Service Area

Chemical Fate & Transport

Gradient’s extensive expertise in chemical fate and transport analysis helps our clients interpret complex environmental data and/or predict chemical concentrations when data are not available. Whether using detailed physical/biogeochemical models, data-driven mass balance approaches, or more complex hybridized techniques, we excel at identifying the most effective combination of modeling and data analysis to solve even the most complicated fate and transport questions.

Sample Projects

Chemical Transport Modeling and Remedy Evaluation at Superfund Site

Gradient developed a groundwater flow and solute transport model to help evaluate benefits associated with remediation options at a Superfund site. We used the model to evaluate steady-state plume extent and long-term plume duration under selected potential future remedial alternatives. Our modeling results were presented in a focused feasibility study.

Cost Allocation at a Complex Contaminated Sediment Site

Gradient analyzed plausible pathways for pollutant transport from a petroleum storage facility to nearby surface water and sediment. We analyzed groundwater flowpaths, estimated chemical travel times, and evaluated other sources of contamination to estimate the proportion of contamination attributable to the facility.

Herbicide Fate and Transport for an Insurance Claim

Gradient evaluated the relationship between applications and detections of a herbicide in groundwater and surface water throughout the United States. We developed a conceptual framework to evaluate herbicide migration in the environment and applied that framework to selected water supply systems over a large portion of the United States.

Remedy Investigation and Design at a Former Pine Tar Processing Facility

We conducted hydrogeologic and contaminant transport modeling evaluations to support the remedial investigation and design efforts for a former industrial site impacted with pine tar DNAPL and wood-treating chemicals. Our involvement also included developing a contaminant transport model to evaluate remedial alternatives and cleanup time for the pine-tar-related groundwater plume at the site.

Air Quality Impacts and Potential Health Risks of Power Plant Soot

Gradient assessed potential air quality impacts and health risks associated with particulate matter (PM) and trace metal constituents, including thallium and arsenic, at a large coal-fired power plant for both upset events and normal operating conditions. We reconstructed emissions and performed air dispersion modeling for short-term soot events, identifying maximum impact areas, and conducted toxicological assessments for potential worst-case exposures.

Probabilistic Sediment Transport Analysis

Gradient performed contaminant fate and transport analysis to understand the migration potential of sediment-bound organic chemicals within a complex urban water body. We analyzed the potential for particles of different size classes to be eroded, transported, and deposited under varying flow conditions. Our probabilistic modeling framework took into account tides, storms, and boat traffic-induced sediment resuspension over monthly to multi-decade periods. The results of our analysis provided our client with a clear understanding of the likelihood for sediment migration that could be used in allocation discussions.

Our Team