Our Team Bios

Dennis E. Williams, Ph.D., PG, CHG

Founder and President

Dr. Dennis Williams is the founder and President of GEOSCIENCE. He has more than 45 years’ experience in groundwater hydrology, directing geohydrologic investigations locally and globally.[read more]

Mark Williams, Ph.D., PE

Vice President

Dr. Mark Williams is Vice President of GEOSCIENCE. His responsibilities include oversight of water quality and engineering portions of GEOSCIENCE projects. [read more]

Johnson Yeh, Ph.D., PG, CHG

Principal Geohydrologist & Groundwater Modeler 

Dr. Johnson Yeh oversees geohydrological investigations, groundwater modeling projects, and environmental and watershed analyses for numerous clients throughout California. [read more]

Brian Villalobos, PG, CHG, CEG

Principal Geohydrologist

Brian has more than 25 years of professional experience in environmental geology and hydrology throughout California. [read more]

Chris Coppinger, PG, CHG

Senior Geohydrologist

Chris’ work includes groundwater basin evaluations, well siting investigations, artificial recharge and conjunctive use studies and desalination feedwater supply studies. [read more]

Terry Watkins, PG, CHG

Senior Geohydrologist

Terry‘s expertise includes well design, construction, testing and development. He also has experience in the management and supervision of water well projects including siting, design, aquifer pumping test analyses and well construction. [read more]

Nathan Reynolds, PG

Project Geohydrologist

Nathan has extensive experience in geohydrologic investigations, groundwater quality studies and artificial recharge projects. [read more]

Sean Stewart

Director of Marketing

Sean has 15 years of service marketing and sales experience, with more than 10 years focused on the engineering and geological consulting industry. [read more]


Alex Arita

Staff Geohydrologist

Alexander has experience in hydrologic investigations, groundwater well development and field data collection.

B.S., Geology, California State University Fullerton, 2017

David Barnes, M.Eng.

Senior Modeler

David has 8 years of professional experience working in the water resources, water supply and mining sectors. His experience includes numerical modeling of surface and groundwater systems, design and construction of water supply and injection wells for fresh, brackish and seawater RO facilities.

B.S., Hydrology and Water Resources, University of Arizona Tucson, 2008
M.Eng., Civil and Environmental Engineering, MIT, Cambridge, 2009

David Bauer

Technical Illustrator/GIS Analyst

David has over 29 years of experience in the water industry with involvement in the production of presentation and technical graphics. He serves as our GIS coordinator whose responsibilities include the organization of all GIS activities, database management and graphic creation within our technical reports.

B.A., Physical Geography, Humboldt State University, 1988 with concentrations in Water Resource Policy and Natural Resources

Edween Hernandez, M.S.

Staff Geohydrologist

Edween’s experience includes geohydrologic investigations, groundwater well development and construction oversight, field data collection and test results analysis.

B.A., Education, University of California, Riverside, 2012
M.S., Geology, California State University, Fullerton, 2017

Tiffany Jensen

Office Manager

Tiffany is responsible for organizing work assignments including meeting deadlines, monitoring report production and office administration. She also works closely with the Director of Marketing on proposal creation, marketing graphics and manages the accounts payable for our company.

Certificate of Paralegal Studies, InterCoast Colleges-West Covina, 2005

Seth Kuiper, M.S.

Staff Geohydrologist

Seth’s responsibilities include field work, geohydrologic investigations and groundwater quality studies. He has also been involved with data collection and analyses on various projects.

B.S., Geology, Calvin College, 2010
M.S., Geoscience, Western Michigan University, 2015

Leo Liu, M.S., EIT

Staff Geohydrologist

Leo has expertise in groundwater flow and solute transport modeling, as well as, geohydrologic investigations. He also has experience using GIS applications.

B.S., Environmental Engineering, Tianjin Institute of Urban Construction, 2010
M.S., Environmental Engineering, University of Southern California, 2013

Wesley Massoll, M.S.

Staff Geohydrologist

Wesley’s experience includes geohydrologic investigations, groundwater well development and construction oversight, field data collection and test results analysis.

B.S., Geology, University of North Carolina Wilmington, 2012
M.S., Geology, University of North Carolina Wilmington, 2017

Coral Shaw

Staff Geohydrologist

Coral is involved in a variety of projects, including geohydrologic investigations, groundwater quality studies, well assessments, water well test drilling programs and the supervision of water well projects.

B.S., Geology, California State University Fullerton, 2012

Si Si, M.S., EIT

Staff Geohydrologist

Si Si has experience in groundwater flow and solute transport modeling, geohydrologic investigations and GIS applications.

B.S., Environmental Science, Ocean University of China, 2010
M.S., Environmental Engineering, University of Southern California, 2013

Amanda VanHaitsma, M.S.

Staff Geohydrologist

Amanda has expertise spanning the spectrum of groundwater services, including geohydrologic investigations, groundwater modeling, water quality studies, desalination feasibility and groundwater wells.

B.A., Hydrogeology, Environmental Studies, Central Michigan University, 2014
M.S., Geosciences, Virginia Polytechnic Institute and State University, 2016

Lauren Wicks, M.S., GIT

Staff Geohydrologist

Lauren’s expertise includes groundwater flow and transport modeling, geohydrologic investigations, groundwater basin and water quality studies. She has also been involved with artificial recharge projects, litigation projects, technical report preparation and GIS applications.

B.S., Integrated Earth Studies/Geology, California State Polytechnic University Pomona, 2009
M.S., Hydrology, University of Idaho, 2011

Logan Wicks, M.S., GIT

Staff Geohydrologist

Logan handles groundwater quality evaluations, well siting investigations, data collection and analyses, and remediation and water supply studies.

B.S., Geology, California Polytechnic University Pomona, 2010                 B.S., Biology, California Polytechnic University Pomona, 2010                  M.S., Geology, California Polytechnic University Pomona, 2014

Meijing Zhang, Ph.D.

Modeler/Staff Geohydrologist

Meijing has modeling expertise in groundwater flow, integrated groundwater-surface water exchange, and land subsidence. She has additional experience in GIS applications and hydrologic investigations.

B.S., Hydrology and Water Resources Engineering, China University Beijing, 2006                                                M.S., Hydrology and Water Resources Engineering, China University Beijing, 2009                  Ph.D, Hydrogeology, Virginia Tech University, 2014