DREDGE IMPOUNDMENT STRUCTURE

Material dredged from the harbor was used to complete the dam portion of project Holcim (US),
Inc. The sole purpose of the dam was for the dredge spoil, as the dam will never hold water. It is
over 150 feet tall, making it the 11th highest dam in the state. 525,000 cubic yards of clay core,
sand filter, gravel transition and shot rock were used to construct the dam. All material was
“mined” from inside the impoundment structure to gain extra capacity for dredge spoil. Clay for
the core was stockpiled from the harbor excavation. However, it was too wet and Team BE
provided the solution to utilize this material in the mitigation area. Existing shale located within
the impoundment met criteria for the formation of the dam’s core material. Hayward Baker
Company performed a subsurface grouting procedure to seal the dam’s foundation below the core
trench to form a grout curtain to avoid seepage.

This area of the project was crucial to not only Team BE’s success, but the existence of the entire
plant itself. If the dam was behind schedule, the harbor was behind schedule, therefore delaying
barge deliveries of equipment vital to plant construction.

The dam was designed to provide 1,300,000 cubic yards of capacity. Approximately 1,000,000
cubic yards was to be dredged from the harbor. Because bulking factor or swell percentage could
not be predetermined, this area of the project needed constant surveying and monitoring by
Team BE.