Author(s): Heather M. Vandewalker; Mark T. Mahoney; Bruce G. Cook; George D. Ashton
Linked Author(s): George Ashton
Keywords: No keywords
Abstract: At the direction of USEPA, Alcoa conducted an Ice Breaking Demonstration Project in March 2007 to evaluate the effectiveness of mechanical ice breaking as an interim measure for avoiding future ice jam-related sediment scour in the lower Grasse River. The work was undertaken based on the occurrence of an ice jam in the river in spring 2003 that disturbed both the cap placed as part of the 2001 Capping Pilot Study and PCB-containing sediments below the cap. In response to the 2003 event, USEPA and Alcoa evaluated both interim and long-term measures to prevent future ice jam events. Mechanical ice breaking in the lower Grasse River was subsequently identified as the only potentially feasible non-structural interim measure. Alcoa is continuing to evaluate long-term structural ice control measures. The Demonstration Project involved mechanical breaking of the intact ice cover in an approximate 7-mile reach of the lower Grasse River with the goal of providing increased conveyance capacity needed to allow the ice floes entering from upstream during natural breakup to be transported through the lower Grasse River without causing a significant ice jam and related scour event. Ice breaking was successfully completed using two excavators operating from a barge that was moved by a shallow-draft tug. Monitoring activities conducted during the course of ice breaking activities included measurement of ice thickness, tracking of ice breaking progress, turbidity monitoring, noise monitoring, warning sign/banner observation, and photographic documentation. Significant efforts were made in the planning stages and during operations to promote community safety because the section of river involved is used for winter recreational activities including snowmobiling. Although the project was completed, Alcoa and USEPA have agreed that ice breaking will not be recommended for the future as an interim ice control measure due to the inherent safety risks and unpredictable conditions that can impact the ability to successfully complete the work.
Year: 2008