Dan practices in Keller Rohrback’s nationally-recognized Complex Litigation Group with a focus on environmental cases and representing government entities in important litigation. He collaborates with his colleagues and clients to identify problems and craft creative, long-lasting solutions.
Dan has litigated important environmental and consumer cases across the country in federal and state court. He presently represents the State of Oregon in its case against Monsanto seeking to hold the corporate giant responsible for natural resource damages related to its sale and marketing of PCBs. He is also part of the Keller Rohrback team representing more than 70 counties, cities, and tribes in the fight to hold drug manufacturers and other entities accountable for the opioid crisis.
Before joining the firm, Dan was an environmental law professor at Lewis & Clark Law School in Portland, Oregon, where he also litigated cases involving toxic waste, water pollution, and natural resource management. He has sat on governmental advisory boards and helped to draft key environmental regulations in place today. Dan uses his passion and experience to protect our environment and the people and communities that rely on clean air, water, and products.
Articles & Presentations
•Panelist, Government as Plaintiff: The Advantages and Hurdles of Litigating on Behalf of a Public Body,Coalition of Civil Advocates (November 14, 2024).
•Speaker, PFAS from the Litigation Perspective, Law Seminars International, A Comprehensive Seminar on the 33rd Anniversary of the Model Toxics Control Act (December 7, 2023).
•Panelist, Toxic Torts and Class Actions, Environmental Law and Policy Conference, University of Michigan, Michigan Law (September 30, 2022).
•Panelist, Accountability for Climate Change Harms in the Pacific Northwest: Scientific, Policy and Legal Perspectives, Lewis & Clark Law Schools Green Energy Institute, the Center for Climate Integrity, and Breach Collective (March 18, 2021).
•Speaker, Alliance of California Judges Symposium on the Economics of Consumer Protection, Federalism and the Preemption of State Public Nuisance Actions (November 2019).
•Speaker, BridgeportEnvironmental Class Action Webinar (March 2016).
•Speaker, Harris Martin Porter Ranch Gas Leak Litigation Conference, Testing of the Air Quality and Expert Witnesses for the Cases (January 19, 2016).
•Daniel P. Mensher, With Friends Like These... The Trouble With Auer Deference, 43 Envtl. Law Rev. 4 (2013).
•Speaker, Oregon Water Law Conference, Addressing issues in Water Quality Trading (November 7, 2013).
•Speaker, Northwest Environmental Conference and Tradeshow, The Precautionary Principle in Environmental Law (December 11, 2013).
•Speaker, RainOps Conference, Spokane, WA, Longview, WA, Clean Water Act stormwater regulation (2013).
•Presenter, Oregon State Bar Environmental and Natural Resources Committee annual Continuing Legal Education Program, Salmon issues in Oregon and the Pacific Northwest, (2013).
•Speaker, Oregon State Bar brown bag CLE debate with Oregon DOJ assistant attorney general about the Supreme Court case Decker v. NEDC (2012).
•Daniel P. Mensher, Common Law On Ice: Using Federal Nuisance Law to Address Global Warming, 37 Envtl. Law Rev. 2 (2007).
•Chris Rycewicz and Dan Mensher, Growing State Authority Under the Clean Water Act, 22 Nat. Resources & Env’t 2 (2007).
Recognitions
Honors & Awards
•The Best Lawyers in America, Seattle, Washington, 2026:
•Mass Tort Litigation / Class Actions - Plaintiffs
•Selected to Rising Stars list in Super Lawyers - Washington, 2025
•Lawdragon 500 Leading Environmental Lawyers - The Green 500, 2025-2026
