Overview | Ice Jam Event Details | Ice Breaking Demonstration Details | Ice Control Structure

Ice Jam Event Details

Post-implementation monitoring conducted as part of the Capping Pilot Study in spring 2003 indicated that a loss of cap material and, in some areas, underlying sediment had occurred within the capped area. A review of photographs of the river taken during the spring 2003 ice breakup indicated that an ice run had occurred in the upper part of the river, and that an ice jam had formed in the lower Grasse River directly over the Capping Pilot Study area.

March 2003 Ice Conditions

In response to this finding, Arconic (formerly Alcoa) assembled an ice expert team and conducted a series of intensive investigations in 2003 and 2004 to understand what happened, why, and how often these events occur. Results of the ice investigations indicated that ice jams capable of scouring and redistributing PCBs buried in the river sediments can occur in the upper approximately 1.8 miles of lower Grasse River (i.e., between the Power Canal and approximately one-third of a mile upstream of the Route 131 Bridge).

This ice jam scour mechanism was not previously known to occur in the Grasse River and the cap installed as part of the Capping Pilot Study was not designed to withstand the forces from these events. As a result, concurrent with the 2003 and 2004 investigations, the company began to evaluate possible long- and short-term options [e.g., installation of a stand-alone ice control structure (ICS) and mechanical ice breaking, respectively] for controlling ice jam related sediment scour for inclusion in the remedial alternative evaluation and remedy selection process for the river.

Overview

Post-implementation monitoring associated with the 2001 Capping Pilot Study was conducted to monitor the longer-term performance of the placed caps. Post-cap monitoring efforts were initiated in 2002, and the data developed from the first year of monitoring indicated that the cap had remained in place and was functioning as designed. Monitoring activities conducted in spring 2003, however, indicated that a loss of cap material and, in some areas, underlying sediment had occurred within the capped area since the previous monitoring was conducted in fall 2002. A review of photographs of the river taken during the spring 2003 ice breakup indicated that an ice run had occurred in the upper part of the river, and that an ice jam had formed in the lower Grasse River directly over the Capping Pilot Study area.

In response to this finding, Arconic (formerly Alcoa) assembled an ice expert team and conducted a series of intensive investigations in 2003 and 2004 to understand what happened, why, and how often these events occur. The ice expert team includes the following individuals.

• Dr. George Ashton, P.E. - Retired technical director of the US Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL)
• Guenther Frankenstein, P.E. - Retired director of the CRREL Ice Engineering Research Division and developer of the test facilities
• Dr. Hung-Tao Shen, P.E. - Professor and Chairman, Department of Civil and Environmental Engineering, Clarkson University
• Andy Tuthill, P.E. - CRREL hydraulics engineer with expertise in ice engineering

Results of the ice investigations indicated that ice jams capable of scouring and redistributing PCBs buried in the river sediments can occur in the upper approximately 1.8 miles of lower Grasse River (i.e., between the Power Canal and approximately one-third of a mile upstream of the Route 131 Bridge). Ice jams of this magnitude appear to occur approximately once every 7 to 10 years, and the event in spring 2003 ice jam appears to be the worst that has occurred over the past 40 to 50 years. The primary mechanism that caused the cap material and sediment scour during the 2003 event was not physical contact of the ice with the river bottom, but rather increased flow velocities and turbulence under the toe of the ice jam (see figure below).

Schematic of an Ice Jam

Water column and fish monitoring data collected after the spring 2003 ice jam did not show a significant change in PCB levels relative to pre-2003 ice jam conditions, although some localized effects were observed in areas in the vicinity of the toe of the ice jam. Further, it was noted that not all sediments in the 1.8-mile stretch will scour during an ice jam event, as approximately 15% of this area was impacted by the 2003 event. The investigations also documented, through the analysis of ice related tree scars, that major ice jams have also occurred historically in the Grasse River upstream of the Village of Massena.

This ice jam scour mechanism was not previously known to occur in the Grasse River and the cap installed as part of the Capping Pilot Study was not designed to withstand the forces from these events. As a result, concurrent with the 2003 and 2004 investigations, the company began to evaluate possible long- and short-term options for controlling ice jam related sediment scour for inclusion in the remedial alternative evaluation and remedy selection process for the river.

Longer-term options include a stand-alone ice control structure (ICS) on the river near the Arconic Massena West operations or possible integration of ice control into the Massena Electric Department (MED) proposed hydropower project. The company's ice expert group previously identified a candidate location for an ICS with necessary physical characteristics in the Town of Louisville, and construction of an ICS at this location was proposed as part of the 2005 Remedial Options Pilot Study (ROPS) for interim and possibly longer term ice management, but this component of the 2005 ROPS was not pursued due to community concerns related to the proposed location. Additional studies were undertaken to evaluate the use of a pier-type ICS in the lower river to retain ice; however, due to public safety concerns associated with the construction of piers in the river, this is no longer under evaluation. Similarly, MED made a decision to not further pursue the hydroelectric dam and therefore the project no longer offered an alternative ice control option for consideration to potentially control ice jam formation in the lower Grasse River.

The only potentially feasible non-structural short-term option identified was mechanical ice breaking, where the ice in the lower 7 miles of river (Alcoa Bridge to confluence with St. Lawrence Seaway) would be broken up in advance of the natural ice breakup to allow ice to pass through the river without jamming. In December 2006, the United States Environmental Protection Agency directed the company to investigate mechanical ice breaking methods and, in March 2007, conduct the lower Grasse River Ice Breaking Demonstration Project

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