Key Personnel

Andrews, Charles B., PhD

Senior Principal

Dr. Andrews is nationally known for his creative solutions to difficult groundwater problems. His areas of expertise include the assessment and remediation of contaminated sites, formulation of groundwater projects, assessment of groundwater flow and quality conditions at hazardous waste sites, design of groundwater remediation systems, and development of new and modification of off-the-shelf numerical simulation models for adaptation to specific field projects. He has provided technical guidance to significant water-rights litigation. Dr. Andrews is a frequently requested member of groundwater advisory panels for the evaluation of state-of-the-art hydrology and for pioneering research and evaluation of contaminant transport in the subsurface. He is the author and co-author of numerous publications on modeling of groundwater flow and transport of chemical constituents, and the use of analytical models in identifying appropriate remediation alternatives for a site.

Barth, Gilbert, PhD

Principal, Boulder Office Manager

Dr. Barth has over 25 years of experience in quantitative assessments of water-resources at the local to watershed-scale addressing water planning, water rights, water quality, and remediation. He specializes in model development and calibration with a focus on quantifying exchanges between groundwater and surface water systems. He has developed and applied groundwater models to assist private and public clients throughout the Western United States. Dr. Barth is the Office Manager of SSP&A's Boulder office.

Cohen, Harvey, PhD


Dr. Cohen has 20 years professional experience in hydrogeology, geology and environmental management.  His expertise includes quantitative evaluation of water resources and environmental contamination, including site investigation and remediation,brownfields redevelopment, risk-based corrective action, and groundwater modeling.  He has completed contaminated site investigations and remediation projects under various federal and state programs including CERCLA, the federally-funded Source Water Assessment program, and state voluntary cleanup programs.  Dr. Cohen has led water resources and geological investigations throughout the United States and in Turkey.  For the United Nations Development Programme (UNDP), he completed the first-ever comprehensive environmental assessment of Cyprus’ largest copper mining and mineral processing complex.  Dr. Cohen has also served as an expert witness in cases related to groundwater contamination with MTBE and chlorinated solvents.  In addition to his research and case-study publications, Dr. Cohen is co-editor of the American Geological Institute’s Geoscience Handbook (AGI Datasheets, 4th Edition).

Grigsby, Bryan, PG


Mr. Grigsby has over 25 years of experience as a hydrogeologist and project manager specializing in the design and management of complex investigations involving drilling, monitoring, aquifer testing, and data collection to support groundwater studies.  Mr. Grigsby has directed geologic, hydrogeologic, and geochemical evaluations over a broad range of environments, from alluvial settings to fractured bedrock regimes.  He has been involved with all stages of site assessment, monitoring, and remediation for Federal- and State-lead projects.  Mr. Grigsby has been involved in several projects assessing impacts of oil and natural gas development on groundwater resources in the western U. S. and in Appalachia.  He has presented findings for several of these projects at public meetings and regulatory hearings.  His background is in structural geology and he previously worked in the uranium mining and oil and gas industries.  Mr. Grigsby is Senior Manager of the Boulder, Colorado, office.

Hennet, Remy J.-C., PhD

Senior Principal

Dr. Hennet has over 20 years of research and field experience in investigating the origin, fate, and transport of organic and inorganic chemicals in natural and man-made environments. He has conducted numerous studies that cover the fields of environmental characterization, remediation, monitoring, cost allocation, and litigation. Dr. Hennet’s expertise includes the forensic interpretation of chemical fingerprints, in particular for PCB congeners, petroleum hydrocarbons, organic solvents, toxic metals, and inorganic ions such as arsenic and selenium chemical species, nitrate, and perchlorate. His expertise also includes the interpretation of stable isotope data as to quantify or qualify environmental processes. Dr. Hennet has authored and co-authored numerous publications on both inorganic and organic geochemistry.

Larson, Steven

Executive Vice President, Senior Principal

Mr. Larson is a recognized authority on numerical simulation models and their application in the analysis of a variety of groundwater problems. He has developed such models for analyzing groundwater flow, mass- and heat-transport in groundwater systems, contaminant migration, recovery of petroleum products from groundwater, saltwater intrusion in coastal aquifers, and thermal energy storage in aquifers. In addition, he has been in the forefront of combining these methods with linear programming techniques to optimize the development of groundwater supplies or remediation of contaminated groundwater. He has conducted training courses on the use of these models and provided technical support on their application to a variety of hydrologic conditions. Mr. Larson has authored and co-authored publications on the application of aquifer simulation models that are widely used by practicing hydrologists. He has served as an expert witness in numerous judicial forums regarding groundwater issues and the application of simulation models for demonstrating the fate of soil/groundwater contamination and the effect of remediation alternatives.

Neville, Christopher J.

Associate, Chief Hydrogeologist

Mr. Neville has over 15 years of experience as a groundwater hydrologist, with particular emphasis on quantitative analysis of groundwater flow and solute transport. He has experience in the synthesis of hydrogeologic data, the evaluation and protection of groundwater resources, and the analysis and design of remedial measures. Mr. Neville has extensive experience in the development of work plans for groundwater projects. He has developed and documented large-scale three-dimensional numerical models for industrial, mining, and government clients, and has reviewed numerous site-specific hydrogeologic analyses and groundwater modeling codes. He is responsible for the testing, documentation, and support of groundwater modeling software at S.S. Papadopulos & Associates, Inc. Mr. Neville has developed and taught professional short courses through S.S. Papadopulos & Associates, Inc. and the International Ground Water Modeling Center. Mr. Neville also assists in teaching graduate courses at the University of Waterloo in groundwater resources evaluation, solute transport, and analytical solutions.

Papadopulos, Stavros S., PhD

Founder, Senior Principal

Dr. Papadopulos is an internationally recognized expert on the analysis of groundwater systems.  His areas of expertise include the evaluation of aquifer test data, the use of analytical and numerical models for interpreting groundwater flow and contamination problems and for resolving groundwater supply issues, assessment of groundwater flow and quality conditions at hazardous waste sites and identification of potential receptors, and the design of monitoring networks and of extraction well systems for groundwater remediation.  He has served on advisory panels offering technical opinion on complex groundwater issues and has provided expert testimony in court proceedings and/or administrative hearings. 

He has planned and directed research on groundwater systems and on the development of new methods for analyzing aquifer tests.  He is the author and co-author of publications on well hydraulics, aquifer test methodology, groundwater resource evaluations, and subsurface waste disposal.  For contributions to the fields of groundwater flow and contaminant transport, he was elected as a member of the National Academy of Engineering in 2009.

Rafferty, Michael T.

Vice President, Principal Engineer

Mr. Rafferty has extensive experience in the design, construction, and operation of groundwater treatment, soil treatment, and oil and chemical process facilities. He has been responsible for the design of process systems (including equipment, piping, and instrumentation); construction, startup, and operation of treatment plants; project material control; and various construction-related activities. He has managed site characterization and remediation programs in compliance with federal, state, and local regulatory guidelines for a wide variety of sites where the soil or groundwater was affected by metals, chlorinated organic compounds, petroleum hydrocarbons as well as non-aqueous phase liquids (NAPLs). Mr. Rafferty has been directly responsible for all phases of these projects, including soil and groundwater investigations; conceptual remedial design studies; development of design drawings and specifications; bid document preparation and evaluation; construction management; field supervision and inspection, and report preparation. He has been an expert witness and has provided technical input for mediation, arbitration, and litigation of environmental and construction claim cases.

Soderberg, Keir, PhD

Senior Associate, Geochemist

Dr. Soderberg is an expert in geochemistry and isotope hydrology. His more than 15 years of professional and research experience includes field and laboratory chemistry, forensic geochemistry, geochemical modeling, and the management of large datasets. As a post-doctoral researcher, he contributed to a long-term project in sub-Saharan Africa directed at understanding evapotranspiration dynamics in semi-arid lands through a novel combination of geochemistry and ecohydrology. At SSP&A, Dr. Soderberg supports and manages environmental remediation and litigation projects involving groundwater, surface water, and sediment, often in support of cost-allocation, expert reports and testimony. This work primarily involves the evaluation of geochemical and hydrological data sets including detailed review of sampling protocols, laboratory practices, and the history of chemical usage.

Spiliotopoulos, Alexandros, PhD

Senior Associate, Senior Hydrologist

Dr. Spiliotopoulos has over 15 years of experience in hydrogeology, aquifer remediation design and water resources management. He has developed and applied analytical and numerical models for groundwater flow and contaminant transport, focusing on pump-and-treat system operation, reactive-transport modeling, and optimization applications for least-cost remediation designs. He has extensive experience in assessing water-resources management in support of inter- and intra-state water resource allocation and conflict resolution, assessment of water quantity and quality data, development and application of statistical tools and numerical interpolation techniques for mapping water-level and water-quality data, and the application of advanced parameter estimation techniques for model calibration.
During his professional years in Greece, he worked as a hydraulic engineer designing water-supply and stormwater management systems, as part of the infrastructure for the 2004 Olympic Games, and supporting modeling of large-scale water distribution networks, including the updating of the main water distribution network of the city of Athens.

Tonkin, Matthew J., PhD


Dr. Tonkin has been with SSP&A for 20 years, during which time he has focused on the synthesis of data to resolve ground- and surface-water issues. This includes the design of data gathering efforts, development and management of databases, application of analytical and numerical models, and visual presentation of information to support decision-making. His programming languages include Fortran and Visual Basic. He co-teaches model calibration and uncertainty analysis courses with Dr. John Doherty, author of PEST. Matt received his PhD in 2008 under the advisement of Dr. John Doherty, investigating efficient methods of predictive uncertainty analysis for large models.

As President of S.S. Papadopulos & Associates, Inc., Dr. Tonkin overviews and serves as technical advisor on all projects. S.S. Papadopulos & Associates, Inc. is a 60-person environmental consulting firm that specializes in the assessment and remediation of contaminated site and groundwater problem solving.