

• The Target: This rule specifically targeted large-scale epidemiological studies (like the Harvard Six Cities Study) which link air pollution to mortality. Because these studies rely on private medical records, their raw data cannot be made public.

• The Outcome: The rule was vacated by a federal court in 2021.

In the second term, the administration resurrected this concept through Executive Order 14303, "Restoring Gold Standard Science," signed in May 2025.55 This order mandates that agencies prioritize data that is "reproducible" and "transparent."

Epistemological Shift: While reproducibility is the standard for experimental physics, it is often impossible in environmental health. One cannot ethically "reproduce" the effects of exposing a community to a carcinogen. By elevating "reproducibility" as the sine qua non of regulatory science, the order structurally devalues observational epidemiology—the primary tool used to detect public health threats.57

7.2 Restructuring Advisory Boards

The administration also systematically reshaped the EPA’s advisory bodies. In both terms, academic scientists were purged from the Science Advisory Board (SAB). The administration argued that academics receiving EPA grants had a financial conflict of interest. Conversely, industry consultants were appointed to "balance" the boards.9

In the second term, the "Day of Deregulation" included a directive to "Reconstitute the SAB and CASAC," ensuring that these bodies—which review the science behind NAAQS and climate findings—would be composed of members skeptical of the agency's traditional regulatory posture.5

Part VIII: Legal Strategy and Federalism

The regulatory rollbacks of the Trump EPA are buttressed by a sophisticated legal strategy designed to insulate deregulation from judicial review.

8.1 The Major Questions Doctrine and Loper Bright

The second term operates in a legal environment fundamentally altered by the Supreme Court.

• West Virginia v. EPA (2022): Established the "Major Questions Doctrine," preventing agencies from taking actions of "vast economic and political significance" without clear congressional authorization.¹⁵

• Loper Bright v. Raimondo (2024): Overturned the Chevron deference doctrine. Courts are no longer required to defer to an agency’s reasonable interpretation of an ambiguous statute.

The Strategy of Self-Deregulation: The Trump EPA utilizes these rulings to justify "self-deregulation." Instead of arguing that a rule is bad policy (which requires a scientific defense), the agency argues that it is illegal for them to regulate. By claiming they lack authority under the Major Questions Doctrine to issue rules like the Clean Power Plan 2.0, the EPA effectively shields its deregulatory actions from scientific scrutiny, shifting the debate entirely to statutory interpretation.⁶⁰

8.2 The "Floor-as-Ceiling" Federalism

While the administration frequently invokes "cooperative federalism" (returning power to states) ⁷, its actions reveal a "floor-as-ceiling" approach. When states attempt to regulate more strictly than the federal government—such as California setting its own vehicle emissions standards or states blocking pipelines under CWA Section 401—the administration has moved to preempt them.⁶² This enforces a policy of energy dominance that overrides state-level environmental preferences, creating a uniform, deregulated landscape for industry.

Conclusion

The transformation of the Environmental Protection Agency under the first and second Trump administrations represents more than a temporary shift in policy; it is a fundamental reimagining of the American regulatory state. Through the doctrines of "Energy Dominance" and "Gold Standard Science," the administration has systematically raised the burden of proof required to justify environmental protection while lowering the barriers to industrial production.

Scientifically, this era is defined by the rejection of the precautionary principle in favor of a rigid empiricism that dismisses modeling and epidemiology. From the thermodynamics of power plants to the chemistry of aquifers, the administration has challenged the consensus methodologies used to assess risk.

Legally, the administration has successfully leveraged—and helped create—a new judicial framework that severely constrains administrative power. By dismantling the "Endangerment Finding," repealing the Clean Power Plan, and narrowing the scope of the Clean Water Act, the Trump EPA has effectively returned the nation's environmental framework to a pre-1970s footing, where the protection of the commons is secondary to the liquidity of the market. As the second term progresses, the collision between this deregulatory agenda and the physical realities of a changing climate will define the ecological future of the United States.

Table 1: Key Regulatory Reversals and Actions (2017–2025)

Policy Area	Obama/Biden Era Regulation	Trump Era Action (Term 1 & 2)	Scientific/Technical Implication
Climate (Power)	Clean Power Plan (CPP) / CPP 2.0 Focus: Generation shifting to renewables; CCS.	ACE Rule (Term 1); Repeal of CPP 2.0 (Term 2) Focus: Efficiency improvements "inside the fence."	Rebound Effect: Higher efficiency may lead to increased coal plant utilization and higher net emissions.
Climate (Methane)	NSPS OOOOb/c Focus: Zero-flaring; continuous monitoring; super-emitter program.	Reconsideration & Delay (Term 2) Focus: Removing continuous monitoring requirements; delaying compliance.	Methane Gap: Delaying advanced monitoring allows discrepancies between reported inventories and actual atmospheric concentrations to persist.
Water (WOTUS)	Clean Water Rule (2015) / 2023 Rule Focus: Connectivity of ephemeral streams and wetlands ("Significant Nexus").	Navigable Waters Protection Rule (Term 1); "Sackett Plus" Rule (Term 2) Focus: Continuous surface connection only.	Hydrological Disconnect: Deregulation of ephemeral streams risks downstream nutrient loading and loss of flood mitigation capacity.
Toxics (Water)	Steam Electric ELG (2015/2024) Focus: Membrane filtration/Zero discharge for Selenium/Arsenic.	Reconsideration (Term 2) Focus: Chemical precipitation; exemptions for low-utilization plants.	Bioaccumulation: Continued discharge of Selenium allows it to accumulate in aquatic food webs, causing reproductive failure in fish.
Pesticides	Chlorpyrifos Ban Focus: Epidemiological evidence of neurodevelopmental harm.	Reversal of Ban (Term 2) Focus: Rejection of epidemiological data; economic utility for agriculture.	Neurotoxicity: Potential for increased incidence of neurodevelopmental deficits in children in agricultural communities.
Science Policy	Open use of peer-reviewed epidemiology	"Secret Science" (Term 1); EO 14303 (Term 2) Focus: Requiring raw data transparency; "Gold Standard."	Data Exclusion: Excludes major public health studies where patient privacy prevents raw data release.

Table 2: Timeline of Major Deregulatory Milestones

Date	Event	Significance
Feb 28, 2017	EO 13778 issued.	Initiated the repeal of the "Waters of the United States" rule.3
June 19, 2019	ACE Rule finalized.	Replaced Clean Power Plan with "inside the fence" efficiency standards.12
Jan 21, 2021	D.C. Circuit vacates ACE Rule.	Legal setback for Term 1 agenda; set stage for West Virginia v. EPA.13
June 30, 2022	West Virginia v. EPA ruling.	Supreme Court validates "Major Questions Doctrine," limiting EPA authority.15
Jan 20, 2025	"Unleashing American Energy" EO.	Term 2 kickoff; mandate to maximize fossil fuel production.2
Mar 12, 2025	"Day of Deregulation."	Administrator Zeldin announces 31 actions to rollback Biden-era rules.6
May 23, 2025	EO 14303 "Gold Standard Science."	Imposes new barriers to using epidemiological data in rulemaking.55
July 2025	Methane Rule Delay.	Extended compliance deadlines for oil and gas methane monitoring.30

Works cited

1. EPA Under a Second Trump Presidency: The Good, Bad, and Ugly, accessed January 10, 2026, https://www.mcglinchey.com/insights/epa-under-a-second-trump-presidency-the-good-bad-and-ugly/

2. Unleashing American Energy - The White House, accessed January 10, 2026, https://www.whitehouse.gov/presidential-actions/2025/01/unleashing-american-energy/

3. Tracking regulatory changes in the second Trump administration - Brookings Institution, accessed January 10, 2026, https://www.brookings.edu/articles/tracking-regulatory-changes-in-the-second-trump-administration/

4. Full article: The environmental legacy of President Trump - Taylor & Francis Online, accessed January 10, 2026, https://www.tandfonline.com/doi/full/10.1080/01442872.2021.1922660

5. EPA Launches Biggest Deregulatory Action in U.S. History, accessed January 10, 2026, https://www.epa.gov/newsreleases/epa-launches-biggest-deregulatory-action-us-history

6. U.S. EPA Announces “Biggest Deregulatory Action in U.S. History” - Environmental Law News - Indianapolis Bar Association, accessed January 10, 2026, https://www.indybar.org/?pg=EnvironmentalLawNews&blAction=showEntry&blogEntry=123578

7. EPA Announces Deregulatory Initiative to "Power the Great American Comeback" | Insights, accessed January 10, 2026, https://www.hklaw.com/en/insights/publications/2025/03/epa-announces-deregulatory-initiative-to-power-the-great

8. Review of Project 2025's Chapter on the Environmental Protection Agency |, accessed January 10, 2026, https://cesp.gmu.edu/review-of-project-2025s-chapter-on-the-environmental-protection-agency/

9. Lawmakers Warned About Shakeup of EPA Advisory Panels | Courthouse News Service, accessed January 10, 2026, https://www.courthousenews.com/lawmakers-warned-about-shakeup-of-epa-advisory-panels/

10. Project 2025 — Environmental Protection Agency — Annotated, accessed January 10, 2026, https://envirodatagov.org/project2025-environmental-protection-agency-annotated/

11. Project 2025's Assault on EPA, Human Health and the Environment Must Never Be Put into Action - UCS blog, accessed January 10, 2026, https://blog.ucs.org/chitra-kumar/project-2025s-assault-on-epa-human-health-and-the-environment-must-never-be-put-into-action/

12. Fact Sheet: Repeal of the Clean Power Plan - EPA, accessed January 10, 2026, https://www.epa.gov/sites/default/files/2019-06/documents/cpp_repeal_fact_sheet_6.18.19_final.pdf

13. Affordable Clean Energy Rule, accessed January 10, 2026, https://stateimpactcenter.org/issues/climate-action/affordable-clean-energy-rule

14. Clean Power Plan - Wikipedia, accessed January 10, 2026, https://en.wikipedia.org/wiki/Clean_Power_Plan

15. Supreme Court Strikes Down Clean Power Plan - National League of Cities, accessed January 10, 2026, https://www.nlc.org/article/2022/07/01/supreme-court-strikes-down-clean-power-plan/

16. Inside EPA's Regulatory Rollback: What Local Leaders Can Expect, accessed January 10, 2026, https://www.nlc.org/article/2025/04/14/inside-epas-regulatory-rollback-what-local-leaders-can-expect/

17. Trump EPA Announces Reconsideration of Biden-Harris Rule, “Clean Power Plan 2.0”, That Prioritized Shutting Down Power Plants While Raising Costs on American Families, accessed January 10, 2026, https://www.epa.gov/newsreleases/trump-epa-announces-reconsideration-biden-harris-rule-clean-power-plan-20-prioritized

18. Q & A: Repeal of the Clean Power Plan 2.0, accessed January 10, 2026, https://americaspower.org/q-a-repeal-of-the-clean-power-plan-2-0/

19. EPA Will Revise Wastewater Rules to Support Electric Energy Reliability and Unleash American Energy | US EPA, accessed January 10, 2026, https://www.epa.gov/newsreleases/epa-will-revise-wastewater-rules-support-electric-energy-reliability-and-unleash

20. August 18th, 2025 The Honorable Lee Zeldin Administrator Environmental Protection Agency 1200 Pennsylvania Avenue NW Washington,, accessed January 10, 2026, https://democrats-science.house.gov/download/2025-08-18-sst-rm-lofgren-amo_-letter-to-administrator-zeldin_-endangerment-finding-repeal

21. Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards, accessed January 10, 2026, https://www.regulations.gov/document/EPA-HQ-OAR-2025-0194-0093

22. A Big Day at EPA – Agency Announces Reconsideration of 31 Major Agency Actions, accessed January 10, 2026, https://www.womblebonddickinson.com/us/insights/alerts/big-day-epa-agency-announces-reconsideration-31-major-agency-actions

23. accessed January 10, 2026, https://en.wikipedia.org/wiki/Global_warming_potential#:~:text=Methane%20has%20an%20atmospheric%20lifetime,chemical%20reactions%20in%20the%20atmosphere.

24. 5 Things to Know About Atmospheric Methane Removal - World Resources Institute, accessed January 10, 2026, https://www.wri.org/insights/atmospheric-methane-removal

25. Chemistry–climate feedback of atmospheric methane in a methane-emission-flux-driven chemistry–climate model - ACP, accessed January 10, 2026, https://acp.copernicus.org/articles/25/5133/2025/

26. The Efficacy of Methane Leak Detection and Repair (LDAR) Programs in Practice - PMC, accessed January 10, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC12624710/

27. Natural Gas Emissions: Measure Top-down or Bottom-up? | Grid Modernization - NREL, accessed January 10, 2026, https://www.nrel.gov/grid/news/program/2018/natural-gas-emissions-measure-top-down-or-bottom-up

28. Actions and Notices about Oil and Natural Gas Air Pollution Standards | US EPA, accessed January 10, 2026, https://www.epa.gov/controlling-air-pollution-oil-and-natural-gas-operations/actions-and-notices-about-oil-and-0

29. Reconsideration of Standards of Performance for New, Reconstructed, and Modified Sources and Emissions Guidelines for Existing Sources: Oil and Natural Gas Sector Climate Review; Correction - Federal Register, accessed January 10, 2026, https://www.federalregister.gov/documents/2025/01/17/2025-01091/reconsideration-of-standards-of-performance-for-new-reconstructed-and-modified-sources-and-emissions

30. Oil and Natural Gas Sector Climate Review: Extension of Deadlines in Standards of Performance for New, Reconstructed, and Modified Sources and Emissions Guidelines for Existing Sources - Federal Register, accessed January 10, 2026, https://www.federalregister.gov/documents/2025/12/03/2025-21788/oil-and-natural-gas-sector-climate-review-extension-of-deadlines-in-standards-of-performance-for-new

31. 2025 Interim Final Rule to Extend Compliance Deadlines | US EPA, accessed January 10, 2026, https://www.epa.gov/controlling-air-pollution-oil-and-natural-gas-operations/2025-interim-final-rule-extend-compliance

32. Trump's Climate and Clean Energy Rollback Tracker, accessed January 10, 2026, https://www.actonclimate.com/trumptracker/

33. Environmental Protection Agency - Sabin Center for Climate Change Law, accessed January 10, 2026, https://climate.law.columbia.edu/content/environmental-protection-agency

34. The Ecological and Hydrological Significance of Ephemeral and Intermittent Streams in the Arid and Semi-arid American Southwest - EPA, accessed January 10, 2026, https://www.epa.gov/sites/default/files/2015-03/documents/ephemeral_streams_report_final_508-kepner.pdf

35. Hydrologic Connectivity and the Contribution of Stream Headwaters to Ecological Integrity at Regional Scales - UNL Digital Commons, accessed January 10, 2026, https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2146&context=usgsstaffpub

36. WOTUS Woes Continue: EPA to Modify the Navigable Waters Protection Rule | Brownstein, accessed January 10, 2026, https://www.bhfs.com/insight/wotus-woes-continue-epa-to-modify-the-navigable-waters-protection-rule/

37. White House Rule on Clean Water Act in 2020 Dramatically Deregulated Waters of the United States - Resources Magazine, accessed January 10, 2026, https://www.resources.org/common-resources/white-house-rule-on-clean-water-act-in-2020-dramatically-deregulated-waters-of-the-united-states/

38. White House Rule Dramatically Deregulated Wetlands, Streams, and Drinking Water, accessed January 10, 2026, https://vcresearch.berkeley.edu/news/white-house-rule-dramatically-deregulated-wetlands-streams-and-drinking-water

39. The Supreme Court just made it easier to destroy wetlands and streams - High Country News, accessed January 10, 2026, https://www.hcn.org/articles/north-water-the-supreme-court-just-made-it-easier-to-destroy-wetlands-and-streams/

40. Waters of the United States (WOTUS): Frequently Asked Questions About the Scope of the Clean Water Act | Congress.gov, accessed January 10, 2026, https://www.congress.gov/crs-product/R47408

41. The Never-Ending Rule: EPA and Army Corps of Engineers Propose Narrowing the Post-Sackett Definition of 'Waters of the United States' - Greenberg Traurig, LLP, accessed January 10, 2026, https://www.gtlaw.com/en/insights/2025/11/the-never-ending-rule-epa-and-army-corps-of-engineers-propose-narrowing-the-post-sackett-definition-of-waters-of-the-united-states

42. Updated Definition of “Waters of the United States” - Federal Register, accessed January 10, 2026, https://www.federalregister.gov/documents/2025/11/20/2025-20402/updated-definition-of-waters-of-the-united-states

43. Steam Electric Power Generating Effluent Guidelines | US EPA, accessed January 10, 2026, https://www.epa.gov/eg/steam-electric-power-generating-effluent-guidelines

44. Steam Electric Power Generating Effluent Guidelines - 2024 Final Rule | US EPA, accessed January 10, 2026, https://www.epa.gov/eg/steam-electric-power-generating-effluent-guidelines-2024-final-rule

45. Technical Development Document for Final Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category - EPA, accessed January 10, 2026, https://www.epa.gov/system/files/documents/2024-04/se11757_steam-electric-elg-tdd_508.pdf

46. EPA Announces It Will Reconsider 2024 Water Pollution Limits for Coal Power Plants to Help Unleash American Energy (ELG: Steam Electric), accessed January 10, 2026, https://www.epa.gov/newsreleases/epa-announces-it-will-reconsider-2024-water-pollution-limits-coal-power-plants-help

47. Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category - Federal Register, accessed January 10, 2026, https://www.federalregister.gov/documents/2024/05/09/2024-09185/supplemental-effluent-limitations-guidelines-and-standards-for-the-steam-electric-power-generating

48. Chlorpyrifos Technical Fact Sheet - National Pesticide Information Center, accessed January 10, 2026, https://npic.orst.edu/factsheets/archive/chlorptech.html

49. Effects of Chlorpyrifos on Cholinesterase and Serine Lipase Activities and Lipid Metabolism in Brains of Rainbow Trout (Oncorhynchus mykiss) - PubMed Central, accessed January 10, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC6813751/

50. Full article: The in vitro and in vivo effects of chlorpyrifos on acetylcholinesterase activity of rainbow trout brain - Taylor & Francis Online, accessed January 10, 2026, https://www.tandfonline.com/doi/full/10.1080/09712119.2015.1031776

51. EPA Launches Biggest Deregulatory Action in U.S. History On March 12, 2025, EPA Administrator Lee Zeldin anno, accessed January 10, 2026, https://www.epa.gov/system/files/documents/2025-03/linked-asbo-march-2025-smallbiz.pdf

52. Trump Executive Orders Signal Potential Changes in Environmental Policy Impacting Agriculture | ArentFox Schiff, accessed January 10, 2026, https://www.afslaw.com/perspectives/alerts/trump-executive-orders-signal-potential-changes-environmental-policy-impacting

53. EPA Releases Proposal to Increase Efficiency, Better Protect Health and the Environment in Chemical Reviews under TSCA, accessed January 10, 2026, https://www.epa.gov/newsreleases/epa-releases-proposal-increase-efficiency-better-protect-health-and-environment

54. The Environmental Protection Agency's “Strengthening Transparency in Pivotal Science” Rule: Don't Let History Repeat Itself - NIH, accessed January 10, 2026, https://pmc.ncbi.nlm.nih.gov/articles/PMC8522296/

55. Restoring Gold Standard Science - The White House, accessed January 10, 2026, https://www.whitehouse.gov/presidential-actions/2025/05/restoring-gold-standard-science/

56. Gold Standard Science at HHS, accessed January 10, 2026, https://www.hhs.gov/gss/index.html

57. Federal Agencies Respond to “Gold Standard Science” Executive Order - WashU Libraries, accessed January 10, 2026, https://library.washu.edu/news/federal-agencies-respond-to-gold-standard-science-executive-order/

58. Opinion: What's worrisome about White House focus on 'gold standard science', accessed January 10, 2026, https://hsph.harvard.edu/news/opinion-whats-worrisome-about-white-house-focus-on-gold-standard-science/

59. EPA seeks feedback on Science Advisory Board nominees - POLITICO Pro, accessed January 10, 2026, https://subscriber.politicopro.com/article/eenews/2025/08/25/epa-seeks-feedback-on-science-advisory-board-nominees-00522513

60. Why the Trump Administration's Environmental Rollback is Increasingly Seeing Pushback - CSIS, accessed January 10, 2026, https://www.csis.org/analysis/why-trump-administrations-environmental-rollback-increasingly-seeing-pushback

61. September 22, 2025 The Honorable Lee Zeldin Administrator U.S. Environmental Protection Agency 1200 Pennsylvania Avenue N.W. Was - Senate Committee on Environment and Public Works, accessed January 10, 2026, https://www.epw.senate.gov/public/index.cfm?a=files.serve&File_id=E54E5788-EB89-4FFC-BC3C-94C1C78D5114

62. Energy under Trump: The Climate Implications of Agenda 47 - Michigan Journal of Public Affairs, accessed January 10, 2026, https://mjpa.umich.edu/2025/01/07/energy-under-trump-the-climate-implications-of-agenda-47/