Gradient

Principals

Samuel A. Flewelling, Ph.D.
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Education

Ph.D., Environmental Sciences, University of Virginia

B.A., Environmental Sciences, University of Virginia

Expertise

  • Contaminant Fate & Transport
  • Hydraulic Fracturing
  • Hydrological Modeling
  • Chlorinated Solvents
  • NAPL
  • Metals
  • Induced Seismicity
  • Water Rights
  • Nutrients
  • Trace Metals
  • Petroleum Hydrocarbons

Samuel A. Flewelling, Ph.D.

Principal Scientist

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Dr. Flewelling is a principal scientist at Gradient who specializes in evaluating water resources and the behavior of chemicals in the environment, including chemical transport through groundwater and surface water, fluid-rock interactions, and underground migration of multiple fluid phases (i.e., DNAPL and LNAPL).  He has published peer reviewed papers on a variety of topics ranging from the natural controls on agricultural chemical migration through the landscape, to the potential for hydraulic fracturing fluid to migrate through fractures and faults to shallow drinking water resources.  As a consultant during the past 15+ years, he has applied in-depth knowledge of fluid-mediated processes to solve a range of complex challenges associated with the oil and gas, electric power, chemical manufacturing, pharmaceutical, mining, agrichemical, and waste disposal sectors.  This work has included site-specific evaluations (e.g., CERCLA sites) as well as large-scale assessments of the potential transport and effects of chemicals across entire states or countries. 

Education

Ph.D., Environmental Sciences, University of Virginia

B.A., Environmental Sciences, University of Virginia

Expertise

  • Contaminant Fate & Transport
  • Hydraulic Fracturing
  • Hydrological Modeling
  • Chlorinated Solvents
  • NAPL
  • Metals
  • Induced Seismicity
  • Water Rights
  • Nutrients
  • Trace Metals
  • Petroleum Hydrocarbons

Services

Representative Projects

Hydraulic Fracturing Risk Evaluation:  Evaluated the potential effects of hydraulic fracturing (HF) of deep shale formations on potable aquifers, including the migration of HF additives through fractures and intact bedrock.  The combination of a literature review and modeling analyses allowed for the estimation of the likelihood for HF additive migration beyond the target shale zone.

Hydraulic Fracturing Risk Evaluation:  Evaluated a US EPA study of potential hydraulic fracturing (HF) impacts to potable aquifers in Pavillion, WY.  Analysis included the assessment of potential migration of HF additives in groundwater, well construction and sampling methods, and inorganic geochemistry of groundwater.

Pesticide Fate and Transport:  Modeled the biodegradation of a wide range of pesticides in soils to determine pesticide residue levels expected from historical applications.  The analysis was used in negotiations over the need for additional sampling and site investigation.

Landfill DNAPL Study:  Evaluated contaminant distribution beneath and adjacent to a large landfill.  Analyzed the direction and magnitude of groundwater flow in the region’s complex geological setting of heterogeneous soils and fractured bedrock.  Developed a site conceptual model to explain the fate and transport of dissolved contaminants and DNAPL that migrated outward from the landfill through a complex system of preferential migration pathways.  Modeled potential vapor intrusion for scenarios where contaminated groundwater lay beneath off-site buildings.  These analyses aided in the development of remediation scope and costs.

Radionuclides in Drinking Water:  For a toxic tort case, analyzed natural and anthropogenic sources of radionuclides to a coastal aquifer and the dominant transport mechanisms downgradient of an industrial facility.

Wood Treatment Chemicals:  Developed an extensive literature review on the fate, transport, environmental, and human health effects of copper.  Developed quantitative models to predict the magnitude of copper leached from pressure-treated wood in aboveground and aquatic applications.  The leaching model was used to quantitatively assess the risk of copper leached from pressure-treated wood into surface waters and sediments to aquatic organisms and humans.

Selected Publications

Flewelling, SA; Sharma, M.  2014. "Constraints on upward migration of hydraulic fracturing fluid and brine." Ground Water 52 : 9-19.

Flewelling, SA; Sharma, M.  2014. "Interpretation of the Data Collected As Part of US EPA's Investigation at Pavillion, WY." American Association of Petroleum Geologists 2014 Annual Convention and Exhibition, Houston, Texas

Fitzsimmons, M; Flewelling, SA; Tymchak, MP.  2014. "Will earthquakes shake up the shale wastewater debate?"

Flewelling, SA; Tymchak, MP; Warpinski, NW.  2013. "Hydraulic fracture height limits and fault interactions in tight oil and gas formations." Geophysical Res. Lett. 40 : 3602-3606.

Flewelling, SA; Sharma, M.  2011. "The Timing of DNAPL Releases In A Fractured-Clay Setting." Presented at the Society of Environmental Toxicology and Chemistry (SETAC) North America 32nd National Meeting, Boston, MA, November 13-17, 30p.

Gu, C; Hornberger, GM; Mills, AL; Herman, JS; Flewelling, SA.  2007. "Nitrate reduction in streambed sediments: Effects of flow and biogeochemical kinetics." Water Resour. Res. 43 : 43-52.