People & Team

Our people are our greatest resource. Today, our agile, collaborative team provides innovative, safe, sustainable, reliable groundwater solutions for private and public clients from offices in San Dimas, CA and Tucson, AZ.

Mark Williams
CEO

Mark Williams

CEO

Mark Williams, PhD, PE

Dr. Mark Williams is Geoscience's CEO. With his unique background combining engineering and geology, Mark brings deep expertise and experience from his 25+ years working in water utility engineering and groundwater quality.

Prior to joining Geoscience in 2014, Mark served as an Engineer with the Process Development Team at the Metropolitan Water District, and subsequently consulted on a variety or water treatment projects including the Doheny Desalination Project and numerous groundwater treatment projects. Mark has presented and published extensively in the areas of water treatment engineering and water quality.

Dennis Williams
President/Principal Geohydrologist

Dennis Williams

President/Principal Geohydrologist

Dennis Williams, PhD, PG, CHG

Dennis Williams is the founder and president of Geoscience Support Services Inc. (Geoscience) He has more than 50 years of experience in groundwater hydrology and has directed more than 2,000 hydrogeologic investigations and groundwater models and overseen design and construction for more than 1,000 groundwater production and monitoring wells. Dennis has been a consultant to the United Nations and several foreign governments, is a research professor at the University of Southern California’s Civil and Environmental Engineering Department and has taught graduate level courses in hydrogeology and ground water modeling since 1980.

Brian Villalobos
Vice President of Operations/ Principal Hydrogeologist

Brian Villalobos

Vice President of Operations/ Principal Hydrogeologist

Brian Villalobos, PG, CHG, CEG

Brian has more than 32 years of professional experience in geohydrology and environmental geology throughout the Southern California region. His specific areas of expertise are in hydrogeologic investigations to support siting and development of subsurface intakes for ocean desalination, indirect potable reuse, groundwater recharge, and groundwater basin characterization projects. He has studied and provided geologic and geohydrologic data for modeling groundwater basins across the State and has led efforts to develop studies and reports including, monitoring well networks, groundwater recharge projects, sustainable yield, water budgets, and more. He currently serves both cities and water districts to develop and assess groundwater recharge projects using stormwater and recycled water, including the City of Oceanside, South Coast Water District, San Bernardino Valley Municipal Water District, Yucaipa Valley Water District, and others. Brian has also supported 20 groundwater related litigation cases serving as either the lead technical advisor or in a support role.

Brian is a frequent speaker at both national and international conferences, particularly on topics relating to desalination and feedwater supply. He is involved in a number of professional associations, including the Association of California Water Agencies (ACWA), CalDesal and the California-Nevada Section of the American Water Works Association.

Johnson Yeh
Principal Modeler

Johnson Yeh

Principal Modeler

Dr. Johnson Yeh is a principal and lead groundwater modeler at Geoscience. During his more than 27 years of career, he has been involved in the project management of the firm’s groundwater modeling efforts, including some of its most high-profile geohydrologic investigations, groundwater basin/water quality studies, and artificial recharge projects. Dr. Yeh also possesses a broad knowledge of GIS tools utilized in support of modeling work and oversees Geoscience’s GIS staff members.

Dr. Yeh spearheads the generation and quality control of technical documents and technical presentations to both clients and regulators, including leading training and workshops on the use of models to the USGS and USEPA.

Lauren Wicks
Senior Geohydrologist

Lauren Wicks

Senior Geohydrologist

Lauren Wicks, PG

Lauren has more than a decade of experience with groundwater and environmental investigations performed for numerous municipalities, state agencies, and private clients throughout California. Lauren’s expertise includes groundwater flow and transport modeling, geohydrologic investigations, groundwater basin and water management studies, and technical report preparation. She has also been involved with artificial recharge projects, litigation projects, and GIS applications. Lauren excels at report writing – summarizing project results, leading the production of supporting graphics and figures, combining input from other project contributors, and conducting quality assurance and control to create a final, comprehensive report. Her efforts and attention to detail result in work products that are timely and well-received by clients. She is also the point of contact on many projects, including day-to-day project communications, presentations to clients, and interfacing with law firms.

When she’s not at work, Lauren enjoys doing yard work and spending time with family.

Logan Wicks
Senior Geohydrologist

Logan Wicks

Senior Geohydrologist

Logan Wicks, PG

Logan has more than 15 years of professional experience on more than 27 municipal direct or alternative supply wells and has completed more than 70 well field assessments and groundwater studies. His experience includes many different types of projects, such as geohydrologic investigations, groundwater quality studies, artificial recharge projects, water well test drilling programs, sea water desalination programs, and the management and supervision of water well and basin studies projects including siting, design, aquifer pumping test analyses, well construction, basin characterization, and hydrogeologic conceptual models. He has managed numerous well and basin studies projects including water supply wells, injection wells, monitoring wells, and groundwater basin management. He has performed various aquifer pump tests analyses and help developed water quality sampling protocols including specialized depth specific sampling and analysis, along with surface/ spring water mapping and analysis. He is also part of a team developing new methodologies for collecting real time flow and water quality data for better and more accurate well design and quality control.

Logan is an active member of the American Water Works Association (AWWA) and Groundwater Resource Association of CA and frequently presents at both events. When he’s not in the field or managing projects, he enjoys woodworking and family time.

Stephen Turnbull
Senior Geohydrologist

Stephen Turnbull

Senior Geohydrologist

Stephen brings nearly 40 years’ experience drilling and installing production and monitoring wells in a wide variety of geologic formations in Hawaii, California, Arizona, and Nevada. In Hawaii, coordinated project efforts between regulatory agencies and a team of more than 70 Navy engineers and professionals delivering groundwater impact evaluations and water production and monitoring well installations in basalt volcanic formations to remediate contamination issues.

His experience with large field data collection, encompassing soil moisture, meteorological, and streamflow measurements including automated stream sampling equipment for surface runoff and sediment and nutrient loads to meet National Pollutant Discharge Elimination System (NPDES) permit and total maximum daily load (TMDL) compliance, adds value to client projects. Stephen holds Master of Science degrees in Hydrology and Computer Science and is a PhD candidate in Civil Engineering at the University of California, Los Angeles.

Tim Chen
Senior Project Manager

Tim Chen

Senior Project Manager

Tim has planning and engineering experience in a broad range of water resource projects for numerous municipalities, state agencies, and private clients throughout the Southern California region. He works with our team to lead and support projects involving groundwater and watershed management, groundwater recharge, injection and extraction well design, and water resource planning. With his project management experience, he focuses on using cutting edge technologies, such as groundwater and surface water modeling, to solve clients’ groundwater issues in an efficient and cost-effective way.

David Barnes
Senior Modeler

David Barnes

Senior Modeler

David Barnes, MEng

David has more than 13 years of experience performing groundwater modeling and regional water supply studies for municipal clients and public agencies, specializing in the development of groundwater, surface water and hydrogeologic models, as well as data processing and GIS to support modeling efforts. Additionally, David is experienced in well design and construction processes with wide-ranging experience in field hydrology, aquifer testing, and characterization methods. His experience has included assisting in the development of a regional groundwater model to support a Habitat Conservation Plan, where he assessed the impacts of water management decisions on shallow groundwater, streamflow, and riparian areas. David’s experience also includes a geohydrologic analysis of future groundwater production, assessing the future proposed pumping operations for a municipal wellfield. To complete the assessment, he developed a local groundwater flow model and also developed a solute transport model to assess water quality in the wellfield.

Coral Shaw
Project Geohydrologist

Coral Shaw

Project Geohydrologist

Coral Shaw, GIT

Coral has nearly a decade of professional experience from working as a field geologist on over 20 well construction projects including high-capacity municipal supply wells, test boreholes, injection wells, and monitoring wells. Coral is experienced performing well construction inspection for tasks such as pilot borehole drilling and reaming, casing inspection and installation, air lifting and swabbing, development by pumping, and down-hole video logging. She has performed various pumping test analyses, including large scale pumping tests and water quality sample collection. Coral also prepares well siting reports, preliminary well design reports, well designs based on data collected during the drilling process, provide final pump design recommendations, and final summary reports.

Robert Sia
Project Geohydrologist

Robert Sia

Project Geohydrologist

Robert Sia

Robert has more than a decade of professional experience on over 30 municipal supply wells, 125 monitoring wells, 400 water quality samples, and 15 groundwater studies. Robert’s experience is derived from serving a variety of roles such as client service manager, project manager, junior leader for Phase I ESA community of practice, and field technician/inspector for geohydrology and environmental consulting firms. Robert has worked on projects with focus on geohydrologic conditions, well siting, well assessments, well design, technical specifications, bidding support, engineering services during construction and testing; groundwater recharge and recovery; environmental site investigations, characterization, monitoring, and remediation; real estate redevelopment/due diligence, and regulatory permit and consent decree compliance.

Robert’s drilling experience includes mud direct rotary, reverse circulation, sonic, hollow stem auger and direct push including limited access rigs, and solid stem auger. In municipal supply wells, Robert is experienced with field aspects of exploratory drilling, well construction, well development, pump testing, well disinfection, well rehabilitation, and water quality sampling in Southern and Northern California.

Seth Kuiper
Project Geohydrologist

Seth Kuiper

Project Geohydrologist

Seth Kuiper, MS, GIT

Seth has more than six years of experience in the groundwater industry performing well construction inspection, groundwater quality sampling, aquifer pump testing and analysis, and well siting studies. Additional experience consists of geohydrologic investigations, groundwater recharge programs, and subsidence studies. He has a leading role in conducting groundwater sampling programs including planning, field supervision, and reporting. Seth also manages field instrumentation including setting up monitoring equipment to report data remotely through analog 4-20mA and Modbus protocol. Seth’s experience in well construction inspection tasks include pilot borehole drilling and reaming, casing inspection and installation, air lifting and swabbing, development by pumping, and down-hole video logging. Types of wells Seth has been involved in include high capacity municipal water supply wells, test boreholes, and monitoring wells using the reverse rotary and sonic drilling methods. Seth has also prepared well designs based on data collected during the drilling process, provided final pump design recommendations, and written final summary reports.

Jack Wada
Project Manager

Jack Wada

Project Manager

Jack has extensive experience providing water resources and environmental project management and technical support for clients. He leverages his strong interpersonal and communication skills to advance projects and find proactive solutions to complex problems. Jack’s expertise in managing hydrogeologic investigations encompasses drilling, well construction, water quality, statistical trend analysis, and groundwater elevation modeling add value to his project management work.

Additionally, Jack excels in data collection and analysis, technical documentation, quality assurance, well field management, multimedia environmental sampling, and site assessments. Jack has a degree in Environmental Earth Science from California Polytechnic State University, San Luis Obispo.

Leo Liu
Project Modeler

Leo Liu

Project Modeler

Leo Liu, MS, EIT

Leo has more than nine years of experience with groundwater and environmental investigations performed for municipalities, state agencies, and private clients throughout California. He conducts groundwater flow and solute transport modeling, hydrogeologic investigations, groundwater basin and water quality studies, watershed modeling and management, and artificial recharge projects. His experience has included supporting efforts to develop and calibrate various groundwater models in the Santa Ana River Watershed, the Upper Mojave River Watershed, the Murrieta‐Temecula Groundwater Basin, the San Juan Basin, the Mission Groundwater Basin, the Santa Maria River Valley Groundwater Basin, and the Salinas Valley Groundwater Basin. In addition to groundwater model experience, he performed numerous solute transport models and MODPATH (i.e., particle tracking) for recycled water recharge and indirect potable reuse projects. Leo also has experience in GIS, database development and management.

Si Si
Project Modeler

Si Si

Project Modeler

Si Si, MS, EIT

Si has over eight years of experience in groundwater and environmental investigations performed for municipalities, state agencies, and private clients throughout California, with specialized experience in modeling. She has conducted groundwater flow and solute transport modeling, hydrogeologic investigations, groundwater basin and water quality studies, watershed modeling and management, groundwater waste discharge permitting, GIS mapping, and database development and management. Si’s experience includes development of a watershed model component for an integrated model of the Upper Santa Ana River Basin, as well as calibrating the watershed model using data from 1966 through 2016 to simulate runoff generated within the watershed and quantify runoff inputs for the integrated model. Si also assisted in a hydrogeologic study of a groundwater basin in Riverside County, where she developed a HSPF model based upon the available data of precipitation, land use, and soil types, and calibrated the model with adjacent or nearby streamflow gages in order to quantify the groundwater storage and safe yield of the basin.

Nathan Reynolds
Hydrogeological Data Manager

Nathan Reynolds

Hydrogeological Data Manager

Nathan has more than 17 years of experience completing hydrogeologic investigations, source contaminant analysis, ground water quality studies, artificial recharge projects, water well test drilling programs, and construction observation for a variety of drilling projects. His experience includes both monitoring and groundwater studies—helping to verify data that aid in the development of groundwater models and studies that reflect basin conditions. He has also worked on water well design and construction oversight, as well as, performed various aquifer pump test analyses for 80+ drilling projects. Nathan has acted as field manager for Cal Am’s desalination feasibility study during the construction of an innovative slant well for subsurface seawater intake in Monterey County. He has managed the construction, data collection, and long-term reporting of extensive monitoring well networks, with special focus on water quality database creation and management. Nathan has assisted in multiple litigation projects where clients value his attention to detail.