Over the last four years, the Trump administration has taken on a massive deregulatory effort. With the issuance of Executive Order 13771, the administration’s two-for-one rule, federal agencies were directed to eliminate two regulations for each new rule issued. Much of this effort has focused on scaling back previous Obama-era regulations and weakening agencies’ statutory authority. Notably, environmental regulation has proven a prominent and easy target, as many existing policies and regulations had never been enshrined into law. The Trump administration has replaced the Clean Power Plan, redefined critical terms under the Endangered Species Act, lifted oil and natural gas extraction bans, weakened the Coal Ash Rule, which regulates the disposal of toxic coal waste, and revised Mercury and Air Toxic Standards–just to name a few.tracking these ongoing deregulations. A sampling of some of the most consequential environmental revisions and rescissions to date are listed below.
Clean Power Plan
Finalized in 2015, the Clean Power Plan (CPP) was proposed by the Obama administration in June 2014 and intended to reduce electricity sector greenhouse gas (GHG) emissions. The CPP established carbon dioxide (CO2) emission performance rates for two subcategories of fossil fuel-fired electric generating units. CO2 is the most prevalent greenhouse gas pollutant, accounting for 82 percent of U.S. GHG emissions (using 2017 figures). At the time of the rule, the electricity sector was responsible for approximately 30 percent of the United States’ overall GHG emissions. EPA estimated that by 2030, CPP would reduce carbon pollution from the electricity sector 32 percent below 2005 levels. Likewise, sulfur dioxide emissions from power plants were predicted to drop by 90 percent and nitrogen oxides emissions by 72 percent. The reductions under CPP were expected to prevent an estimated 3,600 premature deaths each year.
In March 2017, just two months after his inauguration, President Trump issued an Executive Order directing EPA to review the CPP. In October that same year, EPA proposed to rescind the policy. While EPA worked to repeal the Clean Power Plan, the administration considered possible replacement policies in response to EPA’s 2009 endangerment findings that determined current GHG concentrations in the atmosphere posed a threat to public health and welfare. In August 2018, EPA proposed the Affordable Clean Energy (ACE) rule as CPP’s replacement. Unlike CPP, ACE did not set GHG emission guidelines for states using emission performance rates. Instead, ACE defined the “best system of emission reduction” (BSER) for existing power plants as on-site, heat-rate efficiency improvements (HRI), whereas CPP determined BSERs to be CO2 emission performance rates. ACE used these BSERs to provide states with a list of “candidate technologies” to establish standards of performance by the states. EPA’s Regulatory Impact Analysis predicted that, relative to CPP, the replacement rule would increase CO2 emissions by over 60 million short tons by 2030. In June 2019, EPA finalized three rules implementing ACE and its set emissions. The state of New York, along with 21 other states and seven cities, filed a lawsuit seeking a review of the action. The states claimed ACE does not meaningfully reduce GHG emissions, violating EPA’s duty to address carbon pollution from power plants under the Clean Air Act.
Mercury and Air Toxic Standards
Under the Mercury and Air Toxic Standards (MATS), coal- and oil-burning power plants are required to reduce the emission of mercury and other toxic pollutants, including arsenic, nickel, and acid gases. These plants are the foremost emitters of mercury in the U.S., and exposure to mercury has been linked to certain neurological disorders, cardiovascular harm, and weakened immune systems. In 2015, the Supreme Court ruled that EPA must weigh the costs to industry, in addition to public health and environmental risks. In accordance with the Michigan v. EPA ruling, EPA published a cost finding the same year concluding that MATS were “appropriate and necessary” regulations for coal- and oil-based power plants under the Clean Air Act, a key finding that allowed for MATS regulation.
On December 27, 2018, EPA proposed to revise its previous cost finding, altering the calculations used for costs to human health and safety. Under the new cost finding, the agency declared MATS no longer “appropriate and necessary,” although by the time the new finding was issued, power plants had already spent more than $18 billion in MATS compliance costs. The updated finding additionally deemed the residual risks of mercury and hazard air pollutant emissions acceptable, negating the Obama-administration’s original cost finding. EPA received substantive pushback on the revision for disregarding both economically important indirect health benefits and recent research identifying the direct health benefits from reduced emissions. As such, several environmental groups brought forth a lawsuit challenging EPA’s dismissal of the 2012 standards. Recent studies also show that the benefits of reducing mercury are far greater than initially predicted, yet EPA continued to use science from the outdated 2011 regulatory analysis in its cost benefit analysis. EPA’s Science Advisory Board even urged the agency to consider further research on mercury’s impact before concluding its residual risks assessment. Despite these critiques, EPA relaxed the standards and formally withdrew the “appropriate and necessary” finding in April 2020, though some environmentalists speculated EPA would withdraw MATS entirely.
EPA’s revision does not change the MATS requirements themselves. Instead, it undermines the ongoing implementation of those standards. The shift could set a precedent for future public health rules, making it more difficult for EPA to justify future environmental regulations. By removing the “appropriate and necessary” finding, the agency minimizes its regulatory authority over hazardous air pollutants and limits the scope of the Clean Air Act, in addition to walking back previous EPA science. The action has been even been called an illegal misinterpretation of section 112 in line with the administrations’ larger goal of deconstructing the “administrative state.”
Waters of U.S. Rule
One of the Obama administration’s most controversial environmental regulations, the Waters of the United States (WOTUS) rule, expanded the definition of “navigable waters” under the Clean Water Act. The rule initially sought to clarify which waterways fell under federal jurisdiction. In 2015, the term was defined to include tributaries and bodies of water adjacent to federal waters, including wetlands, streams, ponds, and lakes, and the rule makes it unlawful to pollute WOTUS without a permit. Beginning in 2017, the Trump administration sought to rescind these updates. In February of that year, President Trump issued Executive Order 13778, directing EPA and the Army Corps of Engineers to review and potentially revise WOTUS. Subsequently, EPA delayed WOTUS’s implementation date in 2018 and later repealed the rule in September 2019, effectively reversing the Obama-era definitions.
On April 22, 2020, EPA and the Department of Army finalized an updated rule that narrows the definition of WOTUS and significantly reduces the number of federally protected bodies of water. By extension, the rescission also narrows the scope of the Clean Water Act. The rule, effective June 22, 2020, identifies six protected categories of water: traditional navigable waters, tributaries, certain ditches, certain lakes and ponds, impoundments, and adjacent wetlands that physically touch other jurisdictional waters. The revised definition leaves several previously-protected waterways vulnerable to pollution. Specifically, wetlands separated from tributaries by land, dikes, or other features are not included in this definition. Moreover, ephemeral waters that only flow after rain events are also excluded from protection. According to an EPA slideshow obtained by EE News under the Freedom of Information Act, the updated definition excludes at least 18 percent of streams and 51 percent of wetlands nationwide from federal protection, many of which had been protected since the Reagan administration. Most recently, developers received a permit to mine titanium near Georgia’s Okefenokee National Wildlife Refuge, as the impacted wetlands are no longer protected under WOTUS. In response, several states and organizations have challenged the final rule.
Reversal of EPA’s chlorpyrifos ban
Chlorpyrifos, used commonly on corn, soybeans, broccoli and apples, is the most widely used pesticide in the U.S. However, it has been found to impair child brain development and damage adults’ cognitive function. As such, chlorpyrifos registrants voluntarily agreed to cancel almost all residential use of chlorpyrifos products in 2000. In November 2015, after a petition and subsequent legal action from the Natural Resource Defense Council and the Pesticide Action Network of North America, EPA agreed to revoke all chlorpyrifos tolerances. In March 2017, then-EPA Administrator Scott Pruitt signed a controversial order rejecting the previous petition and effectively reversing the chlorpyrifos ban. The decision came just two days prior to EPA’s court-ordered deadline.
More than three years later, in September of 2020, EPA issued three updated chlorpyrifos assessments: a draft ecological risk assessment, a revised human health risk assessment, and an updated drinking water assessment. The assessments invoked EPA’s newly-revised Scientific Transparency Rule—which requires EPA to only consider scientific studies with publicly available underlying data regardless of peer review or replication—to dismiss prior evidence of the pesticide’s health risks, stating that “the science addressing neurodevelopmental effects remains unsolved.” However, the agency excluded several empirical studies cited in its previous decision-making. EPA also neglected to include various animal studies from 2017 and 2018 that conclusively found chlorpyrifos caused decreased learning, hyperactivity, and anxiety. California regulators used these in a state-wide reassessment to ban the pesticide, becoming only the second state after Hawaii to do so. Following the announcement, Corteva Agriscience, the country’s largest chlorpyrifos manufacturer, said it would no longer make or sell the pesticide.
Additionally, attorneys claim that Columbia University researchers involved in a critical study were willing to show their data to agency officials but had not released the information publicly due to privacy concerns. EPA’s invocation of the Scientific Transparency Rule also makes the reversal unique, as many public health studies rely on participants sharing sensitive data protected under confidentiality agreements. The application of this rule to future regulatory science could create significant barriers for the types of studies that influence agency rulemaking. The decision on whether or not to renew chlorpyrifos’ registration will be made in 2022.
Methane emissions standards
On June 3, 2016, near the end of the Obama administration, EPA amended the New Source Performance Standards (NSPS) to limit methane emissions and volatile organic compounds from oil and gas wells. A lesser-mentioned greenhouse gas, methane is 84 times more potent than carbon dioxide, and 60 percent of methane emissions come from just 5 percent of wells. Notably, the 2016 rule included several emitters not previously regulated under NSPS, including fracking wells. Industry firms quickly petitioned EPA to reconsider the rule, and in April 2017, after the change in administrations, the agency announced it would do so. By June of the same year, EPA announced a 90-day stay, and later proposed a two-year extension to delay the rule’s effective date. After several environmental groups challenged the stay, the D.C. Circuit Court of Appeals ruled that EPA lacked the authority to halt implementation of the regulations.
Following the challenge, EPA later proposed revisions to its NSPS provisions regarding methane leak testing and repairs in September of 2018. The following year, the agency proposed another rule rolling back subparts OOOO and OOOOa of NSPS. On August 13, 2020, EPA finalized its rescission of the 2012 and 2016 rules, revoking GHG and volatile organic compounds (VOC) standards. The rollback additionally removes all transmission and storage sources from regulation under the oil and natural gas segment of NSPS. Much like the MATS rollback, the revised methane rule restricts EPA’s authority to regulate pollution control standards under the Clean Air Act. According to EPA’s own estimates, the rule is expected to forego 448,000 short tons in emissions reductions. The administration also notably lowered the social cost of methane to $55 per metric ton, significantly below the Obama-era estimate of $1,400. Such a reduction makes it easier for the administration to forgo future regulations, as they are more likely to fail the cost benefit requirements under E.O. 12866.
In the short term, the administration has been largely successful in weakening existing environmental regulations, although the long-term impact of these environmental rollbacks remains to be seen. Many of the Trump administration’s measures, environmental or otherwise, have failed to stand up in court, with the administration losing 83 percent of litigations. A recent analysis from the Brookings Institution suggests that the administration’s regulatory agenda has strayed from that of past Republican administrations, abandoning the “industry-friendly,” states-centric approach to regulation in lieu of a more chaotic approach.
Moreover, at no point has the outgoing administration shown signs of slowing its deregulation. Most recently, the Forest Service proposed a measure that would permit oil and natural gas leasing on 4.2 million acres of National Forest System lands, and EPA finalized various rules amending the national emission standards for hazardous air pollutants and waste management practices for coal combustion residual facilities. In addition to their obvious environmental impacts, these measures will likely create lasting consequences for how future administrations can apply and enforce environmental legislation even if an incoming Biden administration would presumably act to reverse many of these deregulations.
 The rules identified in this article are by no means an exhaustive list of the administration’s environmental rollbacks. They serve as a curated sampling of some of the major changes to date. The Sabin Center for Climate Change Law at Columbia University maintains a detailed tracker of climate-related deregulations.
 On February 9, 2016, the Supreme Court ruled 5-4 to take the unprecedented step of staying the CPP, pending the exhaustion of the full appeals process for either side–in other words, signing off on the rule’s permissibility.
 According to EPA’s minimum case scenario.
 Similarly, EPA’s 2015 Steam Electric Power Generating (EPG) rule sets limits on toxic waste generated by power plants. Among all industries regulated under the Clean Water Act, steam electric power plants contribute the greatest amount of toxic pollutants discharged to surface waters. In 2019, EPA proposed revisions to the 2015 effluent limitations guidelines and standards (ELGs) for two categories of toxic waste generated from steam EPGs: flue gas desulfurization (FGD) wastewater and bottom ash (BA) transport water. Key changes include amending the technology-basis for wastewater treatment, revising the voluntary incentives program for FGD wastewater, and adding subcategories for FGD and BA wastewater.
 In July of 2020, a federal judge in California blocked the Trump administration’s other major methane rollback regarding waste management, stating that the Department of Interior (DoI) “ignored its statutory mandate under the Mineral Leasing Act, repeatedly failed to justify numerous reversals in policy positions previously taken, and failed to consider scientific findings and institutions relied upon by both prior Republican and Democratic administrations.” The DoI rollback was struck down in U.S. District Court for the District of Wyoming just last week.
 McCoy, forthcoming.
The author would like to thank Siddhi Doshi, Kelly Kennedy, Adam Looney, and Sanjay Patnaik for their invaluable comments and feedback on this piece. Siddhi Doshi contributed substantially to prior research and timelines for these rules.