Alexander Arensberg advises clients on complex litigation and regulatory compliance issues before federal and state agencies. His practice focuses on public lands and natural resource law, renewable energy development, and environmental compliance. He also has extensive experience litigating challenges to administrative decision-making, drafting appellate briefs in both federal and state courts, advising on large-scale infrastructure development projects, and conducting internal investigations and compliance reviews in response to government enforcement actions.

As a member of the firm’s Environmental, Safety & Health Practice Group, Alexander advises clients on permitting and regulatory compliance issues arising under a broad array of federal and state environmental laws, including the National Environmental Policy Act (NEPA), Clean Water Act, Federal Land Policy and Management Act, Mining Law of 1872, Mineral Leasing Acts, Oil Pollution Act, CERCLA, Endangered Species Act and National Historic Preservation Act. This work involves close coordination with federal land managers and other permitting agencies, including the Bureau of Land Management (BLM), US Forest Service (USFS), US Fish and Wildlife Service (USFWS), US Army Corps of Engineers (USACE), Environmental Protection Agency (EPA) and various state agencies.

Alexander has successfully litigated complex cases in state and federal court, including appeals before the Eighth, Ninth, Tenth and D.C. Circuit courts of appeals. His experience includes successfully challenging agency rulemaking and permitting decisions under the federal Administrative Procedure Act and counterpart state laws. He also helps clients participate in the administrative rulemaking process and frequently drafts public comments on their behalf in response to proposed regulations and other agency actions.

Alexander also has significant experience assisting clients to respond to government investigations and enforcement actions, including matters involving investigations by the US Securities and Exchange Commission (SEC), Department of Justice (DOJ) and State Attorneys General.

Alexander graduated from the University of California Berkeley School of Law, where he was the senior executive editor of the Ecology Law Quarterly and received a Certificate of Specialization in Environmental Law. In 2020, 2021, 2022 and 2023, Alexander was named a Rising Star by Colorado Super Lawyers.

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  • Representing a Fortune 200 company in 16-day federal bench trial defending against US$140 million CERCLA contribution claim.
  • Representing a Fortune 200 company in complex environmental litigation before the D. Idaho, S.D. Mo., D. Colo., W.D. Wash., and appeals before the Eighth, Ninth and Tenth Circuits, including successfully defending against claims brought under CERCLA, RCRA, the Clean Water Act and state common law.
  • Representing a Fortune 500 mining company to defend against citizen suit challenges to permitting decisions of the US Army Corps of Engineers under Section 404 of the Clean Water Act.
  • Representing a precious metals mining company before the D.C. Circuit in appeal pursuant to the Administrative Procedures Act of Department of Energy (DOE) rulemaking decision.
  • Representing a specialty chemicals company in litigation related to company’s right to mine lithium from groundwater brine in Nevada, including litigating petitions for judicial review of permitting decisions of the Nevada Department of Water Resources.
  • Representing the State Office of the Attorney General in multistate litigation before the US Supreme Court related to hazardous waste releases from abandoned mine.
  • Representing a financial corporation to defend against US$4.8 million CERCLA contribution claim in the D. Md.
  • Representing a Fortune 200 company to defend against a Clean Water Act citizen suit related to stormwater discharges in the W.D. Wash.
  • Representing a waste disposal facility in appeal of state permitting decision before the Arkansas Pollution Control and Ecology Commission.


  • Advising multinational mining companies on compliance and permitting matters, particularly on Western public lands. Experience includes representing gold, silver, lithium, potash, copper and iron mining companies operating on BLM and USFS land in Colorado, Nevada, New Mexico, Arizona and Minnesota on matters arising under NEPA, FLPMA, CWA, CAA, MBTA, NHPA, the General Mining Laws, the Mineral Leasing Acts and counterpart state laws.
  • Advising a Fortune 500 phosphate and potash producer on federal and state permitting matters related to tailings management, brine and stormwater discharges, land exchanges, mine and closure plan requirements, dam safety requirements, designations of Areas of Critical Environmental Concern (ACECs) and the development of resource management plans.
  • Advising proponents of infrastructure development projects, including projects undertaken as public-private partnerships, on environmental permitting and compliance matters, including matters arising under the Endangered Species Act (ESA), the National Historic Preservation Act (NHPA), the Clean Water Act, and NEPA.
  • Advising an iron mining company with respect to Clean Water Act Section 404 permitting process with the US Army Corps of Engineers for major tailings basin expansion.
  • Advising a municipality in acquisition of federal public lands, including advising on issues arising under FLPMA and the Recreation and Public Purposes Act.
  • Representing a federal national laboratory in administrative hearing before the New Mexico Water Quality Control Commission to amend state surface water quality standards.
  • Advising an iron mining company on responding to EPA request for information under Section 308 of the Clean Water Act.
  • Experience drafting state and federal legislation, advising clients on public policy implications of legislative efforts, and participating in federal notice and comment rulemaking efforts.

Government Investigations

  • Assisting with representation of a consumer data company in an SEC financial reporting investigation, an investigation by the New York Office of the Attorney General into potential antitrust violations, and a federal consumer protection investigation.
  • Assisting with representation of a US public company’s internal review into its Anti-Money Laundering (AML) controls in response to SEC investigation.
  • Assisting with representation of chairmen of the board of directors for a large construction company in relation to an internal investigation by the company’s audit committee.
  • Assisting with conducting an internal investigation for a public company into potential information leaks from its board of directors.
  • Assisting with conducting an internal investigation concerning a US public company’s operations in China.
  • Experience managing large-scale e-discovery projects and in support of internal investigations for both national and international clients.


  • University of California, Berkeley, School of Law, J.D., 2012
  • University of Colorado at Boulder, B.A., magna cum laude, 2007


  • Colorado, 2012
  • New Mexico, 2023

Memberships & Affiliations

  • Co-Vice Chair, American Bar Association, Section of Environment, Energy, and Resources, Book Publishing Board
  • Former Co-Vice Chair, American Bar Association, Section of Environment, Energy, and Resources, Renewable, Alternative, and Distributed Energy Resources Committee
  • Environmental Committee, American Exploration & Mining Association
  • Member, American Bar Association
  • Member, Rocky Mountain Mineral Law Foundation
  • Recognized by Best Lawyers: Ones to Watch in America 2020-2024 for Environmental Law and Land Use and Zoning Law in Denver
  • Named as a key lawyer for Environment: Litigation by The Legal 500 US 2023
  • Recognized by Colorado Super Lawyers as a Rising Star in 2020, 2021, 2022 and 2023
  • Certificate of Specialization in Environmental Law, Berkeley Law
  • Senior Executive Editor, Ecology Law Quarterly, Berkeley Law

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  • Speaker, “New NEPA Amendments and CEQ Phase 2 Proposed Rule: Impacts on Federal Project Planning,” Strafford Webinar, November 14, 2023.
  • Speaker, “How to Mine Lithium from Groundwater – The U.S. Legal Framework,” 63rd Annual Rocky Mountain Mineral Law Institute, 2017.
  • Author, “Are Migratory Birds Extending Environmental Criminal Liability,” Ecology Law Quarterly, volume 38, p. 427, 2011.

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