Stewart Smith, M.S., R.G.
Vice President
Associate Hydrogeologist


Mr. Smith joined Hydro Geo Chem in 1989 as a Hydrogeologist. His responsibilities include management of site characterization and remediation activities, numerical assessment of landfill gas generation and design of LFG collection and control systems, design of soil and groundwater remediation systems, collection and interpretation of chemical and hydrogeologic data, use of numerical models for remedial design and as predictive and interpretive tools, and preparation of interpretive reports. Project management duties have included representation of clients to and negotiation with controlling regulatory agencies.





-M.S. (Hydrology) University of Arizona, 1989
-B.S. (Geosciences) University of Arizona, 1980


Registered Professional Geologist, Utah Registration Number 5336166-2250
Member, National Groundwater Association
Member, Phi Kappa Phi (Honorary Society)
OSHA 40-Hour Health and Safety Training for Hazardous Waste Operations, 1989
8-Hour HAZWOPER annual refreshers

Representative Experience

• Biosparging and bioventing conceptual designs for cleanup of soils and groundwater impacted by liquid phase petroleum hydrocarbons at the Sky Harbor Airport in Phoenix, Arizona. Work has included use of numerical biodegradation models to interpret field and pilot test data, to design a full-scale site bioventing system, and to design a large scale biosparging test system for the site.

• Soil vapor extraction (SVE)/bioventing system design for the U.S. Environmental Protection Agency Ninth Avenue Dump Superfund site, Gary, Indiana. Project manager responsible for the pilot test, design of the remedial system using numerical SVE and biodegradation models, and preparation of the design report.

• Evaluation of SVE system and sparging pilot test performance at the 7th and Arizona site, Tucson, Arizona, and SVE system performance at the Central and Camelback site, Phoenix, Arizona. Both are Water Quality Assurance Revolving Fund (WQARF) sites. Projects included interpretation of pilot test data, and use of numerical flow and transport models to predict SVE and sparging performance.

• Supervision and analysis of an SVE/air sparging pilot test at the site of a gasoline release in Phoenix, Arizona. Work included preparation of site-specific work plans, quality assurance project plans, health and safety plans, and analysis and interpretation of field data using numerical models.

• Conceptual design of an SVE/Enhanced Bioremediation System for clean-up of a fuel oil spill in Phoenix, Arizona. Work included predictive numerical modeling of vapor extraction and biodegradation efficiency for pilot test design, performance of a pilot test, interpretation of pilot test results, preparation of interpretive reports, and recommendations for a full-scale design.

• Design of deep soil vapor extraction systems for protection of groundwater beneath Broadway North, Harrison, and Silverbell Landfills, Tucson, Arizona using three-dimensional numerical gas flow and transport models. Broadway North and Silverbell Landfills are within WQARF sites.

• Management of the design of a groundwater sparging system to prevent offsite VOC migration at a landfill in Brooks County, Georgia. Project elements included a pilot test, development of a conceptual design using numerical flow and transport models, and a conceptual design report.

• Evaluation of the effectiveness of a large-scale deep bioventing system designed to control VOC migration from a shallow perched water zone to the underlying Ogallala aquifer at a site in the Texas Panhandle. The evaluation included the use of numerical flow and transport models that simulate biodegradation. An interpretive report was prepared that recommended minimum air circulation rates needed to meet remedial goals.

• Numerical modeling of the baro-pneumatic landfill gas generation rate measurement technique to support a (successful) patent application. Use of the technique to estimate landfill gas generation rates at sites located in Tucson, Arizona; Albuquerque, New Mexico; Livermore, California; St. Landry’s Parish, Louisiana; Lake Worth in Florida; Tupelo, Mississippi; and several sites in Georgia. Two of the Tucson, Arizona landfills are located within state superfund (WQARF) sites.

• Landfill gas collection and control system designs for 8 MSW landfills in Brooks County, Decatur County, Early County, Grady County, Henry County, Mitchell County, and Terrell County Georgia. Project Manager responsible for site investigation, data analysis using patented baro-pneumatic method, conceptual design using numerical models, and conceptual design reporting. Also used the baro-pneumatic method to design a landfill gas migration control system for a site in Payson, Arizona.

• Numerical modeling of the decomposition of municipal solid waste under both aerobic and anaerobic conditions. Model results were used to support the design of an in-situ pilot aerobic treatment system for a closed City of Tucson landfill and to predict long term methane generation rates for untreated landfills.

• Management of an investigation at a uranium mill site in Blanding, Utah to support the award of a groundwater discharge permit. Elements of the project include site characterization, numerical modeling to select appropriate monitoring well densities, investigation of a localized groundwater VOC plume, report preparation, and presentation of results to and negotiation with controlling regulatory agencies.

• Management of the investigation of a groundwater VOC plume at a uranium mill site in Blanding, Utah. Elements of the project include site characterization, evaluation of an interim remedial action, development of remedial objectives, preparation of a preliminary Contaminant Investigation Report and a preliminary Corrective Action Plan, litigation support, and ongoing interpretive support for the preparation of quarterly monitoring reports.

• Supervision of the development of regional 3-dimensional numerical groundwater flow and transport models at sites near Green Valley and Bisbee, Arizona. Models designed to evaluate sulfate migration, assess remedial alternatives for sulfate mitigation, and evaluate potential impacts on public water supplies. Model development included extensive analysis of aquifer tests using analytical models.

• Optimization of the design of a groundwater extraction and treatment system used to remediate groundwater VOC contamination at Harrison landfill, Tucson, Arizona. Numerical flow and transport models were used to enhance the design to meet the client’s need for more rapid cleanup.

• Development of a three-dimensional numerical model of groundwater flow through a fanglomerate drinking water aquifer located in central Arizona. The modeling was part of an ongoing remedial effort at an Arizona WQARF site. The model was used to predict the hydraulic interaction between the fanglomerate and an overlying alluvial aquifer impacted by acid mine drainage under pre-remedial conditions and under conditions of anticipated future remedial pumping of the alluvial aquifer.

• Numerical modeling of unsaturated flow and transport within mine tailings impoundments at a copper mine (WQARF site) in Arizona and a Trona mine in Wyoming. Three-dimensional numerical models have been used to: 1) predict the impact of past and current wet tailings disposal on regional groundwater, 2) assess remedial options, 3) direct further data collection activities, and 4) provide data for slope-stability studies.

• Development of a three-dimensional numerical flow and transport model to predict the effectiveness of various remedial pumping strategies on acid mine drainage at a WQARF site in central Arizona.

• Hydrogeologic assessment of a mountainous terrain for a Native American tribe in Nevada. Work included estimation of sustainable water supply and water quality, and recommendation of areas most favorable for water development.

• Use of numerical flow and transport models to determine the number of septic systems that can safely be used at proposed residential property developments without excessive nitrogen impacts to groundwater.

• Analysis of multi-depth soil gas data collected at a municipal landfill located within a WQARF site in Tucson, Arizona. Work included supervision of field activities and development of numerical flow and transport models that incorporate groundwater and soil gas data as an aid to understanding past history and current and potential future impacts of VOCs on groundwater.

• Management of a remedial investigation at a U.S. Environmental Protection Agency Non-Time Critical Emergency Response site located in Fort Wayne, Indiana. Work included investigation of on- and off-site subsurface VOC contamination and preliminary design of a soil and groundwater remedial system.

• Numerical modeling to predict the performance of an SVE system to remediate a gasoline spill in Tucson, Arizona, as part of an emergency response action.

• Supervision of the design of an SVE system to remediate a VOC-contaminated Superfund site located in Kalamazoo, Michigan. Work included preliminary system design using numerical models.

• Assessment of the long-term impact of vadose zone VOCs on groundwater at a site located within the North Indian Bend Wash Superfund site in Phoenix, Arizona. Work included use of numerical models and preparation of an interpretive report.

• Supervision of an investigation of subsurface contamination by organic compounds at a Superfund site in the Livermore Valley, California. Duties included planning and direction of soil gas, soils, and groundwater work.

• Supervision of the investigation and remediation of tetrachloroethylene soil contamination at a site located within the San Gabriel Basin Superfund site, southern California. Duties included planning and direction of field activities, design of remedial alternatives, and preparation of interpretive reports.

• Acid mine water contamination study at an Arizona WQARF site. Sampling and on-site analysis of groundwater to delineate the extent and type of contamination, supervision of monitor and production well installation, performance and interpretation of aquifer tests, and preparation of interpretive reports.

• Design and interpretation of aquifer tests. Included preparation of site-specific work plans, supervision of field operations, interpretation of results using analytical models, and preparation of interpretive reports. Tests have been conducted at various sites including state and federal superfund sites.

• Biostimulation soil venting pilot tests. Included preparation of site-specific work plans, supervision of field operations, performance of venting efficiency and tracer tests, interpretation of results using numerical models, and preparation of interpretive reports. Tests have been conducted at various sites including state and federal superfund sites and a site in the Texas Panhandle.

• SVE pre-design investigations. Included supervision of soil gas sampling and soil air permeability tests, and interpretation of results using numerical models.

• Environmental audits. Research and investigation into all aspects of past and present property use which may have an impact on potential site contamination and owner liability, as well as investigation into the possibility of contamination from off-site sources. Preparation of interpretive reports based on the results of research and on-site investigations.

Prior Experience

Geologist/Geological Engineer:

• Analysis of the hydrogeology of the area surrounding a developing mine site in Nevada through interpretation of geologic maps. Recommendation of areas favorable for development of production wells to serve mining operations.

• Interpretation of geophysical data with respect to lithology and structure. Co-author of in-house report relating to major gold districts basin and range structure (as defined by regional gravity and aeromagnetic data). Development of a statistical model to quantify the spatial association of mineralization to aeromagnetic features.

• Geostatistical ore deposit modeling. Transformation of drill-hole data into engineering models used for mine design and planning, corporate financial planning, and published corporate ore reserve statements. Process required detailed analysis of the geologic environment, and analysis of the statistics and geostatistics of element distribution within an ore deposit, to ensure accurate estimation by kriging or inverse-distance techniques.

• Field acquisition, transcription, reduction, and presentation of data. Use of existing software to load, edit, grid, contour, and image process data on Burroughs mainframe, IBM PC, and COMPAC portables.

• Development of computer software to improve data processing procedures and design of routines to process new types of data sets.

• Research and field examination of areas with potential for bulk-minable gold mineralization. Using satellite imagery, located prospects with potential significant enough to warrant property acquisition.

Mineral Exploration Geologist:

• Responsibilities included research and field evaluation of properties with potential for bulk-minable gold, silver, tin, tungsten, and molybdenum mineralization; preparation of geologic reports and recommendations; supervision of drilling operations; and collection and analysis of geophysical data.


General Physics Corporation Short Course, "Bioremediation Engineering" November 1992.

Air and Waste Management Association Seminar, "Bioventing and Vapor Extraction: Uses and Application in Remediation Operations", April 1992.


Improved Method and System for Estimating Gas Production by a Landfill or Other Subsurface Source


Smith, S.J., H.W. Bentley, and K. Reaves. 2006. Systematic Design of Methane Migration Control Systems. Proceedings, 29th Annual SWANA Landfill Gas Symposium, St. Petersburg FL, March 27-30. 18 pp.

Bentley, H.W., S.J. Smith, and T. Schrauf. 2005. Baro-pneumatic Estimation of Landfill Gas Generation Rates at Four Operating Landfills. Proceedings, SWANA’s 28th Annual Landfill Gas Symposium, March 7-10, 2005.

Bentley, H.W., S. Smith, J. Tang, and G.R. Walter. 2003. A Method for Estimating the Rate of Landfill Gas Generation by Measurement and Analysis of Barometric Pressure Waves. Proceedings of the 18th International Conference on Solid Waste Technology and Management, Philadelphia, Pennsylvania, March 23-26, 2003.

Bentley, H.W., G.R. Walter. S.J. Smith., J. Tang, and C.T. Williamson. 2002. (US) Patent No. US 6,611,760 B2 Method and system for estimating gas production by a landfill or other subsurface source, June 19, 2002.

Walter, G.R., S. Smith, H.W. Bentley, and J. Tang. 2002. Comparison of direct techniques for estimating LFG generation rates. Abstracts with Program. SWANA Regional Landfill Conference, Casa Grande.

Bentley, H.W. and S.J. Smith. 1998. Soil Vapor Extraction of Chlorinated VOCs in the Vicinity of a Landfill Equipped with a Landfill Gas Control System. Presentation at the 1998 Arizona Hydrological Society Eleventh Annual Symposium. September 23 to 26, 1998. Abstract with Proceedings.

Bentley, H.W., J. Tang, S.J. Smith, D. Samorano, R.G. Arnold. 1998. Analysis of Remedial Options for Chlorinated VOCs at Harrison Landfill. In: Bioremediation and Phytoremediation, Chlorinated and Recalcitrant Compounds. The First International Conference on Remediation of Chlorinated and Recalcitrant Compounds. Monterey, California, May 18 to 21, 1998. pp. 21-26

Ward, J.J. and S.J. Smith. 1998. Arid Zone Landfills: What Do Investigation and Modeling of Containment Migration Reveal About Transport Mechanisms? Presentation at the 1998 Arizona Hydrological Society Eleventh Annual Symposium. September 23 to 26, 1998. Abstract with Proceedings.

Smith, S.J., J. Pepe, and G.R. Walter. 1995. The Effect of Variable Injection Rates on Air Sparging Patterns in Heterogeneous, Porous Media. Presented at the First International Symposium on In-Situ Air Sparging for Site Remediation. Las Vegas, Nevada.

Smith, S.J. and G. Walter. 1993. Numerical Modeling of “Raining” Soil Vapor Extraction Wells for a Hypothetical Alluvial Aquifer. Presented at Rocky Mountain Ground Water Conference - Ground Water Technology and Tasks in the 90's, Albuquerque, New Mexico, 1993.

Walter, G.R., R.D. Philip, and S.J. Smith. 1993. Chicken/Egg Arguments in the Establishment of Soil Cleanup Standards. Presented at Hazmacon '93, San Jose, California.

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