With five environmental Areas of Concern on Lake Erie, communities all along the North Coast need to know which options will best help them to clean up their harbors. Often, the choices come down to capping the area or dredging out the contaminated sediment. A new computer model created by Ohio Sea Grant researchers Dr. Patrick Fox and Dr. John Lenhart of Ohio State University’s Department of Civil and Environmental Engineering and Geodetic Science can help communities weigh which option may be best for them. The model allows agencies to input the characteristics of the sediment in their harbor to determine exactly how it will behave, helping in the planning process.

"We determined that you need to pay attention to the release of very small particles from the sediments," Lenhart explains. "Those tiny particles are able to get through filters and presses. They’re very mobile, and they often have contaminants attached to them." This mobility causes problems in both types of remediation, capping or dredging.

When a cap is created, the small particles get stirred up and many wind up in the capping layer itself rather than being isolated below. "You’re actually moving the contaminates two-thirds of the way through the cap, which means those contaminates are actually going to work their way through the capping layer much sooner than anticipated, or they might even go all the way through, depending on what the cap is made of," says Lenhart.

As for dredging, it turns out that in physically removing the sediment, you end up widely disbursing the contaminant at a low-level concentration because it’s fairly difficult to completely contain the small particles. Some residual contamination is always left behind.

"The model is really a tool that can be used in risk assessment, remediation plans, and engineering proposals," says Lenhart. "It can help communities figure out the best course of action."

To read more about this Ohio Sea Grant-funded research, visit http://ohioseagrant.osu.edu/_documents/twineline/v31i4.pdf