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Haynes and Boone

Mary Simmons Mendoza

Mary Simmons Mendoza



  • Chemical
  • Climate Change and Corporate Sustainability
  • Energy Regulatory
  • Energy, Power and Natural Resources

WSG Practice Industries


Haynes and Boone
Texas, U.S.A.

WSG Leadership

ABA 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.

Bar Admissions



J.D., University of Texas at Austin School of Law, 1994 with honors, Order of the Coif
B.S., Civil Engineering The University of Texas, 1991 with highest honors; Tau Beta Pi
Areas of Practice

Chemical | Climate Change and Corporate Sustainability | Energy Regulatory | Energy, Power and Natural Resources | Environmental | Environmental Crimes | Environmental Due Diligence | Environmental Litigation | Government Enforcement and Litigation | Greenhouse Gases (GHG) | Internal Investigations and Crisis Management | Litigation | Oil and Gas | Permitting, Regulatory Counseling, and Compliance | Power and Renewables | Project Finance and Development | Remediation and Brownfields Developments

Professional Career

Significant Accomplishments

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.

Environmental Compliance in the Coronavirus Era
Haynes and Boone, April 2020

Many regulated entities are struggling to comply with certain environmental reporting, monitoring and settlement agreement requirements because of the impact of shelter in place orders, supply chain disruptions, and social distancing requirements relating to the COVID-19 pandemic response...

WSG's members are independent firms and are not affiliated in the joint practice of professional services. Each member exercises its own individual judgments on all client matters.

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