SOURCE: Tetra TechDESCRIPTION:
Steve McGee has more than 30 years of experience in the investigation, development, and implementation of sediment remediation projects. He has studied and managed several of the largest sediment remediation efforts in the United States, from the Fox River in Wisconsin to the Kalamazoo River in Michigan. Mr. McGee leads Tetra Tech’s highly experienced team of scientists, engineers, and construction and remediation experts in projects that include sediment and water quality sampling, fluvial geomorphology, hydrodynamic modeling, and high-resolution bathymetric surveys of riverine systems and floodplains. He is adept at integrating and optimizing sustainable construction methods and dewatering waste segregation processes for beneficial reuse.
For more than 15 years, Mr. McGee has been a charter member of the Sediment Management Work Group, which advocates advancing scientifically sound approaches to improve sediment risk assessment, enhance remedial technologies, and promote cost-effective sediment management. Mr. McGee earned his Bachelor of Science degree in Chemical Engineering from Pennsylvania State University.
What factors give rise to sediment remediation projects?
There are two conditions that lead to sediment remediation projects. The first is legacy industrial discharges in a river’s sediment that negatively impact ecological and human health. The second factor is the enforcement of environmental laws created to protect everybody and preserve the environment for our future.
What is the life cycle of a typical sediment remediation project?
There is typically a long life cycle that really starts with understanding the distribution of legacy discharges in a river’s sediment. Understanding not only the distribution but also the risk posed to humans and the ecosystem is important. The front-end phase is where the science happens and can last anywhere from a few years on smaller projects to nearly 15 to 20 years on “mega” projects involving five or more miles of a river. In the United States, mega sites include the Fox River, Kalamazoo River, and Passaic River. These are the types of projects that Tetra Tech studies and discusses with our peers as part of our involvement in the Sediment Management Work Group.
How have sediment remediation projects changed over the years?
Up until the turn of this century, all of the regulatory enforcement work was focused mainly on the remediation of upland properties. One of the first major sediment remediation projects in the United States started in 2001, on the Grand Calumet River in Indiana for the removal of 750,000 cubic yards of PCB-impacted sediment over a 5-mile reach. Since then, the most significant changes have involved the progress in our ability to very closely control the dredging operations working along a modeled and engineering dredging neatline. The neatline is specifically contoured within the sediment matrix as a guide for the dredge operator to follow during implementation and represents a significant improvement over the use of a dredge prism.
For example, 15 years ago the closest we could achieve to removing the targeted material with dredging equipment was two feet. Today, the dredge operator has an on-board computer, and the typical allowance is only six inches using Real-Time Kinematic GPS that is accurate to 0.2/foot. Also, refinements in the application of geostatistics have allowed us to greatly improve efficiency in capturing targeted material (contaminated sediment) without dredging uncontaminated sediment or debris. Removing less non-target material means there is less to be dewatered and transported for disposal. Today, our scientists, engineers, and constructors are working together to become more efficient at achieving project objectives. Since the tremendous proliferation in the use of geotextile tubes for dewatering, we have made great strides in our ability to effectively dewater dredged sediments.
What are the emerging trends in remedial technologies?
I believe one of the most exciting trends is in the application of science to reduce the bioavailability of legacy discharges. We’ve become a lot more efficient at optimizing the amount of material that has to be dredged, and then managing the less-contaminated material in situ. We have modelled, designed, and installed reactive caps and in situ treatment products to accomplish project objectives. Reactive caps are engineered with components—such as Organoclay and powdered activated carbon—that are layered on top of the mudline to capture contaminants as they migrate to the water’s surface. In situ treatment products are applied differently, in a very thin lift directly into the benthic active zone and into the sediment matrix.
How do regional differences affect practices in your field?
Tetra Tech is working on sediment projects in all 10 U.S. Environmental Protection Agency (EPA) regions. The largest regional difference we see is in the northwestern United States due to the tribal framework used to establish sediment remediation endpoints defined by fish consumption assumptions. End points are the levels of concentrations that have to be achieved in the fish tissue to meet regulatory objectives. They are more stringent in the northwest due to the fish consumption by local tribes. The remedial design work we’re doing on the Duwamish River in Seattle, for example, must account for a lot more sediment at a much lower concentration than is typical in other regions.
What are some of the major challenges in the field?
The major challenge we face is agreeing upon the appropriate risk levels for human health and ecological exposure. It is rare that one hundred percent of a contaminant can be removed, and oftentimes projects are delayed because the recommended cleanup levels are really not attainable. To facilitate forward progress in a sediment remediation project, I work with stakeholders to demonstrate, for example, the best approach to performing a risk assessment or fate-and-transport modelling and then make recommendations on how best to meet the cleanup goals based on a specific site’s chemistry and geotechnical properties.
What sets Tetra Tech apart from other firms when it comes to sediment remediation?
Tetra Tech has employed robust science and engineering practices since the company’s founding 50 years ago. But what really sets us apart is that we also perform the remedial construction component. No other science and engineering firm of our caliber also performs mega remedial construction projects. Tetra Tech’s fluvial geomorphology practice allows us to identify and understand the distribution of contaminants more accurately than the industry standard of using geospatial techniques based on a grid. We understand that rivers don’t behave on a grid and apply our knowledge of river formations to minimize removal of non-target material. We applied our understanding of the fluvial fate-and-transport of legacy discharges to develop the EFDC model for U.S. EPA, which became the most widely used hydrodynamic model in the world. Many firms now use this software as a base for developing their own written modules. Tetra Tech also has world-class marine surveying capabilities. We own all of the vessels and specialized survey equipment that are needed to help us understand the progress of the work as it is being conducted.
Tweet me: How does @TetraTech create solutions for #sediment #remediation challenges? Steve McGee, Sediment Remediation Expert, highlights the best approaches to performing risk assessment and modelling to meet cleanup goals: http://bit.ly/2CD48Aq #LeadingWithScience
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