RECOVERY--Z--Project Number 007680, Construction project for Hop Brook Lake Dam Remedial Foundation Grouting, Hop Brook Lake, in the City of Waterbury and the towns of Middlebury and Naugatuck, Connecticut

Hop Brook Lake Dam is located in the City of Waterbury and the towns of Middlebury and Naugatuck, Connecticut. The dam is located on the Hop Brook about 1.4 miles above its confluence with the Naugatuck River. The Corps of Engineers constructed Hop Brook Dam to provide flood protection in the Naugatuck River Watershed in the State of Connecticut. The project is operated as part of a system in conjunction with four other Corps of Engineers flood control reservoirs in the Naugatuck River basin, to reduce flood flows on the Naugatuck and Housatonic Rivers. Construction of the 520 feet long, 97 feet high dam began in December 1965 and was completed in December 1968.

The work of this project involves installing a vertical grout curtain for the dam embankment. The vertical grout curtain will be installed along the same alignment as the foundation cut-off grout curtain that was installed during initial construction. The alignment of the curtain runs from abutment to abutment, and down to the upstream toe in the center, thus forming a V-shape as seen both in plan view and in section view. The curtain consists of three lines; a center line, an upstream line, and a downstream line, with the lines being 5 feet apart. The holes comprising the upstream and downstream lines shall be vertical while the center line shall consist of holes inclined 15% to the south or west along the curtain's alignment. Primary holes shall be 20 feet apart. Holes shall extend from the riprapped upstream dam face down through the riprap and the embankment (0-58 feet thick) and extend an additional 60 feet into the foundation bedrock, a highly fractured and folded schistose gneiss. In order to ease access and perform work on the 2.5:1 riprapped slope, crushed stone shall be placed along the curtain alignment to form an access road. An additional component of this project is the installation of four piezometers, three on the downstream face near the right abutment, and one on the far left abutment.