People / Mary Simmons Mendoza
Mendoza Mary

Mary Simmons Mendoza

Partner | Chair - Environmental Practice Group

Mary Mendoza is a trusted advisor to companies in finding solutions to their environmental issues. Whether the issue is environmental litigation, enforcement actions, day-to-day compliance, site cleanup or toxic tort litigation, Mary helps clients successfully navigate the complex area of environmental law. Mary brings this practical knowledge of environmental law to corporate, real estate and other transactions, to assist clients in identifying environmental risks and manage those risks to a successful conclusion.

During her career, Mary has represented clients from most every industry on environmental risks. Mary’s representations stretch from the oil patch to your local shopping center, and all types of businesses in between.

Mary earned her undergraduate degree in civil engineering from the University of Texas at Austin, where much of her course work focused on environmental issues. Mary uses the technical background to explain complex environmental issues in clear, concise terms for clients, judges and juries.

Mary’s experience includes many significant and high profile matters. For example, Mary recently successfully represented a Fortune 500 company in an environmental enforcement action involving novel theories of liability under air, solid waste and storm water regulations. Mary regularly appears before state and federal agencies on enforcement matters, including representing an oil and gas exploration and production company in a two week UIC permitting contested hearing and a manufacturer of consumer products in Clean Air Act enforcement action. She also represents clients on significant superfund matters. Mary’s technical background is of particular value in addressing the complex technical issues for site remediation, such as her recent representation of a major retailer in the remediation of an urban site for the development of a new retail store.

Mary also assists clients in transactional matters to identify and allocate risk for environmental issues. She assisted a private equity fund in the purchase of a paper recycling facility out of bankruptcy, using the bankruptcy proceedings to leverage settlements of Superfund liabilities and remediation obligations with federal and state authorities.

Mary frequently speaks and writes on environmental issues and is a co-author of the Thomson Reuters Texas Practice 2 –volume treatise on Texas Environmental Law.

Mary is a former chair of the Environmental and Natural Resources Law Section of the State Bar of Texas. Mary’s community involvement focuses on early childhood charities and education at the youngest levels, as shown by her involvement in Any Baby Can of Austin where she has previously served as the chair of the board of directors.

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  • Successfully resolved state environmental enforcement action for a major manufacturing company involving air, waste and stormwater issues.
  • Successfully defended a water treatment technology company in 6 week jury trial to a take-nothing verdict.
  • Oil and gas exploration and production company in UIC permitting hearings.
  • National oil company in a multimedia environmental audit of refinery/chemical production facility.
  • Energy auditing firm in regulatory matters before Texas Real Estate Commission.
  • A major manufacturer in defending a CERCLA cost recovery action.
  • Major retailer in the environmental issues associated with the acquisition and development of store locations.
  • A private equity fund in the acquisition of environmentally impaired assets out of bankruptcy.
  • A major manufacturer in responding to a CERCLA information request.
  • Purchaser of contaminated property in negotiating a bona fide prospective purchaser agreement with EPA.
  • A manufacturer of water treatment equipment in a four week jury trial regarding alleged design defects.
  • A major corporation in a multi-million dollar remediation of a contaminated site under the state voluntary cleanup program.
  • Regulated industries in permit proceeding before the Texas Commission on Environmental Quality.
  • Defendants in enforcement hearings before the Texas Commission on Environmental Quality and the Environmental Protection Agency.
  • Defendant in enforcement action relating to alleged Clean Air Act violations arising out of release from commercial refrigeration system.
  • Defendants in negotiations of RCRA and CERCLA cleanup orders with the Environmental Protection Agency.
  • Multiple companies in the settlement of CERCLA liabilities with the Environmental Protection Agency.
  • A multi state corporation in multimedia compliance audits of plant operations.
  • Major property management companies in the defense of mold lawsuits and in the development of mold policies.
  • An alternative fuels plant in connection with permitting before the TCEQ.
  • A seller in a divestiture involving multi state property transfer notifications.
  • A corporation regarding compliance counseling and divestiture of a water and wastewater supply corporation.
  • Entities in appeals of agency orders.
  • Multiple defendants in toxic tort litigation regarding a commercial waste disposal facility.
  • Manufacturers in negotiations with the Consumer Product Safety Commission relating to product recalls.
  • Entities in a contested case hearing related to horse race track licensing before the Texas Racing Commission.
  • Recognized in The Best Lawyers in America, Woodward/White, Inc., Environmental Law, 2006-2024; Litigation - Environmental, 2011-2024
  • Recognized as a leading individual in Environmental Law (Texas) by Chambers USA, Chambers and Partners, 2006, 2011-2024
  • Recognized in Lawdragon 500 Leading Environmental and Energy Lawyers listing, Lawdragon Inc., 2021, 2023, 2024
  • Selected for inclusion in Austin Business Journal's list of Who's Who in Energy, American City Business Journals, 2013
  • Who's Who Legal, Law Business Research Ltd., Texas Environmental Law, 2007 and 2008, 2023
  • Texas Super Lawyers - Rising Stars Edition, Thomson Reuters, 2005-2007
  • "Control of Methane in the Oil Patch: Low Hanging Regulatory Fruit?" co-author, Thomson Reuters Practical Law, June 2, 2023.
  • “Texas Environmental Law,” co-author, Volumes 45-46, Chapter 12 Storage Tanks, Chapter 13 Brownfields and Texas Risk Reduction Program, Chapter 33 Environmental Aspects of Business Transactions, Thomson Reuters, 2020-2021.
  • “Texas Environmental Law,” co-author, Volumes 45-46, Chapter 12 Storage Tanks (UST, AST, and Solid Waste), Chapter 13 Brownfields – VCP, IOP & TRRP, Chapter 33 Environmental Aspects of Business Transactions, Thomson Reuters, 2019-2020.
  • “2002: PFAS: the Fast-Changing Regulatory and Litigation Landscape,” presenter, SOCMA Week 2019, New Orleans, LA, December 5, 2019.
  • “Identifying and Indemnifying Against Environmental Risks,” co-author, republished by American College of Mortgage Attorneys, Annual Meeting, Monterey, California, September 5, 2019.
  • “Federal vs. State Liability Protections and Due Care Obligations During Property Acquisitions: How 'Certain' is Certain?” panelist, American Bar Association: Environment, Energy, and Resources Section, CERCLA Master Class on Complex Environmental Liability Resolution: State of the Art Strategies from Superfund to Brownfields, Atlanta, Georgia, June 12, 2019.
  • “Water-Energy Interface – Thirst for Power,” moderator, EarthX Law Symposium, Dallas, Texas, April 26, 2019.
  • “Environmental Issues in the Oil Patch,” panelist, 30th Annual Texas Environmental Superconference, Austin, Texas, August 3, 2018.
  • “Texas Environmental Law,” co-author, Volumes 45-46, Thomson Reuters, 2017 and 2018.
  • “Integrating Corporate Sustainability and Ethical Considerations Into Corporate Decision-Making,” co-moderator, Environmental Law & Policy Legal Symposium - Earth Day TX 2017, Dallas, Texas, April 21, 2017.
  • “Identifying and Indemnifying Against Environmental Risk,” Jeff Civins and Mary Mendoza, The University of Texas School of Law, 49th Annual William W. Gibson, Jr. Mortgage Lending Institute, Austin, Texas, September 17 and November 6, 2015.
  • “Toe the Line – Environmental Ethics,” 27th Annual Texas Environmental Superconference, Austin, Texas, August 5, 2015.
  • “Ethical Issues in Environmental Law: It's Not Easy Being Green,” with J. Civins, 5th Annual Texas Environmental Law Journal Symposium, University of Texas School of Law, Austin, Texas, April 24, 2015.
  • “Environmental Compliance Strategies,” Hispanic National Bar Association Corporate Counsel Conference, San Antonio, Texas, March 20, 2015.
  • “Environmental Update: Due Diligence and Other Issues for Loan Arrangers,” University of Texas School of Law Mortgage Lending Institute, Dallas, Texas, October 2-3, 2014.
  • “Drilling Down, Environmental Diligence in Oil and Gas Fields,” Environmental Impacts of Oil and Gas Development 2014, State Bar of Texas CLE, San Antonio, Texas January 31, 2014.


J.D., The University of Texas School of Law, 1994, with honors, Order of the Coif

B.S., Civil Engineering, The University of Texas at Austin, 1991, with highest honors; Tau Beta Pi



Press Release
Five Haynes Boone Lawyers Recognized Among Nation’s Leading Environmental Lawyers
February 16, 2023

Five Haynes and Boone, LLP lawyers are featured in the Lawdragon 500 directory of standout environmental lawyers in the United States. Lawdragon selected the 500 honorees through submissions, journalistic research, and editorial vetting from a board of the honorees’ peers. The following lawyers were included this year: Partner Ann Al-Bahish – Environmental Litigation Ann litigates environmental an [...]