Material Matters Team Members

Material Matters is staffed with a group of highly specialized and qualified individuals. When you establish a relationship with Material Matters, know that you will be working with experts in the field. Take some time to see what our team can do for you...


Trudy Johnston, Chief Executive Officer*
Dr. Robin Brandt, Vice President*
Aaron Stephens, Vice President*
Stefan Weaver, Sr. Project Scientist*
Lisa Challenger, Project Manager*
Wade Yankey, Project Scientist
Kathleen Bertoldi, Sr. Environmental Scientist
Mark Younkins, Soil Specialist
Jade Triton, Executive Assistant
*Material Matters, Inc. shareholder

Trudy Johnston
Trudy Johnston

Trudy is CEO and partner with Material Matters, and has over 29 years in the municipal and industrial wastewater processing and solids treatment and management field, with 25 years as a consultant. Her primary interests include developing innovative uses and strategies for residuals, optimizing solids processing, conducting solids master studies, assessing compliance with biosolids regulatory standards, data/sample collection and validation, evaluating and resolving odors from residuals, and water quality nutrient trading. She participated in the WERF study with UMASS to assess biosolids stability standards and authored the protocol for the AVSR testing. Trudy has a BS degree in Earth Science from Penn State and is a certified wastewater treatment operator.
Dr. Robin C. Brandt
Dr. Robin C. Brandt, Ph.D., PE

Robin is a partner and Vice President of Material Matters. He has over 35 years’ experience in agricultural, municipal, industrial, and food processing residuals assignments. He directs the company’s efforts involving water reclamation and composting facility odor emission studies and biosolids-derived-product odor assessments (current-in-practice and research). Robin contributes to field-trial and plot studies, and participates in the conceptualization/ development of emerging beneficial use strategies such as Deep Row Hybrid Poplar biosolids recycling programs (and related research). He serves as technical project manager on selected assignments and functions as liaison for projects involving consultation with the Pennsylvania State University (PSU) and other selected technical service providers. Robin is a full-time faculty member with PSU (17 years), at the University Park, PA main campus, in the Department of Agricultural and Biological Engineering, where he serves as Senior Lecturer and Director of the PSU Odor Assessment Laboratory.
Aaron Stephens
Aaron Stephens, MS, EIT

Aaron is Vice President and partner with Material Matters, responsible for data and information management projects. He began as a consultant for Material Matters in 2002 for the development of the Material Manager™ database for biosolids, and now serves as a project manager since 2006. He works with multiple industrial and food processing clients, and has project experience involving waste heat utilization, data visualization and mapping with GIS and KML, and large-scale feasibility analysis in conjunction with master planning. He is a problem solver, specializing in data analysis, software development, and numerical modeling. Aaron is an E.I.T. with an MS degree in Agricultural and Biological Engineering from Penn State.
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Stefan Weaver
Stefan Weaver, MS, CPSS

Stefan is a Senior Project Scientist, project manager and partner with Material Matters, with over 22 years of professional experience, mostly in biosolids and residuals management. He is Certified Professional Soil Scientist by the Soil Science Society of America, and is responsible for conducting technical soil site investigations for beneficial use (agricultural and disturbed land) projects. His understanding of regulatory challenges allows him to be involved in a variety of projects focusing on innovative uses such as deep row hybrid poplar reclamation, mine reclamation, site qualification, site mapping, conservation planning, nutrient assessment, database validation, and interacting with regulatory agencies. Stefan has an MS degree in Soil Science from Penn State.
Lisa Challenger
Lisa Challenger

Lisa is a Project Manager with Material Matters. She is responsible for supporting clients with the management of water quality nutrient credits, developing comprehensive biosolids market evaluations, evaluating and reporting on permitting and regulatory compliance, and assisting with site and soils evaluation. She is also responsible for assisting clients with biosolids master plan decisions by providing information about the technologies, marketing techniques, and end uses utilized by other biosolids programs. Lisa has a BS degree in Environmental Resource Management from Penn State.
Wade Yankey
Wade Yankey

Wade is an Environmental Scientist with Material Matters, responsible for providing support to municipal wastewater clients related to optimizing wastewater treatment plant operations, permitting, solids management studies, developing bid specifications and request for proposal (RFP) documents, and water quality nutrient trading. He conducts process-related assessments and reports including solids processing and dewatering evaluations to optimize plant performance. He also assists in biosolids market assessment and master planning activities.
Kathleen Bertoldi
Kathleen Bertoldi, EIT

Kathleen is a Senior Environmental Scientist responsible for providing support to municipal wastewater clients related to permitting, solids management, and market research analysis. She has eight (8) years of experience in environmental and/or water resource engineering with six (6) years as a licensed engineer in training (EIT). In addition, she has experience working in regulatory, consulting, and industry settings. In the public sector she worked as a hydrologist for an interstate water resource management agency, and as staff engineer for a county municipal solid waste (MSW) landfill. Kathleen has a BS in Environmental Engineering from Penn State.
Mark Younkins
Mark Younkins

Mark has experience in GIS, marketing, permitting, and managing biosolids and residual materials. His responsibilities include assisting project managers in conducting comprehensive biosolids market evaluations, and biosolids characterization. Mark is also responsible for building custom maps to demonstrate key opportunities and challenges identified during biosolids market assessments. He also plays an instrumental role in assisting clients with regulatory compliance related to biosolids land application programs, which includes conducting site and soil assessments, developing agronomic rates, and assisting with the development of regulatory documents required for new and ongoing biosolids land application programs.
Jade Triton
Jade Triton

Jade has more than 20 years of administrative experience with accounting and finances, program management, editing and printing project production, and office management as Director of Operations for an arts in education nonprofit in New York City. In her current role with Material Matters, she manages the office bookkeeping and provides administrative assistance to the professional staff members including providing support for project managers, preparing a variety of internal reports, and overseeing invoice generation.