- About Gradient
- Services & Projects
- Product Stewardship and Safety
- Risk Sciences
- Environmental Sciences
- Environmental Cost Analysis
- Global Regulatory Compliance
- People
- Principals
- Barbara D. Beck
- Leslie A. Beyer
- Andrew B. Bittner
- Teresa S. Bowers
- Catherine Petito Boyce
- Eric L. Butler
- Samuel A. Flewelling
- Julie E. Goodman
- Kurt Herman
- David E. Langseth
- Tom A. Lewandowski
- Ari S. Lewis
- Christopher M. Long
- David E. Merrill
- Kim Reynolds Reid
- Lorenz R. Rhomberg
- Manu Sharma
- Peter A. Valberg
- Tim Verslycke
- A. Dallas Wait
- Senior Scientists
- Lisa A. Bailey
- Ali Boroumand
- Nicole L. Briggs
- Joel M. Cohen
- Travis J. Cook
- David G. Dodge
- Eric M. Dube
- Grace I. Greenberg
- Mary L. Hixon
- Laura E. Kerper
- Jessie M. Kneeland
- Cynthia J. Langlois
- Julie C. Lemay
- Laurent C. Levy
- Tamara D. Lunsman
- Heather N. Lynch
- Rosemary Mattuck
- David B. Mayfield
- Matthew J. Mayo
- Isaac Mohar
- Michael K. Peterson
- Daniella M. Pizzurro
- Margaret C. Pollock
- Robyn L. Prueitt
- Kathleen A. Radloff
- James W. Rice
- Jeffrey T. Rominger
- Mara Seeley
- Daniel Skall
- Meghna H. Swamy
- Caroline B. Tuit
- Matthew P. Tymchak
- Jiaru Zhang
- Kirsten (Ke) Zu
- Research & Information Specialists
- Principals
- Evolving Issues
- News & Events
- Recent Scientific Papers
- Careers
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Principals
Gradient's Principals are nationally recognized experts and active contributors to the promotion of sound science. We maintain our position as leaders in our scientific specialties through professional certifications, peer-recognized publishing, panel and conference participation, continuing education, and hands-on work on some of the world's most challenging environmental issues.
Barbara D. Beck, Ph.D., DABT, ATS
Principal
Expertise
- Inhalation Toxicology
- Historical Understanding of Toxicology
- Regulatory Comment
- Risk Communication
- Metals Toxicology
Leslie A. Beyer, M.S., DABT, CIH
Principal Scientist
Expertise
- Occupational Health
- Solvents
- Historical Toxicology
- Risk Assessment
- Toxicology
- Epidemiology
- Toxic Tort Litigation Support
Andrew B. Bittner, M.Eng., P.E.
Principal Scientist
Expertise
- NAPL Transport
- Groundwater & Surface Water Modeling
- Groundwater Hydrology
- Soil Vapor Intrusion Modeling
- Hydraulic/WWTP Modeling
Teresa S. Bowers, Ph.D.
Principal
Expertise
- Statistical Methods
- Geochemical Modeling
- Exposure Modeling
- Blood Lead Modeling
- Lead, Arsenic, & PCBs
- Cleanup Levels
- Risk Communication
Catherine Petito Boyce, S.M.
Principal Scientist
Expertise
- Exposure Modeling
- Toxicity Assessment
- Regulatory Comment
- Cleanup Negotiations
- Probabilistic Methods
- Risk Assessment
Eric L. Butler, Ph.D.
Principal
Expertise
- Environmental Forensics
- Chemical Fingerprinting
- Analytical Methods
- Source Allocation
- TPH, PAH, PCBs, Dioxins, Solvents, & Metals
- Contemporary Archeology
Samuel A. Flewelling, Ph.D.
Principal Scientist
Expertise
- Contaminant Fate & Transport
- Hydraulic Fracturing
- Hydrological Modeling
- Chlorinated Solvents
- NAPL
- Metals
- Induced Seismicity
- Water Rights
- Nutrients
- Trace Metals
- Petroleum Hydrocarbons
Julie E. Goodman, Ph.D., DABT, FACE, ATS
Principal
Expertise
- Epidemiology
- Toxicology
- Risk Assessment
- Product Safety
- Carcinogenesis
Kurt Herman, M.Eng., P.G.
Principal
Expertise
- Contaminant Fate & Transport
- Environmental Forensics
- NAPL
- MGP and Wood Treating Sites
- Historical Operations & Waste Practices
- Environmental Cost Analysis
David E. Langseth, Sc.D, P.E., D.WRE
Principal
Expertise
- Surface & Groundwater Hydrology
- Water Quality Evaluation
- Environmental Liability Evaluation
Tom A. Lewandowski, Ph.D., DABT, ERT, ATS
Principal
Expertise
- Product Safety
- Metals Toxicology
- Pharmacokinetic Modeling
- Risk Assessment
- Alternative Assessment
- Developmental Toxicology
Ari S. Lewis, M.S.
Principal
Expertise
- Metals Toxicology
- Molecular Toxicology
- Human Health Risk Assessment
- Arsenic Toxicology
Christopher M. Long, Sc.D., DABT
Principal Scientist
Expertise
- Indoor/Outdoor Air Pollution
- Air Sampling, Measurement, & Modeling
- Exposure Assessment
- Inhalation Risk Assessment
- Electric and Magnetic Fields (EMF)
David E. Merrill, M.S.
Principal
Expertise
- Risk-based Cleanup Negotiations
- PCBs & Sediments
- Multimedia Modeling
- Statistical & Monte Carlo Methods
- Database Design & Synthesis
Kim Reynolds Reid
Principal Scientist
Expertise
- Environmental Chemistry
- Sampling & Analysis Design
- Inorganic/Organic Data Interpretation
- Project Management
- Quality Assurance Oversight
Lorenz R. Rhomberg, Ph.D., ATS
Principal
Expertise
- Weighing Toxicologic Evidence
- Quantitative Risk Methods
- Pharmacokinetic Modeling
- Chlorinated Solvents
- Risk Policy & Methodology
- Cumulative Risk
Manu Sharma, M.S., P.E.
President
Expertise
- Contaminant Fate & Transport
- Environmental Forensics
- Hydraulic Fracturing
- Risk-based Remediation
- Cost Allocation/Liability Assessment
- Water Resources
Peter A. Valberg, Ph.D., ATS
Principal
Expertise
- Risk Communication
- Inhalation Toxicology
- Exposure Modeling
- Airborne Pollutants & Particulates
- Radiation & Radionuclide Risk
- Electromagnetic Fields
Tim Verslycke, Ph.D.
Principal
Expertise
- Environmental Risk Assessment
- Standard & Regulatory Chemical Screening & Testing
- Endocrine Disruptors
- Pharmaceuticals in the Environment
- Product Safety
A. Dallas Wait, Ph.D.
Principal
Expertise
- Consumer Product Characterization
- Natural Product Chemistry
- Environmental Chemistry & Forensics
- Test Method Evaluation & Design
- Historical Analytical Chemistry Practices
- Data Quality
Barbara D. Beck, Ph.D., DABT, ATS
Principal
Expertise
- Inhalation Toxicology
- Historical Understanding of Toxicology
- Regulatory Comment
- Risk Communication
- Metals Toxicology
Leslie A. Beyer, M.S., DABT, CIH
Principal Scientist
Expertise
- Occupational Health
- Solvents
- Historical Toxicology
- Risk Assessment
- Toxicology
- Epidemiology
- Toxic Tort Litigation Support
Andrew B. Bittner, M.Eng., P.E.
Principal Scientist
Expertise
- NAPL Transport
- Groundwater & Surface Water Modeling
- Groundwater Hydrology
- Soil Vapor Intrusion Modeling
- Hydraulic/WWTP Modeling
Teresa S. Bowers, Ph.D.
Principal
Expertise
- Statistical Methods
- Geochemical Modeling
- Exposure Modeling
- Blood Lead Modeling
- Lead, Arsenic, & PCBs
- Cleanup Levels
- Risk Communication
Catherine Petito Boyce, S.M.
Principal Scientist
Expertise
- Exposure Modeling
- Toxicity Assessment
- Regulatory Comment
- Cleanup Negotiations
- Probabilistic Methods
- Risk Assessment
Eric L. Butler, Ph.D.
Principal
Expertise
- Environmental Forensics
- Chemical Fingerprinting
- Analytical Methods
- Source Allocation
- TPH, PAH, PCBs, Dioxins, Solvents, & Metals
- Contemporary Archeology
Samuel A. Flewelling, Ph.D.
Principal Scientist
Expertise
- Contaminant Fate & Transport
- Hydraulic Fracturing
- Hydrological Modeling
- Chlorinated Solvents
- NAPL
- Metals
- Induced Seismicity
- Water Rights
- Nutrients
- Trace Metals
- Petroleum Hydrocarbons
Julie E. Goodman, Ph.D., DABT, FACE, ATS
Principal
Expertise
- Epidemiology
- Toxicology
- Risk Assessment
- Product Safety
- Carcinogenesis
Kurt Herman, M.Eng., P.G.
Principal
Expertise
- Contaminant Fate & Transport
- Environmental Forensics
- NAPL
- MGP and Wood Treating Sites
- Historical Operations & Waste Practices
- Environmental Cost Analysis
David E. Langseth, Sc.D, P.E., D.WRE
Principal
Expertise
- Surface & Groundwater Hydrology
- Water Quality Evaluation
- Environmental Liability Evaluation
Tom A. Lewandowski, Ph.D., DABT, ERT, ATS
Principal
Expertise
- Product Safety
- Metals Toxicology
- Pharmacokinetic Modeling
- Risk Assessment
- Alternative Assessment
- Developmental Toxicology
Ari S. Lewis, M.S.
Principal
Expertise
- Metals Toxicology
- Molecular Toxicology
- Human Health Risk Assessment
- Arsenic Toxicology
Christopher M. Long, Sc.D., DABT
Principal Scientist
Expertise
- Indoor/Outdoor Air Pollution
- Air Sampling, Measurement, & Modeling
- Exposure Assessment
- Inhalation Risk Assessment
- Electric and Magnetic Fields (EMF)
David E. Merrill, M.S.
Principal
Expertise
- Risk-based Cleanup Negotiations
- PCBs & Sediments
- Multimedia Modeling
- Statistical & Monte Carlo Methods
- Database Design & Synthesis
Kim Reynolds Reid
Principal Scientist
Expertise
- Environmental Chemistry
- Sampling & Analysis Design
- Inorganic/Organic Data Interpretation
- Project Management
- Quality Assurance Oversight
Lorenz R. Rhomberg, Ph.D., ATS
Principal
Expertise
- Weighing Toxicologic Evidence
- Quantitative Risk Methods
- Pharmacokinetic Modeling
- Chlorinated Solvents
- Risk Policy & Methodology
- Cumulative Risk
Manu Sharma, M.S., P.E.
President
Expertise
- Contaminant Fate & Transport
- Environmental Forensics
- Hydraulic Fracturing
- Risk-based Remediation
- Cost Allocation/Liability Assessment
- Water Resources
Peter A. Valberg, Ph.D., ATS
Principal
Expertise
- Risk Communication
- Inhalation Toxicology
- Exposure Modeling
- Airborne Pollutants & Particulates
- Radiation & Radionuclide Risk
- Electromagnetic Fields
Tim Verslycke, Ph.D.
Principal
Expertise
- Environmental Risk Assessment
- Standard & Regulatory Chemical Screening & Testing
- Endocrine Disruptors
- Pharmaceuticals in the Environment
- Product Safety
A. Dallas Wait, Ph.D.
Principal
Expertise
- Consumer Product Characterization
- Natural Product Chemistry
- Environmental Chemistry & Forensics
- Test Method Evaluation & Design
- Historical Analytical Chemistry Practices
- Data Quality