Wachusett Aqueduct Pump Station and Upgrades to John J. Carroll Water Treatment Plant

Massachusetts Water Resources Authority (MWRA)

Marlborough, MA

Stephens Associates Consulting Engineers (SA) served as geotechnical engineer for a new pump station to increase hydraulic gradeline of the Wachusett Aqueduct to supply the MWRA’s Carroll Water Treatment Plant. The Project included three below-grade levels requiring deep excavations up to 30 ft. below ground surface in loose silts and 20 ft. below groundwater to install the wet well, surge tank and 7 and 10-ft. diameter pipelines to connect to the existing 10-ft. diameter aqueduct pipeline.

Geotechnical evaluation included geologic data review, subsurface explorations, laboratory testing, and evaluation of foundation type and constructability, and liquefaction susceptibility as well as construction-related factors including rock excavation, support of deep excavations, and dewatering. SA recommended shallow and deep foundations for varying components in consideration of differential settlements and varying depths of excavation. SA also designed micropile foundations to support a guardhouse without imposing loads on a nearby buried pipeline.

During construction, SA assisted the Client and MWRA in review of Contractor’s alternate support of excavation system in consideration of risks, costs and benefits to the Owner. SA reviewed contractor submittals and geotechnical instrumentation data and consulted with Client and MWRA on geotechnical aspects of construction. SA observed H-pile driving, support of excavation and grouted tieback installation, construction of micropile foundations, rock excavation near to existing historic structures, and subgrade preparation on site.

The MWRA received the 2020 Sustainability in Civil Engineering Award for the Project from the Boston Society of Civil Engineers.