Gradient Senior Scientists

Samuel A. Flewelling, Ph.D.

Dr. Flewelling specializes in the source, transport, and fate of a broad range of chemicals associated with natural processes and human activities.  He has consulted on CERCLA sites and other facility types, such as chemical and pharmaceutical manufacturing, wastewater treatment, petroleum extraction and storage, mining and mineral processing, and waste disposal.  Dr. Flewelling has evaluated the fate of hydraulic fracturing additives and flowback chemicals, as well as the potential human health risks and environmental impacts associated with these constituents.  He has dealt with a wide range of contaminants at other sites, including chlorinated solvents, DNAPL and LNAPL, VOCs, pesticides, PCBs, dioxins, petroleum hydrocarbons, radionuclides, metals, and nutrients.  Dr. Flewelling's creative scientific approaches have helped clients resolve complex environmental liabilities, as well as environmental litigation.  

Representative Projects

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.

Hydraulic Fracturing Risk Assessment: Evaluated the potential for hydraulic fracturing (HF) of deep shale formations to affect potable aquifers, including 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.

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.

Industrial Wastewater Treatment: Served as a court-appointed liaison between plaintiff group and defendant. Characterized human health and environmental risks posed by a resin manufacturing plant, which included a detailed analysis of the plant’s wastewater treatment system and quantitative modeling of air emissions from a bioremediation lagoon.

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 above-ground 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; Hornberger, GM; Herman, JS; Mills, AL; Robertson, WM. 2013. "Diel patterns in coastal-stream nitrate concentrations linked to evapotranspiration in the riparian zone of a low-relief, agricultural catchment." Hydrol. Processes doi: 10.1002/hyp.9763.

Flewelling, SF; Tymchak, MP; Sharma, M. 2013. "A Scaling Function to Predict Hydraulic Fracture Limits in Deep Shale and Tight Gas Formations." Presented at American Association of Petroleum Geologists Annual Convention and Exhibition, Pittsburgh, PA, May 20-22.

Flewelling, SF; Tymchak, MP; Warpinski, NW. 2013. "Hydraulic fracture height limits and fault interactions in tight oil and gas formations." Geophysical Res. Lett.

Flewelling, SF; Sharma, M. 2013. "Constraints on upward migration of hydraulic fracturing fluid and brine." Ground Water

Flewelling, SA; Emanuel, R. 2006. "Water Stewardship in a Changing Climate." Virginia Water Conservation District, Ivy Creek Park, Charlottesville, VA 44p




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