Extreme Weather Events Further Complicate Sediment Sites

News & Events

November 18, 2021

A newly released study on extreme weather’s potential environmental impacts draws attention to sediment mobilization.


Extreme Weather Events, Flooding, Sediment Transport, Contaminant Mobilization, Climate Change


Extreme Weather Events Further Complicate Sediment Sites

With less than two weeks remaining in the North Atlantic hurricane season, the National Weather Service (NWS) has exhausted its list of potential storm names for the second year in a row. This feat marks only the third time the NWS has eclipsed the allotted number. Although not all tropical storms make landfall, when they do, damage costs can soar into the billions. Despite widespread media coverage of these damages, hidden environmental costs from extreme weather lie beneath the water’s surface, due to unintended contaminant migration. A newly released study on extreme weather’s potential environmental impacts draws attention to sediment mobilization and the potential redistribution of associated chemicals. This issue could be particularly acute near urban areas where waterways have a rich history of industrial activity, and contaminant remobilization could potentially reopen previously closed sites.


A range of contaminants are typically found at large, complex sediment sites and may include metals, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dioxins, pesticides, and solvents, among others. These constituents are often adhered to, or intermixed with, sediments at the seafloor or river bottom and can be remobilized during floods or extreme tides, further complicating an understanding of release timing, source identification, and transport. Figure 1 shows the geographic regions of the country that are most susceptible to tropical storm impacts, as well as the locations of the nation’s Superfund sites. This figure illustrates how broad these effects could be, even for a single storm. For example, although Hurricane Ida made landfall in Louisiana, extensive flooding occurred in northern New Jersey and New York City, a region with many large, complex Superfund sites.

As a result of sediment mobilization and mixing caused by hurricanes and other extreme weather, understanding chemical movement through urban waterways and coastal environments often requires a multidisciplinary technical approach. For more than two decades, Gradient has addressed a wide range of contaminated sediment issues at some of the nation’s most complicated sites. Specific areas of Gradient’s expertise relevant to these matters include:

  • Quantifying sediment transport in urban waterways that have been disrupted by flooding, storm surges, currents, and bioturbation, in addition to human influences such as dredging or barge traffic;
  • Experience with state-of-the-art chemical testing and oversight of data collection efforts to support liability claims, cost allocation, and remedy selection;
  • Evaluating forensic patterns with multiple fingerprinting techniques to determine release timing, source(s), and the age of numerous chemical contaminants;
  • Identifying potentially responsible parties (PRPs) that may have contributed contaminants identified during post-storm sampling events; and
  • Understanding how extreme weather events may affect remedy selection and implementation, in addition to potential effects on liability and cost allocation matters.

Gradient has deep expertise in several technical areas associated with sediment transport and environmental forensics, and is well positioned to help parties evaluate these issues at complex sediment sites.



Figure 1. Paths of Storms in the North Atlantic Tracked by the National Weather Service from 1970 – 2020 and the Locations of Superfund Sites in the Eastern US. The storms include tropical depressions, tropical storms, and hurricanes (categories 1-5), and the Superfund sites include deleted, proposed, and active sites.



If you have any questions about Gradient’s capabilities, please visit our website or contact:

Eric L. Butler, Ph.D.

Jessie M. Kneeland, Ph.D.

Principal Scientist


Jeffrey T. Rominger, Ph.D.

Senior Environmental Engineer


Tim Verslycke, Ph.D.


Kurt Herman, M.Eng., P.G.


James W. Rice, Ph.D.

Senior Environmental Scientist


Caroline B. Tuit, Ph.D.

Senior Environmental Chemist

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