50 Kearney Square, Lowell, Massachusetts
Architect: Burt Hill Kosar Rittleman Assoc.
Geotechnical Engineers: Haley and Aldrich
Prime Contractor: J. Slotnick Company
Project Period: mid-August thru mid-November, 2002
The project was completed on schedule.

Penstocks two centuries old are still in operation, channeling water from the Pawtucket Canal to the Concord River whereby a turbine is powered to generate electricity. These penstocks underlie the Federal Building, which is now part of Middlesex Community College. The penstocks were leaking, resulting in water seepage along the walls of the building.

As part of a complete renovation of the Federal Building, ABC Soils, Inc. excavated nearly 450 cubic yards of soil and construction debris from beneath the building to expose the penstocks for waterproofing and underdrain installation, then backfilled around the drains and leveled off the area to maintain structural stability.

ABC Soils accessed the penstocks through 8-inch holes cut through a concrete floor. There were two feet of soil above the penstocks. The excavation extended ten- to twelve- feet deep. Shoring was not needed because the excavation was supported by the foundation wall for the basement on one side and the stone arch wall of the penstock on the other. There was a constant flow of water into the excavation from the leaking penstocks that was managed by periodic pumping and installation of drainage pipe. A de-flocculating agent was periodically added to minimize caking of soil within the vacuum hose. A number of large rocks too big to move were cut in place and then removed from the excavation. Other relatively large rocks and debris were set aside and not handled by the excavator.

Materials removed from the excavation were tested for contaminants and initially were trucked by ABC Soils to a City-designated location. The drain line and waterproofing application process began after the first sixty feet of trench was exposed and ABC Soils began backfilling with the material removed from further down the trench. This was accomplished using an intermediate hopper located in line between the machine and the end of the hose. This hopper was also used to install crushed stone to replace the soil that was hauled away. Finally, the rocks and other debris previously set aside were thrown back on top of the excavation.