- About Gradient
- Services & Projects
- Product Stewardship and Safety
- Risk Sciences
- Environmental Sciences
- Environmental Cost Analysis
- Global Regulatory Compliance
- People
- Principals
- Lisa A. Bailey
- Barbara D. Beck
- Andrew B. Bittner
- Teresa S. Bowers
- Eric L. Butler
- Joel M. Cohen
- David G. Dodge
- Samuel A. Flewelling
- Julie E. Goodman
- Kurt Herman
- Jessie M. Kneeland
- David E. Langseth
- Tom A. Lewandowski
- Ari S. Lewis
- Christopher M. Long
- David E. Merrill
- Michael K. Peterson
- Robyn L. Prueitt
- Kim Reynolds Reid
- Lorenz R. Rhomberg
- Jeffrey T. Rominger
- Manu Sharma
- Caroline B. Tuit
- Peter A. Valberg
- Tim Verslycke
- A. Dallas Wait
- Senior Scientists
- Steven R. Boomhower
- Ali Boroumand
- Lindsey Borton
- Chase Butler
- Rachel Y. Chang
- Jiayang Chien
- Amy Dale
- Anna M. Engel
- Grace I. Greenberg
- Mary L. Hixon
- Laura E. Kerper
- John M. Kondziolka
- Cynthia J. Langlois
- Julie C. Lemay
- Charlotte Marsh
- Rosemary Mattuck
- Matthew J. Mayo
- Isaac Mohar
- Rajib Mozumder
- Margaret C. Pollock
- Kathleen A. Radloff
- James W. Rice
- Naomi L. Slagowski
- Meghna H. Swamy
- Rebecca C. Ticknor
- Matthew P. Tymchak
- Andrew Yeh
- Jiaru Zhang
- Shuo Zhao
- Research & Information Specialists
- Principals
- Evolving Issues
- News & Events
- Recent Scientific Papers
- Careers
- Directions
Senior Scientists
Gradient is proud to have a diverse, skilled, and well-trained technical staff who work collaboratively to manage our projects, perform research, and deliver innovative solutions with superior quality.
Steven R. Boomhower, Ph.D.
Senior Toxicologist
Expertise
- Metals Toxicology
- Developmental Toxicology
- Neurotoxicology
- Psychopharmaceuticals
- Cannabis
- Animal Testing and Extrapolation
- Statistical Modeling
Ali Boroumand, Ph.D., P.E.
Senior Environmental Engineer
Expertise
- Contaminant Fate & Transport
- Groundwater Hydrology
- Remedial Investigation & Design
- Groundwater Modeling
- Multiphase Flow and Reactive Transport
- "Green and Sustainable Remediation"
Lindsey K. Borton M.P.H.
Senior Toxicologist
Expertise
- Product Safety
- Medical Device Regulations
- Risk Assessment and Biocompatibility
- Pharmaceutical Non-clinical Safety Assessment
Chase Butler, M.S.
Senior Environmental Chemist
Expertise
- Environmental Chemistry
- Read-Across Assessment
- Materials Science and Degradation Pathways
- Analytical Testing Methods
Rachel Y. Chang, Ph.D.
Senior Toxicologist
Expertise
- Consumer Product Safety
- Developmental Toxicology
- Proposition 65
- Medical Device Biocompatibility
- Extractables and Leachables
Jiayang Chien, M.P.H.
Senior Environmental Scientist
Expertise
- Human Health Risk Assessment
- Exposure Assessment
- Epidemiology
- Electric and Magnetic Fields (EMF)
- GHS Hazard Assessment
Amy L. Dale, Ph.D.
Senior Environmental Engineer
Expertise
- Contaminant Fate & Transport
- Numerical Modeling
- Nanomaterials
- Hydrology
- Climate Change Impacts and Adaptation
- Decision Analysis
Anna M. Engel
Senior Research Associate
Expertise
- Epidemiology
- Exposure Science
- Specific Causation Analysis
- Historical State-of-Knowledge
- Site History Assessment
Grace I. Greenberg, M.P.H., BCES
Senior Environmental Toxicologist
Expertise
- Exposure Modeling
- Human Health Risk Assessment
- Ecological Risk Assessment
- Database Construction and Management
- Data Analysis and Interpretation
Mary L. Hixon, Ph.D.
Senior Toxicologist
Expertise
- Reproductive and Developmental Toxicology
- Toxicogenomics
- Mode of Action Analyses
- Human Exposure
Laura E. Kerper, Ph.D.
Managing Toxicologist
Expertise
- Risk Assessment
- General and Molecular Biology
- Heavy Metals Toxicity
- Solvent Toxicity
- Toxicology
- Perfluorinated Chemicals
- Talc
John M. Kondziolka, M.S., E.I.T.
Senior Environmental Engineer
Expertise
- Contaminant Fate and Transport
- Risk Assessment
- Fluid Dynamics
- Numerical Modeling
Cynthia J. Langlois, M.S.
Senior Health Scientist
Expertise
- Risk Communication
- Exposure Assessment
- Data Quality
- Toxicology
Julie C. Lemay, M.P.H.
Senior Environmental Health Scientist
Expertise
- Risk Communication
- Human Health Risk Assessment
- Exposure Assessment
- Epidemiology
- Public Health
- Data Analysis and Interpretation
Charlotte Marsh, M.S.
Senior Toxicologist
Expertise
- Human Health Risk Assessment
- Toxicology
- Product Safety Evaluation
- Product Stewardship
- GHS Hazard Assessment
Rosemary Mattuck, M.S.
Senior Environmental Engineer
Expertise
- Exposure Assessment
- Blood Lead Modeling
- Product Safety
- Risk Assessment
- Proposition 65
Matthew J. Mayo, M.S., GISP, CPG, PG
Senior GIS/Environmental Scientist
Expertise
- Hydrogeology
- GIS Management
- 2D and 3D Geospatial Modeling
- Remote Sensing and Aerial Imagery Analysis
- Database Construction and Management
- Geospatial Data Acquisition and Visualization
- Web-based GIS Mapping and Analysis Applications
Isaac Mohar, Ph.D., DABT
Senior Toxicologist
Expertise
- Risk Assessment
- Toxicology
- Immunology
- Liver Pathology
Rajib Mozumder, Ph.D.
Environmental Engineer
Expertise
- Contaminant Fate & Transport
- Environmental Forensics
- Hydrogeology
- Remedial Investigation/Design
- Numerical Modeling
- Geostatistics
- Groundwater Geochemistry
- Environmental Cost Allocation
Margaret C. Pollock, M.S.
Managing Environmental Scientist
Expertise
- Statistical Methods
- Exposure Assessment
- Database Development
- Cost Estimation and Allocation
Kathleen A. Radloff, Ph.D.
Senior Environmental Engineer
Expertise
- Contaminant Fate & Transport
- Aqueous Geochemistry
- Lead, Arsenic, and Metals
- Groundwater Hydrology
- Risk-based Remediation
James W. Rice, Ph.D.
Senior Environmental Scientist
Expertise
- Contaminant Fate & Transport
- Vapor Intrusion
- Polycyclic Aromatic Hydrocarbons (PAH)
- Read-Across Assessment
- Environmental Sampling and Data Interpretation
Naomi L. Slagowski, M.S.
Senior GIS/Environmental Engineer
Expertise
- Remedial Investigation/Design
- Database Development
- GIS and Spatial Analysis
- Data/Document Validation
- Historical Information Review
Meghna H. Swamy, M.S.
Managing Environmental Engineer
Expertise
- Contaminant Fate & Transport
- NAPL Transport
- Remedial Investigation & Design
- Risk-based Remediation
- Environmental Cost Analysis
- Manufactured Gas Plants
- Site Characterization and Remedial Strategy
Rebecca C. Ticknor, M.S.
Senior Toxicologist
Expertise
- Inhalation Toxicology
- Risk Communication
- Product Safety
- Risk Assessment
- Medical Device Regulations and Biocompatibility
- Occupational Safety and Health
- Human and Environmental Toxicology
Matthew P. Tymchak, M.S.
Senior Hydrologist
Expertise
- Remedial Investigation & Design
- Hydraulic Fracturing
- NAPL
- Contaminant Fate and Transport
- Environmental Cost Analysis
- Groundwater-Surface Water Hydrology
Andrew Yeh, Ph.D., DABT
Senior Toxicologist
Expertise
- Risk Communication
- Product Safety
- Risk Assessment
- Toxicology
- Causation Analysis
Jiaru Zhang, M.P.H., DABT
Senior Toxicologist
Expertise
- Product Safety Evaluation
- Product Stewardship
- Medical Device and Pharmaceutical Safety Assessments
- GHS hazard assessment, SDS, and Label
Shuo Zhao, M.S.
Senior Environmental Engineer
Expertise
- Database Construction and Management
- Numerical Modeling
- Stormwater Management
- Full Stack Development
- Geospatial Analysis
- Watershed Hydrology